Factors influencing estrus and ovulatory activity in hair ewes

Abstract

Objective: To evaluate the effects of eCG dose and timing of administration, breed, and reproductive season on estrus and ovarian activity in hair ewes.
Design/methodology/approach: A total of 216 hair ewes (62 Dorper, 69 Katahdin, and 85 Pelibuey), including 91 in the high and 125 in the low reproductive season, were synchronized using intravaginal sponges containing 20 mg of fluorogestone acetate (FGA) and intramuscular equine chorionic gonadotropin (eCG; 200 or 300 IU). Treatments included breed, reproductive season, eCG dose, and timing of eCG administration. The presence of ovulation, ovulation without estrus, and estrus without ovulation was analyzed using a logistic regression model. Statistical analysis was performed with the PROC LOGISTIC procedure in SAS.
Results: None of the studied factors (reproductive season, breed, or eCG dose and timing) significantly influenced the likelihood of ovulation (p > 0.05). However, Dorper ewes showed a higher incidence of silent estrus compared to the other breeds (OR = 0.56, CI = 0.02–0.59; p = 0.0094). Estrus without ovulation was also significantly affected by breed; Dorper ewes were 7.41 times more likely (p = 0.0373) to exhibit estrus without ovulation compared to Pelibuey ewes.
Limitations/implications: Crossbred animals were excluded to meet inclusion criteria, which limited the sample size.
Findings/conclusions: Estrus and ovarian activity in hair sheep synchronized with progestogens is primarily influenced by breed.