<P> Many cattle ranches and stations run bulls with cows , and most dairy or beef farms traditionally had at least one , if not several , bulls for purposes of herd maintenance . However , the problems associated with handling a bull ( particularly where cows must be removed from its presence to be worked ) has prompted many dairy farmers to restrict themselves to artificial insemination ( AI ) of the cows . Semen is removed from the bulls and stored in canisters of liquid nitrogen , where it is kept until it can be sold , at which time it can be very profitable , in fact , many ranchers keep bulls specifically for this purpose . AI is also used to increase the quality of a herd , or to introduce an outcross of bloodlines . Some ranchers prefer to use AI to allow them to breed to several different bulls in a season or to breed their best stock to a higher quality bull than they could afford to purchase outright . AI may also be used in conjunction with embryo transfer to allow cattle producers to add new breeding to their herds . </P>
what are bulls used for on a farm
herd maintenance