There is no reason in sharee’ah why he should not feed wheat to livestock. The basic principle concerning food is that it is permissible unless there is evidence to the contrary, as is stated in the principles of fiqh that are well known to the scholars.
This is as far as the principle is concerned. But if there is some harm that will result from feeding wheat to the livestock, such as if people are in need of this wheat as one of their basic needs, and there is no surplus of wheat to feed the livestock, then in that case it is haraam because of the harm that will be done to the people, and the livestock should be fed something other than wheat.
And Allaah knows best.