Mineral of the Month: Calcium

Young growing horses, late-gestation broodmares, and lactating mares have higher calcium requirements than the average mature horse.

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Growing horses have higher Ca requirements than idle, mature horses to support growth and bone health. | Photo: iStock

The first recorded use of calcium (Ca), and perhaps unknowingly so, was in the form of limestone and gypsum. Builders and construction workers used compounds in many different applications but, most interestingly perhaps, the ancient Egyptians used them in constructing the pyramids. Later, doctors recorded that gypsum was particularly useful to set broken bones; however, it was only in the 1700s that researchers discovered that Ca was a component of bones themselves.

The majority of the Ca (almost 99%) in a horse’s body is found in bones and teeth. However, Ca also has other important bodily functions. For example, it plays a role in muscle contraction, cell membrane function, blood clotting, and some enzymes’ function, as well. As such, the body must regulate blood Ca concentrations carefully. To do so, bone can act as a storage pool for extra Ca, but it is always best if a horse’s diet provides sufficient Ca.

The National Research Council’s Nutrient Requirements of Horses (NRC, 2007) recommends that a mature idle horse weighing 500 kilograms (1,100 pounds) consume 20 grams of Ca daily. This requirement increases to 30 to 40 grams per day for the same horse in light to heavy exercise. Calcium requirements for pregnant mares (weighing 500 kilograms) only increase about mid-way through pregnancy to 28 grams per day and topping out at 36 grams per day towards the end of pregnancy (NRC, 2007). Early lactating broodmares have the highest Ca intake recommendations, starting at 59 grams per day for a 500 kilograms horse, tapering off throughout lactation. Growing horses have high Ca requirements to support growth and bone health, as well (NRC, 2007)

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