Number of oocytes retrieved per donor during OPU and its relationship with in vitro embryo production and field fertility following embryo transfer

ABSTRACT

The association of OPU-IVEP is an important instrument to drive genetic progress. In vitro embryo production (IVEP) has remarkably expanded in the last decade compared to in vivo embryo production. Because of the high repeatability of oocyte retrieval within oocyte-donors, studies exploring the relationship between the number of oocytes recovered per OPU section with IVEP efficiency, as well as with field fertility (pregnancy results following embryo transfer; P/ET) are extremely important to guide cow-donor selection and optimize field reproduction efficiency and the herd’s genetic gain. Based on this rationale, our group conducted a retrospective analysis of a large database comprising IVEP records from several cattle breeds, including Bos indicus and Bos taurus for either beef or dairy purposes. A total of 205,140 oocytes recovered from 7,906 OPU procedures of 6,902 donors (5,227 beef and 1,675 dairy) of Brazilian farms were analyzed. Beef breeds analyzed were Nelore (Bos indicus) and Senepol (Bos taurus) and dairy breeds Were Gyr (Bos indicus) and Holstein (Bos taurus). According to our analysis, the IVEP in beef cattle had a great improvement throughout the last years, with a remarkable increase in numbers of pregnancies per OPU compared to late 90’s (averaging only 1 pregnancy per OPU in 1998 vs 2,4 in 2014). As for the distribution of oocytes retrieved, both Bos indicus beef (Nelore = 27.2) and dairy (Gyr = 23.8) breeds seem to yield greater average numbers of oocytes per OPU compared to Bos taurus (Senepol = 21.8; Holstein = 19.3).