Horsemen used to think that a diet of rich alfalfa could cause kidney problems in horses, but this is untrue. A healthy horse can handle extra protein just fine.
The exception might be a horse working hard in hot weather, since protein metabolism creates more heat than does metabolism of fat or carbohydrates. The added heat created by processing the extra protein can cause problems with heat dissipation and the horse might suffer from heat stress.
Credit: BHN File Photo
Extra protein cannot be stored in the body and must be excreted. If a horse is fed more protein than he needs, it goes to waste and is broken down so it can be excreted. The end group of amino acids on the protein structure is chopped off, converting the balance to carbohydrates, which can be used as energy or stored as fat — but the unneeded nitrogen portion becomes ammonia or urea, which are both excreted in the urine (producing smelly urine).
A horse eating more protein than the body can use will also drink more water (to help flush out the additional waste products). This creates more urine, with a strong ammonia smell. This may be why horsemen thought the kidneys were damaged by high protein feed. In truth, however, the only damage is to the horseman's pocketbook, when feeding the excess protein. Protein is the most costly nutrient fed to horses. There is also more expense and labor in providing extra bedding to replace that which is soiled by increased urination.
Another undesirable factor is the lowered air quality in a barn where too much protein is fed. The ammonia in stalls can irritate a horse's air passages and make him more susceptible to respiratory problems. This is especially true with foals, since they are smaller (breathing air in the lower portion of the stall) and spend a lot of time lying down. Ammonia is heavier than air and tends to be most highly concentrated near ground level.
Feeding extra protein is wasteful, but aside from the disadvantage of more urine and ammonia in a barn stall, or more heat to dissipate during exertion in hot weather, the high protein diet in itself does not hurt a healthy horse. It CAN be detrimental, however, to a horse that already has impaired kidneys or a damaged liver. These individuals have problems processing and excreting protein, and should always be kept on a very low protein diet.
Heather Smith Thomas has raised and trained horses for 50 years and has been writing about them nearly that long. She and her husband raise beef cattle and horses on their ranch near Salmon, Idaho.