Diet-induced hyperlipidemia in cattle modifies the intrafollicular cholesterol environment, modulates ovarian follicular dynamics, and hastens the onset of postpartum luteal activity
Wehrman, M.E. | Welsh, T.H. Jr | Williams, G.L.
Three experiments were conducted with female cattle during the postpartum period and during the estrous cycle to examine the effects of diet-induced hyperlipidemia on lipoprotein-cholesterol and triglyceride (TG) metabolism, ovarian follicular dynamics, and incidence of postpartum luteal activity. Dietary-lipid effects were examined independently of metabolizable energy intake. Feeding a high-lipid (HL) diet (8% total lipid) for the first 3 wk of the puerperium (Experiment 1) increased (p < 0.0001) the concentration of total cholesterol and high-density lipoprotein-cholesterol (HDL-CH), but not TG, within follicular fluid (FF) of estrogen-active (E-A) and inactive (E-I) follicles. Increases (1.4- to 1.7-fold) were similar in proportion to those observed in peripheral blood serum, but absolute concentrations were about 45% of that in serum. Greater than 95% of the cholesterol in FF was HDL-CH, with a greater (p < 0.06) proportion of HDL-CH sequestered by E-A compared to E-I follicles. The HL diet increased (p < 0.06) the number of medium-sized (3.1-9.9 mm) follicles present at ovariectomy 19-21 days postcalving and increased (p < 0.03) concentrations of FF androstenedione in E-I follicles 5-fold. Granulosa cells from preovulatory follicles (Experiment 2) of heifers fed HL diets secreted 2.1- to 3.5-fold greater (p < 0.03) quantities of pregnenolone and progesterone in vitro. Finally, feeding HL supplements to postpartum range cattle for 30 days increased (p < 0.05) the incidence of ovarian luteal activity by 18% (Experiment 3). Shifts in lipid metabolic status modify reproductive potential in cattle, independently of dietary energy intake.
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