Performance of Bos indicus-influenced bulls in serving capacity tests and multiple-sire breeding groups

Three experiments were conducted with Santa Gertrudis (SG) or F1 (Gelbvieh x SG or Red Angus x SG) bulls to assess factors that influence copulatory activity and fertility of Bos indicus-influenced genotypes. In Exp. 1, 3-yr-old SG bulls (n = 20) with sexual experience and 20-mo-old virgin SG bulls (n = 34) were allotted in a split-plot design (age, bull within age group, test day, and heifer treatment). Number of mounts (Mt), intromissions (I), and ejaculations (E) were measured 14 d apart during two 30-min serving capacity (SC) tests. Estrus was either induced via progesterone+estradiol cypionate (PE) injections or synchronized with Syncro-Mate B (SMB). There were more (P less than .05) I and E on Test d 2 than on Test d 1. Heifers treated with SMB received more (P less than .001) Mt, I, and E than did heifers treated with PE. Sixteen 20-mo-old bulls from Exp. 1 were allotted to breeding pastures at a bull:heifer ratio of 4:119 +/- 3 for 50 d in Exp. 2. Breeding pasture treatments either included or excluded low-SC bulls. Neither pregnancy rate nor least squares mean day of conception differed between treatments. Experiment 3 evaluated copulatory activity with a 2 x 2 factorial arrangement (breed and test day) in 14- to 16-mo-old SG (n = 45) and F1 (n = 16) bulls. The F1 bulls had more Mt, I, and E than did the SG bulls (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)