The problem with these ages is that the cow's maximum productivity is reached around the sixth year. If she is culled before that, it's because of a medical iss

The problem with these ages is that the cow's maximum productivity is reached around the sixth year. If she is culled before that, it's because of a medical issue which is not economically treatable. If that happens all the time, then very probably these issues could be avoided by proper care. Breeding has a lot to do with it, also.