Free-Choice Salt for Lactating Broodmares and Growing Horses

The microminerals sodium, chloride, and potassium are important in the development and function of many body systems. Though some foals begin to eat small amounts of solid feed within the first one to two weeks of life, many do not drink any water, relying completely on the mare’s milk as the only source of fluids. Thus, the lactating mare can sustain substantial losses of both fluid and electrolytes.

Foals can consume upwards of 25% of their body weight in fluid each day, so a foal weighing between 80 and 100 kg (175 and 220 lb) could rely on its dam for as much as 20 to 25 liters (45 to 55 lb) of milk each day. Assuming sodium and potassium concentrations in milk of around 0.17 and 0.51 g/liter, respectively, the demands of the foal could result in the requirement for an additional 3 to 4 g of sodium and 10 to 12 g of potassium for the lactating mare.

For both the lactating mare and the growing horse, sufficient quantities of potassium and chloride can normally be provided by a diet that includes an adequate quantity of grass or hay. Sodium content may be low in some feeds, so salt should be made available at all times, either through the provision of a salt block or by adding salt to the grain ration at a rate of 0.5 to 1% DM to ensure that horses receive sufficient sodium and chloride. For a mare receiving five pounds (2.3 kg) of grain a day, this means top-dressing one or two teaspoons of salt onto feeds that have a minimal salt content.

During the first two months of life, a growing foal’s requirements for sodium, potassium, and chloride can be met by adequate intake of the mare’s milk. After this period, the growing horse should be provided with unlimited access to water and a salt supplement. Often this is a trace-mineralized salt that also contains significant quantities of copper, zinc, and selenium.