A comparative study of intramuscular versus epidural administration of follicle-stimulating hormone for embryo production in Wagyu Cattle.

Abstract

Background: The increasing demand for high-quality livestock products necessitates the optimization of reproductive technologies, particularly superovulation and embryo transfer, to enhance genetic improvement and productivity. Superovulation increases embryo availability and accelerates genetic enhancement. The success of these techniques depends on factors such as hormone protocols, donor-recipient selection, and environmental conditions.

Aim: This study aimed to compared two superovulation protocols-conventional intramuscular injection (P₁) and combined epidural-intramuscular injection (P₂)-in Wagyu donor cows to evaluate their effects on corpus luteum (CL) formation, embryo yield, and quality.

Methods: The study was conducted from May to November 2024. Twelve cows were divided into two treatment groups (n = 6 per group), with follicle-stimulating hormone administered either through multiple intramuscular injections (P₁) or a single-dose epidural-intramuscular injection (P₂). Selection criteria included superior genetics, normal reproduction, regular estrus cycles (18-24 days), high fertility, prior calving, and disease-free status. Donor cows had a Body Condition Score of 2.5-3.5 and were confirmed to have normal reproductive organs via rectal examination. They were housed in a free-stall system and fed a controlled diet. Evaluated reproductive parameters included CL formation, embryo recovery rates (ERRs), and embryo quality.Results: There were no statistically significant differences between P₁ and P₂ in CL formation (p = 0.480), ERRs (p = 0.810), or embryo quality (p = 0.871). Both protocols supported comparable follicular development, embryo recovery, and transferable embryos across developmental stages (morula, early blastocyst, and blastocyst). While P₂ produced slightly more CL and blastocysts, the differences were not significant. Both protocols yielded similar proportions of unsuitable embryos, indicating no adverse effects on fertilization or embryonic viability.

Conclusion: The findings suggest that the combined epidural-intramuscular protocol (P₂) is a viable alternative to the conventional intramuscular protocol (P₁), providing comparable reproductive outcomes while potentially reducing handling stress and labor intensity. Future research should address the pharmacokinetics of hormonal delivery, its long-term reproductive impacts, and its applicability across other breeds to further optimize superovulation strategies for sustainable livestock production and genetic improvement.