Ovarian Activity in Superovulated Dairy Cattle Following Cloprostenol Injection on the Day of Embryo Collection.

Abstract

Superovulation (SO) with FSH was induced in 23 dairy cows and 12 dairy heifers which were treated on the day of embryo collection (Day 7) with a single luteolytic injection of either 500 mg or 1000 mg of Cloprostenol (Clp). The animals were clinically examined and their plasma progesterone (P4) levels were monitored for 30 days after Clp injection. Estrus signs were checked twice daily. The ovaries were scanned by ultrasonography to follow corpora luteal (CL) regression, follicular, development and ovulation. The CLs regressed in all 34 animals responding to SO. Estrus signs occurred within 16 days after Clp injection in 91.2% of the population (19 cows and 12 heifers); ovulation occurred in 55.9% of the 34 animals responding to SO (12 cows and 7 heifers ). Of the animals showing estrus, the 7 cows and 5 heifers (38.7%) that did not ovulate either became cystic (4 cows and 3 heifers) or had follicular growth waves which never reached ovulation(3 cows and 2 heifers). Furthermore, 3 cows (8.8%) did not show estrus signs during this period. In the second cycle following Clp administration, the interestrus interval was within normal ranges (17 to 24 days) and estrus was followed by ovulation even in most of those animals with previously non-ovulated follicular waves. The cystic cases (20.6%) and 1 anestrus case, however, remained. Heifers had a significantly shorter interval from embryo collection to first estrus than cows. No significant differences in the effect of the 2 Clp dosages assayed on the interval from embryo collection to the first ovulatory estrus were found in those animals having a normal ovulatory estrus. The P4 plasma profiles confirmed both luteolysis after Clp injection and the occurrence of ovulation. In heifers, the concentration of P4 on the day of embryo collection and 24 h thereafter was positively correlated with the interval from collection to first estrus. Besides the satisfactory luteolytic effect of Clp, the resumption of cyclicity seemed to be more influenced by the disturbed ovarian dynamics at the time when Clp was injected than by its dosage.