How Season Impacts Horses’ Insulin Secretion, Metabolism

Horses secrete more insulin during winter, which could pose problems for some pregnant mares, researchers say.

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How Season Impacts Horses
Horses secrete more insulin during winter, which could pose problems for some pregnant mares, researchers say. | Photo: Anne M. Eberhardt/The Horse
When it comes to pregnancy and metabolism, management can sometimes be a real balancing act. Austrian and German researchers have learned that season’s effect on horses just adds to the complications.

Horses, regardless of sex or pregnancy status, release more insulin in response to glucose in winter compared to summer. And pregnant mares become more insulin resistant from about eight months’ gestation onward—often right at the height of winter. In mares that are already at metabolic risk for laminitis, this can create significant management challenges, said Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute in Neustadt, Germany.

“Insulin resistance during pregnancy is normal and helps to direct nutrients toward the fetus,” Aurich said. “Via the endocrine mechanism of partial insulin resistance in pregnant mares, usually enough energy is provided for fetal growth. But in winter, the insulin release to glucose increases, directing more glucose to the mother and her insulin-sensitive tissues (in particular, the laminae).”

Essentially, during the last two-thirds of gestation, most of the cells in pregnant mares’ bodies respond less to insulin when they consume sugars than they normally would, making them temporarily insulin-resistant, she said. While that would cause metabolic issues in a nonpregnant horse, it’s normal—and useful—in pregnancy because the incoming nutrients and related hormones just “skip over” the mare and go directly to her growing fetus, Aurich said

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Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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