Count 21 days from date of breeding, look for signs of heat within a few days of the 21 day mark. If you see no signs of heat, proceed to next steps.
A drop in milk production may occur. We have one cow that this is a great indicator of pregnancy, because she reliably breeds on the first try and 20-30 days, bloop: down goes her milk production! In this particular cow, she usually drops ½ to 1 gallon over the next month or two. (A drop in production over ONE DAY is common when a cow comes into heat. A pregnant cow more gradually loses a little over the next MONTH or two after becoming pregnant.)
If the cow comes back into heat on an odd date, her body may have tried to hold a pregnancy that was not quite ready to stick. If she comes back in heat more than 21 days up to around 42 days, this may be the case. Consider why she may not have bred (see suggestions above). Try to correct any possible issues and continue breeding when the cow has a good, strong heat. Recurring problems may require a vet call to determine if the cow is cystic or unhealthy in her reproductive system. Late-term miscarriages – the cow should be tested for Neospora.