We know that a pregnant mare’s diet and nutritional status can affect her foal’s growth. But recent study results suggest the effects can be far more long-term than previously thought. So long-term, in fact, they can even impact the foal’s future performance.
“The quality of the nutrition of both mares and foals is essential to optimize chances of athletic and reproductive performance in adulthood,” said Morgane Robles, PhD, of the French National Institute for Agricultural Research’s French Institute for Horses and Equitation, in Jouy-en-Josas.
Robles and her fellow researchers continued their FOETALIM project that focuses on the short-term and long-term effects of gestational environment on a foal’s future (read more about FOETALIM studies from 2015 and 2017 on TheHorse.com). In this phase of the project, they explored two diets’ impact on 24 pregnant Anglo-Arab mares. They fed half the mares forage only and the other half concentrated feeds and forage.
Because the hay quality and quantity given to the mares was not enough to meet their energy needs along with their foals’, the forage-only mares lost body condition during the second half of pregnancy, Robles said. Still, they produced foals of normal birthweight. The nutrient deprivation’s effects on the foals didn’t appear until more than a year later.
“Undernourishment of mares in late gestation modified bone growth, which was detectable starting at 19 months of age,” Robles said. “It also slowed testicular development, detectable at 12 months of age, suggesting a delay in puberty.” The effects of those modifications on breeding and bone density are not yet known, however.
On the other hand, foals born to mares fed concentrated feeds had a higher osteochondrosis (one of the most common developmental orthopedic diseases in young horses) incidence at six months of age, she said. However, feeding concentrates in the late trimester allowed the mares to maintain their body condition compared to those fed hay only.
The researchers noted that by 24 months of age, there were no differences in osteochondrosis rates between the groups. “Unfortunately we didn’t get to measure these rates at 12 and 18 months, but I’m sure it would have been interesting to see that,” Robles said.
As a part of their study, the researchers also overfed grain to all yearlings between the ages of 20 and 24 months. This affected the carbohydrate metabolism of the foals whose dams had been on forage only, said Robles. And that could have negative consequences on their athletic ability.
“The overfeeding made them not only fatter but also more resistant to insulin, which can affect the muscles’ capacity to store glucose in its useful form of glycogen, the principal source of energy in a muscle,” she said. “So, theoretically, the foals would tire more easily. But at the moment this is just our hypothesis; it remains to be proven.”
Based on their study and their review of previous studies, the FOETALIM researchers developed some feeding and management recommendations for broodmare and foal managers:
- At breeding, aim to have the mare at a moderate body condition score of 3 to 3.5 on a 5-point scale, avoiding anything higher than 4.
- Feed the mare throughout gestation with plenty of high-quality forage, plus vitamin and mineral supplements. Feed as little grain or concentrate as possible, ideally divided into several small meals per day (at least more than two).
- Similarly, after weaning the foal, feed him sufficient forage with vitamin and mineral supplements and as little hard feed as possible. If he needs grain or concentrates to meet caloric and protein needs, provide it in at least four meals per day to reduce his sugar intake at one particular time. Additionally, aim for consistent growth and monitor growth rates regularly; avoid rapid growth spurts, as these could put foals at risk for developmental orthopedic diseases.
The FOETALIM project is ongoing. Researchers will soon be investigating broodmare obesity’s effects on foals.