The number of copulations is not hugely important. Its a good question though because most ppl want to know the minimum number of copulations need to have success (so the male can be maximized to multiple females)

The answer is complicated.

I believe that copulations early in the season helps kickstart follicle growth. Its also true that if several months pass while the female has good sized follicles she may reabsorb them and not produce that year. In addition, even if they do go through to ovulation with no relatively recent copulations, there may not be live sperm awaiting the eggs as they move down the oviduct... resulting in slugs.

My method is to get one successful copulation early in the season, then get at least one when I can see follicular development and one when the follicles get to a large size and ovulation is less than a month away.

If you're unsure about how to measure follicles by palpating or ultrasound, breeding them at least once per month through the season should deliver good results. I think breeding more often than that would likely be more than what is needed.

Justin