Frank Gravlee does not recommend feeding soybean meal or alfalfa hay.
“Although soybean meal is an excellent source of quality protein, it is also high in phytates (phosphorus) and contains anti-nutritional factors,” says the equine nutritionist, veterinarian and founder of Life Data Labs. “The relatively high levels of phytates in soybean meal alter the calcium-to-phosphorus ratio and can interfere with calcium absorption. The anti-nutritional factors include protease inhibitors, phytoestrogens and goitrogens.
While alfalfa hay is high in the percentage of protein, he says the protein is actually low quality. The excess nitrogen present in the low-quality protein not only leads to nervousness and metabolism problems, but will also increase the ammonia in the horse’s urine, which can lead to respiratory problems in stalled horses.
Gravlee says crude protein is calculated from a measurement of the amount of nitrogen in the feedstuff. Poor quality proteins may contain an abundance of some amino acids, along with a deficiency of other amino acids.
“The limiting amino acid of a foodstuff is the amino acid that is lacking relative to the other amino acids, and once utilized the formation of a protein that requires that particular amino acid can no longer occur,” he says. “High-quality protein has amino acids in the proper ratio to allow the amino acids to be fully utilized in the creation of protein.”
You can read more about feeding horse for optimum performance in the September/October 2013 issue of American Farriers Journal.