Evaluation of bull fertility in Italian Brown Swiss dairy cattle using cow field data

Abstract

Dairy bull fertility is traditionally evaluated using semen production and quality traits; however, these attributes explain only part of the differences observed in fertility among bulls. Alternatively, bull fertility can be directly evaluated using cow field data. The main objective of this study was to investigate bull fertility in the Italian Brown Swiss dairy cattle population using confirmed pregnancy records. The data set included a total of 397,926 breeding records from 1,228 bulls and 129,858 lactating cows between first and fifth lactation from 2000 to 2019. We first evaluated cow pregnancy success, including factors related to the bull under evaluation, such as bull age, bull inbreeding, and AI organization, and factors associated with the cow that receives the dose of semen, including herd-year-season, cow age, parity, and milk yield. We then estimated sire conception rate using only factors related to the bull. Model predictive ability was evaluated using 10-fold cross-validation with 10 replicates. Interestingly, our analyses revealed that there is a substantial variation in conception rate among Brown Swiss bulls, with more than 20% conception rate difference between highfertility and low-fertility bulls. We also showed that the prediction of bull fertility is feasible as our cross-validation analyses achieved predictive correlations equal to 0.30 for sire conception rate. Improving reproduction performance is one of the major challenges of the dairy industry worldwide, and for this, it is essential to have accurate predictions of service sire fertility. This study represents the foundation for the development of novel tools that will allow dairy producers, breeders, and artificial insemination companies to make enhanced management and selection decisions on Brown Swiss male fertility.

Bull fertility and semen quality are not correlated with dairy and production traits in Brown Swiss cattle

“…Several QTL that affect bull fertility and ejaculate characteristics have been identified in beef and dairy breeds (Peñagaricano et al, 2012;Rezende et al, 2018;Butler et al, 2019). In Brown Swiss (BSW) cattle, considerable heritable variation in male reproductive success has been identified between bulls (Hiltpold et al, 2020;Pacheco et al, 2021). Some of this variation is due to largeeffect QTL for sperm motility, sperm anomalies, and bull fertility located on chromosomes 1,6, 18, 25, and 26 (Hiltpold et al, 2020(Hiltpold et al, , 2021.…”

Deciphering the genetic basis of male fertility in Italian Brown Swiss dairy cattle

“…We evaluated more than 1200 Brown Swiss bulls based on cow field data, including 400k breeding records from 130k lactating cows. Interestingly, we found a substantial variation in conception rate among Brown Swiss bulls, with more than 20% conception rate difference between high-fertility and low-fertility bulls 11 . As such, the present study was specially performed to identify genetic factors that explain part of the variation observed in sire conception rate among Italian Brown Swiss bulls.…”

“…The evaluation model included factors related to the bull under evaluation, such as bull age, bull inbreeding, and AI organization, and factors associated with the cow that receives the dose of semen, including herd-year-season, cow’s age, parity, and milk yield. Notably, we revealed a substantial variation in conception rate among Brown Swiss bulls, with more than 20% conception rate difference between high-fertility and low-fertility bulls 11 .…”

“…Phenotypic data consisted in sire conception rate (SCR) records from a total of 1102 Italian Brown Swiss bulls. These sire conception rate records were estimated using cow field data 11 . Briefly, we first evaluated cow pregnancy success (binary trait; 0 = failure, 1 = pregnancy) using factors related to both the bull under evaluation and the cow that receives the dose of semen.…”

“…Europe has the largest Brown Swiss population, which is led by Switzerland, Germany, and Italy. Interestingly, we recently developed a bull fertility evaluation in the Italian Brown Swiss population using cow field data 11 . We used almost 400k breeding records from 130k lactating cows and more than 1200 bulls.…”