Relationship between doses of prostaglandin F 2α and stages of the breeding season for synchronization of estrus and ovulation in ewes

Abstract

Two experiments were conducted to compare estrous response to three doses (8, 16 and 24 mg) of prostaglandin F 2α (PGF 2α) administered by intramuscular injection to ewes between day 6 and 12 of the estrous cycle (Experiment I) and to ewes on unknown days of the estrous cycle during four different stages of the breeding season (Experiment II). In experiment I, a total of 41 ewes were treated with PGF 2α. The injection of 24 mg PGF 2α resulted in a higher proportion of ewes exhibiting estrus ( 13 14 , 92.9%) within 5 days after treatment as compared to the other two doses ( 2 12 and 10 15 , for 8 and 16 mg PGF 2α, respectively). However, there was no significant difference for the proportion between 16 mg and 24 mg PGF 2α. In experiment II, PGF 2α was given to ewes on the 3rd of February (early breeding season), the 28th of February (mid-early breeding season), the 10th of April (mid breeding season) and the 27th of May (late breeding season). These was a significant difference for the proportion of ewes exhibiting estrus between the early breeding season and the other three seasons (P < 0.05) but not for ewes ovulating. Throughout the breeding season, 16 mg PGF 2α appeared to be slightly better than the other two doses (8 and 24 mg) although there was no overall difference in the estrous responses to treatment among the three doses. However, a significant difference in the proportion of ewes ovulating was found among the three doses of PGF 2α (P < 0.05). Especially, 16 mg PGF 2α was significantly superior to 8 mg (P < 0.01) and 24 mg (P < 0.05). It was considered that there was a complicated relationship between the doses of PGF 2α and the stages of the breeding season for induction of estrus and ovulation in the ewe.