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

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 (411 +/- 24.3 kg of BW) were fed Foxtail millet hay starting 1 d postpartum at 1.68% of BW (DM basis) and 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, blood was collected every 3 d for sera. Cows 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 >or= 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 <or= 0.03) from follicles less than 15 mm in diameter. In Exp. 2, twenty-four 3-yr-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 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 were given PGF(2alpha) and were checked for estrus and artificially inseminated until 80 d postpartum. The magnitude of GnRH-induced release of LH (P = 0.82) or FSH (P = 0.86) did not differ between treatments. However, peak serum concentrations of estradiol during proestrus after treatment with PGF(2alpha) were less (P = 0.04) in linoleate than control 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.