Study | Understanding Stallions, Smart Mares May Abort Knowingly

Female horses can be very clever when the topic is procreation and paternity. Researchers in the Czech Republic have tracked the histories of mares mated away from home, compared to those who become pregnant at home and in the presence of known stallions vs a foreign stallion.

The study from Luděk Bartoš and colleagues from the Institute of Animal Science is published online in the Springer journal Behavioral Ecology and Sociobiology.

It known that fetal loss is a common phenomenon in domestic horses after away-mating, a frequent way of breeding mares in the Czech Republic. After becoming pregnant, the female horses are returned to their home environments, which often include familiar males.

In their study the researchers compared the frequency of abortion between mares which mated with a home stallion versus a foreign stud muffin. They also studied the sexual behavior of mares returning from away-mating.

Mares that conceived with a foreign stallion aborted in 31 percent of the cases, while none of the home-mated foals were aborted. Foreign-mated mares housed near home males in adjacent enclosures, unable to make sexual contact, were at even higher additional risk for abortion.

Bartoš and colleagues’ results suggest that they have uncovered a new phenomenon in domestic horses: a female counter-strategy to male infanticide, a common problem with foals not fathered by stallions in the home herd. If the dominant home male is not the father, he often kills the baby horse.

It appears that the first choice of female mares is to have promiscuous sex with home males to confuse the paternity of her offspring and protect her foal. In the case where the mare is mated with a foreign stallion or is inseminated artifically and then is separated from home males, she is seven times more likely to abort the fetus.

It’s as if the mare aborts the fetus ‘to prevent the waste of energy in producing offspring likely to be lost’, say the researchers. Amazing! Anne