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Fertility in the Beef Heifer following Treatment with 6-Chloro ⁶-17 Acetoxyprogesterone

Eli Lilly and Company, Greenfield, Indiana

Abstract

A total of 187 heifers in two experiments was used to measure the effect of 6-chloro A6–17 acetoxyprogesterone (CAP) on ova fertilization rate and 60-day pregnancy rate. CAP-treated heifers bred on the first post treatment estrus had a lower (P<.05) fertilization rate (61%) than the controls (82%). The 60-day pregnancy rate in CAP-treated heifers also was lower (P<.10) than controls (33% vs. 55%, respectively). Given a fertile ovum, the percentage of ova surviving was estimated for both CAP-treated and control heifers (54% vs. 67%, respectively). However, these percentages were not significantly different. In both CAP-treated and control heifers, the 60-day pregnancy rate was significantly (P<.01) lower than the 3-day fertilization rate. The stage of the estrous cycle when CAP treatment was started may have had an effect on the ova fertilization rate at the first estrous period following CAP treatment.