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Macdonald Campus of McGill University,,4 Ste. Anne de Bellevue 800, Quebec, Canada
Abstract
Six experiments were conducted to study the maintenance of corpora lutea (CL) and pregnancy in prepuberal gilts (55 kg body wt) which were induced to ovulate by injecting 1,000 IU pregnant mare's gonadotrophin followed 2 to 3 days later by 500 IU human chorionic gonadotrophin (HCG). Injecting 10 mg diethylstilbestrol at the same time as the HCG induced standing estrus, facilitated the inseminations, increased (P<0.05) uterine weight, increased (P<0.05) the percentage of fertilized eggs but reduced (P<0.05) luteal tissue weight. The day of ovulation, 2 days after HCG, was considered to be day 1 of the induced cycle or pregnancy. The induced CL were normal in structure and progesterone content on days 5 and 10 but had partially regressed by day 20 in pregnant gilts and in gilts that were hysterectomized on day 8. Injecting 5 mg estradiol benzoate from day 11 to 17 did not maintain the CL in intact gilts. Injecting 100 IU HCG into hysterectomized females from day 8 to 25 increased (P<0.05) luteal tissue weight and the concentration of progesterone. The proportion of gilts with live embryos at day 25 was increased from 0 in controls to 50% in females given 500 IU HCG daily. Progesterone per gram of CL was greater (P<0.05) in pregnant females treated with 200 or 500 IU HCG than in non-pregnant gilts given 500 IU HCG. The above results indicated that the CL in PMSG-HCG treated gilts undergo normal formation but regress during pregnancy due to a lack of luteotrophic support. Daily administration of HCG showed that CL and pregnancy in prepuberal gilts can be maintained to at least day 25 by exogenous gonadotrophin treatment.
1 This study was supported by Canada Department of Agriculture Operating Grant No. 9074.
2 Present Address: Department of Biomedical Sciences, University of Guelph, Guelph, Ontario, Canada.
3 The authors gratefully acknowledge the generosity of G. A. Shaw, Ayerst Laboratories, Montreal, for supplying the PMSG and HCG and J. R. White, Glaxo Canada Ltd., Toronto, for supplying the estradiol benzoate.
4 Department of Animal Science.
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