Sire field fertility does not correlate with sire conception rate (SCR) score

Abstract Accurate sire fertility evaluation remains a significant challenge in the livestock industry. Sire conception rate (SCR) has been used since 2008 in the dairy industry to rank sire fertility. The objective was to characterize individual sire pregnancy rate, pregnancy loss, and determine the correlation with the sire’s respective SCR. Our main hypothesis is that large variances in fertility parameters by sire cannot be explained by variance of the SCR values. Data from 6,570 timed artificial inseminations (AI) and 25,287 timed embryo transfers (ET) from 55 dairy farms were retrospectively analyzed to assess: pregnancy rate at day 30 (P30), pregnancy rate at day 60 (P60) and pregnancy loss (PL) during this interval. The effect of sire (AI: n = 39; ET: n = 81) for each reproductive parameter was evaluated. SCR records published prior to individual service were obtained to correlate with fertility parameters. For AI mating, pregnancy rate at P30 was 33.13% (2,177/6,570), and 27.6 % for P60 (1,815/6,570) and PL occurred in 16.6% (362/2,177) of pregnancies. Large variance was observed between sires for each parameter but no or negligible correlation (r < 0.2) with published SCR was observed. For ET, pregnancy rate at P30 was 47.8% (12,082/25,287) and 40.5% for P60 (10,246/25,287) with an overall PL of 15.2% (1,836/12,082). Similar to AI, all fertility parameters were highly variable among sires but no or negligible correlation (r < 0.03) with respective SCR was observed. In summary, the current method to evaluate sire fertility using SCR does not truly represent the field fertility status. Large variance in pregnancy loss between days 30 and 60 of gestation were observed among sires and these phenotypes should be considered when evaluating sire fertility to increase the score reliability.