Do nursing cows have a breeding cycle?

Yes. A cow that is nursing a calf will come back into heat around 18 to 24 days after she has calved, but should NOT be bred until at least 45 days after she has calved (for reasons why see related question below). Cows that have given birth to a stillborn calf, aborted early or has lost a calf within a week after it is born and dry up (cows will only dry up if you haven't grafted a calf to her) will almost always cycle a bit earlier.