The most important job of zinc (Zn) in your horse's body is to be a part of enzymes. It is a part of many important enzymes, including carboxypeptidases, which are responsible for insulin production, blood clotting, wound healing, and a whole host of other things.
In the body, the highest concentrations of Zn are found in the eye and prostate gland. The lowest concentrations of Zn are found in milk, blood, and brain, while muscle, bone, and skin fall somewhere in the middle.
Most of the feeds your horse consumes contain somewhere between 20 and 40 mg of Zn per kilogram of dry matter. Since the recommendation for intake is 40 mg/kg dry matter, its relatively easy to ensure that your horse gets enough Zn, unless his entire diet consists of feeds on the lower level of normal.
Here are the concentrations of Zn in some common feedstuffs:
(mg/kg dry matter)
|Wheat Middlings||91 mg/kg|
|Rice Bran||71 mg/kg|
|Oats (rolled)||41 mg/kg|
|Grass Pasture (cool-season grasses)||34 mg/kg|
|Legume Pasture||33 mg/kg|
|Corn (ground)||27 mg/kg|
|Grass Hay (mid-maturity)||25 mg/kg|
|Alfalfa Hay (mid-maturity)||24 mg/kg|
|Beet Pulp (molasses)||22 mg/kg|
Zn deficiency has been reported in horses, and can have some moderate consequences. Signs of Zn deficiency include:
However, like I mentioned above, creating a Zn deficiency in the average horse's diet is not extremely easy, unless the horse is fed only feeds that are on the low end of Zn content.
Horses are one species that tolerates excess dietary Zn very well. In fact, they tolerate it so well, that the maximum tolerable level has been set at 500 mg/kg of ration...
...close to TEN TIMES the recommended intake (depending on water content of the diet)!
In some horses living near Zn smelters, or grazed in industrial areas where the grasses contained high levels of Zn, some signs of Zn toxicity were noticed, including:
However, it appears that excess Zn is not the direct blame of these problems. Rather, it appears that extremely high levels of Zn cause a secondary copper deficiency, which then leads to these problems.
The zinc:copper ratio is important in your horse's diet because Zn and copper compete for the same transport mechanisms in your horse, much like calcium and phosphorus compete for the same absorption sites.
However, there isn't a set ideal ratio like the calcium:phosphorus ratio. This is because the amount of Zn required to cause a copper deficiency depends on how much copper is already stored in the liver, which varies from animal to animal.
In general, it appears that higher Zn to copper ratios are what will cause problems.
Zn is a fairly important micromineral in your horse's diet. Thankfully, dietary sources abound...in fact, almost everything your horse eats contains Zn.
He is also very tolerant of excess Zn, which is good for you since symptoms of Zn deficiency aren't exactly desirable (I don't want to ride a bald horse!)