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The objectives were to determine the effects of nicotinic acid (NA) on blood metabolites (experiment 1) and whether successive doses of NA could induce sustained reductions of plasma nonesterified fatty acids (NEFA; experiment 2) in feed-restricted, nonlactating Holstein cows. Experiment 1 was a single 4 x 4 Latin square with 1-wk periods. Each period consisted of 2.5 d of feed restriction to increase plasma NEFA and 4.5 d of ad libitum feeding. Treatments were abomasal administration of 0, 6, 30, or 60 mg of NA/kg of body weight (BW), given as a single bolus 48 h after initiation of feed restriction. Plasma NEFA concentration decreased from 546 µEq/L to 208 ± 141 µEq/L at 1 h after the infusion of 6 mg of NA/kg of BW, and to less than 100 ± 148 µEq/L at 3 h after the abomasal infusion of the 2 highest doses of NA. A rebound occurred after the initial decrease of plasma NEFA concentration. The rebound lasted up to 9 h for the 30-mg dose of NA, and up to 6 h for the 6-mg dose. Experiment 2 was a randomized complete block design with 3 treatments and 6 cows. Starting at 48 h of feed restriction, cows received 9 hourly abomasal infusions of 0, 6, or 10 mg of NA/kg of BW. Plasma NEFA concentrations decreased from 553 µEq/L ± 24 immediately before the initiation of treatments to <100 µEq/L during hourly infusions of 6 or 10 mg of NA/kg. Data suggest that the maximal antilipolytic response was achieved with the lowest dose of NA. A rebound of NEFA started 2 to 3 h after NA infusions were terminated. In both experiments, the NEFA rebound period coincided with increases in insulin and no change or increased glucose concentrations, suggesting a state of insulin resistance induced by elevated NEFA. This model for reducing plasma NEFA concentration by abomasal infusions of NA can be used to study the metabolic ramifications of elevated vs. reduced NEFA concentrations. The data demonstrate potential benefits and pitfalls of using NA to regulate plasma NEFA and prevent lipid-related metabolic disorders. [ABSTRACT FROM AUTHOR]

Sixty-five Holstein cows were used to evaluate management schemes involving altered dry period (DP) lengths on subsequent milk production, energy balance (EB), and metabolic variables. Cows were assigned to one of 3 treatments: traditional 56-d DP (fed a low-energy diet from -56 to -29 d and a moderate energy diet from -28 d to parturition; T), 28-d DP (continuously fed a high energy diet; S), and no planned DP (continuously fed a high energy diet; N). Prepartum DM intake (DMI), measured from 56 d prepartum through parturition, was lower for cows on the T treatment than for cows on the S treatment and was higher for cows on the N treatment than for cows on the S treatment. There were no differences in prepartum plasma glucose, and β-hydroxybutryric acid; there was a treatment by time interaction for prepartum plasma nonesterified fatty acid (NEFA). There was no difference in prepartum liver triglyceride (TG); postpartum liver TG was decreased for cows on the N treatment compared with cows on the S treatment, but was similar for cows on the T and S treatments. Postpartum NEFA was similar between cows on the T and S treatments, but was greater for cows on the S treatment than for cows on the N treatment. Postpartum glucose was greater for cows on the N treatment compared with cows on the S treatment and tended to be greater for cows on the S treatment than for cows on the T treatment. There was no difference in postpartum solids-corrected milk (SCM) production or DMI by cows on the T vs. S treatment. However, there was a tendency toward lower postpartum SCM production by cows on the N vs. S treatment and a tendency for greater postpartum DMI by cows on the N vs. S treatment. Postpartum EB was greater for cows on the S vs. T treatment and the N vs. S treatment. In general, T and S management schemes had similar effects on DMI, SCM, and metabolic variables in the first 70 d of the subsequent lactation. Eliminating the DP improved energy and metabolic status. [ABSTRACT FROM AUTHOR]

The objective was to determine the effects of linoleic acid and different isomers of conjugated linoleic acid (CLA) at different concentrations on hepatic lipid and glucose metabolism in the bovine. Monolayer cultures of hepatocytes obtained from 7- to 10-d-old Holstein bull calves were exposed to treatments from 16 to 64 h after plating. The treatments included 1.0 mM palmitic acid plus either 0.1 or 1.0 mM of cis-9, cis-12 linoleic acid, cis-9, trans-11 CLA, or trans-10, cis-12 CLA. Metabolism of palmitic acid to cellular triacylglycerol (TAG) was decreased when media contained cis-9, trans-11 compared with trans-10, cis-12 CLA. Total cellular TAG content was increased for the CLA isomers compared to cis-9, cis-12 linoleic acid. Both CLA isomers increased palmitic acid incorporation into phospholipids, cholesterol, and media triacylglycerol compared with cis-9, cis-12 linoleic acid at a concentration of 1.0 mM. Increasing the concentration of treatment fatty acids from 0.1 to 1.0 mM decreased oxidation of palmitic acid to acid-soluble products, but no effects of fatty acids were observed. There was no treatment effect on rates of gluconeogenesis from propionic acid. Overall, CLA isomers elicited changes in palmitic acid metabolism to cellular and media triacylglycerol, and cellular phospholipids and cholesterol, but had little or no effect on other measured pathways of lipid metabolism or gluconeogenesis in bovine hepatocytes. [ABSTRACT FROM AUTHOR]

Deals with a study which determined the long-term effects of specific long chain fatty acids on hepatic lipid and glucose metabolism in monolayer cultures of bovine hepatocytes. Primary end-products of fatty acid oxidation; Glucose formation from propionic acid; Influence of fatty acids on lipid and glucose metabolism in monolayer cultures of bovine hepatocytes.

Studies net uptake of nonesterified long chain fatty acids by the perfused caudate lobe of the caprine liver of goats. Method of the study; Results and discussion; Conclusion.

The objective was to investigate the relationship between elevated plasma nonesterified fatty acid (NEFA) concentration and insulin resistance in Holstein cows. Six nonlactating, nongestating, ruminally cannulated Holstein cows were blocked by body condition score and randomly assigned to a sequence of 2 treatments in a crossover design. Cows were offered legume and grass hay ad libitum supplemented with minerals and vitamins and were allowed free access to water and a trace mineralized salt block. Mobilization of body reserves was stimulated by withdrawing forage for 48 h before initiation of treatments. Treatments consisted of 11 hourly abomasal infusions of water (control) or nicotinic acid (NA; 6 mg/h per kg of body weight) as an antilipolytic agent. Infusions of NA decreased plasma NEFA concentration from 545 µEq/L to approximately 100 µEq/L within 2 h after initiation of treatments, and differences were maintained throughout infusions. Intravenous glucose tolerance test was performed 8 h after initiation of treatments and was followed by 3 h of blood sampling. The reduction of plasma NEFA concentration led to significantly greater glucose clearance rate (1.9 vs. 1.2%/min) and to decreased glucose half-life (37 vs. 58 min), time to reach basal concentration (81 vs. 114 min) and glucose response area under the curve during 180 min of sampling [6,942 vs. 10,085 (µIU/mL) x 180 min]. Enhanced glucose clearance was achieved when plasma NEFA was reduced by NA, despite lower insulin concentration (70.0 vs. 97.9 ± 13.4 µIU/mL) and a tendency for smaller insulin response area under the curve during 180 min of sampling [7,646 vs. 12,104 ± 2,587 (µIU/mL) x 180 min], reflecting an increased response to endogenous insulin. Based on literature, we do not expect NA to have altered glucose metabolism directly; therefore, this experiment demonstrates a cause and effect relationship between elevated NEFA and insulin resistance in Holstein cows. [ABSTRACT FROM AUTHOR]

The objective was to test whether the induction of elevated blood nonesterified fatty acids (NEFA) by i.v. infusion of a tallow emulsion altered glucose tolerance and responsiveness to insulin in Holstein cows. Six nonlactating, nongestating Holstein cows were assigned to a crossover design. One cow was excluded before initiation of the experiment because of complications from mastitis. Treatments consisted of 11-h i.v. infusions of saline (control) or a 20% (wt/vol) triacylglycerol (TG) emulsion derived from tallow (tallow) to elevate plasma NEFA. Each period consisted of two 11-h infusions (INF1 and INF2), separated by 1 d in which cows were not infused. Intravenous glucose tolerance tests (IVGTT) and insulin challenges (IC) were performed 8 h after initiation of INF1 and INF2, respectively. The infusion of treatments continued during the 3 h of sampling for IVGTT and IC. Cows were fed every 4 h at a rate to meet energy requirements for 5 d prior to each period, and every 2 h during the first 8 h of infusions. Infusion of tallow induced hyperlipidemia by increasing plasma NEFA (295 ± 9 vs. 79 ± 7 µEq/L), serum TG (41.0 ± 6 vs. 11.4 ± 4.4 mg/dL), and glycerol (0.81 ± 0.09 vs. 0.23 ± 0.1 mg/dL) concentrations during INF1. During INF2, tallow treatment increased plasma NEFA (347 vs. 139 ± 18 µEq/L), serum TG (20.8 ± 4.6 vs. 13.1 ± 2.3 mg/dL), and glycerol (0.88 ± 0.04 vs. 0.31 ± 0.02 mg/dL) concentrations. Induction of hyperlipidemia impaired glucose clearance during IVGTT, despite the greater endogenous insulin response to the glucose infusion, leading to a lower insulin sensitivity index [0.29 vs. 1.88 + 0.31 x 10-4 min-1/(µIU/mL)]. Accordingly, hyperlipidemia impaired glucose clearance during IC (1.58 vs. 2.72 %/min), reflecting lower responsiveness to insulin. These data show that induction of hyperlipidemia causes insulin resistance in Holstein cows by impairing both sensitivity and maximum responsiveness to insulin. The induction of insulin resistance by TG, NEFA, or both may increase the availability of glucogenic nutrients to the periparturient dairy cow. Yet excessive elevation of NEFA may potentially lead adipocytes to become more insulin resistant, further increasing plasma NEFA concentration and the risk of metabolic disorders. [ABSTRACT FROM AUTHOR]

The objective of these experiments was to determine effects of sampling protocol on plasma nonesterified fatty acid (NEFA) concentration. In experiment 1, 8 nonlactating, nongestating dairy cows were blood sampled from a jugular vein catheter (basal, 0 min), moved to an exercise lot for 15 min, returned to stanchions, and sampled immediately and at 5, 15, 30, 60, and 120 min following return to their stalls. Following 15 min of exercise, plasma NEFA concentration increased, peaking at 5 min (225 µEq/L) and returning to basal (84 µEq/L) by 30 min (110 µEq/L). Cows were then moved to box stalls overnight, and 24 h after the basal sample, they were locked up and sampled again. Housing cows in a box stall overnight and locking them in headlocks increased plasma NEFA concentration (184 µEq/L). In a second experiment at a large free-stall commercial dairy, 11 late-gestation nonlactating dairy cows were locked in headlocks at feeding, blood was sampled from the coccygeal artery or vein (0 min), and cows were then released and allowed to finish eating and return to their stalls. Cows were then herded to headlocks and sampled immediately at 120 min after initial sampling and at 135, 150, and 180 min. Plasma NEFA concentration was highest at initial lockup (0 rain; 284 µEq/L), lowest at 180 min (178 µEq/L), and intermediate at time points in between. A second group of 10 late-gestation nonlactating dairy cows were locked in headlocks at feeding, and blood was sampled immediately and at 5, 15, 30, and 60 min. Plasma NEFA concentration was highest 15 min after being placed in headlocks and lowest 60 min after lockup (221 and 113 txEq/ L, respectively). At each time point in experiments 1 and 2, a behavior score was given (1 to 10; 1 = calm; 10 = extremely excited). In both experiments, there was a significant correlation between the plasma NEFA concentration and behavior score. In conclusion, plasma NEFA concentration was affected by sampling protocol. [ABSTRACT FROM AUTHOR]

There has been substantial recent interest in shortening dry periods; however, the effects of this management change on reproduction have not been adequately evaluated. Holstein cows (n = 58) were assigned in a randomized block design to 1 of 3 treatments: 1) traditional (T) dry period (-56 d) in which cows were fed a low energy diet from 56 to 29 d prepartum followed by a moderate energy diet for 28 d; 2) shortened (S) dry period (∼28 d) in which cows were fed continuously a high energy diet; or 3) no planned (N) dry period in which cows were fed continuously a high energy diet. All cows received a high energy lactation diet after calving. Ovaries were evaluated by ultrasound and blood samples collected 3 times weekly beginning at d 6 or 7 postpartum until 7 d after second ovulation. Average days from calving until first detection of a 10-mm follicle were fewer in N (8.0 d) and S (8.9 d) than in T (10.5 d) cows. Time from calving to first ovulation was earlier in N (13.2 d) than in S (23.8 d) and T (31.9 d) cows. A greater percentage of follicles of the first follicular wave ovulated in N (89%; 16/18) than in T (42%; 8/19), with S (62%; 13/21) cows being intermediate. Double ovulation rate at the first ovulation was greater in T (61%) than N (16%), with S (35%) intermediate. No difference was detected in double ovulation rate at second ovulation (13/56). Number of cows with persistent corpus luteum (>30 d; 15/56) was not different among groups; however, short luteal phases were greater in N (28%; 5/18) than S (0%; 0/20) cows. Days to first artificial insemination were fewer in N (69.4 d) and S (68.0 d) than in T (75.0 d). First-service conception rate was greater in N (55%; 11/20) than in T (20%; 4/20), with S (26%; 6/23) cows being intermediate. Days open in pregnant cows were fewer in N (93.8 d) than in T (145.4 d), with S (121.2 d) cows being intermediate. Thus, shortening or eliminating the dry period leads to earlier postpartum ovulation and the result. [ABSTRACT FROM AUTHOR]

The objective was to determine the effects of intravenous infusion of triacylglycerol (TAG) emulsions derived from different lipid sources on energy metabolism during a 4-d fast. Six nonpregnant, nonlactating multiparous Holstein cows were randomly assigned to treatments in a replicated 3 x 3 Latin Square design. Treatments included intravenous infusion of tallow, linseed oil, or fish oil emulsions at a rate of 0.54 g of TAG/kg of body weight per day; infusions were concurrent with a 4-d fast. The emulsions were administered for 20 to 30 min every 4 h throughout the 4-d fast. Cows were fed ad libitum for 24 d between the fast/infusion periods. Infusion of tallow, linseed oil, or fish oil emulsions increased plasma concentrations of palmitic acid, linolenic acid, and eicosapentaenoic and docosahexaenoic acids, respectively. Infusion of linseed oil emulsion decreased plasma TAG concentrations compared with tallow and fish oil treatments, which were similar. Infusion of the tallow emulsion resulted in the highest concentrations of plasma nonesterified fatty acid (NEFA), insulin, and glucose, whereas the infusion derived from linseed oil had the lowest NEFA and β-hydroxybutyric acid concentrations. The different TAG emulsions had no effect on total or peroxisomal oxidation of [1-14C]oleic acid in liver homogenates. Liver TAG content increased 12.0, 7.8, and 14.1 µ/µg of DNA during the fast for tallow, linseed oil, and fish oil treatments, respectively; linseed oil was different from fish oil and tended to be different from tallow. [ABSTRACT FROM AUTHOR]

A study was conducted to evaluate the effect of including alfalfa preserved either as silage or long-stem or chopped hay on DMI and milk fat production of dairy cows fed corn silage-based diets with supplemental tallow (T). Fifteen Holstein cows that averaged 117 DIM were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments (DM basis) were: l) 50% corn silage:50% concentrate without T (CS); 2) 50% corn silage:50% concentrate with 2% T (CST); 3) 25% corn silage:25% short-cut alfalfa hay:50% concentrate with 2% T SAHT); 4) 25% corn silage:25% long-cut alfalfa hay:50% concentrate with 2% T (LAHT); and 5) 25% corn silage:25% alfalfa silage:50% concentrate with 2% T (AST). Cows were allowed ad libitum consumption of a TMR fed 4 times daily. Diets averaged 16.4% CP and 30.3% NDF. Including 2% T in diets with corn silage as the sole forage source decreased DMI and milk fat percentage and yield. Replacing part of corn silage with alfalfa in diets with 2% T increased milk fat percentage and yield. The milk fat of cows fed CST was higher in traps-10 C18:1 than that of cows fed diets with alfalfa. No effect of alfalfa preservation method or hay particle length was observed on DMI and milk production. The milk fat percentage and yield were lower, and the proportion of traps-10 C 18:1 in milk fat was higher for cows fed LAHT than for cows fed SAHT. Alfalfa preservation method had no effect on milk fat yield. Ruminal pH was higher for cows fed alfalfa in the diets, and it was higher for cows fed LAHT than SAHT. Feeding alfalfa silage or chopped hay appears to be more beneficial than long hay in sustaining milk fat production when 2% T is fed with diets high in corn silage. These results support the role of traps fatty acids in milk fat depression. [ABSTRACT FROM AUTHOR]

The objectives were to assess the use of nicotinic acid (NA) to chronically (i.e., 74 h) manipulate plasma nonesterified fatty acid (NEFA) concentrations in partially feed-restricted lactating cows, determine whether the reduction of plasma NEFA altered responses to i.v. glucose tolerance test (ivGTT) and whether NA would attenuate an acute lipolytic stimuli of a β-agonist challenge (ivBAC). Eight lactating dairy cows [244 ± 31 d in milk; 696 ± 63 kg of body weight (BW)] were blocked by breed and body condition score (3.2 ± 0.4) and randomly assigned to a sequence of 2 treatments in a crossover design. Treatments were 74-h continuous abomasal infusion of NA solution (3 mg/h per kg of BW) as an antilipolytic agent to decrease plasma NEFA concentrations or the same volume of water (200 mL/h), concomitant with partial feed restriction. From 0 to 74 h of each experimental period, cows were feed-restricted to 33% of the ad libitum intake recorded during the prior 5 d. An ivGTT (0.25 g/kg of BW of glucose i.v.) and an ivBAC (4 nmol/kg of BW of isoproterenol hydrochloride, i.v.) were performed at 48 and 72 h, respectively. Intake was 24.1, 8.2, 8.0, and 8.0 kg of dry matter/d before restriction, on d 1, 2 and 3, respectively. Nicotinic acid decreased plasma NEFA and increased insulin and glucose concentrations during feed restriction. Nicotinic acid also led to greater glucose and insulin response areas under the curve during ivGTT [glucose: 6,562 vs. 5,056 (mg/dL)×180 min; insulin: 6,042 vs. 2,502 (μIU/mL)×180 min] and ivBAC [glucose: 535 vs. 240 (mg/dL)×120 min; insulin: 1,283 vs. 222 (μIU/mL)×120 min], and enhanced NEFA area under the curve during ivBAC [45,521 vs. 22,862 (μEq/L)×120 min]. Milk, fat, and protein yields (29.1, 1.2, and 0.93 kg on d-2, respectively) decreased to 17.9, 0.81, and 0.56 kg for control, and 11.5, 0.54, and 0.39 kg for NA on d 3, respectively. Nicotinic acid may have decreased production by inhibiting the supply of NEFA for energy and milk fat synthesis. Milk urea nitrogen was increased by NA on d 2 (12.8 vs. 19.1 mg/dL) and d 3 (11.6 vs. 17.8 mg/dL), probably due to a greater reliance on mobilized amino acids. Somatic cell count was increased by NA on d 3 (187 vs. 848 ×1,000 cells/mL). Patterns of glucose and insulin concentration observed during 74 h of NA infusion reflect a state of insulin resistance, which contrasts with shorterterm responses in nonlactating cows. Data suggest that long-term supraphysiological infusion of NA affected intermediary metabolism beyond antilipolysis and did not inhibit acute lipolytic stimuli of ivBAC. [ABSTRACT FROM AUTHOR]

The relationship between energy status and fertility in dairy cattle was retrospectively analyzed by comparing fertility with body condition score (BCS) near artificial insemination (AI; experiment 1), early postpartum changes in BCS (experiment 2), and postpartum changes in body weight (BW; experiment 3). To reduce the effect of cyclicity status, all cows were synchronized with Double-Ovsynch protocol before timed AI. In experiment 1, BCS of lactating dairy cows (n = 1,103) was evaluated near AI. Most cows (93%) were cycling at initiation of the breeding Ovsynch protocol (first GnRH injection). A lower percentage pregnant to AI (P/AI) was found in cows with lower (≤2.50) versus higher (≥2.75) BCS (40.4 vs. 49.2%). In experiment 2, lactating dairy cows on 2 commercial dairies (n = 1,887) were divided by BCS change from calving until the third week postpartum. Overall, P/AI at 70-d pregnancy diagnosis differed dramatically by BCS change and was least for cows that lost BCS, intermediate for cows that maintained BCS, and greatest for cows that gained BCS [22.8% (180/789), 36.0% (243/675), and 78.3% (331/423), respectively]. Surprisingly, a difference existed between farms with BCS change dramatically affecting P/AI on one farm and no effect on the other farm. In experiment 3, lactating dairy cows (n = 71) had BW measured weekly from the first to ninth week postpartum and then had superovulation induced using a modified Double-Ovsynch protocol. Cows were divided into quartiles (Q) by percentage of BW change (Q1 = least change; Q4 = most change) from calving until the third week postpartum. No effect was detected of quartile on number of ovulations, total embryos collected, or percentage of oocytes that were fertilized; however, the percentage of fertilized oocytes that were transferable embryos was greater for cows in Q1, Q2, and Q3 than Q4 (83.8, 75.2, 82.6, and 53.2%, respectively). In addition, percentage of degenerated embryos was least for cows in Q1, Q2, and Q3 and greatest for Q4 (9.6, 14.5, 12.6, and 35.2% respectively). In conclusion, for cows synchronized with a Double-Ovsynch protocol, an effect of low BCS (≤2.50) near AI on fertility was detected, but change in BCS during the first 3 wk postpartum had a more profound effect on P/AI to first timed AI. This effect could be partially explained by the reduction in embryo quality and increase in degenerate embryos by d 7 after AI in cows that lost more BW from the first to third week postpartum. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effect of a rumen-protected niacin product (RPN; 65% nicotinic acid; NiaShure, Balchem Corp., New Hampton, NY) on lipid metabolism, oxidative stress, and performance of transition dairy cows. Thirty nonlactating multiparous Holstein cows in late gestation were paired according to expected calving date and randomly assigned to 12 g/ cow per day of RPN product or to an unsupplemented control (CON) diet. Treatment diets were fed from 21 d before expected calving through 21 d after parturition. Blood samples were taken on d -21, -14, -7, 1, 7, 14, and 21 relative to calving for plasma nonesterified fatty acid (NEFA), β-hydroxybutyrate (BHBA), glucose, and superoxide dismutase (SOD) analyses. Liver samples were taken by biopsy on d 1 and 21 relative to calving for triglyceride (TG) analysis. Data were analyzed for a randomized complete block design with repeated measures. Pre- and postpartum dry matter intake, milk yield, and protein were unaffected by treatment. Milk fat percentage (5.08 vs. 4.44%) and somatic cell score (3.93 vs. 2.48) were reduced for RPN. Treatment x time interactions were observed for energy-corrected milk (ECM) and fat-corrected milk (FCM) yields; RPN reduced ECM and FCM yields by 8.5 and 8.9 kg/ cow per day, respectively, in the first week of lactation. Although body weight and condition score decreased during the experimental period, no differences due to treatment were observed. However, calculated postpartum energy balance tended to be improved for RPN because of the reduction in ECM yield. Time and treatment x time effects were observed for plasma NEFA. On d 1 postpartum, NEFA reached 1,138 ± 80 µEq/L for CON compared with 698 ± 80 µEq/L for RPN. Cows supplemented with RPN tended to have lower plasma NEFA concentrations than CON cows on d 7 and 14 postpartum. Plasma BHBA, glucose, and SOD and liver TG concentrations were unaffected by treatment. In conclusion, supplementation with 12 g/cow per day of the RPN product provided a bioavailable source of niacin that modified lipid metabolism but did not affect milk yield over the first 3 wk of lactation or oxidative stress of transition dairy cows. [ABSTRACT FROM AUTHOR]

Some studies have reported improved reproductive performance with dietary fat supplementation. This study examined effects of fatty acids with different lengths, or desaturation, or both, on metabolism of estradiol (E2) and progesterone (P4) in bovine liver slice incubations (experiments 1 and 2) and in vivo (experiment 3). In experiment 1, effects of fatty acids C16:0 (palmitic acid), C16:1 (palmitoleic acid), C18:1 (oleic acid), and C18:3 (linolenic acid) were evaluated at 30, 100, and 300 μM on P4 and E2 metabolism in vitro. In experiment 2, stearic acid (C18:0) and C18:3 were evaluated in the same incubation conditions. In experiment 1, all of the fatty acids had some significant inhibitory effect on metabolism of P4, E2, or both (300 μM C16:0 on E2; 100 μM C16:1 on E2; 300 μM C16:1 on both P4 and E2; 300 μM C18:1 on P4; and 100 and 300 μM C18:3 on both P4 and E2). In experiment 2, C18:3 (100 and 300 μM) but not C18:0 decreased P4 and E2 metabolism. Overall, the most profound increase (~60%) in half-life of P4 and E2 was observed with incubations of 300 μM C18:3 in both in vitro experiments. Based on these in vitro results, in experiment 3 linseed oil (rich in C18:3) was supplemented into the abomasum and acute effects on metabolism of E2 and P4 were evaluated. Cows (n = 4) had endogenous E2 and P4 minimized (corpus luteum regressed, follicles aspirated) before receiving continuous intravenous infusion of E2 and P4 to analyze metabolic clearance rate for these hormones during abomasal infusion of saline (control) or 70 mL of linseed oil every 4 h for 28 h. Linseed oil infusion increased C18:3 in plasma by 46%; however, metabolic clearance rate for E2 and P4 were similar for control cows compared with linseed-treated cows. Thus, in vitro experiments indicated that E2 and P4 metabolism can be inhibited by high concentrations of C18:3. Nevertheless, in vivo, linseed oil did not acutely inhibit E2 and P4 metabolism, perhaps because insufficient C18:3 concentrations (increased to ~8 μM) were achieved. Further research is needed to determine the mechanism(s) of fatty acid inhibition of P4 and E2 metabolism and to discover practical methods to mimic this effect in vivo. [ABSTRACT FROM AUTHOR]

The objective was to determine the effects of abomasal infusion of linseed oil on liver triglyceride (TG) accumulation and adipose tissue lipolysis during an experimental protocol for induction of fatty liver. Eight nonpregnant, nonlactating Holstein cows were randomly assigned to treatments in a replicated 4 x 4 Latin square design. Treatments were abomasal infusion of water (W), tallow (T), linseed oil (LO), or half linseed oil and half tallow (LOT) at a rate of 0.56 g/kg of body weight per day. Each experimental period consisted of a 4-d fast concurrent with administration of treatments into the abomasum in 6 equal doses per day (every 4 h). Cows were fed ad libitum for 24 d between periods of fasting and lipid infusion. Infusion of linseed oil (LO and LOT) increased a-linolenic acid (C18:3n-3) content in serum (12.2, 10.4, 4.2, and 4.6 g/100 g of fatty acids for LO, LOT, T, and W, respectively), but not in the nonesterified fatty acid (NEFA) fraction of plasma. Treatments had no effect on plasma NEFA concentrations. Abomasal infusion of lipid increased in vitro stimulated lipolysis in subcutaneous adipose tissue, compared with W (4,294, 3,809, 4,231, and 3,293 nmol of glycerol released x g-1 tissue x 2 h-1 for LO, LOT, T, and W, respectively), but there was no difference between fat sources. Hepatic TG accumulation over 4-d fast was 2.52, 2.60, 2.64, and 2.09 ± 0.75 μg of TG/μg of DNA for W, LO, LOT, and T, respectively, which did not differ. Abomasal infusion of LO did not reduce liver TG accumulation, plasma NEFA concentration, or alter in vitro adipose tissue lipolysis when compared with T. These results contrast with a previous study involving i.v. infusion of lipid emulsion derived from LO. Discrepancies might be explained by the use of different administration routes and a relatively modest induction of liver TG accumulation in the current experiment. [ABSTRACT FROM AUTHOR]

Days dry may influence reproductive measures such as days to first postpartum ovulation, days open, and pregnancy per artificial insemination (AI). Holstein cows (n = 781) from an approximately 3,000-cow commercial dairy operation were randomly assigned to 1 of 2 treatments with different targeted dry period (DP) lengths. Treatments were 1) a traditional DP of 55 d (T) or 2) a shortened DP of 34 d (S). All dry cows on T were fed a low-energy diet until 35 d before expected calving, and then at 34 d before expected calving, cows on T and S were fed a moderate energy diet until parturition. After parturition, all cows consumed the same diets that included a postcalving diet followed by a lactation diet. Actual days dry for each treatment were close to expected values, 34 and 56 d for S and T, respectively. Median days until first postpartum ovulation occurred sooner for S compared with T (35 vs. 43 d). The percentage of cows that were classified anovular by 70 d in milk (DIM) was more than 2-fold greater for cows on T than S (18 vs. 8%). Cows received AI after standing estrus starting at d 45, and the percentage of cows pregnant at 70 DIM tended to be greater for S than T; younger cows were similar (20.2 vs. 18.8%), but there was a difference between S and T in older cows (20.3 vs. 10.6%). Similarly, median days open tended to be fewer for cows on S than T. At 300 DIM, 85% of cows in both treatments were pregnant. Combining data from first and second service, pregnancies per AI were greater in older cows on S than T (32 vs. 24%). Thus, shortening the DP appeared to increase reproductive efficiency in older cows by shortening time to first ovulation, reducing numbers of anovular cows, and improving fertility. Future studies at more locations with varying reproductive management strategies are needed to confirm and provide the mechanistic basis for these results. [ABSTRACT FROM AUTHOR]

Holstein cows (n = 781) in a commercial dairy herd were used in a randomized design to evaluate 2 dry period (DP) management strategies on milk production, milk components, milk quality, colostrum quality, and incidence of metabolic disorders. Cows were randomly assigned to a traditional 55 d (T) or shortened 34 d (S) DP. Cows assigned to T were fed a low-energy diet until 34 d before expected calving at which time all cows were fed a moderate-energy transition diet until calving. Postpartum, cows assigned to T produced more milk and tended to produce more solids-corrected milk than cows on S. Treatment differences in milk and solids- corrected milk yield were accounted for by cows in their second lactation. Milk fat percentage did not differ between treatments, but milk protein percentage was greater for cows assigned to S. Colostrum quality measured as IgG concentration did not differ between management strategies. Somatic cell score and cases of mastitis were not affected by management strategy. There was a tendency for prepartum nonesterified fatty acid (NEFA) to be lower for cows assigned to T compared with S. However, postpartum, cows assigned to S had significantly lower NEFA concentrations than those assigned to T. The incidences of ketosis, retained placenta, displaced abomasum, and metritis did not differ between treatments. Postpartum energy balance, as indicated by plasma NEFA, may have been improved for cows assigned to S; there was no detectable effect on animal health. [ABSTRACT FROM AUTHOR]

The objective was to study the effects of abomasal infusion of linseed oil, a source rich in n-3 C18:3, on whole-body response to insulin (experiment 1) and on insulin antilipolytic effects during feed restriction (experiment 2). In experiment 1, eight nonlactating, nongestating cows were assigned to a crossover design, fed to meet maintenance requirements, and infused abomasally with either linseed oil (LIN) or tallow (TAL) at a rate of 0.54 g/kg of body weight per d for 5.5 d. Infusions were performed every 8 h during the first 3 d of each period and every 4 h thereafter. Intravenous glucose tolerance tests (IVGTT) were performed on d 5 of each period, followed by i.v. insulin challenges (IC) 12 h later. In experiment 2, six nonlactating, nongestating cows were assigned to a replicated 3 x 3 Latin square design. The experimental protocol included a water (WTR) treatment and feeding was suspended on d 3, leading to 50 and 62 h of feed restriction before IVGTT and IC, respectively. Clearance of glucose during IVGTT and IC was not affected by treatments in either experiment. However, LIN had an insulin sensitizing effect in experiment 1, because a lower insulin concentration led to the same clearance of glucose as TAL. In experiment 1, plasma nonesterified fatty acid (NEFA) concentration was low, reflecting a postprandial state, but NEFA was greater for LIN than TAL during IVGTT (108 vs. 88 ± 4 µEq/L) and IC (133 vs. 83 ± 9 µEq/L). In experiment 2, insulin concentrations during IVGTT did not differ across treatments. Basal plasma NEFA concentration before IVGTT tended to be greater for LIN than for TAL (612 vs. 508 µEq/L). Plasma NEFA clearance rate during IVGTT was greater for LIN than for TAL (2.8 vs. 2.5%/min), leading to a shorter time to reach half NEFA concentration (25 vs. 29 min) and greater absolute value of NEFA response area under the curve [AUC; -64,150 vs. -46,402 (µEq/L) x 180 mini. Data suggest that LIN enhanced the antilipolytic effects of insulin. Yet, other factors could have been involved because plasma NEFA concentration before IVGTT was 104 µEq/L greater for LIN than TAL for unknown reasons. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate if supplementing rumen-protected choline (RPC; Reashure, Balchem Encapsulates, Slate Hill, NY) could prevent or alleviate fatty liver in dairy cattle. The first experiment evaluated the effect of supplementing RPC on hepatic triacylglycerol (TAG) accumulation during fatty liver induction. Twenty-four dry cows between 45 to 60 d prepartum were paired by body weight (BW) and body condition score (BCS) and randomly assigned to control or supplementation with 15 g of choline as RPC/d. From d 0 to 6, before treatment application, all cows were fed 1.4 kg/d of concentrate and forage ad libitum. Samples of blood and liver, obtained during the pretreatment period, were used for covariate adjustment of blood metabolites and liver composition data. During fatty liver induction (d 7 to 17), cows were fed 1.4 kg/d of concentrate with or without supplementation with RPC, and forage intake was restricted, so cows consumed 30% of the total energy requirements for pregnancy and maintenance. Supplementation with RPC during fatty liver induction did not affect plasma glucose and plasma β-hydroxybutyrate (BHBA) concentration but did decrease plasma nonesterified fatty acid (NEFA; 703 vs. 562 µEq/L, SE = 40) and liver TAG accumulation (16.7 vs. 9.3 µg/µg of DNA, SE = 2.0). In the second experiment, we evaluated the effect of supplementing RPC on the clearance of liver TAG when cows were fed ad libitum after the induction of fatty liver by feed restriction. Twenty-eight cows between 45 and 60 d prepartum were paired according to BCS and BW and assigned to treatments. Fatty liver was induced by feeding 1.4 kg/ d of concentrate (without RPC) and restricting forage intake, so cows consumed 30% of maintenance and pregnancy energy requirements for 10 d. From d 11 to 16, after feed restriction, cows were fed forage ad libitum and 1.4 kg/d of concentrate with or without RPC. Treatments were not applied during fatty liver induction; however, following feed restriction, liver for cows assigned to control and RPC treatments contained 6.8 and 12.7 µg of TAG/µg of DNA, respectively. Measurements obtained before treatment served as covariates for statistical analysis. During the depletion phase, plasma glucose, BHBA, and NEFA were not affected by treatment. Liver TAG, expressed as covariate adjusted means, was 6.0 and 4.9 µg/µg of DNA (SE = 0.4) on d 13, and 5.0 and 1.5 µg/µg of DNA (SE = 0.9) on d 16 for control and RPC, respectively. Rumen-protected choline can prevent and possibly alleviate fatty liver induced by feed restriction. [ABSTRACT FROM AUTHOR]

Forty-eight Holstein cows were used in a randomized block design to evaluate different dry period lengths and prepartum milking frequencies (MF) on subsequent milk production, milk composition, solids-corrected milk production, dry matter intake (DMI), and energy balance. Lactating cows, milked 2 times/d, began a 7-d covariate period 35 d prior to the expected calving date. Cows were milked 0 times/d (0x), 1 time/d (1x), and 4 times/d (4x) for the last 28 d of gestation. If milk production decreased to less than 0.5 kg/milking or 1 kg/d, milking via machine ceased; however, teat stimulation continued 1 or 4 times/ d according to the treatment assignment. All cows were milked 2 times/d postpartum (wk 1 to 10). Prepartum DMI tended to be greater for lx and 4x compared with 0x. Prepartum, cows milked lx produced 17% less milk than cows milked 4x (5.9 and 7.1 kg/d, respectively). There were no differences in prepartum and postpartum body condition scores, body weights, and DMI. Postpartum milk production by cows following their third or greater gestation was greater for 0x and 4x compared with 1x. Postpartum milk production by cows following their second gestation was significantly decreased with increased MF (0x vs. 1x and 4x). Regardless of parity, postpartum solids-corrected milk was greater for 0x compared with 1x and 4x. Postpartum fat yield was greater for 0x vs. 4x, with lx being intermediate. Postpartum protein yield was greater for 0x vs. 4x, whereas 0x tended to have greater protein yield than lx. Postpartum energy balance was greater for 1x and 4x relative to 0x. Continuous milking (1x and 4x) resulted in a loss of milk production in the subsequent lactation for cows following their second gestation; however, for cows following their third or greater gestation, increasing the MF from 1x to 4x in the last 28 d of gestation alleviated the loss in milk production. [ABSTRACT FROM AUTHOR]

Effects of dietary energy density during late gestation and early lactation on metabolic status of periparturient cows were studied. Four weeks before expected calving, animals were fed a low (DL; 1.58 Mcal of NEL/ kg) or high energy density diet (DH; 1.70 Mcal of NEL/ kg). After calving, half of the cows from each prepartum treatment were assigned to a low (L; 1.57 Mcal of NEL/ kg) or high energy density diet (H; 1.63 Mcal of NEL/kg) until d 20 postpartum. After d 20, all animals were fed H until d 70. Animals fed DH had a more positive energy balance during the prepartum period. Animals fed DH had higher plasma concentrations of glucose and insulin and lower concentrations of plasma nonesterified fatty acid (NEFA) on d -7 relative to calving compared with animals fed DL. No differences in blood concentrations of metabolites, insulin and liver triglycerides (TG) content were observed on d 1. Liver TG content at d 1 and 21 were more related to magnitude of change in energy intake prepartum than to energy intake in the last week of gestation. Cows fed H had higher concentrations of plasma glucose and insulin, but similar plasma NEFA during the postpartum period compared with cows fed L. Plasma concentrations of β-hydroxybutyrate (BHBA) and liver TG content on d 21 were 46 and 30% lower, respectively, for cows fed H compared with cows fed L. Interactions between prepartum and postpartum treatments indicated that negative effects of delaying higher concentrate feeding until d 21 postpartum can be partially offset by increasing concentrate in the diet before calving. Cows fed L had a higher increase in white line hemorrhage scores between prepartum and 10 wk postpartum compared with cows fed H. Energy density of prepartum diets had a minor influence on metabolic status of cows postpartum. A more favorable metabolic profile occurs when increasing the concentrate content of the diet immediately postpartum compared with delaying the increase until d 21 postpartum. [ABSTRACT FROM AUTHOR]

Provides information on a study that examined the impact of corn silage particle length on rumen function and milk fat production of lactating dairy cows fed supplemental tallow in diets with processed high grain-yielding corn silage as the only forage source. Methodology of the study; Results and discussion on the study; Conclusions.

Compares the effects of dietary energy density during late gestation and early lactation on lactation performance and ruminal parameters of dairy cows. Prepartum performance and ruminal parameters; Parity interactions; Effects of increasing prepartum diet energy density on overall postpartum performance.

The objectives were to determine effects of 12 hourly infusions of different quantities of nicotinic acid (NA) on plasma nonesterified fatty acid (NEFA; experiment 1) and whether longer (108 h) continuous infusions of NA could induce sustained reductions of plasma NEFA (experiment 2) in nonlactating, nongestating Holstein cows that were feed restricted. Experiment 1 was a 5×5 Latin square with 6-d periods and 9 recovery days between each period. Each period consisted of 5 d of partial feed restriction to increase plasma NEFA concentration. Treatments were abomasal infusions of 0, 0.25, 0.5, 1, or 3 mg of NA/h per kilogram of body weight (BW), infused as hourly boluses for 12 h, starting 4 d after initiation of partial feed restriction. Plasma NEFA was decreased for the highest dose: from 448 μEq/L to 138±75 μEq/L at 1 h after the first bolus of 3mg of NA/h per kilogram of BW. This initial reduction in plasma NEFA concentration was followed by an increase in concentration at 2, 3, and 4 h relative to initiation of infusions. Plasma NEFA then decreased to 243 μEq/L 6h after initiation of treatments and remained low until termination of infusions. A rebound in plasma NEFA concentration occurred at 3 and 4 h after termination of infusion for cows that received 3 mg of NA/h per kilogram of BW. Experiment 2 was a 5×5 Latin square with 7-d periods and 9 recovery days between each period. Each period consisted of 5 d of partial feed restriction to increase plasma NEFA concentration. Treatments were continuous abomasal infusion of 0, 0.5, 1, or 3 mg of free NA/h per kilogram of BW for 4.5 d starting at feed restriction or 0.5 mg of NA/h per kilogram of BW infused directly into the rumen in a form protected from microbial degradation. The ruminal administration of protected NA was initiated 2 d before abomasal infusions and initiation of feed restriction to establish steady postruminal delivery of NA by start of abomasal infusions. Plasma NEFA was approximately 70 μEq/L before initiation of feed restriction and increased to 509, 587, 442, 850, and 108 μEq/L at 4.5 d for cows that received 0, 0.5 (protected NA), 0.5 (free NA), 1, and 3 mg of NA/h per kilogram of BW, respectively. An antilipolytic response was achieved with the highest abomasal dose, which maintained plasma NEFA concentration lower than the control group. An increase in plasma NEFA concentration was observed after termination of infusions for cows that received 1 and 3 mg of NA/h per kilogram of BW. Plasma NEFA was 1,900 μEq/L at 4h after termination of infusion for cows receiving 1 mg of NA/h per kilogram of BW and 1,360 μEq/L at 5h after termination of infusion for cows receiving 3 mg of NA/h per kilogram of BW. In nongestating, nonlactating cows it is unlikely that a dose of NA exists that will reduce plasma NEFA concentration and prevent the rebound that occurs following termination of NA administration., (Copyright © 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Sixty-five Holstein cows were used to evaluate management schemes involving altered dry period (DP) lengths on subsequent milk production, energy balance (EB), and metabolic variables. Cows were assigned to one of 3 treatments: traditional 56-d DP (fed a low-energy diet from -56 to -29 d and a moderate energy diet from -28 d to parturition; T), 28-d DP (continuously fed a high energy diet; S), and no planned DP (continuously fed a high energy diet; N). Prepartum DM intake (DMI), measured from 56 d prepartum through parturition, was lower for cows on the T treatment than for cows on the S treatment and was higher for cows on the N treatment than for cows on the S treatment. There were no differences in prepartum plasma glucose, and beta-hydroxybutryric acid; there was a treatment by time interaction for prepartum plasma nonesterified fatty acid (NEFA). There was no difference in prepartum liver triglyceride (TG); postpartum liver TG was decreased for cows on the N treatment compared with cows on the S treatment, but was similar for cows on the T and S treatments. Postpartum NEFA was similar between cows on the T and S treatments, but was greater for cows on the S treatment than for cows on the N treatment. Postpartum glucose was greater for cows on the N treatment compared with cows on the S treatment and tended to be greater for cows on the S treatment than for cows on the T treatment. There was no difference in postpartum solids-corrected milk (SCM) production or DMI by cows on the T vs. S treatment. However, there was a tendency toward lower postpartum SCM production by cows on the N vs. S treatment and a tendency for greater postpartum DMI by cows on the N vs. S treatment. Postpartum EB was greater for cows on the S vs. T treatment and the N vs. S treatment. In general, T and S management schemes had similar effects on DMI, SCM, and metabolic variables in the first 70 d of the subsequent lactation. Eliminating the DP improved energy and metabolic status.

The objectives of this study were to develop and validate a model for predicting dry matter intake (DMI) of Holsteins during the prefresh transition period. The original database (ODB) for model development was established by compiling parity, body condition score (BCS), and DMI data during the final 3 wk of gestation from 366 Holsteins fed 24 different diets that were used in eight experiments conducted at three universities. For model validation, a validation database (VDB) was established by compiling data from 333 prefresh transition Holsteins fed 25 different diets that were used in eight experiments conducted at five universities. Dry matter intake during the prefresh transition period was fitted to an exponential function: DMI(t) = a + pe(kt), where DMI(t) = DMI as a percentage of body weight (BW) at time t, a = asymptotic intercept at time--infinity, p = change in intake (kg) from the asymptotic intercept until parturition, k = rate constant influencing the shape of the curve, and t = day relative to parturition expressed as days pregnant--280. The model developed from the ODB predicted DMI of heifers in the VDB with satisfactory accuracy and precision. However, this was not true for cows, probably due to differences in BCS of cows and diets fed to cows from the two data sets. When a subset of cows was selected from each data set that had similar BCS (> 4.0) and were fed similar diets, accuracy and precision of the model predicting DMI was improved. Finally, both databases were combined to develop final models for predicting DMI of heifers and cows. Proposed models for predicting mean daily DMI of heifers and cows during the prefresh transition period were DMI(t) = 1.713-0.688e(0.344t) (R2 = 0.96) and DMI(t) = 1.979-0.756e(0.154t) (R2 = 0.97), respectively. Adjustment factors for animal and dietary factors were generated to demonstrate the plausibility of adaptive fitting of the prediction. The regression coefficients of prediction models (a, p, and k) were affected by BCS and dietary organic macronutrient concentrations.

Parity, body condition score (BCS), and dry matter intake (DMI) data of 699 Holsteins fed 49 different diets during the final 3 wk of gestation (prefresh transition period) were compiled from 16 experiments conducted at eight universities. The objectives of this study were to determine the effects of animal and dietary factors on DMI and to elucidate interactions between animal and dietary factors and among dietary factors on DMI during the prefresh transition period. Animal factors examined were parity and BCS, whereas dietary factors examined were rumen undegradable protein (RUP), rumen degradable protein (RDP), neutral detergent fiber (NDF), and ether extract (EE). DMI decreased 32% during the final 3 wk of gestation, and 89% of that decline occurred during the final week of gestation. Day of gestation, animal factors, and dietary factors accounted for 56.1, 19.7, and 24.2% of explained variation in DMI, respectively, and R2 of this linear multivariable model was 0.18. Cows had higher DMI than heifers. DMI decreased linearly as BCS, RUP, and NDF increased, decreased quadratically as EE increased, and increased quadratically as RDP increased. Moreover, the magnitude of DMI depression as animals approached parturition was affected by characteristics of animals and dietary nutrient composition. There were significant parity x EE, BCS x NDF, RUP x NDF, RDP x NDF, NDF x EE, and RUP x EE interactions on DMI. In conclusion, parity, BCS, and concentrations of organic macronutrients in diets affected DMI during the prefresh transition period, and the magnitude of DMI depression as animals approached parturition.

The objectives were to determine the metabolic fate of different long-chain fatty acids, and their effects on palmitic acid metabolism and gluconeogenesis in bovine hepatocytes. Hepatocytes were isolated from four ruminating calves and exposed in suspension for 3 h to one of the following treatments: 1 mM palmitic acid (1C16), 2 mM palmitic acid (2C16), or 1 mM palmitic acid plus either 1 mM oleic (C18:1), linoleic (C18:2), linolenic (C18:3), eicosapentaenoic (C20:5), or docosahexaenoic acid (C22:6). Oxidation of [1-(14)C]palmitic acid or one of the [1-(14)C]-labeled treatment fatty acids to CO2 or incorporation into cellular triglycerides (TG), phospholipids, cholesterol, and cholesterol esters were measured. Rates of oxidation to CO2 were 3- to 4-fold higher for C22:6 than for other fatty acids, with the exception of C20:5, which had intermediate rates of oxidation to CO2. In general, treatments 2C16 and C18:1 yielded the highest rates of incorporation into most cellular lipids, whereas the polyunsaturated fatty acids were poor substrates for incorporation into cellular lipids. The most pronounced change was a large reduction of polyunsaturated fatty acid incorporation into cellular TG compared to 1C16, 2C16, and C18:1. The unsaturated fatty acids also influenced palmitic acid metabolism. The addition of C20:5 yielded the highest rates of palmitic acid oxidation to CO2 followed by addition of C18:1 and C22:6. Treatments containing polyunsaturated fatty acids decreased palmitic acid metabolism to TG and total cellular lipids compared with treatments 2C16 and C18:1. Rates of gluconeogenesis from propionate were significantly higher for the treatment containing C18:1. Long-chain fatty acids vary in their routes of metabolism and influence palmitic acid metabolism and gluconeogenesis in bovine hepatocytes.

Twelve Holstein cows and eight heifers were used in a randomized block design to examine changes in rumen fermentation and blood metabolites as animals fed diets containing 9.1 (low protein, LP) or 11.2% crude protein (moderate protein, MP) approached parturition. Animals were blocked by expected calving date and parity. Diets were isocaloric (1.58 Mcal/kg of dry matter), and the difference in dietary crude protein was achieved by the addition of urea. Diets were fed as total mixed rations for ad libitum intake. Dry matter intake decreased from 12.2 kg/d on d -21 to 9.1 kg/d on d -1 relative to parturition and was unaffected by dietary crude protein or parity. Rumen ammonia concentrations were higher for animals fed the MP diet compared with those fed the LP diet (1.8 vs. 3.7 mM). In situ neutral detergent fiber disappearance was not affected by dietary crude protein after 8 h of incubation, but it did decrease from 25.8% on d -21 to 23.3% on d -1. After 16, 24, and 48 h of incubation, neutral detergent fiber disappearance was greater for animals consuming MP than for animals consuming LP (30.6 vs. 34.4%, 37.0 vs. 44.1%, and 57.9 vs. 65.1%, respectively). There was a parity x treatment interaction after 48 h of incubation. Fiber disappearance was 55.7 or 65.9% for heifers and 60.0 or 64.7% for cows fed LP or MP, respectively. The solids rate of passage was not affected by treatment, parity, or day relative to parturition. Concentrations of plasma nonesterified fatty acid (NEFA) increased from 218 microEq/L on d -21 to 619 microEq/L on d -1. There was an interaction between day relative to parturition and parity on NEFA concentrations. Heifers had plasma NEFA concentrations of 272 and 772 microEq/L on d -21 and -1, respectively. Cows had NEFA concentrations of 164 and 467 microEq/L on d -21 and -1, respectively. Plasma glucose concentrations were affected by parity (65.8 and 58.8 mg/dl for heifers and cows). Plasma urea, NEFA, beta-hydroxybutyrate, and glucose concentrations were not affected by dietary treatment. In conclusion, heifers tended to have higher plasma concentrations of NEFA and glucose, but did not have elevated concentrations of beta-hydroxybutyrate. Rumen fermentation was relatively unaffected by day relative to parturition, but feeding less than 11% crude protein to prefresh transition cows may limit ruminal fiber degradation.

The objective of this experiment was to determine whether there is a dose of slow-release insulin (SRI) that decreases concentrations of plasma nonesterified fatty acids (NEFA) and liver triglyceride (TG) without decreasing plasma glucose concentration, dry matter intake (DMI), and milk yield. Forty-three Holsteins weighting 765 +/- 70 kg with body condition score of 3.29 +/- 0.25 (mean +/- SD) were fed for ad libitum consumption of the same diet from 2 wk before parturition through 6 d postpartum. Cows were blocked according to actual calving date and parity and then assigned randomly to intramuscular injection of a single dose of 0, 0.14, 0.29, or 0.43 IU of SRI per kilogram of body weight (BW) on d 3 postpartum. On the day of injection, cows were fed hourly to minimize fluctuations in blood hormones and metabolites due to feed intake pattern. Blood samples were collected via jugular catheter every hour from 0 to 24 h and every 6 h from 24 to 48 h postinjection. Pre- and postinjection period liver samples were taken on d 2 and 5 postpartum. One cow injected with 0.29 and two cows injected with 0.43 IU of SRI per kilogram of BW could not complete the trial due to severe hypoglycemia (< 20 mg/dl). Both DMI and milk yield during d 3 to 5 postpartum tended to increase quadratically by increasing dose of SRI. Concentrations of serum insulin and glucagon increased linearly, concentration of plasma glucose decreased linearly, and concentrations of plasma NEFA and beta-hydroxybutyrate decreased quadratically from 0 to 24 h postinjection by increasing dose of SRI. Serum insulin concentrations remained higher in cows injected with SRI (CISRI) than in cows injected with sterile water (CISW; 0 IU of SRI/kg of BW), the quadratic effect of SRI on plasma NEFA concentration continued, and the linear effect of SRI on plasma glucose concentration diminished from 24 to 48 h postinjection. Concentration of hepatic TG for CISRI tended to be lower than for CISW, and increasing dose of SRI quadratically decreased hepatic accumulation of TG. Increasing dose of SRI tended to increase concentration of hepatic glycogen (GLY) quadratically and decreased the ratio of TG to GLY quadratically. In conclusion, a low dose of SRI (0.14 IU/kg of BW) could be considered for prophylactic use against hepatic lipidosis and ketosis.

A study was conducted to investigate the response to supplemental tallow of lactating cows fed basal diets with different alfalfa silage:corn silage ratios. We postulated that supplemental tallow will have decreasing negative effects on rumen fermentation, dry matter intake (DMI), and milk fat percentage as the dietary ratio of alfalfa silage:corn silage is increased. Eighteen Holstein cows averaging 134 +/- 14 d in milk were used in a replicated 6 x 6 Latin square design with 21-d periods. Treatments were arranged as a 2 x 3 factorial with 0 or 2% tallow (DM basis) and three forage treatments: 1) 50% of diet DM as corn silage, 2) 37.5% corn silage and 12.5% alfalfa silage, and 3) 25% corn silage and 25% alfalfa silage. Cows were allowed ad libitum consumption of a total mixed ration. Diets were formulated to contain 18% crude protein and 32% neutral detergent fiber. No fat x forage treatment interactions were observed. Fat supplemented cows had lower DMI and produced more milk with less milk fat content relative to non-supplemented cows. Concentration of trans-octadecenoic acids was higher in milk fat of tallow-supplemented cows. Tallow supplementation had no effect on ruminal pH and acetate:propionate ratio, but tended to decrease total volatile fatty acid (VFA) concentration in the rumen. Increasing the proportion of alfalfa silage increased DMI, milk fat percentage, and milk fat yield regardless of the fat content of the diet. Total VFA concentration and acetate:propionate ratio in the rumen were increased in response to higher levels of alfalfa in the diets. These results suggest that replacing corn silage with alfalfa silage did not alleviate the negative response of dairy cows to tallow supplementation at 2% of diet DM.

The objective of this study was to investigate the effects of tallow and choice white grease (CWG) fed at 0, 2, and 4% of the diet dry matter (DM) on rumen fermentation and performance of dairy cows when corn silage is the sole forage source. Fifteen midlactation Holstein cows were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments were 0% fat (control), 2% tallow, 2% CWG, 4% tallow, and 4% CWG (DM basis). The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (DM basis). Cows were allowed ad libitum consumption of diets fed twice daily as total mixed rations. Cows fed supplemental fat had lower DM intake and produced less milk and milk fat than cows fed the control diet. Feeding 4% fat reduced milk production and milk fat yield relative to feeding 2% fat. Treatments had little effect on the concentration of trans-octadecenoic acids in milk fat. Total trans fatty acids were poorly related to changes in milk fat percentage. Ruminal pH and total volatile fatty acids concentration were not affected by supplemental fat. The acetate:propionate ratio, NH3-N, and numbers of protozoa in the rumen were significantly decreased when fat was added to the diets. Source of dietary fat did not affect rumen parameters. There was no treatment effect on in situ corn silage DM and neutral detergent fiber disappearance. Including fat in corn silage-based diets had negative effects on milk production and rumen fermentation regardless of the source or level of supplemental fat.

The objectives of this experiment were to determine: 1) if Cys in hydrolyzed feather meal (HFM) can contribute to the supply of sulfur amino acids for meeting requirements of dairy cows; 2) if the feeding value of meat and bone meal (MBM) can be enhanced by HFM or ruminally protected Met (rpMet); and 3) the value of HFM sulfur amino acids relative to rpMet. Fifteen multiparous Holstein cows were used in a replicated 5 x 5 Latin square design with 21-d periods. The control (CTRL) diet was designed to contain feeds that were low in RUP and Met and consisted of 50% alfalfa silage and 50% corn-based concentrate. Additional treatments were modifications of CTRL in which MBM (4% of DM), MBM + rpMet (Smartamine M) (4 and 0.08% of DM), MBM + HFM (4 and 2% of DM), and MBM + rpMet + HFM (4, 0.04, and 1% of DM) replaced corn grain. Feeding MBM depressed milk and 3.5% fat-corrected milk (FCM) yields. Adding rpMet to MBM enhanced dry matter intake, milk and 3.5% FCM yields, and milk crude protein percentage. Milk fat percentage and 3.5% FCM yield were increased when HFM and rpMet were added to MBM. Supplementing HFM to a diet containing MBM could not duplicate the response of adding rpMet to MBM. Results of this study indicate that feeding HFM may not alleviate Met deficiency in lactating dairy cows.

The objective of this trial was to compare the effects of increasing dietary energy density from 1.51 to 1.65 Mcal/kg of dry matter (DM) by replacing forage with concentrate or by further increasing concentrate via the substitution of corn silage and alfalfa silage by a mixture of straw, starch, and soybean meal. Our hypothesis was that the latter diet would be more glucogenic while increasing rumen fill and be potentially desirable for transition cows. Nine far-off dry cows (greater than 3 wk before parturition at the end of the trial) were fed three diets: low energy diet, [LE, 1.51 Mcal/kg of DM, 14.0% crude protein (CP) and 35% nonfiber carbohydrates (NFC)], high energy diet, (HE, 1.65 Mcal/kg of DM, 13.9% CP and 39.5% NFC) and high energy diet, where a portion of alfalfa and corn silage was replaced by straw, soybean meal, and cornstarch (HES, 1.65 Mcal/kg of DM, 13.5% CP and 40.5% NFC). The experiment was a replicated 3 x 3 Latin square design with 21-d periods. Six cows from two squares were used to examine kinetics of DM disappearance from nylon bags suspended in the rumen. Two contrasts of interest were: LE versus HE, HES (effects of energy density) and HE versus HES (method of increasing energy density). Increasing energy density increased the potentially degradable (B) and decreased the undergradable (C) DM fractions of the diets. Because HES had greater B and a faster rate of degradation of fraction B (k), effective rumen degradable DM (ERDDM) was higher in HES compared to HE. Cows fed high energy diets had greater DM intake. No differences in DM intake were observed between HE and HES. Rumen volume or DM pool sizes were not affected by treatment. High energy diets increased total ruminal fluid volatile fatty acid concentration compared with LE. Propionate concentration was higher in cows fed high energy diets compared with cows fed LE. The partial replacement of alfalfa and corn silage by straw, soybean meal, and cornstarch further increased propionate concentration. The greatest increase in serum insulin concentration following feeding was observed in cows fed HE. Cows consuming high energy diets had lower plasma nonesterified fatty acids (NEFA) before and after feeding. The HES diet was less effective in decreasing plasma NEFA concentration after feeding compared to HE. In conclusion, increasing diet energy density of far-off dry cows positively affected DMI, ruminal propionate, serum insulin, and plasma NEFA. Increasing energy density with a blend of feeds that represent extremes in rates of carbohydrate fermentation may be a strategy to provide greater amounts of glucogenic precursors. Applicability of this strategy should be examined in transition cows.

The effect of supplemental chromium as chromium-methionine (Cr-Met) on production and metabolic parameters was investigated in 48 cows from 28 d before expected calving date through 28 d of lactation. Average body weight (BW) was 730 +/- 61 kg before treatment. Treatments were supplementation of 0, 0.03, 0.06, and 0.12 mg of Cr as Cr-Met/kg of BW(0.75). Dry matter intake increased linearly and quadratically during the prepartum and postpartum periods, respectively, and body condition score loss decreased linearly during the postpartum period with increasing Cr-Met. Increasing Cr-Met supplementation caused quadratic increases in milk, fat, and lactose yields. Treatments did not affect concentrations of blood metabolites and liver triglyceride. Serum insulin concentration and molar ratio of insulin to glucose for cows receiving Cr-Met were lower than for cows not receiving Cr-Met, but they increased quadratically with increasing Cr-Met. Glucose tolerance tests (GTT) were conducted on d 10 prepartum and d 28 postpartum. Chromium-methionine supplementation attenuated insulin sensitivity prepartum and enhanced glucose tolerance postpartum, but not prepartum. Basal insulin concentrations for cows receiving Cr-Met were higher than for cows not receiving Cr-Met during the prepartum GTT. During the postpartum GTT, peak glucose concentration and clearance rate decreased and half-life (t(1/2)) and time to reach basal concentration (T) were prolonged quadratically by increasing Cr-Met. Additionally, peak insulin concentration, area under the curve, and molar ratio of insulin to glucose were higher for cows not receiving Cr-Met than for cows receiving Cr-Met and t(1/2) and T were shortened quadratically by increasing Cr-Met.

We conducted three experiments to determine the effects of nutritional and hormonal status on microsomal triglyceride transfer protein (MTP) activity and mass. In experiment 1, 18 nonlactating Holstein cows, 75 d before expected calving date, in their second gestation or greater were monitored from d 75 to 55 prepartum. Cows were fed a control diet from d 75 to 62 prepartum for covariable measurements. From d 61 to 55 prepartum, six cows continued to receive the control diet, six cows were restricted to 2.3 kg of grass hay/d, and six cows were fed the control diet plus 1.8 kg of concentrate/d and 500 ml of propylene glycol given 2 times/d as an oral drench. Plasma glucose and serum insulin concentrations were highest in cows that received propylene glycol and lowest in feed restricted cows. Plasma nonesterified fatty acids (NEFA) and liver triglyceride (TG) concentrations were highest in feed restricted cows and not different between cows that received the control diet and cows that received propylene glycol. Hepatic MTP activity and mass were not affected by treatment in experiment 1. In experiment 2, bovine hepatocytes isolated from the caudate process of five preruminating Holstein bull calves were incubated with either 0, 0.5, 1.0, or 2.0 mM NEFA for 48 h. Intracellular TG increased linearly as NEFA concentration in the media increased. Concentration of NEFA in the incubation media had no effect on MTP activity or mass. There was a quadratic effect of concentration of NEFA in the incubation media on MTP mRNA. In experiment 3, bovine hepatocytes isolated from the caudate process of five preruminating Holstein bull calves were incubated with 2 mM [1-14C]oleate for 24 h to accumulate TG, followed by a 36-h period of TG depletion, during which hepatocytes were incubated with no hormone, 10 nM insulin, or 10 nM glucagon. There was no effect of insulin or glucagon on intracellular TG, MTP activity or mass. Cells incubated with no hormone had higher levels of MTP mRNA compared to cells incubated with insulin or glucagon during the depletion period. Results suggest that hepatic MTP mRNA may be affected by TG accumulation, insulin, and glucagon in vitro. However, hepatic MTP activity and mass are not affected by nutritional status of nonlactating dairy cows, TG accumulation in vitro, or insulin and glucagon in vitro.

We determined the relationship between microsomal triglyceride transfer protein (MTP) (activity, mass, and mRNA) and liver triglyceride concentration in 16 dairy cows (13 multiparous and three primiparous) from 27 d before expected calving (d -27) to 35 d postpartum (d 35), the time period when fatty liver is most likely to develop. In addition, dry matter intake, plasma nonesterified fatty acids (NEFA), and plasma glucose were monitored. There were no significant parity x time interactions. Dry matter intake, plasma NEFA, plasma glucose, and liver triglyceride were significantly affected by day of sampling. Dry matter intake was 10.7, 8.0, and 19.5 kg/d on d -27, 2, and 35, respectively. Plasma NEFA concentration was higher on d 2 (1113 microEq/L) compared with d -27 (201 microEq/L) and 35 (358 microEq/L). Plasma glucose concentration was 63.3, 54.3, and 57.8 mg/dl on d -27, 2, and 35, respectively. Hepatic triglyceride (TG) concentration increased from 1.8 to 11.8% liver TG (DM basis) on d -27 and 2, respectively. There was no difference between hepatic triglyceride concentration on d 2 and 35. There was a significant effect of day of sampling on hepatic MTP activity and mRNA. Hepatic MTP activity decreased from 2.08 to 1.79 nmole triolein transferred/ h per mg of microsomal protein on d -27 and 2, respectively, and increased from 1.79 to 2.17 nmole triolein transferred/h per mg of microsomal protein on d 2 and 35, respectively. Hepatic MTP mRNA increased from d -27 to 2 and remained elevated from d 2 to 35. There was no effect of day of sampling on MTP mass. There were no significant correlations between hepatic MTP activity, mass, or mRNA with either liver TG or plasma NEFA on any of the sampling days. The cause of a decrease in hepatic MTP activity and increase in mRNA on d 2 is unknown. However, the lack of correlation between MTP activity, mass, or mRNA with either liver TG or plasma NEFA on d 2 postpartum suggests that MTP probably does not play a role in the etiology of fatty liver that occurs in dairy cows at calving.

Two experiments were conducted to test the following two hypotheses: 1) fatty liver could hamper hepatic conversion of ammonia to urea and increase circulating ammonia or Gln% [Gln% = Gln x 100/(Gln + Glu)] in cows around parturition; 2) decreased ureagenesis might cause alkalosis and in turn reduce blood Ca. In the first experiment, 14 Holstein cows were monitored from 27 d prepartum to 35 d postpartum. There was a rise in circulating ammonia and Gln% at calving, suggesting an increase in ammonia passing to and through the liver. Stepwise regression analysis revealed the following relationship for plasma samples at 22 h and liver triglyceride at 2 d postpartum: ammonia (microM) = 32.1+/-0.89 triglyceride (% DM), Gln% = 71.2 + 0.23 triglyceride (% DM) + 1.31 urea (mM). The positive correlation between liver triglyceride and plasma ammonia and Gln% suggests that hepatic triglyceride accumulation might inhibit ureagenesis, thereby increasing ammonia concentration at the perivenous hepatocytes where Gln synthesis occurs and increasing ammonia concentration in blood leaving the liver. In the second experiment, 28 rats were used to determine whether hepatic triglyceride accumulation, induced by choline deficiency, affects urinary ammonia N and blood pH homeostasis. There was a trend for a positive correlation between urinary ammonia N and liver triglyceride. No correlation between liver triglyceride and blood pH, bicarbonate, pCO2 or plasma Ca was found. In conclusion, hepatic triglyceride accumulation may inhibit ureagenesis and result in increased circulating ammonia, Gln% and urinary ammonia N in vivo. Hepatic triglyceride accumulation did not affect blood pH homeostasis.

An experiment was conducted to determine if initiation of milking 10 d prior to expected calving could prevent fatty liver by circumventing intake depression and by providing an alternative route for fatty acid metabolism. Prepartum milking tended to increase DMI before calving; liver triglyceride, plasma nonesterified fatty acids, and milk yield were not affected.

Two trials were conducted to examine the effects of supplemental methionine, provided as methionine hydroxy analog 13 g/d), or fat (454 g of calcium salts of long-chain fatty acids/d) on hepatic triglyceride concentration. In the first experiment, methionine hydroxy analog or fat was fed during feed restriction to determine if hepatic triglyceride accumulation is affected. The objective of the second experiment was to determine if feeding fat or methionine hydroxy analog influences the rate of triglyceride depletion from the liver of cows in positive energy balance following the induction of fatty liver by feed restriction. In experiment 1, feeding methionine hydroxy analog decreased plasma glucose, increased plasma nonesterified fatty acids, and had no effect on liver triglyceride. Feeding fat increased plasma nonesterified fatty acids and increased hepatic triglyceride during the 10-d feed restriction period. In experiment 2, feeding fat decreased the rate of triglyceride depletion from liver when cows were allowed to resume ad libitum consumption of feed; methionine hydroxy analog had no effect. Results of these studies indicate that feeding supplemental fat or methionine hydroxy analog at levels tested does not prevent or alleviate fatty liver induced by feed restriction.

The effect of induced parturition and estradiol on feed intake, liver triglyceride, plasma metabolites, and milk yield was evaluated in fifty-six Holstein cows and heifers. Cows were assigned to treatments on d 260 of gestation and were on trial until d 10 postpartum for measurement of dry matter intake (DMI), plasma metabolites, and liver triglyceride and until d 31 postpartum to measure milk yield. Fourteen animals per group (9 cows and 5 heifers) received either a placebo, 1 mg of fenprostalene, 50 mg of estradiol-17 beta benzoate, or both on d 276 of gestation. Cows that received fenprostalene consumed more dry matter (DM) for the last 8 d prepartum than did cows that did not receive fenprostalene (9.6 kg/d vs. 8.5 kg/d, respectively) but consumed less DM for the first 10 d postpartum (10.9 kg/d vs. 13.1 kg/d, respectively). Cows injected with estradiol-17 beta benzoate tended to consume less DM postpartum than did cows not injected with estradiol-17 beta benzoate (11.3 kg/d vs. 12.7 kg/d, respectively). There was no effect of treatment on milk yield; however, a fenprostalene by day interaction resulted from lower milk yield on d 3, 4, 5, 7, and 10 relative to calving in cows that received fenprostalene. Administration of fenprostalene resulted in a delay in the peak plasma nonesterified fatty acid (NEFA) concentration until 2 d after calving. Plasma glucose concentrations were greatest 1 d prior to calving for cows that received fenprostalene, whereas plasma glucose concentrations peaked on the day of calving for cows that did not receive fenprostalene. Liver triglyceride increased over time; however, there was no effect of treatment on liver triglyceride. Calving induction improved DMI for the last 8 d prepartum, but a concomitant decrease in liver triglyceride after calving did not result. Estradiol-17 beta benzoate had no effect on plasma metabolites or liver triglyceride, indicating that the physiological rise in estradiol prior to calving does not have a primary role in lipolysis or hepatic fatty acid metabolism in the dairy cow.

Eight ruminally cannulated Holstein cows (four multiparous and four primiparous) were used in a replicated 4 x 4 Latin square with an extra period to determine the effects of postruminal protein on fatty acid digestibility. Samples were collected during the last 4 d of each 14-d period. Total mixed rations were composed of 41% alfalfa haylage, 42% corn silage, 12% concentrate based on corn, and 5% tallow. Cows were fed at 90% of ad libitum intake. Treatments were abomasal infusion of guar gum or guar gum plus urea, corn gluten meal, or blood meal in 12 L of water. The basal ration contained 12% crude protein (CP), and infusion of N sources increased CP to approximately 14%. Dry matter intake was similar for cows on all treatments. Milk, 3.5% fat-corrected milk, milk protein, and milk fat yields increased for cows receiving postruminal CP. Postruminal CP did not affect milk fat and protein percentages. Dry matter, organic matter, and CP digestibilities were greater in cows receiving postruminal CP. Total fatty acid and total C18 fatty acid digestibilities were not affected by treatment. Total C16 fatty acid and C18:0 fatty acid digestibilities were greater for cows receiving nonprotein N than for those receiving true protein.

A relationship between increased lipid concentration in the liver and reduced hepatic function has been suggested; however, there is little direct evidence of change in specific hepatic functions. Hepatocytes were obtained from ruminating calves and were incubated as monolayers for 36 h. The media contained a mixture of nonesterified fatty acids (NEFA) at 0, 0.5, 1.0, and 1.5 mM NEFA with molar proportions of 0.435 oleate, 0.319 palmitate, 0.144 stearate, 0.049 linoleate, and 0.053 palmitoleate. Ureagenesis or gluconeogenesis was measured from 48 to 51 h after plating using hepatocytes that had only previous (12 to 48 h), only concurrent (48 to 51 h), or previous and concurrent (12 to 51 h) exposure to NEFA. A previous 36-h exposure to NEFA caused cell triglyceride accumulation, yielding triglyceride concentrations that corresponded with liver that is clinically described as normal to moderately fatty. Previous, prolonged exposure to NEFA reduced ureagenesis and increased gluconeogenesis. Concurrent exposure to NEFA did not significantly affect gluconeogenesis or ureagenesis and did not alter the residual effect of prolonged incubation with NEFA. Reduced ureagenesis was related to increased cell triglyceride accumulation independently of other direct NEFA effects. Decreased ureagenic capacity may play a role in the morbidity associated with periparturient fatty liver in dairy cows.

The accumulation of triglycerides in the liver has been associated with reduced hepatic function; however, direct evidence that fat accumulation causes decreased liver function is lacking. Hepatocyte monolayers isolated from ruminating calves with an initial low triglyceride concentration were either loaded or not loaded with triglycerides by incubation with 1.5 or 0 mM exogenous nonesterified fatty acids from 12 to 48 h after plating. Basal rates of synthesis of albumin and protein were not affected by triglycerides in the cell. Inclusion of insulin and glucagon from 12 to 72 h after plating increased rates of albumin and protein synthesis. Hepatocytes loaded with triglycerides were less sensitive to the hormonal stimulation of albumin and protein synthesis than were normal hepatocytes. Insulin clearance rates were also lower in hepatocytes loaded with triglycerides than in normal hepatocytes. Decreased insulin clearance and hormonal control of protein synthesis could contribute to the etiology of metabolic disorders that are associated with periparturient fatty liver in dairy cows.

Fifty Holstein cows and 25 Holstein heifers were used in a randomized complete block design. Treatments were a standard nonfiber carbohydrate diet beginning at 19 d prepartum, a high nonfiber carbohydrate diet beginning at 19 d prepartum, a standard nonfiber carbohydrate diet plus niacin (12 g/d) beginning at 19 d prepartum, a high nonfiber carbohydrate diet plus niacin beginning at 19 d prepartum, and a standard nonfiber carbohydrate diet beginning at 19 d prepartum plus niacin beginning at 14 d postpartum. Treatments were applied through 40 wk postpartum. Niacin did not significantly affect production parameters or blood and liver metabolites. Prepartum intakes of dry matter and energy and energy balance were greater for cows and heifers fed the high nonfiber carbohydrate diets. Plasma glucose concentrations tended to be significantly higher, and nonesterified fatty acids and beta-hydroxybutyrate concentrations were significantly lower, when animals were fed diets that were high in nonfiber carbohydrates. Diets containing high nonfiber carbohydrates increased concentrations of liver glycogen and tended to reduce concentrations of liver triglyceride. Milk production tended to be higher, milk fat percentage tended to be lower, and milk protein percentage and production were significantly greater when diets that were high in nonfiber carbohydrates were fed. An increase in dietary nonfiber carbohydrates improved the metabolic parameters during the transition period and improved lactation performance.

Control [1.61 Mcal of net energy for lactation (NEL)/kg of dry matter (DM)], high grain (1.70 Mcal of NEL)/kg of DM), or high fat [1.70 Mcal of NEL/kg of DM with 2.3% tallow (DM basis)] diets were fed to 43 cows (150 +/- 3.1 d in milk) during mid to late lactation to determine effects on performance characteristics, metabolic parameters, or both during mid to late lactation, the dry period, and the first 100 d of the next lactation. All cows received identical diets during the dry period and during early lactation. Increasing the energy density of the diets during mid to late lactation increased DM intake (DMI), plasma nonesterified fatty acid concentration, milk production, and milk protein yield. Compared with the high grain diets, fat supplementation decreased DMI and the percentage of milk protein but increased plasma nonesterified fatty acid concentration without causing elevation of liver triglyceride at the end of mid to late lactation. Increased energy density of the diets did not affect body condition score during mid to late lactation. There were no residual effects for any of the treatments on DMI, lactation performance, or body weight in the subsequent lactation. However, energy supplementation during mid to late lactation increased liver triglyceride content after calving. Compared with high fat diets, high grain diets fed during mid to late lactation increased plasma beta-hydroxy-butyrate concentration in the subsequent lactation. High energy diets fed during mid to late lactation may influence lipid metabolism during the following lactation.

Primary cultures of hepatocytes were used to study the effects of extracellular oleate concentration and hormones on fatty acid metabolism and gluconeogenesis. Rates of oleate uptake and oxidation to acid-soluble products varied linearly as oleate concentrations increased (0.1 to 2 mM), but rates of triglyceride accumulation varied quadratically. Insulin increased the proportion of oleate that was esterified by 22% without affecting the formation of acid-soluble products. Cells incubated with 2 mM [1-(14)C]oleate for 24 h eliminated 9.6% of the labeled intracellular lipid as acid-soluble products in the following 24 h when no oleate was present during depletion and eliminated 7.7% when 2 mM oleate was present. Insulin reduced labeled triglyceride depletion by 49%. Gluconeogenesis from [2-(14)C] propionate was depressed by 24%, and formation of acid-soluble products was increased by 46% in cells infiltrated with lipid because of previous exposure to 2 mM oleate for 45 h. Rates of gluconeogenesis from propionate were reduced 23% when 2 mM oleate was present during the 3-h period that gluconeogenesis was measured, and the effect was not modified by lipid infiltration. Lipid infiltration influenced hepatic function, and insulin regulated hepatic triglyceride concentration.