Duration of Estrus, Time of Ovulation and Fertilization Rate in Beef Heifers Synchronized with Dihydroxyprogesterone Acetophenide

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Abstract
The effects of estrus synchronization on duration of estrus, time of ovulation, fertilization rate and rate of ova transport were determined in heifers where observations were made on estrus and ovulation at 4-hr, intervals. Fertilization rate and rate of ova transport were determined approximately 48 hr. after ovulation. Synchronization was accomplished in Trial I by feeding 500 mg. of the 16α, 17 dihydroxyprogesterone acetophenide (DHPA) daily for 20 days. Ninety-six percent of the synchronized heifers came into estrus during a 48-hr, period. The average length of the estrous period was 21.0 hr. for the control heifers and 16.5 hr. for the synchronized heifers (P<.01). The interval from beginning of estrus to ovulation was approximately 33 hr. for both groups. Eighty-six percent of the control heifers and 56% of the synchronized heifers had fertilized eggs 48 hr. after ovulation. The percent of heifers having embryos 34 days after ovulation was 26 and 54 for the control and synchronized heifers, respectively. This difference was not significant (P>.05). Estrus was synchronized in Trial II by feeding 400 mg. of DHPA daily for 9 days, with an injection of 5 mg. of estradiol valerate on the second day of feeding. Eighty-four percent of the treated heifers were in estrus during a 96-hr, period. Fertilization rate, ova transport, duration of estrus, interval from beginning of estrus to ovulation and fertiilty were not significantly affected by this treatment. The duration of estrus and the interval from end of estrus to ovulation for the control animals were about the same in both trials.