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The present study evaluated the interaction of pregnancy type [PT; single (S) vs. twin (T)] and dry period feeding management [D; close-up (CU) diet (NEl= 1.54 Mcal/kg of DM)] throughout the entire dry period (8W) vs. far-off (FO) diet (NEl= 1.32 Mcal/kg of DM) from 60 to 21 d before expected calving date (ECD) followed by CU diet until calving (3W). Treatments were arranged in a 2 × 2 factorial with a randomized block design with primiparous (n = 8) and multiparous (n = 39) Holstein cows. We hypothesized that increasing the duration of feeding a CU diet would improve metabolic status and lactation performance for cows with T, but not for cows with S. All cows were fed similarly in late lactation (90 to 60 d before ECD; diet NEl= 1.58 Mcal/kg of DM) and in early lactation (calving to 105 DIM; diet NEl= 1.71 Mcal/kg of DM). Prepartum DMI as percentage of BW did not differ (P> 0.10) with D but tended to be greater (P= 0.10) for cows with S than with T. Cows with T tended to have greater (P= 0.08) BW than cows with S, but conceptus-free BW was less (P= 0.001) for cows with T than for cows with S. No differences (P> 0.10) were detected in prepartum BCS or BCS change with PT or D. Energy balance (EB) was greater for cows with S than with T (P< 0.001) and for cows fed 8W vs. 3W (P= 0.01). Cows with T had greater (P< 0.001) NEFA and a tendency for greater liver triglycerides (TG; P= 0.07) and plasma β-hydroxybutyrate (BHBA; P= 0.06) than cows with S. Prepartum cows fed 3W had greater (P= 0.01) liver TG and greater (P= 0.02) plasma NEFA, but less (P= 0.02) plasma BHBA than cows fed 8W. Plasma glucose (P< 0.004) and liver glycogen (P= 0.02) were less for cows with T but were not affected (P> 0.10) by D. Postpartum, there was no effect (P> 0.1) of PT or D on mean DMI as percentage of BW, BW, and BCS, but there was an interaction (P= 0.02) of PT × D for mean BCS. Cows that calved T were in a more positive (P= 0.004) EB than cows that calved S. Milk production was 5.2 kg/d greater (P= 0.04) for cows fed 8W; however, they were in less (P= 0.01) EB than cows that received 3W. Postpartum cows that calved T had decreased concentrations of plasma NEFA (P= 0.02) and liver TG (P= 0.04) but greater concentrations of plasma glucose (P= 0.03) than cows that calved S. Plasma BHBA (P= 0.07) and NEFA tended (P= 0.06) to be greater for cows that received 8W than 3W. Neither PT nor D affected (P> 0.1) plasma glucose and liver glycogen. There was a tendency for an interaction of PT × D for plasma NEFA and liver TG. In contrast to our hypothesis, response to D was independent of PT. Based on milk production data from the present experiment, 8W is a more desirable feeding strategy than 3W.

Forty-eight second, third and fourth parity crossbred sows were randomly allotted to four dietary treatments: corn:alfalfa-orchardgrass hay (46%; CH); CH plus lasalocid (CHL); corn-soybean meal (CS) or CS plus lasalocid (CSL). Sows were fed these diets through two successive gestations with dietary treatment initiated at 35 d post-coitum and continued until parturition. To equalize daily metabolizable energy intake (6.6 Mcal/sow), 2.64 kg of CH and CHL diets and 1.86 kg of CS and CSL diets were fed. Lasalocid intake was 130 mg · sow−1· d−1. Sows were weighed and backfat measurements were taken at 35 and 109 d of gestation. Sows also were weighed 14 d postpartum. A 14% crude protein corn-soybean meal diet was fed ad libitum to all sows during lactation and feed intake was recorded. Colostrum samples were obtained within 4 h of farrowing. All live piglets were weighed at birth and 14 d of age. There were no significant differences among dietary treatments in number of live piglets born, piglet birth weight, piglet weight at 14 d of age or sow rebreeding efficiency. Sows fed CHL and CSL diets had more (P<.12) live piglets at 14 d postpartum and lower (P<.03) total fat in colostrum than did CH- and CS-fed sows. Alfalfa-orchardgrass hay feeding resulted in less (P<.04) backfat deposition during gestation, more (P<.04) weight loss from 109 d postcoitum to 14 d postpartum and increased (P<.002) feed consumption during lactation. These results indicate that the corn:alfalfa-orchardgrass hay (46%) diet was essentially equal to the corn-soybean meal diet with regard to sow reproductive performance. Dietary lasalocid reduced fat percentage of sow colostrum.

Improved reproductive performance and reduced incidence of metabolic disorders have been postulated to be benefits of feeding supplemental fat to dairy cows. Increased plasma nonesterified fatty acid concentrations during fat supplementation may result from incomplete tissue uptake of fatty acids after lipoprotein lipase hydrolysis of very-low-density lipoprotein triglyceride; however, evidence suggests that net adipose tissue triglyceride hydrolysis may be increased during fat supplementation. Plasma 3-OH-butyrate concentrations remain relatively constant during fat supplementation but may have a tendency to be reduced if fat is supplemented to cows having relatively high basal plasma 3-OH-butyrate concentrations. Because plasma ketone levels usually increase when nonesterified fatty acid concentrations are elevated, it is hypothesized that potential antiketogenic effects of added fat are due to a glucose sparing effect. Supplemental fat does not seem to reduce hepatic lipid infiltration near the time of calving. Potential mechanisms by which supplemental fat may improve reproductive performance include stimulation of prostaglandin F2 a synthesis and secretion and enhanced utilization of blood cholesterol for progesterone synthesis. Days postpartum until first ovulation and luteal function of dairy cattle have been related to energy balance during the first 3 wk postpartum. Energy balance data for early lactation cows fed supplemental fat are not plentiful; however, slight but statistically nonsignificant increases have been observed when feeding fat. Cows fed supplemental fat that experience improved energy balance may begin to cycle sooner because of enhanced follicular growth and development. Applied studies examining the effects of supplemental fat on reproductive performance have provided inconsistent results.

Cholesterol utilized for steroid synthesis by ovarian tissue may be derived from de novo synthesis or cellular uptake of lipoprotein cholesterol. The majority of blood cholesterol is transported by either low (LDL) or high (HDL) density lipoproteins, depending on the animal species. Prior to vascularization, only HDL are in follicular fluid and contribute sterol to granulosa cells because other lipoproteins are unable to traverse the basement membrane due to their molecular masses. Following vascularization, both LDL and HDL bathe luteal cells. Most species preferentially use LDL cholesterol as a precursor for ovarian steroid synthesis. The LDL uptake by ovarian tissue occurs by receptor-mediated endocytosis. The receptor recognizes apolipoprotein B of LDL and apolipoprotein E found on some, but not all, HDL. Within a species, a positive relationship may exist between HDL apolipoprotein E content and importance of HDL cholesterol as a precursor for steroidogenesis. A “HDL pathway” exists for uptake of sterol from HDL void of apolipoprotein E. The HDL receptor exhibits broad binding specificity. Unlike LDL, the HDL particle is not internalized, and cholesterol preferentially is taken up relative to other HDL constituents. In most species, lipoproteins, rather than de novo synthesis from acetate, contribute the majority of cholesterol used for steroid production. Trophic hormones increase lipoprotein binding, internalization, degradation and conversion of lipoprotein-derived sterol to steroids, effects that are mediate through cyclic adenosine monophosphate. Knowledge recently acquired regarding lipoprotein sterol utilization by the ovary may be useful in developing nutritional, pharmacological or endocrine manipulations that may positively affect cholesterol clearance by the ovary, steroidogenesis and reproductive performance.

Summary.Interactions of bovine follicular fluid glycosaminoglycans (GAGs) with extracellular matrix (ECM) components fibronectin and laminin and with low-density lipoproteins (LDL) were examined using affinity chromatography. Glycosaminoglycans from small (diameter < 5 mm) and large (diameter 11–20 mm) follicles were isolated from follicular fluid. The dermatan sulphate or heparan sulphate from small or large follicles was applied to Fn–, Lm– or LDL–Sepharose columns. Portions of each fraction of the bound or unbound GAG were then subjected to gel filtration h.p.l.c. for quantification. The binding interaction between dermatan sulphate and fibronectin was significantly greater than between heparan sulphate and fibronectin (P< 0·05); the binding interaction between GAGs from small follicles and fibronectin was significantly greater than between GAGs from large follicles (P< 0·05). The binding interaction between GAGs from small follicles and laminin was significantly greater than for GAGs from large follicles (P< 0·05). Dermatan sulphate from small follicles bound to fibronectin (42%), laminin (36%) and LDL (14%) and that from large follicles bound to fibronectin (14%), laminin (23%) and LDL (14%). Heparan sulphate from small follicles bound to fibronectin (17%), laminin (15%) and that from large follicles bound to fibronectin (13%), laminin (10%) and LDL (6%). These results suggest that dermatan sulphate, but not heparan sulphate, from follicles at different stages of development exhibit a varied ability to interact with components of the ECM. Both substances bound to LDL comparably in small amounts.Keywords:follicle; glycosaminoglycans; fibronectin; laminin; extracellular matrix; lipoproteins; cow