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Conception Rate and Ovarian Function Following Estrus Control by Progesterone Injections in Dairy Cattle¹

Cornell University^,3

Abstract

The effects of daily progesterone injections on ovarian function and conception rate in dairy cattle were investigated with 30 cows. Dosages used were either 50, 75, or 100 mg. daily and the injections were started at varying intervals in the estrous cycle but predominantly on the 15th day.

The interval from one estrus to another was successfully controlled. The cows came into estrus an average of 4.6 days after treatment ceased. The estrous cycle for the control period was 20.8 days compared to 26 days for the experimental period. Progesterone treatments provided an opportunity for shifting the time of estrus, but had no advantage in predicting estrus on a particular day.

No ovarian abnormalities were detected before, during or after estrus for the 30 cows during the control period. However, during the experimental period, 16 of these cows had early follicular development. Following estrus the corpus luteum was normal for all 30 cows during the control period, but after the experimental period 15 cows had abnormal ovarian conditions involving luteal development.

The length of estrus and the time of ovulation were available for 25 cows. During the control period the average length of estrus was 19.3 hours and ovulation time averaged 10.4 hours after the end of estrus.

During the experimental period only 14 cows had estrous periods of normal length, 4 had a silent estrus (ovulation without estrus), and 7 had a marked disturbance of either the length of estrus or ovulation time. A number of cows had unusually large follicles during the estrus following progesterone treatment.

The treatments with progesterone provided a marked influence on conception. Only 3 cows, or 12.5 percent, conceived from the first service for 24 cows bred by natural service to bulls with high fertility. The estrus following the one after the progesterone treatment had a normal cycle length from the previous estrus and normal conception rates were indicated with a 65.2 percent conception among the 23 cows bred. This indicated that the low fertility following progesterone treatment was temporary and was limited to the estrus following treatment.

¹ Supported in part by state funds and in part by funds from the regional project N. E.-l, entitled Causes and Prevention of Reproductive Failures in Dairy Cattle, a cooperative study by agricultural experiment stations in the northeastern region and the Bureau of Dairy Industry, U.S.D.A.

² The authors gratefully acknowledge the assistance of the Cornell Herd Superintendent, Paul Dean, and his co-workers for their help in conducting this experiment.

³ Dept. of Animal Husbandry, Ithaca, New York.