Copper is one of the most important microminerals for horses. It is essential for proper functioning of enzymes involved in the synthesis and maintenance of elastic tissue, mobilization of iron stores, preservation of the integrity of mitochondria, proper skeletal growth and development, and detoxification of superoxide.
Copper supplementation has proven to be related to the incidence of DOD in Thoroughbred foals. In a trial conducted in New Zealand, pregnant Thoroughbred mares were divided into four treatment groups: (1) mares supplemented with copper, but their foals were not supplemented; (2) both mares and foals were supplemented with copper; (3) mares were not supplemented, but their foals received supplementation; (4) neither mares nor foals received supplementation. Mares were supplemented for the final 13 to 25 weeks of gestation. Foals were supplemented from 21 to 150 days of age.
At 150 days of age, researchers examined all limb and cervical spine joints of the foals. The number of cartilage lesions was noted for each treatment group along with a score for physitis (inflammation of the growth plates). Copper supplementation of mares was associated with a significant reduction in the physitis scores and number of cartilage lesions for their foals. Foals from mares that received no supplementation had higher physitis scores and more cartilage lesions. When only foals were supplemented with copper, no significant effects were found for physitis scores or number of cartilage lesions.
In the same study, oral copper supplementation of mares in late gestation altered the copper balance in these horses and resulted in an increase in the foal’s liver copper stores at birth. Increased liver copper stores of the neonate may be important for ensuring healthy development of the skeleton during the period of maximum postnatal growth.
Copper deficiencies may be due to lack of copper intake (primary) or due to interactions with other substances in the ration (secondary). Zinc and molybdenum have often been implicated as minerals that can interfere with copper absorption in horses, but several studies have suggested that neither of these minerals should affect copper utilization when fed at levels found in practical diets.
Digestion trials at Kentucky Equine Research showed significant negative correlations between true copper digestibility and the concentration of both crude protein and calcium in thirty different diets. These interactions may be particularly relevant where horses are fed predominantly legume forage.