A heifer bull is not a commonly used term in the cattle industry, and it is not found in any of the search results. However, we can define what a heifer and a bull are separately. A heifer is a young female bovine that has not yet had her first calf. Once a heifer has a calf, she becomes a cow. On the other hand, a bull is a mature male bovine that is used for breeding purposes. Bulls are typically not used for meat and are not castrated because they have desired traits that producers want to use for breeding.