Any shortcoming in sire fertility during breeding season could contribute to differences in pregnancy rate. There
were no differences among bulls in BS-PR in AI-NS and NSO groups (P > 0.1). We inferred that the differences in
reproductive performance between these two breeding programs were partly because of the use of AI programs. It
should be noted, in farms that used AI, 41% to 64% of the heifers with different RTS become pregnant within 8 to 10
days from the beginning of the breeding season. In addition, heifers in AI-NS group become pregnant at least
25 days earlier compared with NSO group, irrespective of RTS.