Investigating the Sire Contribution to Embryonic Mortality in Cattle
Abstract
First, we characterized the association between sire fertility and pregnancy loss in cattle. Bos Taurus beef cows had a large variance in pregnancy loss between days 24 and 31 of gestation (1.8 to 11.7%) and between days 31 and 60 of gestation (2.3 to 12.6%) among service sires used for timed artificial insemination (TAI). Similarly, same variance was observed among sires used for TAI and timed embryo transfer (TET) in dairy cattle. Pregnancy loss during the second month of gestation ranged from 5 to 35-40% among sires used in both TAI and TET, and no correlation was observed with their respective sire conception rate (SCR) index. These sire phenotype characterization studies suggest that current methods to evaluate sire fertility may be limited in assessing overall reproductive success and incidence of late gestation pregnancy loss should be considered when evaluating sire fertility, as it can significantly affect final pregnancy rate. To investigate the physiological mechanism of paternal contribution to conceptus formation, parthenogenetic embryos (PA) were compared to control embryos (CON) during blastocyst stage and post elongation stage. Pregnancy development was monitored by ultrasonography and blood based placental secretions. In all 19 cows that established a pregnancy with PA embryos, circulating concentration of placental products (PAG and ISG) throughout gestation were lesser compared to cows carrying CON embryos. Even though these embryos survived up to day 40-45 of gestation, no active site of implantation and attachment to endometrium was observed, suggesting that trophoblast tissues are not properly formed in the absence of paternal genes. These findings strongly suggest that paternal genetics contribute significantly to placenta formation in cattle, which could explain most of the sire variance observed in pregnancy loss during the period of active placentation. The development of markers to identify sires of high or low pregnancy loss would improve sire fertility evaluations and increase beef and dairy reproductive efficiency.
Citation
Araujo Franco, Gessica (2021). Investigating the Sire Contribution to Embryonic Mortality in Cattle. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /200827.