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Synchronization of Estrus and Ovulation in Superovulated Gilts^{1, 2,}

Missouri Agricultural Experiment Station, Columbia 65201

Abstract

A total of 103 crossbred gilts were group fed methallibure (100 mg in 1.8 kg feed/gilt/day) for 20 days. Twenty-three gilts were designated as controls (Group I). Gilts in Group II (n=23) and Group III (n=57) received 1,500 IU of PMS 24 hr. after the last feeding of methallibure. Group III gilts received 500 IU of HCG 80 hr. after the PMS to synchronize ovulation. The gilts were inseminated 12 and 24 hr. after either the onset of estrus (Groups I and II) or after an injection of HCG (Group III) and were slaughtered 23 to 29 days later.

The administration of PMS:HCG following the suppression of estrus with methallibure provided an improved method of synchronization of gilts. Seventy-four percent of the control gilts exhibited estrus on days 5 and 6 after the last feeding of methallibure, while 95% and 93% of the gilts of Groups II and III, respectively, exhibited estrus on days 4 and 5. That successful synchronization of ovulation was achieved by HCG administration during proestrus is indicated by the similar pregnancy rates for gilts of Group III mated at a precise time after HCG and those of Groups I and II inseminated according to the onset of estrus. Ovulation rate, total number of embryos and number of normal embryos were significantly (P<.01) increased in both groups of gilts receiving gonadotropin treatment as compared to control gilts.

The present study demonstrates a successful modification in existing techniques to permit the use of superovulation in conjunction with the precise control of ovulation so that matings at a predetermined time can be made.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 6409. Approved by the Director.

² This investigation was supported in part by a PHS Training Grant No. HD-00170 from the National Institutes of Health, Public Health Service. The authors express their appreciation to Ayerst Laboratories, New York, N.Y. for providing the methallibure, PMS and HCG used in this study and to Mrs. Betty Nichols for secretarial assistance.

³ Present address: U.S. Meat Animal Research Center, U.S.D.A., Clay Center, Nebraska 68933.