Insulin resistance and laminitis in broodmares

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Take-home message

The endocrine changes associated with pregnancy can increase the risk for laminitis in mares. All broodmares should be monitored and managed for laminitis and endocrine disorders. The annual health check or breeding soundness evaluation for broodmares should include careful evaluation of the feet for evidence of laminitis, such as abnormal growth rings on the external hoof wall, solar abscesses, seedy toe, or dropped soles.

Pregnancy and insulin sensitivity

Pregnancy in women and dogs is associated with a 60% and 43%, respectively, decrease in insulin sensitivity and an increased insulin response to glucose [1], [14]. This physiological IR of pregnancy facilitates glucose delivery to the fetus and is caused by the insulin counter-regulatory and post-receptor actions of progesterone, estradiol, growth hormone, placental lactogen, and placental cytokines [14].

In women, elevated cytokine and lipid concentrations during pregnancy are believed to

Equine pregnancy and insulin sensitivity

A recent study in Thoroughbred mares detected decreased insulin sensitivity and glucose effectiveness and a higher acute insulin response to glucose in pregnant (196 days’ gestation) vs. nonpregnant mares [16]. The pregnant mares had prolonged hyperglycemia and HI in response to meal feeding that was particularly apparent following a high-starch meal [16]. The IR was no longer significant at 336 days’ gestation, but that may have been due to noninsulin-mediated glucose disposal from the mother

Pregnancy-associated IR and laminitis risk

For mares that have underlying IR prior to pregnancy, the additional metabolic stress of pregnancy could greatly increase the risk for laminitis, although epidemiological studies are needed to verify this suspected risk. Using data from the Laminitis Discovery Database, we uncovered an obese mare that became acutely laminitic at approximately 90 days’ gestation and was euthanized 8 weeks later due to unstable chronic laminitis and unmanageable pain. The additive effects of obesity and pregnancy

Late gestation and parturition

Late gestation and parturition are associated with physiologic and endocrine changes that could have protective or aggravating effects on laminitis incidence in mares. As noted, glucose uptake by the fetus is expected to increase greatly during the last gestational trimester. Fowden et al. [17] reported an arteriovenous difference in insulin concentration across gravid uteri of mares when arterial insulin levels were > 30 μU/ml, which they interpreted as indicative of insulin uptake by the

Periparturient endocrine changes and the hoof

The possible protective effects of late-gestational insulin dynamics might be countered by the effects of periparturient endocrine changes on the suspensory apparatus of the distal phalanx (SADP). Increases in estrogen and relaxin increase the laxity of connective tissue structures associated with the birth canal, but can also cause pregnancy-associated joint hypermobility and other connective tissue disorders [21].

Research on this topic in the mare is lacking, but studies in the dairy cow have

Preventing laminitis in broodmares

Although further research is needed to better define insulin and glucose dynamics, laminitis risk factors, and endocrine effects on the SADP in pregnant and periparturient mares, all broodmares should be monitored and managed for laminitis and endocrine disorders. The annual health check or breeding soundness evaluation should include a careful and critical physical evaluation of the feet for evidence of laminitis, such as abnormal growth rings on the external hoof wall, solar abscesses, seedy

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Supported by the Bernice Barbour Foundation, Inc. and the University of Pennsylvania Fund for Laminitis Research.

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