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Relationship between Number of Induced Ovulations in the Prepubertal Gilt to the Level of Progesterone and to the Number of Spontaneous Postpubertal Ovulations¹

University of Illinois, Urbana 61801

Abstract

A Series of experiments were conducted to investigate the relationship between the number of corpora lutea (CL) and concentration of progesterone (P₄) on different days after induced and spontaneous ovulation of gilts of different ages. Possible relationship between the number of ovulations after injection of gonadotropin into the prepubertal gilt and the number at a second induced ovulation and finally the number of postpubertal, spontaneous ovulations, was also studied. Number of CL was related (r = .75 to .95, P<.01) to levels of P₄ on d 3 to 10 after induced ovulation of prepubertal gilts of 105 to 180 d of age. Relationship between the number of CL and level of P₄ in cyclic gilts ranged from r = .28 to .67 with the highest relationship at d 4 to 9. Number of CL induced at 135 d of age was correlated (r = .67 to .91, P<.01) with number of CL induced at 195 d. There were correlations (r = .75 to .99, P<.01) between levels of P₄ and number of CL on d 7 to 9 after induction of ovulation of gilts of 135 and 195 d of age with either pregnant mare's serum gonadotropin (PMSG) followed in 96 h by human chorionic gonadotropin (hCG) or estradiol benzoate (EB) followed in 72 h by hCG. There was a correlation (r = .84, P<.001) between number of CL at the first spontaneous postpubertal estrus and number of CL at third estrus. Number of ovulations induced by PMSG in the prepubertal gilt was found to be correlated (r = .58, P<.00l) to number of postpubertal spontaneous ovulations. Based upon these findings, we concluded that the level of P₄ in plasma on d 3 to 10 following induced ovulation of gilts between 105 and 180 d of age, gives an estimate of the number of CL and this in turn is related to number of spontaneous ovulations at puberty. These relationships might be used to identify prepubertal gilts with potentially high or low postpubertal numbers of ovulations. Because correlations between the level of P₄ and number of CL in cyclic gilts was lower than in prepubertal gilts, P₄ determinations after spontaneous ovulation appear to be less useful in the prediction of number of potential ovulations than after induced ovulation.

¹ These studies conducted while G. Dial held a fellowship from the National Institute of Health training grant HD07028 and was supported by the Illinois Agr. Exp. Sta. The authors are grateful to R. S. Wilkinson for assistance in bleedings, C. L. Warner for animal care and to J. E. Hixon and D. J. Kesler for help in preparing this manuscript and G. E. Abraham for P₄ antiserum.

² Present address: Dept. of Food Anim. and Equine Med., School of Vet. Med., North Carolina State Univ., 4700 Hillsborough Street, Raleigh, NC 27606.

³ Send correspondence to: Dr. P. J. Dziuk, Dept. of Anim. Sci.