The Effect of Mare Obesity on Offspring

The study concluded that mare obesity altered metabolism and increased low-grade inflammation in both dams and foals.

The risk of developing OCD at 12 months of age is also higher in foals born to obese dams. iStock/Nigelb10

An equine veterinarian’s role in counseling clients to keep excess weight off their horses is an important responsibility.

Equine obesity leads to many health problems, such as insulin resistance, equine metabolic syndrome, low-grade inflammation, laminitis and fertility issues. Obesity can also have significant consequences for the mares and their offspring.

A recent French study identified effects of maternal obesity at the time of insemination on the growth, inflammation and osteochondrosis lesions of offspring through 18 months of age (Robles, M.; Nouveau, E.; Gautier, C.; Mendoza, L.; Dubois, C.; Dahirel, M., et al. Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age. PLoS ONE 2018, 13(1): e0190309).

Mares underwent numerous tests during their gestation periods. Foals from birth until 18 months of age were measured regularly for plasma SAA, leptin, adiponectin, T3, T4 and cortisol concentrations.

An intravenous glucose tolerance test was performed on mares at 300 days of gestation and on foals at 6, 12 and 18 months of age. At those same intervals, foals also underwent osteoarticular examinations via radiography of the hocks, stifles and fetlocks. Expression of genes involved in testicular maturation was evaluated following gelding of male colts at one year of age.

The authors identified several relevant findings:

  • During gestation, plasma urea and adiponectin decreased in obese mares, while SAA and leptin increased compared to normal mares. (Liver production of urea tends to be less in obese animals due to modifications in urea cycle enzymes.)
  • Obese mares experienced more insulin resistance than normal mares by late gestation.
  • Birth weights were similar at birth between the two groups, but foals born to obese mares were somewhat lighter and smaller by two months of age for foals, possibly due to less milk production by obese mares.
  • Growth of offspring did not differ between foals born to either normal or obese mares.
  • Plasma SAA concentrations were higher in foals born to obese mares until six months of age, reflective of systemic inflammation. Insulin resistance was greater in these foals at 6 and 18 months of age.
  • At 12 months of age, osteochondrosis (OCD) was more prevalent in foals born to obese mares compared to foals from mares with normal BCS.
  • By 18 months, 30% of foals born to obese mares had OCD lesions compared to 10% of the normal mare foals.
  • All other parameters evaluated— triglycerides, T3, T4, cortisol, testicular maturation, leptin and adiponectin— were equivocal between the two groups of foals.

Studies in humans and rats have demonstrated that low-grade inflammation initiated by maternal obesity is able to transfer from dam to offspring.

The article pointed out that inflammatory effects in the brain can lead to anxiety, behavioral abnormalities and learning difficulties. That increases the possibility of behavioral problems in growing horses with the potential to affect future sporthorse performance.

The study concluded: “Maternal obesity altered metabolism and increased low-grade inflammation in both dams and foals. The risk of developing OCD at 12 months of age is also higher in foals born to obese dams.”

While it is prudent to avoid obesity in broodmares, the authors stressed that under-nutrition of broodmares should be avoided due to its adverse effects on foal development. 

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