Q. My horse eats grass hay and doesn’t need additional calories. I know I need to add a source of minerals and vitamins to balance the ration. Why do ration balancing feeds have 1-2-pound serving sizes while most of the supplements have 3-6-ounce serving sizes? Why are they so different?

A. Ration balancing feeds and vitamin mineral supplements designed to balance rations might appear similar. For example, ration balancing feeds often have a zinc content of between 400 and 600 ppm (milligrams per kilogram), so if feeding 2 pounds per day you would be feeding slightly less than 400 to 600 milligrams. The vitamin and mineral supplements that claim to support a forage-based diet might have 300 or more milligrams per 3-6-ounce serving. The same is true for the other trace minerals such as copper, manganese, and selenium. Similarities exist in the amounts of various vitamins, as well, with both product types tending to provide somewhere between 500-1,000 IU of vitamin E per serving. I understand why the serving sizes being so different, because clearly the difference can’t be explained by these nutrients. Differences become apparent when looking at amounts of macrominerals, such as calcium, phosphorus, magnesium, and sodium. One vitamin mineral supplement guarantees a minimum of 8% calcium and 4% phosphorus. With a serving size of 115 grams, this means each serving provides 9.2 grams of calcium and 4.6 grams of phosphorus. On face value, the amount of calcium in ration balancers looks lower, because it’s typically in the range of 3-4%, while phosphorus is about 1%. But with the larger 1-2-pound serving size, this equates to a possible daily calcium intake of between 13.6 to 36.4 grams and 9 grams of phosphorus.

Daily macromineral requirements are in gram quantities, whereas horses only need trace minerals in milligram quantities. When you have a serving size of up to 2 pounds per day for the ration balancer, manufacturers have a lot more volume in which to add macrominerals. This is especially true when you consider that ingredients aren’t made entirely of the desired nutrient. For example, calcium carbonate is not 100% calcium. In the case of calcium carbonate, just less than 40% is actually calcium, so if 20 grams of calcium from calcium carbonate are needed per serving, the serving must provide 50 grams of calcium carbonate. Adding more macrominerals therefore results in a much larger product serving size.

The same is true when adding protein. Most ration balancers provide protein from soy or another high-protein ingredient. This improves the overall amino acid profile of the horse’s forage-based diet. Again, protein and amino acids are required in gram quantities per day, so adding this protein source increases the serving size. Vitamin and mineral supplements typically get around this by providing a pure source of essential amino acids such as lysine and methionine. If ration balancing feeds provide around 2% as lysine and 0.6% as methionine, then a 2-pound serving size includes 18 grams of lysine and 5.5 grams of methionine. The percentage of lysine and methionine in the vitamin mineral supplement might be 3% and 2%, respectively, but that only yields 3.45 grams of lysine and 2.3 grams of methionine per 4-ounce (115-gram) serving.

When you take a more careful look, it becomes clear that if your horse needs amino acid support or to ensure adequate calcium intake, a ration balancing feed is likely the better choice. If these are not concerns or you have an easy keeper and minimizing caloric intake is a greater concern, then the supplement version might be a better solution.