Horse breeders who wish to improve their lines may mate their mares to selected stallions living at other locations. According to a new study by researchers from the Institute of Animal Science in the Czech Republic, this process of being mated to foreign males does not suit the ladies. Upon returning home, 31% of the mares aborted the resultant fetuses.
Apparently, inducing abortion was not the first choice of most mares. If possible, returning pregnant mares did their best to mate with the local males, especially the most dominant ones. Those that were able to mate with local males did not abort their fetuses, whereas mares that were prevented from mating with males aborted in great numbers.
The authors speculate that the females are using this strategy to avoid wasting their time and energy on an infant that is likely to be killed by the dominant male in the group. In many types of animals, males will routinely kill the offspring of other males. For example, when a new male lion takes over a pride, he will immediately kill all the cubs that had been the progeny of the previous pride master. This brings the females into estrus much more quickly so that they can get to work producing the new lion’s offspring.
The domestic mares returning from a foreign assignation may be mating with the local dominant males in an attempt to confuse paternity. Barring that, they may abort the fetus. This suggests that breeders should encourage returning pregnant mares to mate with the local males. It’s really a win-win for everybody.