Evaluation of response to hormonal therapy in prepubertal gilts of different genetic lines

Research was conducted to determine the effect of genetic line on hormonally induced puberty. Two studies were conducted, the first to evaluate estrus response (n = 120 gilts) and the second to evaluate follicular development (n = 24 gilts). Gilts were allotted to treatments in a 2 x 2 factorial arrangement. Gilts from two genetic lines (Age at Puberty x Yorkshire [APY] and Relaxed Selection x Yorkshire [RSY] received either P.G. 600 [symbol: see text] (P) or no injection (C). The percentage in estrus within 5 d after treatment was greater (P < .05) for P than for C gilts. However, no difference was detected for the percentage of P or C gilts that had ovulated within 14 d. For the APY line, P gilts had greater (P < .05) ovulation rates than C gilts. However, for the RSY line, P and C gilts did not differ in ovulation rate. More P gilts than C gilts had follicular cysts (P < .05). At 48 h after onset of estrus, plasma progesterone concentration tended to be greater (P = .13) for P gilts than for C gilts. In Exp. 2, gilts were ovariectomized 18 h after the onset of estrus. Ova were dissected from follicles on one ovary, and follicular fluid was aspirated from the other ovary. No differences were detected for the percentages of ova in various stages of meiosis. For APY gilts, follicular fluid estradiol concentration for P gilts tended to be lower (P = .12) than that for C gilts; however, no differences were detected for RSY gilts. Progesterone concentration in follicular fluid tended (P = .14) to be greater in P gilts than in C gilts. These results indicate that the effect of genetic line on age at puberty should be considered when inducing puberty.