Relationships among dietary lipid intake, serum cholesterol and ovarian function in Holstein heifers

Experiments were performed to determine whether serum concentrations of total cholesterol (TC) undergo cyclic changes during the estrous cycle of dairy heifers and to assess the relationship between serum concentrations of TC and ovarian steroid hormones. The effects of a hypercholesterolemic diet upon luteal progesterone secretion also were determined. Experiment 1 involved five dairy heifers exhibiting normal estrous cycles. Serum concentrations of TC, progesterone, testosterone and estradiol-17 beta were determined in blood samples collected throughout a complete estrous cycle. A transient decline in TC was observed during the luteal phase of all heifers beginning on d 2 and reached a nadir 6 d after estrus. Highest mean concentrations of TC occurred between d -2 and +2 (96.3 +/- 8.2 mg/dl), which were markedly higher (P less than .05) than the lowest mean concentrations (76.3 +/- 10.3 mg/dl) observed on d 6. Concentrations of serum TC were negatively correlated (r = -.40; P less than .01) with progesterone between d 2 and 9. Serum TC was not correlated with testosterone or estradiol-17 beta. In Exp. 2, seven cycling Holstein heifers were fed a control diet for 70 d (Stage I), a diet containing 15% whole sunflower seed as a source of supplemental dietary lipid for 70 d (Stage II) and then the control diet for 70 d (Stage III). Diets were isocaloric and isonitrogenous. All heifers were synchronized with prostaglandin F2 alpha after wk 5 in each of the three feeding stages.(ABSTRACT TRUNCATED AT 250 WORDS)