Little is known about the serving capacity or calf output of bulls in large multiple sire commercial herds. The objective of this Washington State Univ. study was to evaluate the calf output of 19 mature Wagyu bulls in a multiple sire setting through the use of DNA parentage verification. The bulls were turned out with 420 first-calf Angus-cross heifers on a Western Montana ranch for a 45-day breeding period. The 392 calves that resulted from these matings were tested for paternal identity.

Of the 19 bulls used, 10 of them (52.6%) sired 70.6% of the calves to which parentage was assigned. Amongst those 10 bulls, 5 (26.3% of all bulls) sired 42.6% of the calf crop. Conversely, the 5 (26.3%) least prolific bulls sired only 12.4% of the calves, with the 2 bottom ranking bulls siring only 6 (1.6%) calves each. Scrotal circumference (SC) measurements were available for 15 of the 19 bulls; there was no correlation between SC and the number of calves sired.

The study clearly shows there are differences in the serving capacity of individual bulls used in multiple sire herds.