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Feeding a pregnant mare isn’t just about maintaining body condition, it's about programming the future health of her foal. One of the most overlooked aspects of broodmare nutrition is the starch and sugar (NSC) content of the diet. Diets high in non-structural carbohydrates (NSC), typically found in grains, molasses, sweet feeds, and lush pasture, can contribute to serious health problems in both mares and their offspring. High-NSC diets during pregnancy may increase the risk of gestational diabetes in the mare, and insulin resistance, tying up, developmental orthopaedic disease (DOD), and metabolic dysfunction in foals and weanlings.
NSCs (non-structural carbohydrates) include starches, sugars, and fructans. While they provide quick energy, excess NSCs can cause metabolic disruptions, especially in horses with low workloads or sensitive systems, like pregnant mares and growing foals
Pregnant mares naturally become more insulin resistant in late gestation. This is a normal physiological adaptation that prioritises glucose supply to the developing foal. However, when mares are fed high-NSC diets, this temporary insulin resistance can worsen and mimic gestational diabetes in horses. Feeding high NSC diets, such as those rich in cracked barley, can lead to gestational diabetes and insulin resistance (IR) in pregnant mares. Research from the University of Queensland indicates that high NSC intake causes glycemic and insulinemic peaks, potentially mimicking gestational diabetes by elevating plasma glucose and insulin levels. Obese mares are particularly at risk, showing lower insulin sensitivity and higher glucose effectiveness during late gestation (300 days). This can stress the mare’s metabolism, increasing the risk of equine metabolic syndrome (EMS), characterized by insulin dysregulation, obesity, and laminitis risk.
Consequences:
A diet too high in carbohydrates can increase muscle glycogen stores and alter calcium regulation in muscle cells, leading to tying up or exertional rhabdomyolysis, especially in mares with a genetic predisposition (like PSSM).
Signs of tying up in mares include:
Poor maternal nutrition doesn’t just affect the mare, it sets the blueprint for the foal’s lifelong health.
High-NSC diets increase insulin and glucose levels in the mare, which can affect the growth cartilage of the foal. This can increase the risk of:
Excess insulin and IGF-1 (insulin-like growth factor) are known contributors to abnormal skeletal development.
The foal's metabolic system is influenced by the in utero environment. High NSC diets during pregnancy can predispose foals and weanlings to metabolic disorders, including insulin resistance and early markers of equine metabolic syndrome. Maternal overnutrition alters fetal programming, affecting long-term metabolic health. When exposed to high glucose and insulin levels before birth, foals may be more likely to develop:
This is known as fetal programming, what the foal experiences in the womb impacts its long-term metabolic health.
To reduce the risk of gestational and foal-related issues, aim to:
CoolStance® copra meal is a valuable feedstuff for pregnant mares prone to insulin issues or tying up. It offers:
Copra meal is ideal for mares needing extra calories without the risk of insulin dysregulation.
To complement a low-NSC, high-fibre base diet, GroStance® provides essential nutritional building blocks to support reproductive mares, stallions, and growing foals.
Key Benefits of GroStance:
Feeding high-NSC diets to pregnant mares can do more harm than good. From increasing the risk of gestational insulin resistance and tying up, to predisposing foals to DOD and metabolic disease, the consequences are far-reaching.
By prioritising low-NSC, high-fibre, and balanced nutrition, and including safe energy sources like copra meal, you can support the long-term health of both mare and foal.
