Essential trace element, zinc forms a component of over 100 enzymes and is found in variable concentrations in all the body tissues. Most plants contain some zinc and manufactured feeds are normally fortified with it. There is no clear evidence as to whether inorganic zinc supplements like the sulphate or oxide offer better or worse absorbtion and retention than the organic chelated forms, which are more expensive. Absorbtion of zinc is regulated by the zinc status of the animal and falls in the 1%-15% range according to NRC.
Zinc is found in high concentration in the pancreas and is important for production of pancreatic enzymes for digestion. It is also essential for skin and hoof health being involved in the process of forming keratin. A decrease in hoof quality and strength has been found in horses on low zinc diets.
Since soil zinc levels can vary significantly in different regions there is potential for low levels in forage feeds growing on deficient soils and consequently supply to grazing horses may be marginal and require supplementation. Use of a suitably fortified supplementary feed, mineral supplement or block is often appropriate, particularly for young growing horses, pregnant and lactating mares and working stallions.
Excess zinc may potentially interfere with the absorbtion of other trace elements, particularly copper and for this reason the desirable ratio of Zinc: Copper should be in the range 3: 1 to 5: 1. Zinc toxicity is very rare and usually the result of errors in supplement use or industrial pollution of pasture from zinc smelters.