Teaser bull with chin ball harness After three weeks of breeding, there should be at least 90% of the cows served and one would be hoping that about 60% of these will be in calf with a viable pregnancy. A couple of percent, usually around 5% will be pregnant but unfortunately will not have a viable pregnancy and will probably come cycling at a later date. Because the amount of bulling activity in the next few weeks will be much less than the previous weeks, it may be harder to pick up cows in heat. For example, if there are three or four cows bulling on the one day, they will usually congregate together and be mounting each other.