# Breed and Season: Key Determinants of Efficiency in Large-Scale Commercial In Vitro Sheep Embryo Production

## TL;DR

This study shows that matching sheep breeds with the right season improves the success of in vitro embryo production in commercial sheep farming.

## Contribution

The study identifies breed-season combinations that optimize in vitro embryo production efficiency in sheep.

## Key findings

- Autumn and winter are the most productive seasons for in vitro embryo production in sheep.
- Certain breeds, like Black-headed Suffolk, perform best in specific seasons for embryo production.
- Oocyte quantity does not predict developmental potential or pregnancy success.

## Abstract

Reproductive technologies like in vitro embryo production (IVEP) allow farmers to rapidly multiply the best genetics in their sheep flocks. A key step is collecting oocytes from valuable donor ewes using a technique called laparoscopic ovum pick-up (LOPU). However, the success of this process can vary. Our study investigated how the sheep’s breed and the season affect the entire production chain, from oocyte collection to the birth of a lamb via embryo transfer. We found that the best outcomes are achieved by matching specific breeds to their optimal season. The breeds demonstrated a clear functional division of labor: some were identified as superior oocyte donors, while others showed greater efficacy in supporting pregnancy. Crucially, we show that autumn and winter are the most productive seasons. By aligning breeding schedules with these breed-season combinations, sheep farmers can significantly improve the efficiency and success of their advanced breeding programs.

The efficiency of the laparoscopic ovum pick-up and in vitro embryo production (LOPU-IVEP) system in sheep is governed by a complex interplay of genetic and environmental factors. This study comprehensively evaluated the effects of breed, season, and their interaction on oocyte retrieval, embryonic development, and pregnancy outcomes in a commercial setting. A 20-month longitudinal analysis of a large commercial cohort revealed that breed was the dominant factor determining oocyte quantity, whereas season exerted a stronger influence on developmental competence. Specifically, autumn and winter provided optimal conditions, resulting in significantly higher cleavage rate and blastocyst rate (p < 0.05). A significant breed-by-season interaction further identified synergistic combinations, such as Black-headed Suffolk in autumn or winter, which achieved superior embryo production outcomes. Importantly, correlation analysis revealed that oocyte quantity was not predictive of developmental potential or pregnancy success. These findings underscore the necessity of a precision management strategy that aligns LOPU schedules with breed-specific seasonal advantages to maximize annual embryo production efficiency.