Proper nutrition for the broodmare during lactation is essential to make certain that she produces adequate milk for the foal and also maintains her body condition so that she will re-breed successfully and safely carry the next year’s foal.
The broodmare has substantial increases in requirements for digestible energy, protein, lysine, methionine, threonine and minerals as she goes from the last month of gestation to the first month of lactation.
For a 500 kg (1100 lb) mare, her DE requirement goes from 21.4 Mcal per day to 31.7 Mcal per day, her protein requirement goes from 630 grams to 1535 grams per day, her lysine requirement goes from 27.1 grams to 84.8 grams per day and her calcium requirement goes from 20 grams per day to 59.1 grams per day, with similar increases in other amino acids and minerals. (Nutrient Requirements of Horses, Sixth Edition, pages 298-299).
If her feed/nutrient intake is not increased to provide these nutrients, she will attempt to maintain milk production by depleting her body stores for energy, amino acids(primarily from muscle mass) and minerals, causing loss of weight, loss of body condition, loss of muscle mass and some bone mineral losses.
To meet her increased DE requirement, an additional 3.43 kg or 7.5 pounds of grain containing 3.0 Mcal/kg (1364 Calories/lb) will need to be added to her diet gradually post foaling.
This need to be adjusted to maintain her body condition as mares vary widely in milk production!
Fortunately, she also can consume more dry matter during lactation, so she is actually able to eat more forage and more feed.
If she is fed a product that is labeled as suitable for lactating mares, the additional feed will provide the additional energy as well as the other important nutrients.
She will also require unlimited access to water and access to salt free choice along with good quality forage.
If she does lose weight during lactation (reflected by loss of both body condition score and topline score, she is much less likely to cycle normally during lactation and less likely to become pregnant and carry the next foal. This may explain why some mares are “every other year” mares in producing foals.
They are frequently mares that produce large foals and milk very heavy during lactation. As a result, they do NOT maintain body condition and do not re-breed and carry a foal the next year. When they are not in foal and not lactating, they gain weight and come back into the next breeding season in good flesh and breed successfully.
This is even more likely if they are not in a suitable body condition (BCS 6+) prior to foaling. The nutrient requirements will start to decrease at the 3rd month of lactation and will gradually decrease until the foal is weaned, when she can then be fed at maintenance levels adjusted as needed.
Monitoring body condition and topline score of the mare and the body condition score and growth rate of the foal are the best ways to determine if the feeding program for both is producing the desired results!