SIRE CONTRIBUTION TO PREGNANCY ESTABLISHMENT AND MAINTENANCE IN BEEF COWS

Pregnancy loss is a major component of reproductive inefficiency and economic loss in both the beef and dairy industry. Research tends to focus on female contribution to pregnancy maintenance and overlook the role of the especially beyond early embryonic development stages. The aim of this study was to identify sires associated with high or low pregnancy loss and to investigate their effect on placental function, using circulating concentrations of pregnancy-associated glycoprotein [PAGs]. For the first part of the study, multiparous beef cows were randomly timed artificially inseminated [FTAI] with semen from either of 6 Angus sires of proven fertility and later, sires were retrospectively classified according to amount of pregnancy loss between days 30 and 100 of gestation. Pregnancies sired by high pregnancy loss sires had lower (P=0.05) circulating PAG concentration compared with pregnancies sired by low embryonic loss. For the second part, cows were artificially inseminated with either Nelore or Angus sires. Cows receiving semen from Nelore sires had greater (P < 0.001) pregnancy rate, greater (P = 0.014) pregnancy loss and lesser (P = 0.002) PAG concentrations at day 30 of gestation compared with cows receiving Angus semen. Estrus expression were evaluated in all cows using detector patches. Cows that expressed estrus prior to FTAI had higher pregnancy rate at day 30 and higher odds of maintaining pregnancy up to day 100 of gestation. Moreover, the effect of estrus in pregnancy rates was highly variable between sires. In summary, PAG concentrations reflected probability of pregnancy maintenance and were influenced by both sire and sire breed used at FTAI. A large variation in the incidence of pregnancy loss was detected among sires that could not be predicted with standard semen fertility evaluations. Exploring the relationship of sire and PAG production might be promising to improve sire selection with regard to pregnancy loss.