Assessment and selection of the recipient cows' corpus luteum at the time of embryo transfer, and its influence on conception rate.

Abstract

OBJECTIVES: To describe the influence of physical traits of the corpus luteum (CL), as described by transrectal ultrasonography on day 6 post-oestrus, on the conception rate following embryo transfer (ET) in recipient beef cows. To investigate if higher recipient utilisation rates were achievable, without compromising conception rates to ET. DESIGN/RESULTS: Data were analysed from Holstein Friesian embryos (n&#xa0;=&#xa0;1075) frozen in ethylene glycol thawed for direct transfer into one herd of Angus recipient cows. For pregnancies achieved in the program (n&#xa0;=&#xa0;693), no statistically significant effect was found for the physical traits of the recipients' CL on conception rate (CL volume (P&#xa0;=&#xa0;0.20), CL side (P&#xa0;=&#xa0;0.14). Conception rates were similar for recipients with a central lacuna (62%, n&#xa0;=&#xa0;245) and recipients with no central lacuna (66%, n&#xa0;=&#xa0;448) (P&#xa0;=&#xa0;0.10). Of the pregnant recipients with a central lacuna (n&#xa0;=&#xa0;245), 98.3% had no remaining luteal cavity by the 30-day pregnancy ultrasound. No effect on conception rate was found with either the small (<50% of CL diameter) or large (>50% of CL diameter) central lacunae (P&#xa0;=&#xa0;0.18). For recipients with CLs that did not meet previous industry selection guidelines (n&#xa0;=&#xa0;172, 16% of study population), the conception rate (63%) was not significantly different to the routinely selected recipient CLs (n&#xa0;=&#xa0;903, conception rate 65%) (P&#xa0;=&#xa0;0.83). CONCLUSIONS: The suitability of a potential ET recipient is determined by observing an appropriately timed oestrus and a detectable CL, regardless of size or quality.