MOET Efficiency in a Spanish Herd of Japanese Black Heifers and Analysis of Environmental and Metabolic Determinants

Simple Summary Embryo transfer procedures have been widely implemented in bovine all around the world. These techniques help to accelerate the increase in the genetic merit and to keep the level of inbreeding under control, which is especially important in breeds, such as Japanese Black cattle, in areas outside of Japan, where there are scarce individuals and few herds. Our study describes an adequate embryo productivity of Japanese Black heifers under Spanish management and environmental conditions, like that which has been previously reported, demonstrating the adequate adaptation capacity of these animals. No effect on embryo production or quality was found due to plasma metabolic parameters of the donors, suggesting an optimal nutritional and body conditioning of the donors' herd. Pregnant recipients after embryo transfer showed significantly higher levels of cholesterol-related parameters, glucose, and urea, which may be related to higher availability of nutrients for the future pregnancy. Heat stress at embryo transfer negatively impacted conception rates as expected, while larger parity and ET number corresponded to numerically higher conception rates. Multiple ovulation and embryo transfer (MOET) systems have been intensively implemented in Japanese Black cattle in Japan and to create Japanese Black herds out of these areas. Environmental conditions influence MOET efficiency. Thus, we describe results of 137 in vivo, non-surgical embryo flushings performed between 2016-2020, in a full-blood Japanese Black herd kept in Spain and the possible effects of heat, year, bull, donor genetic value, and metabolic condition. Additionally, 687 embryo transfers were studied for conception rate (CR) and recipient related factors. A total of 71.3% of viable embryos (724/1015) were obtained (5.3 +/- 4.34/flushing). Donor metabolites did not affect embryo production (p > 0.1), although metabolite differences were observed over the years, and by flushing order, probably related to the donor age. CR was not affected by embryo type (fresh vs. frozen), recipient breed, and whether suckling or not suckling (p > 0.1). CR decreased significantly with heat (44.3 vs. 49.2%; (p = 0.042)) and numerically increased with recipient parity and ET-number. Pregnant recipients showed significantly higher levels of cholesterol-related metabolites, glucose, and urea (p < 0.05). Therefore, adequate MOET efficiency can be achieved under these conditions, and heat stress should be strongly avoided during Japanese Black embryo transfers. Moreover, recipients' metabolites are important to achieve pregnancy, being probably related to better nutrient availability during pregnancy.