Do Low Mineral Levels Predispose Horses to Lameness?

Decreased levels of minerals directly involved in bone health, namely calcium, phosphorus, and magnesium, could predispose horses to lameness. Because lameness is one of the costliest conditions affecting horses, researchers have investigated the effects of mineral deficiencies.

Sixty adult horses, thirty sound and thirty lame, were recruited from equestrian clubs to participate in a study evaluating calcium, phosphorus, and magnesium levels.^* These minerals were measured in two seasons, summer and autumn. None of the horses were offered any nutritional supplements for at least one month prior to the start of the study.

Results of the study reveal average calcium and magnesium levels were higher in sound horses in both seasons. Levels of phosphorus were only higher in sound horses during the autumn.

Calcium, phosphorus, and magnesium play critical roles in muscle contraction as well as bone mineral structure. Not only are the absolute levels important but also the balance between these minerals.

“Calcium and phosphorus are carefully balanced by the body, with calcium in higher abundance than phosphorus. If there is more phosphorus in the body at the same time there is less calcium, the body will start drawing calcium out of the bones to try to get the minerals back in balance,” said Crandell.

A desirable calcium-to-phosphorus ratio in the ration of horses is 2:1. Imbalance of this ratio can result when (1) more phosphorus than calcium is present in the diet, (2) a deficiency of calcium in the diet occurs, or (3) oxalates in the diet interfere with calcium absorption.

When an imbalance occurs over a protracted period, nutritional secondary hypoparathyroidism, or big head disease, may develop. The disease is characterized by cancellous bone deposits in the head and jaw as well as lameness. In this study, however, the researchers did not analyze the rations of the horses for calcium or phosphorus, so it is not possible to link lameness with mineral deficiencies.

“The National Research Council guidelines for dietary intake of a 1,100-lb (500-kg) horse at maintenance for calcium, phosphorus, and magnesium are 20 g/d, 14 g/d, and 7.5 g/d, respectively. These requirements increase with work, pregnancy, lactation, and growth,” Crandell explained.

While these intake levels can typically be met with good-quality forage, when mineral amounts are inadequate, a concentrate feed and or supplement is recommended to balance out these deficits.

“For horses that do not need the extra calories over and above what the forage supplies, a ration balancer may fulfill the diet’s shortcomings,” Crandell recommended.

^*Etemadi, F., A.T. Naeini, and M. Aminlari. 2023. Assessment of calcium, phosphorus, magnesium, vitamin D and PTH levels in sera of lame horses. Veterinary Medicine and Science 9(5):2070-2077.