PROLONGED INCREASED CONCENTRATIONS OF 17-BETA-ESTRADIOL ASSOCIATED WITH DEVELOPMENT OF PERSISTENT OVARIAN FOLLICLES DO NOT INFLUENCE CONCEPTION RATES IN BEEF-CATTLE

Objectives were to evaluate conception rates and time to estrus follow ing cessation of treatments designed to either cause prolonged elevate d concentrations of 17 beta-estradiol associated with development of p ersistent ovarian follicles or to inhibit elevated concentrations of 1 7 beta-estradiol and development of persistent ovarian follicles. Beef heifers (n = 80) and 2-yr-old nonlactating cows (n = 39) were stratif ied by age, blocked by estrual status (previously exhibited estrus or anestrus) and assigned to receive either 1) four norgestomet implants (4 Norg; n = 59) for 9 d (d 0 = treatment initiation) or 2) one norges tomet implant from d 0 to 7 and three additional norgestomet implants from d 7 to 9 (1 + 3 Norg; n = 60). All animals received PGF(2 alpha) on d 0 to lyse corpora lutea. All implants were removed on d 9 followe d by estrus detection every 6 h for 7 d following implant removal. Fem ales exhibiting estrus were artificially inseminated 6 to 12 h after d etection of estrus. A treatment x day interaction (P < .01) for concen trations of 17 beta-estradiol from d 0 to 9 of the experiment with ele vated 17 beta-estradiol occurring in females treated with 1 + 3 Norg i mplants. The interval from treatment withdrawal to estrus was longer ( P < .01) in females treated with 1 + 3 Norg (105 h) than in those trea ted with 4 Norg (61 h). Synchrony of estrus among anestrous females wa s greater (P < .10) in females treated with 4 Norg (97%) than in femal es treated with 1 + 3 Norg (67%) but was similar in estrual females. C onception rates (number conceiving to AI/number bred by AI) did not di ffer (4 Norg = 67%; 1 + 3 Norg = 72%; P > .10). Pregnancy rates (numbe r conceiving to AI/number in treatment group) also did not differ betw een treatment groups of either estrual or anestrous females. Conceptio n rates are not compromised in females that develop persistent ovarian follicles and have prolonged elevated concentrations of 17 beta-estra diol when persistent ovarian follicles are not allowed to ovulate.