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Ovulation and Embryonic Survival in Pubertal Gilts Treated with Gonadotropin Releasing Hormone^1,2,

Oregon State University, Corvalis 97331

Abstract

An experiment was conducted to evaluate the effect of exogenous gonadotropin releasing hormone (GnRH) on ovulation and embryonic survival in pubertal gilts. Gilts were assigned in replicates to a control (n = 10) and treatment (n = 10) group. Treatment consisted of an iv injection of 200 µg of GnRH immediately after initial mating on the first day of detected estrus. Control gilts were similarly injected with physiological saline. Blood samples were collected from the anterior vena cava immediately prior to injection, thereafter at 15-min intervals for 90 min, and subsequently, before slaughter on d 30 of gestation. Serum samples were analyzed for luteinizing hormone (LH) and progesterone by radioimmunoassay. Treatment with GnRH increased the quantity of LH released (P<.05), with highest serum concentrations (ng/ml, ± SE) of gonadotropin in treated gilts (17.3 ± 3.5) occurring at 75 min post-injection. In control gilts, serum concentrations of LH were not affected by injection of saline. Mean number of ovulations in treated gilts was also greater (P<.05) than that of control animals (14.5 ± .7 vs 12.1 ± .6). However, treatment with GnRH did not enhance the number of attached conceptuses (normal and degenerating) present (treated, 10.9 ± .9 vs control, 10.5 ± .7) nor the percentage of viable fetuses (treated, 74.7 ± 6.9 vs control, 83.5 ± 5.0%) on d 30 of gestation. Although GnRH increased ovulation rate, mean weight of corpora lutea of treated and control gilts did not differ (402.8 ± 16.3 vs 389.5 ± 11.3 mg, respectively). Similarly, serum concentrations of progesterone (ng/ml) on d 30 of gestation did not differ between treated and control animals (25.0 ± 2.6 vs 22.1 –± 2.9, respectively). These data indicate that a GnRH-induced increase in number of ovulations in the pubertal gilt is not accompanied by an increase in embryonic survival or litter size at 30 d of gestation.

¹ Technical paper no. 8079, Oregon Agr. Exp. Sta.

² The authors thank Dr. Myron Brown, CEVA Lab., Overland Park, KS for the generous donation of GnRH.

³ Address reprint requests to: Dept. of Anim. Sci.