Effects of feeding high-linoleate safflower seeds on postpartum reproduction in beef cows

Authors: Scholljegerdes, Eric; HESS, BRET - UNIV. OF WYOMING; GRANT, MARK - UNIV. OF WYOMING; LAKE, SCOTT - UNIV. OF WYOMING; ALEXANDER, BRENDA - UNIV. OF WYOMING; WESTON, TERRILL - UNIV. OF WYOMING; HIXON, DOUGLAS - UNIV. OF WYOMING; VAN KIRK, EDWARD - UNIV. OF WYOMING; MOSS, GARY - UNIV. OF WYOMING

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2009
Publication Date: 5/22/2009
Citation: Scholljegerdes, E.J., Hess, B.W., Grant, M.H., Lake, S.L., Alexander, B.M., Weston, T.R., Hixon, D.L., Van Kirk, E.A., Moss, G.E. 2009. Effects of Feeding High-Linoleate Safflower Seeds on Postpartum Reproduction in Beef Cows. Journal of Animal Science.87:2985–2995.

Interpretive Summary: Adequately meeting the nutritional needs of young lactating beef females is difficult because of competing demands for nutrients. Consequently, provision of energy-dense lipid supplements has evolved into a management strategy that may enhance reproductive function. Two experiments were conducted to evaluate reproductive responses to supplemental high-linoleate safflower seeds in postpartum beef cows. In Exp. 1, 18 primiparous crossbred beef cows were fed Foxtail millet hay and either a low-fat control (Control) or a supplement (Linoleate) containing cracked high-linoleate safflower seeds. Beginning 1 d postpartum, cows were bled every 3 d for collection of sera and were slaughtered at 37 ± 3 d postpartum for collection of tissues important to reproduction. In Exp. 2, 24 three-year-old multiparous beef cows were fed chopped bromegrass hay starting 1 d postpartum and either a low-fat supplement (Control) or a high-linoleate supplement (Linoleate) until 80 d postpartum. Cows were observed for estrus twice daily from d 30 to 80 postpartum, and treated with GnRH between 40 and 45 d postpartum. Seven days after GnRH administration cows received PGF2alpha and were artificially inseminated. Based on the number of secondary follicles observed in Exp. 1, fat supplementation did not appear to enhance follicular development by d 35 postpartum but did appear to affect formation and function of CL structures in response to treatment with GnRH later in the postpartum period (Exp. 2). Fatty acid composition of diets appeared to modulate circulating concentrations of serum IGF-I (Exp. 1). These differences, however, may not be long-lived, because mean serum concentrations of IGF-I did not differ between treatments in Exp. 2 in which changes in BW differed between groups. Overall, cows fed Control conceived earlier in the breeding season than Linoleate fed cows (Figure 3). Conception at first-service AI tended to be greater for Control than Linoleate and more Controls conceived during the 50 d AI period than Linoleate. Ultimately, 92% of both groups became pregnant by the end of the breeding season but all of the Control cows conceived to AI (first plus second service conception rates) compared to seven Linoleate cows. Fat supplementation with high-linoleate safflower seeds did not improve the development of ovarian follicles and detrimentally affected early postpartum fertility possibly because of a reduction in IGF-I concentrations in tissues essential to reproduction.

Technical Abstract: Two experiments were conducted to evaluate reproductive responses to supplemental high-linoleate safflower seeds in postpartum beef cows. In Exp. 1, 18 primiparous, crossbred beef cows (BW 411 ± 24.3 kg) were fed Foxtail millet hay at 1.68% of BW (DM basis) and either a low-fat control (Control: 63.7% cracked corn; 33.4% safflower seed meal; and 2.9% liquid molasses; DM basis) at 0.35% of BW (n = 9) or a supplement (Linoleate) containing 95.3% cracked high-linoleate (79% 18:2n-6) safflower seeds and 4.7% liquid molasses (DM basis) at 0.23% of BW (n = 9). Beginning 1 d postpartum, cows were bled every 3 d for collection of sera and were slaughtered at 37 ± 3 d postpartum for collection of hypothalami, anterior pituitary glands, liver, ovarian follicles, and uterine tissue. By 37 ± 3 d postpartum dietary treatment did not influence ovarian follicular development (P > 0.17), hypophyseal concentrations of LH (P = 0.14) or concentrations of IGF-I in liver (P = 0.15). In contrast, anterior pituitary glands from Linoleate cows contained more FSH (P = 0.02) than Control cows and Linoleate cows had less IGF-I in the medial basal hypothalamus (P = 0.05), preoptic area (P = 0.06), and in follicular fluid (P < 0.03) from follicles less than 15 mm in diameter. In Exp. 2, 24 three-year-old multiparous beef cows (initial BW 473.9 ± 9.2 kg) were fed chopped bromegrass hay at 2.1% of initial BW starting 1 d postpartum and either a low-fat supplement (Control) fed at 0.6% of initial BW or a high-linoleate supplement (Linoleate) fed at 0.4% of initial BW until 80 d postpartum. Cows were observed for estrus twice daily from d 30 to 80 postpartum, and treated with GnRH between 40 and 45 d postpartum. Seven days after GnRH administration cows received PGF2a and were artificially inseminated. The magnitude of GnRH-induced release of LH (P = 0.80) or FSH (P = 0.90) did not differ between treatments. However, peak serum concentrations of estradiol during proestrus following treatment with PGF2a were lower (P = 0.04) in Linoleate than Control cows. First service conception rates tended (P = 0.10) to be greater in Control (66.7%) than Linoleate (33.3%) cows. Although conception rates were identical by the end of the breeding season, conception occurred earlier (P = 0.02) postpartum in Control (60 ± 5 d) than Linoleate (81 ± 6 d) cows. In conclusion, fat supplementation with high-linoleate safflower seeds did not improve the development of ovarian follicles and detrimentally affected early postpartum fertility possibly because of a reduction in IGF-I concentrations in tissues essential to reproduction.