Abstract With the nearly exclusive use of females in the dairy industry, male dairy calves have traditionally been regarded as a low value by product. Beef on dairy matings are now a popular method for increasing the value of the excess offspring, while minimizing impact on the dairy cow. While high numbers of black hided offspring have been produced, further improvements can be made in beef on dairy performance, starting with bull selection. To make it easier for dairies to pick optimal beef bulls, indexes such as the HOLSim list by the American Simmental Association and Holstein Association USA have been developed to satisfy not only the dairy’s demand for calving ease but also the feedlot and packer needs for growth and carcass value. Despite its inception in 2019, there have been no studies investigating the impact of using the HOLSim index for sire selection. The objective of this study is to compare performance between the resulting beef on dairy calves from a HOLSim ranked and an unranked sire for calving, growth, and carcass performance. Additionally, comparisons will be made between beef calves resulting from the same sires. Calves were born in Fall of 2025, with beef on dairy calves sired from the ranked (n = 31) and unranked sire (n = 39) born to Holstein cows on a dairy in Eastern Missouri, and beef calves sired from the ranked (n = 19) and unranked (n = 24) sires born to SimAngus cows in Mid-Missouri. Beef on dairy calves were fed milk replacer in individual pens until weaning at 56 days of age at which point they were group housed. Beef calves will be raised on their dam on pasture until weaning around 205 days of age. Both groups will then enter the feedlot. Using a 2x2x2 factorial design, linear mixed models were run in R to evaluate the relationship between calf gestation length, calving ease, and birth weight with sire. The effect of sire (ranked vs unranked), herd (dairy or beef), sex, and twin status were accounted for in the model. There were no significant interactions and therefore the simplest model using only the main effect is reported. While the ranked sire increased gestation by 2.4 days (P = 0.004), neither calving ease nor birth weight affected (P 0.10). The lack of impactful differences at birth demonstrates that dairy producers can choose bulls with high EPDs for growth and carcass traits and not see detrimental effects. Future comparisons in performance between calves as they grow will outline the potential benefits to calf ranches and feedlots.
Donlick et al. (Wed,) studied this question.