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Relationships among Dietary Lipid Intake, Serum Cholesterol and Ovarian Function in Holstein Heifers^1,2,

North Dakota State University^,4, Fargo 58105

Abstract

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-17β 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<.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<.01) with progesterone between d 2 and 9. Serum TC was not correlated with testosterone or estradiol-17β. 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± after wk 5 in each of the three feeding stages. Feeding whole sunflower seed increased (P<.01) mean TC by 70% (R = 60 to 100%) and increased (P<.05) mean progesterone concentrations during the mid- to late luteal phase and mean highest progesterone concentrations relative to the control diet. Serum TC declined (P<.09 to P<.02) to lowest levels during the mid-luteal phase of all cycles, except Stage III. These results suggest that phase of the estrous cycle should be considered when studying serum TC in cycling females and that hyperlipidemic-hypercholesterolemic diets may enhance luteal progesterone biosynthesis, release or clearance in heifers.

¹ Published with the approval of the Director, North Dakota Agr. Exp. Sta.

² Contribution to Regional Project W-112, Reproductive Performance in Domestic Ruminants.

³ Reprint requests and correspondence: Dr. G. L. Williams, Texas A&M Univ. Agricultural Research Station, HCR-2, Box 43-C, Beeville, TX 78102.

⁴ Dept. of Anim. Sci.

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