Alberta Pork Research Centre/ 1Department of Agricultural, Food and Nutritional Science, University of Alberta; 2Alberta Agriculture, Food and Rural Development, Swine Research Group; 3Alberta Swine Genetics Corporation, Box 3310, Leduc.
During feed restriction and body weight loss (catabolism) in lactating sows the release of the pituitary gonadotropin, LH is blocked and may be one cause of reduced fertility after weaning. As LH secretion is controlled by GnRH release from the brain, exogenous GnRH treatment can be used to increase LH secretion. This experiment was therefore carried out to test the hypothesis that GnRH treatment in lactating, primiparous sows undergoing feed-restriction, would improve reproductive performance.
Primiparous Camborough sows were allocated to one of three treatments. Group AA sows (n=8) acted as positive controls and were fed to appetite throughout a 28 day lactation. AR (n=12) and AR+GnRH (n=11) sows were fed to appetite from d 1 to 21 and feed allocations were then reduced to 50% of the ad lib intakes from d 22 to 28 of lactation. Group AR+GnRH sows received 800 ng of GnRH iv in 4ml of sterile saline every 6 h from d 22 to 28. Group AR and AA sows received equivalent saline injections. All sows were allowed ad lib access to feed after weaning. Onset of estrus was checked twice daily at 07:00 and 19:00h, in the presence of a vasectomized boar for 15 minutes. At 12 and 24 h after onset of heat, sows were artificially inseminated with the same pooled semen. After mating feed allowances were reduced to normal NRC (1988) requirements for gestation. All sows were slaughtered on day 28 of gestation, reproductive tracts recovered and number of embryos and ovulation rates estimated.
The number of corpora lutea (18.0, 16.6 and 17.5), total number of embryos (13.4, 12.6 and 14.2), number of viable embryos (12.4, 12.4 and 13.4) and embryo survival rate (68.7, 73.8 and 77.0%) for AA, AR and AR+GnRH groups, respectively, were not different (P>0.05). Feed restriction in AR and AR + GnRH groups increased (P=0.02) the weaning-to-estrus interval compared with AA sows.
Implications: Endogenous GnRH treatment in AR+GnRH sows had no effect on ovulation rate,
weaning-to-estrus interval and subsequent embryo survival compared to untreated feed restricted
AR sows. Restricted feeding and lactational catabolism may therefore exert detrimental effects on
reproductive performance at a local ovarian level.