Seasonal pregnancy rates in primiparous Holstein-Friesian cows following transfer of in vitro-produced embryos versus artificial insemination under chronic heat stress Embryo transfer and artificial insemination across seasons
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Abstract
Reproductive performance in dairy cattle is highly susceptible to heat stress (HS), which negatively affects oocyte quality, fertilization, and early embryonic survival. Embryo transfer (ET) using in vitro-produced embryos may mitigate these adverse effects by allowing early embryonic development to occur under controlled laboratory conditions. Objective: To compare pregnancy rates following ET and artificial insemination (AI) in primiparous Holstein-Friesian cows exposed to chronic HS across seasons. Methods: A total of 275 primiparous Holstein-Friesian cows were assigned to ET (n = 124) or AI (n = 151). All cows underwent standardized hormonal synchronization protocols. Pregnancy diagnosis was performed by transrectal ultrasonography at 30 and 44 days post-service. A generalized linear model with binomial distribution was used to evaluate the effects of each reproductive method and season on pregnancy outcome. Results: The combined overall pregnancy rate was 33.5 %, with no significant differences between ET and AI across seasons (P > 0.05). Logistic regression analysis showed no significant effect of reproductive method (odds ratio = 1.07; 95 % Confidence interval: 0.64–1.78; P = 0.798) or season (P = 0.158) on pregnancy outcome. Although not statistically significant, a numerical trend favoring ET during summer was observed. Conclusions: Under chronic HS conditions, ET using in vitro-produced embryos did not significantly improve pregnancy rates compared with AI.
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