Case study: Influence of seminal, physical, and mating behavior traits of bulls on number of calves sired per bull in a multisire herd

A study was conducted to quantify the influence of behavior, physical characteristics, and seminal traits of bulls on reproductive performance in a multisire herd. Braunvieh (n = 6) and Bonsmara (n = 6) bulls (18 to 24 mo) were evaluated for BCS, social dominance rank (SDR), serving capacity, sperm motility and morphology, and fertility-associated antigen classification of an ejaculate. Bulls (n = 12) were mated with multiparous cows (n = 305) for 90 d. Paternity was verified by DNA typing. All bulls were fertility-associated antigen-positive. Bull breed, sperm motility and morphology, and SDR were associated with number of calves sired per bull (P < 0.05, R 2 = 0.75). More calves born early in the calving period (P < 0.025) were sired by bulls with ≥ 80% normal sperm. Results indicate that assessment of SDR in conjunction with a breeding soundness exam can determine number of calves sired per bull. Furthermore, selection of bulls that produce at least 80% morphologically normal sperm may enhance the percentage of cows impregnated early in the breeding season. bull fertility semen mating behavior