Thats USUALLY why (to my understanding) Why you want males to be of good size before breeding. Because often they go off of feed whilst breeding. So I have always been told to have them AT LEAST 500g before starting to breed, incase they just refuse to eat all breeding season. Sometimes you may just have to stop breeding a male if he starts dropping toomuch weight.

Again this is only what I understand, and hopefully someone more knowladgable can make in put?