As discussed in our blog post “Interpreting the Feed Tag Part 1 – Understanding Crude Protein, Fat, and Fiber”, the guaranteed analysis on a feed tag provides concentrations of specific nutrients, which should be used to correctly pair concentrates with forages so the horse’s nutrient requirements are met. Feed manufacturers are required to list:
  • Minimum levels of crude protein, crude fiber and crude fat (expressed as percentages) (discussed in Part 1)
  • Minimum and maximum percentages of calcium (percent)
  • Minimum values for phosphorus (percent), copper (parts per million or ppm), zinc (ppm), selenium (ppm) and vitamin A (International Unites per pound)

Part 2 of our Interpreting the Feed Tag series will focus on the minimum and maximum percentages  of calcium, and the minimum values for phosphorus, copper, zinc, selenium, and vitamin A.

Minimum and Maximum Percentage of Calcium, Minimum Percentage of Phosphorus

Calcium and phosphorus are two macro minerals required to be guaranteed on feed tag. These minerals are vital for:

  • Development
  • Maintenance and repair of the musculoskeletal system

Lactating mares and growing horses require higher intakes of calcium and phosphorus than mature horses at maintenance. For example, a weanling ration should provide at least 0.7 percent calcium and 0.4 percent phosphorus, whereas a mature horse can consume a ration that contains 0.3 percent calcium and 0.2 to 0.5 percent phosphorus. Many commercial products contain added levels of calcium and phosphorus, generally in the range of 0.8 - 0.9 percent calcium and 0.6 - 0.8 percent phosphorus. Calcium should always be fed at a higher percentage than phosphorus to prevent skeletal disorders. In other words, the amount can vary but the ratio of the two minerals should remain within 1.1:1 up to 2:1 parts calcium to phosphorus in the total ration. Horses can tolerate large amounts of calcium because they can eliminate excesses in the urine (ever see that cloudy whitish urine in a horse being fed excellent quality alfalfa hay?). However, recent studies have shown that excessive calcium intakes can cause higher excretion rates of magnesium, causing low serum magnesium levels in affected horses. This can affect bone formation and recently, low serum magnesium has been linked to Insulin Resistance in humans and may be a causative factor of the syndrome in horses.

Feeds may be formulated to take into account the calcium and phosphorus content of forages being utilized. Legume hay (such as alfalfa) has higher calcium content than grass hay. Therefore, feeds formulated to be fed with grass hay will contain a higher percentage of calcium than a feed designed to be fed with alfalfa. Some feed labels will go into detail as to which forage is most appropriate to be fed with such a concentrate.

Minimum Copper, Zinc and Selenium in Parts Per Million (ppm)

Micro minerals are required in smaller amounts compared to calcium and phosphorus. Copper and zinc are important for growth and normal bone and joint development. Selenium is "linked" with vitamin E as a powerful anti-oxidant combination and for increasing immunity. As the content of these minerals in hays and forages is variable, commercial feeds commonly are formulated with small amounts added to ensure adequate intakes. Optimum concentrations are copper, 50 ppm; zinc, 150 ppm; and selenium, 0.1 ppm if in the inorganic form or 0.3 ppm if in the safe, more available organic form (Sel-Plex™ made by Alltech, Inc., sponsors of the 2010 World Equestrian Games in Lexington, KY)

Salt (sodium, chloride)

Salt is generally added to concentrate mixes at the rate of 0.5 percent for idle, non-working horses and 1.0 percent for working horses. Horses also will consume 1 to 3 ounces of free-choice salt daily if provided with a salt block or loose salt. White salt is preferable to trace mineralized salt as the latter contains excessive amounts of iron, which the normal equine diet already provides for adequately. Excessive iron intake has also been implicated in development of Insulin Resistance in humans and rats.

Take Home Message

With all the feed products and supplements available today, selecting the right products for an individual horse or stable of horses requires a complete understanding of what the level of performance required is, what type of forage is available and then selecting concentrates and supplements to balance the whole diet. By closely analyzing available products and matching them to the needs of the horse, optimum nutrition can be obtained.