Gestational Diabetes: Feeding the Pregnant Mare

Gestational Diabetes in Horses

Just like humans, horses can experience pregnancy diabetes, known as Gestational Diabetes Mellitus (GDM). This condition affects 4-12% of women and has an equivalent in mares, increasing their risk of pregnancy-associated laminitis. Both humans and horses experience changes in blood glucose and insulin levels due to this condition.

Understanding Insulin Resistance in Pregnancy

Around 12-14 weeks into pregnancy for women, and at approximately 21 weeks (5-6 months) for mares, insulin sensitivity begins to decline, a condition known as insulin resistance. This evolutionary adaptation ensures that the mother's tissues do not respond normally to insulin, which typically moves glucose from the blood into body tissues. As a result, less glucose is absorbed by the mare's tissues, allowing more to be diverted to the foetus and placenta. We’ve often heard that ‘she gives it all to the foal’, and after the fifth month of pregnancy, this is precisely what nature intended. The growing foal's high demand for glucose is met by reducing the amount the mare uses.

Diet and Its Impact on Pregnancy-Associated Laminitis

The choice of diet plays a crucial role in managing the risks associated with pregnancy-associated laminitis. Feeds high in starch and sugar are linked to insulin resistance, obesity, and laminitis. Since pregnancy itself increases the risk of laminitis, especially after five months, mares on high-starch/sugar diets face compounded dangers. Processing methods that enhance feed digestibility in the small intestine can further elevate blood glucose and insulin levels.

Broodmares are at a higher risk for obesity and laminitis, making weight management challenging. The additional stress on their hooves from increased body weight, particularly during early to mid-pregnancy, exacerbates the risk. This stress is largely due to the development of the placenta and the enlargement of the uterus.

Improper Nutrition in Broodmares and Its Effects on Foals

Improper nutrition in broodmares significantly impacts the developing foal. Foals born to overweight or obese mares, or those fed high-sugar/starch concentrates, exhibit altered blood glucose levels and lower insulin sensitivity for up to 18 months after birth. This period is critical for the Development of Orthopaedic Diseases (DOD).

High-sugar/starch feeds, including grains (wheat, barley, corn), cereal by-products (bran, pollard), and molasses, cause spikes in blood glucose and insulin. These spikes are causative factors in laminitis and DOD in foals. Additionally, processing methods like micronisation and extrusion that increase feed digestibility also heighten blood glucose and insulin responses.

Foals from mares fed high-starch/sugar diets during pregnancy are more susceptible to osteoarticular lesions, including all forms of DOD, such as bone cysts, physitis, and OCD.

Feeding Strategies for Pregnant Mares

Pregnant mares are often fed concentrates to meet increased nutrient needs in late pregnancy. However, the need for amino acids and minerals rises, not energy, which only increases during lactation. Ensuring feeds are low in starch and sugar and preventing mares from becoming overweight is crucial. Diets based on fibre and oil have minimal impact on insulin and protect against laminitis and DOD.

Balancing Nutritional Needs

Feeding to match requirements is fundamental. Overfeeding risks increase with complete feeds if amounts are raised to meet vitamin and mineral needs. Conversely, underfeeding vitamins and minerals can occur if complete feeds are given below recommended amounts. A well-formulated, complementary amino acid/mineral/vitamin/antioxidant supplement, like Jenquine all-4-feet, allows for adjusting energy intake without compromising vitamin and mineral intake.

Dr Jennifer Stewart
BVSc BSc PhD Equine Veterinarian and Consultant Nutritionist