It is not uncommon for dog breeders to mate the dogs of the same litter. But when the breeding is done over generations, some serious problems can occur. Most animals suffer the same effects as humans do like reduced fertility, slower growth rates, increased incidence of disease, and higher mortality rates. Also like humans, animals have anti-incest mechanism that allows them to identify if they are from same kin or not. For example: Female lemurs can tell if a male’s genes are too similar to her own by smelling the pheromones that emit from his genitals.
Another animal that uses smell is mice. Mice also use their smell like humans in the ‘smelly t-shirt’ test to find out if the other one is potential partner or not. According to experiments, having a brother and sister mouse in a same cage in isolation can result into mating but if the female is given with another unrelated male then she is often known to have abandon her brother. Even if she is impregnated with her brother, she aborts the pregnancy before mating with the unrelated mouse.
Hyenas don’t have the sense of smell but they still don’t mate among their group. The females mate with a hyena from a new group or the one which does not belong to that group. This forces young male hyenas to go to another group to search for female mating partner which reduces inbreeding.
But there are exceptions to it too like bedbugs. The estimated 500-percent growth of the bedbug population in recent years was partially caused by a chemical resistance to insecticides but also the bedbug’s ability to thrive on inbreeding. The resistance power of bedbugs grows as it inbreeds making the population as well as resistance power double the stronger. It must be only one of few examples when inbreeding actually benefits a species.