Reproductive studies of Brahman cattle

Abstract

To determine if luteinizing hormone (LH) patterns were different between ovariectomized Brahman and Hereford cows, before and after 500 ug of GnRH, animals were bled at 15-min intervals for periods of 4 and 6 hr. Serum was collected and analyzed via radioimmunoassay (RIA) for LH. Objectives were to determine if ovariectomized Brahman and Hereford cows without treatment have pulsatile LH patterns, if breed of animal influenced LH patterns, and if ovariectomized Brahman and Hereford cows differ in GnRH-induced LH response. Brahman and Hereford ovariectomized cows had pulsatile LH patterns. Although trends were for higher LH levels in Hereford than Brahman cows, there were no significant differences in mean serum LH levels, number or magnitude of LH peaks or serum LH pulse height. Ovariectomized Brahman and Hereford cows injected I.M. with 500 ug of GnRH showed increased serum LH. There were no differences in duration of response between ovariectomized Brahman and Hereford cows. Ovariectomized Brahman cows had significantly lower (P < .005) LH values per period than ovariectomized Hereford cows. Forty prepuberal, purebred Brahman heifers (X age 13.7 months and X weight 224 kg) were randomized by age and weight into four treatment groups. Animals in the progesterone (P) treatment group received exogenous progesterone via intravaginal pessary (PRID) administered for 5 days..