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Fertility in mares refers to their ability to conceive, maintain pregnancy, and deliver a healthy foal. In general, mares cycle every 21 days and have a gestation period of around 340 days, or 11 months. For breeding programs, the goal is for mares to produce one live foal every 12 months. This leaves a critical 30-day window after foaling for the mare to return to heat, conceive, and begin the next pregnancy.
To maintain this yearly cycle, a mare must:
A mare’s body condition score (BCS) is a direct reflection of her energy intake and diet composition. The standard BCS scale ranges from 1 (emaciated) to 9 (obese). For optimal reproductive performance, mares should be at a condition score of 5–6 at both foaling and mating. Undernourished mares may fail to cycle or ovulate due to low glucose production and energy availability. Conversely, over-conditioned or obese mares may experience hormonal imbalances, insulin resistance, and delayed return to oestrus.
Reproductive cycling in mares is strongly linked to blood glucose levels. Rising glucose production signals the body that energy is available for reproduction. Mares on a rising plane of nutrition are more likely to ovulate and conceive. However, lactation doubles a mare’s energy demands. If her diet doesn’t meet these requirements, the mare will mobilise body fat and muscle to produce milk, potentially compromising her ability to cycle. Mares in good condition can temporarily “milk off their backs,” but to maintain fertility and prevent excessive weight loss, they must receive a balanced, high-energy diet at least four months before and after foaling.
Obesity can negatively impact fertility by disrupting hormone balance. Research (Vick et al., 2009) shows that obese mares experience longer oestrous cycles, increased leptin and insulin levels, and reduced insulin sensitivity. Some mares even develop insulin resistance, (gestational diabetes) a condition similar to Type 2 diabetes in humans. This can lead to irregular anoestrus and possible ovarian dysfunction, such as polycystic ovarian syndrome. This can also lead to insulin resistance in the foal,
NSC refers to sugars and starches in feed. These carbohydrates provide quick energy, but excessive intake, especially over 12%, can cause serious metabolic issues such as:
To support mare fertility:
CoolStance copra provides
Vitastance provides the trace minerals, vitmains and amno acids to complement the Coolstance
The key to supporting mare fertility is balanced nutrition tailored to reproductive stage. Avoid extreme body conditions, whether too thin or too fat, and select energy sources that provide steady, sustained glucose without triggering metabolic stress. With proper feeding strategies, mares are more likely to cycle regularly, conceive successfully, and produce strong, healthy foals year after year.
