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Effect of Repeated Superovulation on Ovulatory Response of Dairy Cows^{1 ,2,}

University of Illinois⁴, Urbana 61801

Abstract

Sixteen lactating dairy cows were superovulated with either FSH-LH or PMSG four successive times; first three at consecutive 16-day cycles and the fourth after one ovulation without the use of exogenous hormones. The response to repeated superovulation with the same gonadotrophin in the fourth superovulation period was similar to that in the first period in terms of both number of ovulations and recovered ova, indicating that refractoriness to repeated gonadotrophin injection did not develop within the 3- to 4-month period required for the four superovulatory treatments. A decreased response of the cows in the second and third superovulation periods was attributed to a short recovery time from the previous superovulation.

¹ Supported in part by funds from the Illinois Agr. Exp. Sta.

² The authors express their appreciation to J. W. Lauderdale, The Upjohn Co., Kalamazoo, MI. for the PGF₂ used in this study.

³ Present address: Univ. of Jordan; Amman, Jordan.

⁴ Dept. of Dairy Science.