Beef bulls mated to estrus synchronized heifers: Single- vs multi-sire breeding groups.

Beef bulls of approximately 15 months of age were placed with heifers at bull to female ratios (BFR) of 1:20 (n = 3) and 2:40 (n = 3) to compare the breeding efficiency of bulls used in either a single- or a multi-sire group. Prior to the breeding period, each bull was given a breeding soundness exam and two exposures to a libido/serving capacity test. For the purpose of synchronizing estrus, heifers received a nine-day Syncro-Mate-B((R)) (G. D. Searle & Co.) treatment. Twenty-seven hr after removal of the implants, bulls were placed with heifers and sexual activity was observed continuously for the succeeding 30 hr. With the exception of number of services per heifer, the mating performance of bulls and pregnancy rates at both BFR's were not different (P>.05). Heifers in single-sire groups were serviced more times (P<.05) than those in multi-sire groups (4.1 +/- 0.6 vs 2.6 +/- 0.2, respectively). Approximately 50% of heifers in multi-sire groups were serviced by both bulls. Due to the overlap in servicing heifers and the non-significant difference in pregnancy rates between the two BFR's, it was concluded that a single-sire mating program was more efficient.