Protein requirements for healthy horses

When feeding hay through the winter, horse owners should be aware of their horses' protein requirements and the protein content of the feed, according to a Montana equine specialist.

“There is no problem with feeding too much protein to the mature horse, but excessive protein may cause developmental orthopedic disease in the young growing horse," said Sandy Gagnon, Montana State University equine specialist of Bozeman, Mont. “On the other hand, there could be problems if the horse doesn't have enough protein in its diet.”

Protein is composed of a chain of amino acids, which contain nitrogen, and are used as building blocks in synthesizing body tissues. The body can make some of these amino acids, but others must be supplied by the horse's diet.

Most protein in grain and protein supplements are digested and absorbed in the small intestine whereas protein from forages is digested and absorbed from the large intestine. When excess protein is ingested the excess nitrogen is removed in the form of ammonia and the remainder is used for energy or stored in the form of fat or glycogen. The ammonia is then converted by the liver to urea and passed out in the urine. This is what gives the ammonia smell in horse barns that are feeding alfalfa hays, said Gagnon.

“When horses use excess protein for energy, three to six times more heat is produced as compared to that of carbohydrates,” he added. “Consequently, mature horses on high protein diets will sweat more and may contribute to heat exhaustion during exercise in hot weather.”

One of the most common sources of excess protein in the horse's diet is alfalfa hay. Most alfalfa hay has a crude protein content ranging from 14 to 20 percent, said Gagnon.

“The crude protein maintenance requirement for the average mature light horse is 8 percent, and for the exercised horse, depending on the level of activity, is 10 percent,” he said. “Consequently, horses on this type of roughage are usually over on their protein requirements and the old timers called this soft fat when horses were used hard and sweated a lot.”

Horses of different ages require varying amounts of protein in their diet. It is important to make sure the horse's diet has the right amount of protein, especially in young, growing horses, to prevent growth abnormalities. Knowing the protein requirement for each class of horse is important.

Younger horses require more protein in their diets than older horses, as protein aids in growth.

Foals weaned at 4 months require 16 percent protein in a 90 percent dry matter basis, while those weaned at 6 months require 14.5 percent crude protein. Yearlings, or horses 12 to 18 months old, require 12.5 percent crude protein, while 2-year-olds require only 11 percent, said Gagnon. A 3-year-old horse is considered mature and requires 9 to 10 percent crude protein in a maintenance diet.

Horses undergoing more strenuous activities may require more protein than those that spend most of their time in the pasture, said Gagnon.

Horse owners need to remember that only 70 to 75 percent of crude protein in a diet is digestible, or usable by the horse, said Gagnon.

“When you do your hay analysis and look at the charts, remember your horse won't be able to use all of the crude protein in the hay,” he said. “The horse will be able to use only 70 to 75 percent, depending on the source of the crude protein.”

Gagnon recommends horse owners feed a diet containing one-third alfalfa, which is good roughage, to help keep the protein levels up in the horse's diet. “Young, growing horses should be fed a mix of alfalfa and grass hay because straight alfalfa hay is too high in calcium,” he said. “Straight alfalfa hay has a calcium-to-phosphorus ratio of 6:1, when those young, growing horses need a ratio of 1:1.

Otherwise, the young, growing horses could experience orthopedic problems such as abnormal epiphyseal cartilage growth commonly called epiphysitis. There are various forms of this and the cause varies.

However, that of alfalfa hay is commonly an imbalance of calcium and phosphorus as well as too rapid of growth. Most often this is seen as a swelling at the pastern area and a knuckling over at this area when moving.”

In addition to feeding a mix of alfalfa and grass hay during the winter months, Gagnon suggests horse owners feed a mineral supplement to meet the daily requirement of three ounces per day

“One mineral supplement that is made for cattle but fits horses really well is Bronze - it is a loose mineral made by CHS,” he said. “Do not feed any any mineral supplements that have medication in them. Many cattle mineral supplements contain a medication such as monensin or rumensin that are lethal to horses. The Bronze comes in both medicated and non-medicated mineral; consequently, you need to be careful when buying.”

Gagnon said he prefers feeding loose mineral to horses as opposed to block mineral, but acknowledged the decision is mostly personal preference.

“If you use loose salt the intake will be greater and you can be more assured they will meet their requirement. Symptoms of salt deficiency take a long time to appear and may be missed,” he said. “However, with loose mineral weather is a concern.”