Effect of insemination of estrus-induced prepuberal gilts on ensuing reproductive performance and body weight

Prepuberal gilts reared and managed to 85-90 kg live weight in a common sys tem were allocated at random to one of three first-mating treatments in an experiment conducted over a period of more than 5 years. In two of the trea tments, gilts received a single i.m. injection of 400 IU equine chorionic g onadotropin (eCG) and 200 IU human chorionic gonadotropin (hCG) (PG600; Int ervet) and were either inseminated 4 and 5 days later on a fixed-time basis regardless of oestrus (treatment A), or at the second oestrus following tr eatment (treatment B). The third group of gilts remained untreated and was inseminated on the first spontaneous oestrus (treatment C). Thereafter, all gilts were managed in the same way and those observed in oestrus were re-i nseminated. Significantly more gilts returned to oestrus after the first se rvice in treatment A (35%) than in treatment B and C (12 and 17%, respectiv ely; P < 0.01). Gilts farrowed to the first or repeat inseminations at a si gnificantly younger age (P < 0.01) in treatment A (304 days) than treatment B (324 days) and C (320 days). The age difference at farrowing remained in surviving gilts at the end of their third parity. The first farrowing perf ormance of the gilts was significantly affected by treatment in terms of li tter size at birth (A 7.0, B 8.4 and C 8.3 live piglets per gilt; P < 0.01) , litter size at weaning (A 6.2, B 7.2 and C 7.2 live piglets per gilt, P < 0.05), and piglet birth weight (A 1.4, B 1.3 and C 1.3 kg; P < 0.05) but p iglet survival rate and weaning weight were not affected by treatment. The live weights of the gilts were significantly different between the treatmen ts at first insemination (A 95.7, B 106.5 and C 109.2 kg; P < 0.01) but not when the first litter was weaned (A 133.6, B 135.1 and C 136.6; P > 0.05). After the first farrowing there were no differences between the treatments in terms of the survival rate, productive or reproduc tive performance of the gilts/sows and their offspring. Without conducting a detailed cost-bene fit-calculation it was deduced that, from an economical point of view, diff erences between treatment A and treatments B and C are negligible because t he savings associated with farrowing at a younger age on this treatment jus t about compensated for any additional costs associated with the treatment and the lower number of piglets born at the first farrowing. (C) 1999 Elsev ier Science B.V. All rights reserved.