Reproductive, metabolic, and endocrine responses to feed restriction and GnRH treatment in primiparous, lactating sows

The current experiment was carried out to determine whether exogenous GnRH treatment in primiparous, lactating sows undergoing feed restriction would improve reproductive performance after weaning. Sows were allocated to one of three treatments: AA sows (n = 8) were fed to appetite throughout a 28-d lactation, AR (n = 12) and AR + GnRH (n = 12) sows were fed as AA sows fro m farrowing to d 21 of lactation, and feed intake was reduced to 50% of the ad libitum intakes from d 22 to 28. The AR + GnRH sows received 800 ng of GnRH i.v. every 6 h from d 22 to 28 of lactation, and AA. and AR sows recei ved saline. Sow weight, backfat, and litter weight were recorded weekly. Wi thin 2 d after farrowing, litter size was standardized to 8 to 10. At d 17 of lactation, an indwelling jugular catheter was surgically implanted in ea ch sow,,Blood samples were taken for characterization of plasma LH, FSH, in sulin, IGF-I, and leptin by RIA at d 21 and before and after weaning on d 2 8 of lactation. After weaning, all sows were given ad libitum access to fee d, checked for onset of standing estrus twice daily with mature vasectomize d boars, and inseminated 12 and 24 h after onset of standing estrus with po oled semen from the same fertile boars (3 x 10(9) sperm/AI). After breeding , feed allowance was reduced to NRC (1988) requirements for gestation. At d 28 +/- 3 of gestation, sows were killed and ovulation rate and embryo surv ival were determined. Restricted sows lost more weight during lactation tha n AA sows (P < .02). During the period of feed restriction, plasma IGF-I an d postprandial insulin and leptin in AR and AR + GnRH sows, and LH pulse fr equency in AR sows, were lower than those in AA sows (P < .04). Association s (P < .004) between plasma insulin and leptin and between leptin and mean LH concentrations were established. The LH pulse frequency in AR + GnRH sow s did not differ from that in AA sows before weaning. After weaning, maximu m, mean, and minimum LH concentrations in the AA and AR sows, and FSH conce ntrations in AR sows, increased (P < .05) in response to weaning. Paradoxic ally, GnRH treatment in lactation seemed to suppress the expected LH and FS H responses to weaning. Ovulation rate and embryo survival were not differe nt among the three groups. In conclusion, although exogenous GnRH therapy r estored LH secretion in feed-restricted sows, it did not improve overall re productive performance.