Most experts agree that an experienced bull (> 2 years of age) that passes a breeding soundness exam should easily service 30 females in a 60- to 70-day breeding season.
Inexperienced bulls (< 2 years of age) cannot service as many females and should only be exposed to 15 to 20 females in a 60- to 70-day breeding season. One rule of thumb is that a bull can service about as many cows as his age in months. Therefore, a 15-month-old bull should be able to service approximately 15 cows in a typical 60-day breeding season.
Some data have been published that indicate that experienced bulls that pass a breeding soundness exam can service as many as 60 females in a 70-day season without pregnancy rates being compromised. Most producers and educators are more conservative because the ability of a bull to service cows is not predictable. The breeding soundness exam is extremely accurate in determining non-fertile bulls but is limited in its ability to pinpoint bulls with low fertility.