Last Updated on February 23, 2022 by Allison Price
Nature strives for balance between species and their environment. For example, mice have high mortality rates that leave them with very few survivors in their first year. However, their terrible attrition rate is compensated by the ability of each female mouse, which can produce many litters of 10 or more offspring per year. Horses, on the other hand, have low attrition rates. Their natural makeup limits them to a single year of pregnancy, and ideally a single foal.
Equine fertility has been affected by veterinary medicine in two ways. The first is that advances in breeding technology have increased breeding efficiency, improved the breeding capacity of stallions, and improved the breeding success of both stallions as well as mares with impaired fertility. The average live-foal rate per cycle for major horse breeds has been 60 to 65 percent over the past 25 years. This is a remarkable statistic when you consider that veterinary advancements have allowed popular stallions and mares to be serviced by larger stallions. Tom Bowman, DVM says that “the fact that we can still achieve the same live foal rates” as 25 years ago shows that we have made significant progress.
Science has also had a less positive impact on horse breeding. It perpetuates fertility problems. Horses with inherited reproductive issues, such as a tendency to twinning, have a hard time reproducing in the wild. The problems can become self-limiting. Wild herds are known to have high fertility. Medical advances have made it possible for domesticated horses to breed abnormally and foals can survive and reproduce, creating a population of weak reproducers. Patricia Sertich (VMD), assistant professor and clinical educator of theriogenology, University of Pennsylvania, says that “man’s intervention” has allowed males and women to breed in a way that would not have been possible otherwise. This means we have effectively selected for a population with less breeding potential.
What level of success can you anticipate? It depends on many factors. However, reproductive experts suggest that the average breeder can achieve high success rates.
Ideal management can produce nearly 100 percent fertility for the 80-90 percent of horses that are reproductively normal. However, normal horses may sometimes not reproduce due to undetectable reasons. You may still be able to get a lot of foals from your mare, even if she has an abnormality. Bowman says that the bottom line is that “I’m certain that every owner goes into breeding season assuming all mares will be foals by the end of each year.” It is reasonable to expect that 75 percent of your broodmare bands will produce live foals every year. It’s a great achievement to have 80-85 percent of your broodmares producing live foals.