| Two experiments were conducted at the Texas A&M Agricultural Research and Extension Center at Uvalde. Selected physical, behavioral, and social interaction traits of bulls were assessed to develop methods to more accurately predict number of calves sired per bull in multi-sire herds.; During experiment one, Braunvieh (n = 6) and Bonsmara (n = 6) bulls (18–24 mo of age) were evaluated for body condition score (BCS), social dominance, serving capacity, spermatozoal motility and morphology, and fertility-associated antigen (FAA) status (positive or negative). Bulls were joined with multiparous, crossbred females (n = 305) for 90 d. Paternity was verified for 251 calves born the subsequent spring. All bulls were FAA-positive and more calves were sired by Braunvieh (P < 0.05) than by Bonsmara bulls. Breed of bull, spermatozoal motility, spermatozoal morphology, and social dominance rank were associated with variability in number of calves sired by each bull (P < 0.05, R-square = 0.748). Bulls with more morphologically normal sperm sired more calves early in the calving season (P < 0.05) than bulls with fewer normal sperm.; During experiment two, Bonsmara (n = 6, 13–14 mo of age), Tuli (n = 6, 15–18 mo of age), and Waygu (n = 6, 18–19 mo of age) bulls were evaluated for characteristics as in experiment one, along with body weight and scrotal circumference. Bulls were joined with multiparous, crossbred females (n = 290) for 90 d. Sires were positively determined for male calves (n = 125) born the following spring. More calves were sired by older (Waygu) bulls than by younger (Bonsmara or Tuli) bulls (P < 0.05). Age of bull, FAA-status, and body weight of bulls accounted for the majority of variability in number of calves sired by each bull (P < 0.01, R-square = 0.635). There was an inverse relationship (P < 0.05) between mount to service ratio and number of calves sired per bull.; Seminal traits and mating behavior may account for more of the variability in number of calves sired by bulls that are at least 18 mo of age. Assessment of spermatozoal FAA classification, social dominance, and mount to service ratio in conjunction with a conventional breeding soundness evaluation would enhance accuracy of selection for bulls capable of siring increased numbers of early-born progeny in multi-sire herds. |
