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Multiparous Holstein cows (n = 16) were used in a replicated (n = 4) Latin square design with 2-wk periods to determine whether length of the experimental period chosen within Latin square designs would influence experimental outcomes for performance-related variables. Cows were fed a basal TMR formulated to supply Lys in excess of the predicted requirements and either no rumen-protected Met (RP-Met; control), or 6 (M6) or 12 (M12) g/d of RP-Met (Mepron), or 12 (S12) g/d of RP-Met (Smartamine M). Performance outcomes were evaluated separately using data collected at the end of each week of each period, and as overall means for each period. Milk yield was not affected by treatment in any period. Supplementation of RP-Met from all sources tended to increase milk fat percentage when evaluated using wk-1 data, but responses evaluated using wk-2 data only were not significant. Supplementation of M12 and S12 tended to increase milk fat percentage over the entire experimental period. Supplementation of M6 and M12 tended to increase milk true protein percentage when evaluated using wk-1 data only; however, responses to treatments during wk 2 were not significant. All supplemental RP-Met treatments either tended to increase (M6 and S12) or increased (M12) milk true protein content over the entire experimental period relative to the control treatment. Yields of fat and true protein were not affected by treatment. Carryover effects of treatment on production variables were largely not significant. Predictions of nutrient supply with 3 models used in dairy ration formulation and evaluation (CPM-Dairy, AminoCow, and 2001 NRC Dairy) indicated that energy, protein, and Met all were supplied in excess of requirements for all treatments. Overall, results suggest that interpretation of performance outcomes can vary depending on selection of the experimental period in Latin squares, and responses to increased Met supply based on ratio-based formulation may not be independent of the grams of Met supplied. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the mechanism of action through which conjugated linoleic acid (CLA) beneficially affects reproduction. Lactating Holstein cows (n = 45, 20 ± 1 DIM) were assigned to 1 of 3 treatments: 70 g/d of Ca salts of tallow (control); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis- 9, trans-11 CLA and 2.4 g/d of trans-10, cis-12 CLA (CLA 75:25); or 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis-9, trans-11 and trans-10, cis-12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and blood samples were taken 3 times per week. At 30 ± 3 DIM, ovulation was synchronized in all cows with a modified Ovsynch protocol, and on d 15 of the cycle cows received an oxytocin injection; blood samples were obtained frequently to measure 13,14 dihydro, 15-keto PGF&2α. On d 16 of the cycle cows received a PGF&2α injection and ovarian follicular aspiration was performed 54 h later. Follicular fluid was analyzed for fatty acids, progesterone, and estradiol. Endometrial biopsies were taken before and again near the end of the supplementation period for fatty acid analysis. The CLA resulted in decreased milk fat content of 14.1 and 6.1% at wk 5 of treatment of CLA 50:50 and CLA 75:25, respectively. There were no differences in energy balance or plasma nonesterified fatty acids; however, plasma IGF-I was greater in cows supplemented with CLA 50:50. The CLA isomers were not detectable in endometrial tissue, but cis-9, trans-11 CLA tended to be greater in follicular fluid of supplemented cows. Response to the oxytocin challenge was not different among treatments. Progesterone during the early luteal phase and the estradiol:progesterone ratio in follicular fluid tended to be greater in cows supplemented with CLA 50:50. Overall, these results indicate that short periods of CLA supplementation do not alter uterine secretion of PGF&2α. The mechanism through which CLA affects reproduction may involve improved ovarian follicular steroidogenesis and increased circulating concentrations of IGF-I. [ABSTRACT FROM AUTHOR]

Twenty multiparons Holstein cows, 4 of them surgically fitted with ruminal cannulas, were used in a replicated 4 x 4 Latin square to compare the effects of whole-plant silage and grain produced from NutriDense (ND), leafy NutriDense (LND), or a conventional yellow dent (YD) hybrid on ruminal fermentation, total tract nutrient digestibility, and performance of lactating dairy cows. On a DM basis, diets contained 30.6% corn silage and 27.7% corn grain provided from the 3 hybrids according to the following combinations: 1) YD grain and YD silage, 2) YD grain and LND silage, 3) ND grain and YD silage, and 4) ND grain and LND silage. The average concentrations of crude protein, neutral and acid detergent fiber, and ether extract of LND silage and ND grain were higher, but the contents of nonfibrous carbohydrates and starch were lower than those of their YD counterparts. Although DM intake was similar among treatments, feeding ND grain, LND silage, or both reduced the intakes of nonfibrous carbohydrates and starch but increased the intake of ether extract. Apparent digestibility of starch in the total tract was highest for the diet that contained LND silage and YD grain, whereas the amount and percentage of ether extract that were apparently digested in the total tract was increased and tended to be increased, respectively, by the addition of ND grain, LND silage, or both to the diets. Ruminal fermentation parameters were unaffected by treatments except for the concentration of ammonia nitrogen in the ruminal fluid, which tended to be increased by the feeding of ND grain, LND silage, or both. Production of milk, crude and true protein, fat, lactose, and total solids did not differ among diets. Concentration of milk urea nitrogen increased when the ND grain, LND silage, or both were fed to the cows. Results indicate that ND grain and LND silage were similar to the conventional grain and silage for the feeding of lactating dairy cows. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate uterine PGF2α release (PGFM) in response to an oxytocin challenge after dietary supplementation with different CLA isomers. Lactating Holstein cows (n = 45, 20 ± 1 DIM) were assigned to one of 3 treatments: 70 g/d of Ca salts of tallow (CTL); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis 9, trans 11 CLA and 2.4 g/d of trans 10, cis 12 CLA (CLA 75:25), or ; 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis 9, trans 11 and trans 10, cis 12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and milk components measured weekly. Blood samples were taken 3x per wk for NEFA and 1x per wk for IGF-I analyses. At 30 ± 3 DIM ovulation was synchronized in all cows with a modified Ovsynch protocol. On d 15 of the cycle cows received an i.v. injection of 3 mg of estradiol 17β and 4 hr later an i.v. challenge with 100 IU of oxytocin; blood samples were obtained frequently over a 4 hr period. PGFM was determined by RIA and area under the curve was calculated. CLA 50:50 caused 16.6% reduction in milk fat content after wk 4 (P < 0.03), but milk fat content for CLA75:25 was not different from CTL. Milk fat yield was similar among treatments due to a trend (P < 0.07, wk 4) to increase milk yield of cows treated with CLA50:50 (43.5, 42.6 and 41.9 kg/d for CLA50:50, CLA75:25 and CTL, respectively). The oxytocin challenge resulted in an immediate elevation of circulating PGFM which gradually returned to basal levels over the next 4 h Area under the curve was not different among treatments (P = 0.2); likewise DMI and NEFA were similar among treatments (P > 0.05). Plasma IGF-I tended to be higher (P < 0.07) in cows treated with CLA 50:50 compared to CTL (81.4, 76.3 and 72.5 ng/ml for CLA50:50, CLA75:25 and CTL, respectively). Overall, results suggest that short periods of CLA supplementation do not impact reproductive performance via affects on uterine release of PGF2α . [ABSTRACT FROM AUTHOR]

The objectives of this study were to evaluate uterine PGF2α secretion and production responses in dairy cows fed different commercially available sources of rumen-protected fatty acids (FA). Postpartum Holstein cows (n = 45, 21 ± 1 DIM) were assigned to isoenergetic diets providing: calcium salts of tallow (180 g FA/d; C), calcium salts of trans-fatty acids as EnerGI Trans formula (180 g FA/d; Virtus Nutrition, Fairlawn OH; T), or calcium salts of omega-3 fatty acids as StrataG 1.0 (150 g FA/d; Virtus Nutrition; N-3). Cows were fed for 37 d and feed intake and milk yield were monitored over this period. Blood samples for determination of IGF-1 and NEFA were collected 3x/wk. At 30 ± 3 DIM, ovulation was synchronized in all cows with a modified Ovsynch protocol. On d 15 of the cycle cows were infused with 3 mg of estradiol-17β (iv) and challenged with 100 IU of oxytocin (iv) 4 h later to stimulate uterine PGF2α secretion; blood plasma was collected frequently over a 4 h period for determination of PGFM. Cows fed the T diet tended (P = 0.11) to have a greater PGFM response to the oxytocin challenge. Differences in IGF-1 were not significant. A treatment by day effect for decreased circulating NEFA was evident on d 11 on diet for cows fed N-3 and on d 18 for cows on N-3 compared to those fed T. Milk production (43.4, 42.2, and 41.8 kg/d for C, T, and N-3, respectively) and weekly fat and protein yield were similar (P > 0.05) across treatments although cows fed T tended (P = 0.07) to have increased milk fat percentage (3.20, 3.37, and 3.03%, respectively) compared to cows fed diet N-3 and tended (P = 0.06) to have a higher milk protein percentage (2.43, 2.55, and 2.51%, respectively) than cows fed diet C. Although FA treatments did not change milk or component yields, cows fed diet T tended to have increased uterine PGF2α secretion in addition to increased milk fat and protein content. [ABSTRACT FROM AUTHOR]

A previous study showed carryover effects on production parameters in Latin square designs assessing RP-Met sources. Multiparous Holstein cows (n=16) were used in a replicated (n=4) Latin square design to determine effects of different sources of RP-Met on performance. Squares were balanced to enable determination of carryover effects. The basal TMR was predicted to supply Met at 1.75% of metabolizable protein (MP) supply (NRC, 2001). Treatments consisted of 0 g/d RP-Met (control; C), 6 g/d RP-Met as Mepron (M6), 12 g/d RP-Met as Mepron (M12), and 12 g/d RP-Met as Smartamine M (S). The daily treatment for each cow was mixed into 0.45 kg of wheat middlings and combined with the basal TMR at the mixer. Cows were fed treatments for 2-wk periods and data were collected on the last 2 d of each week. Statistical analysis (GLM of SAS) was conducted separately for data collected during wk 1 and 2 of each period. RP-Met resulted in varying positive effects on DMI and content of milk fat and true protein during wk 1; however, these differences were not significant after 2 wk of treatment. Carryover effects were not significant. Predicted Met supplies (g/d) were in excess of predicted requirements for all treatments. Increasing Met supply (% MP) through use of RP-Met resulted in small increases in milk true protein content. Results suggest that length of study period can affect productive variables of cows fed RP-Met sources. [ABSTRACT FROM AUTHOR]

In vivo insulin (INS) challenges were used to evaluate peripheral tissue responses to insulin in the late prepartum (PRE), early postpartum (POST) and midlactation (ML) periods in Holstein cows. Periparturient (n=7) cows were studied during 4 periods (-30 to -26 d and -12 to -8 d PRE; 3 to 7 d and 26 to 30 d POST) and ML (n=5) cows were studied from d 148 to 152 DIM. During each period, cows were administered a randomized sequence of 5 doses of INS (0.2, 0.4, 0.8, 1.2 and 1.6 μg/kg BW) by i.v. challenge conducted once daily. Blood was sampled frequently via jugular catheter from 30 min pre-challenge to 2 h post-challenge. Plasma glucose and insulin responses to 0.8 and 1.6 μg INS/kg BW were used to estimate tissue sensitivity and responsiveness, respectively. Plasma glucose (mg/dl*min-1) area under the curve (AUC) decreased and plasma insulin (ng/ml*min-1) AUC increased dose-dependently following INS challenge. Plasma glucose AUC after 0.8 μg INS/kg BW was lower during PRE than during d 3 to 7 POST and ML; however, glucose AUC following 1.6 μg INS/kg BW was similar among PRE and POST and lower than ML. Plasma insulin AUC after 0.8 μg INS/kg BW was greater during d -12 to -8, d 3 to 7, and d 26 to 30 compared with d -30 to -26 and ML and was greatest after 1.6 μg INS/kg BW during d -12 to -8 and intermediate during d 3 to 7 POST compared to other study periods. Collectively, these data suggest that peripheral tissue responses to INS are greatest during ML and least during the immediate prepartum period. [ABSTRACT FROM AUTHOR]

In vivo epinephrine (EPI) challenges were used to evaluate changes in peripheral tissue responses to catecholamines in the late prepartum (PRE), early postpartum (POST) and midlactation (ML) periods in Holstein cows. Periparturient (n=6) cows were studied during 4 periods (-30 to -26 d and -12 to -8 d PRE; 3 to 7 d and 26 to 30 d POST) and ML (n=5) cows were studied on d 148 to 152 POST. During each period, cows were administered a randomized sequence of 5 doses of EPI (0.2, 0.4, 0.8, 1.2 and 1.6 μg/kg BW) by i.v challenge. Blood was sampled frequently via jugular catheter from 30 min pre-challenge to 2 h post-challenge. Plasma NEFA and glucose responses to 0.8 and 1.6 μg/kg BW of EPI were used to estimate tissue sensitivity and responsiveness. Both plasma glucose (mg/dl*min-1) and NEFA (μEq/L*min-1) area under the curve (AUC) increased dose-dependently following EPI challenge. Periparturient cows had larger NEFA response during POST than PRE for both 0.8 and 1.6 μg/kg BW of EPI, suggesting both greater sensitivity and responsiveness of adipose tissue to EPI during POST. Periparturient cows had larger glucose responses to both doses only at d 26 to 30 POST. Responses of NEFA for cows studied in ML were intermediate compared to those during PRE and POST. Responses of glucose for cows studied during ML were comparable to those at d 26 to 30 POST. Overall, responses of peripheral tissues to EPI were greater during lactation than during late pregnancy; those differences were more pronounced for release of NEFA from adipose tissue. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate uterine PGF2α release (PGFM) in response to an oxytocin challenge after dietary supplementation with different CLA isomers. Lactating Holstein cows (n = 45, 20 ± 1 DIM) were assigned to one of 3 treatments: 70 g/d of Ca salts of tallow (CTL); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis 9, trans 11 CLA and 2.4 g/d of trans 10, cis 12 CLA (CLA 75:25), or ; 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis 9, trans 11 and trans 10, cis 12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and milk components measured weekly. Blood samples were taken 3x per wk for NEFA and 1x per wk for IGF-I analyses. At 30 ± 3 DIM ovulation was synchronized in all cows with a modified Ovsynch protocol. On d 15 of the cycle cows received an i.v. injection of 3 mg of estradiol 17β and 4 hr later an i.v. challenge with 100 IU of oxytocin; blood samples were obtained frequently over a 4 hr period. PGFM was determined by RIA and area under the curve was calculated. CLA 50:50 caused 16.6% reduction in milk fat content after wk 4 (P < 0.03), but milk fat content for CLA75:25 was not different from CTL. Milk fat yield was similar among treatments due to a trend (P < 0.07, wk 4) to increase milk yield of cows treated with CLA50:50 (43.5, 42.6 and 41.9 kg/d for CLA50:50, CLA75:25 and CTL, respectively). The oxytocin challenge resulted in an immediate elevation of circulating PGFM which gradually returned to basal levels over the next 4 h Area under the curve was not different among treatments (P = 0.2); likewise DMI and NEFA were similar among treatments (P > 0.05). Plasma IGF-I tended to be higher (P < 0.07) in cows treated with CLA 50:50 compared to CTL (81.4, 76.3 and 72.5 ng/ml for CLA50:50, CLA75:25 and CTL, respectively). Overall, results suggest that short periods of CLA supplementation do not impact reproductive performance via affects on uterine release of PGF2α . [ABSTRACT FROM AUTHOR]