Many mammals have been used to produce antibodies, ranging from the horse, sheep, and goat down to mice and guinea pigs. Often an animals species is selected for antibody production because it will produce less-cross-reactive antibodies to a given tissue. Larger mammals, such as goats and sheep, are used to obtain larger volumes of serum to be used therapeutically in humans. A recent fear has been that animals such as sheep or cows may have eaten animal foddage contaminated with prion disease. Thus, polyclonal antibody production for therapeutic uses has often been limited to countries like Australia or New Zealand where there have been no recorded cases of prion disease in mammals.