SYNCHRONIZATION OF ESTRUS AND OVULATION IN CATTLE WITH THE PROSTAGLANDIN ANALOGUE AY 24655

Abstract

In 97 experiments, cattle (mostly dairy heifers) were treated with AY24655 by intrauterine (i.ut.), subcutaneous (s.c.) or intramuscular (i.m.) routes during the luteal phase of the estrous cycle. Responses were assessed by observation for estrus and ovarian palpation in 97 cases, plasma progesterone determinations in 84 and by inspection of the ovary in 41. Doses of 10–50 mg i.ut. led to dose-related responses but inadequate synchronization. Both animals receiving 40 + 8 mg s.c. at 24-h intervals were synchronized, but 50 mg as a single i.m. injection was inadequate (2/5 synchronized). A dose of 100 mg i.m. was effective as a single injection (37/40 synchronized) or as two 6-h-spaced injections (8/10 synchronized). Progesterone concentrations showed sustained declines in all 61 synchronized animals and temporary declines in 15/23 non-synchronized animals. Ten of 18 synchronized animals became pregnant when used as recipients of embryos. Ten of 13 treated animals were synchronized by 100 mg following PMSG treatment for superovulation and 13/22 embryos transferred from these donors survived. Adverse side effects were confined to one batch of the compound which may have been impure. Though less potent than some prostaglandin analogues, AY24655 compared favorably with them for synchronizing cattle without marked adverse effects on embryos.