We probably need to come up with a more respectable name than, 'cleanup bull' for this important part of the cow-calf operation.
One of the benefits of estrus synchronization and AI is purchasing and maintaining fewer bulls. However, an idea has been circulating that synchronized females not becoming pregnant to AI will return to estrus at the same time and require the same number of bulls as natural service without AI.
Research has indicated cows not conceiving to AI will return to estrus over a 12d period following a single timed AI. The most active day had 18 percent of the herd in estrus, with the remainder of the distribution of a bell curve. Each cow’s estrous cycle is slightly different. Some cows have 2 follicular waves during the estrous cycle, while others have 3. This results in a natural variation in cycle length, causing the non-pregnant cows’ return to estrus to vary.
Clean-up bull can mean different things like using a different breed bull, such as in the old days, a chi bull to clean up the missed or later/longer cycling females so that you could tell the difference visually, or so the later born calves could "catch up" with a higher growth curve so you could sale all your calves as one "consistent" lot. others could be Herefords on Angus or vice versa for clean-up. clean-up to me, means making sure you got a calf, even if it was late so you didn't have to sell open females, at least you got a calf out of them, and would just cull them for their interval.
