and in sheep and goats.: 77–80 in horses, a fetus may be aborted or resorbed if it has lethal white syndrome (congenital intestinal aganglionosis). foal embryos that are homozygous for the dominant white gene (ww) are theorized to also be aborted or resorbed before birth. in many species of sharks and rays, stress-induced abortions occur frequently on capture. viral infection can cause abortion in dogs. cats can experience spontaneous abortion for many reasons, including hormonal imbalance. a combined abortion and spaying is performed on pregnant cats, especially in trap–neuter–return programs, to prevent unwanted kittens from being born. female rodents may terminate a pregnancy when exposed to the smell of a male not responsible for the pregnancy, known as the bruce effect. abortion may also be induced in animals, in the context of animal husbandry. for example, abortion may be induced in mares that have been mated improperly, or that have been purchased by owners who did not realize the mares were pregnant, or that are pregnant with twin foals. feticide can occur in horses and zebras due to male harassment of pregnant mares or forced copulation, although the frequency in the wild has been questioned. male gray langur monkeys may attack females following male takeover, causing miscarriage.