Myths abound in equine nutrition, especially when it comes to protein.
One of the most common of these is that high protein can damage the kidneys. Excess protein is processed in the liver to urea, which is excreted in the urine. However, the kidneys can handle this easily and there is no risk of injury. The only effect is increased drinking and increased urine output.
High protein has also been named as a risk factor in developmental orthopedic disease (DOD) which includes conditions like physitis and osteochondrosis. There is no truth to this and no plausible mechanism to explain how protein could even theoretically be a cause. The real dietary culprits here are unbalanced and/or deficient minerals and excess calories causing rapid growth. If protein is involved at all it would be low intakes, not high.
Does a high protein diet make the horse hard to handle? Not likely. Some horses become “hot” when fed alfalfa but the reason for this is not clear. A quality grass hay with only 11% protein fed at levels necessary just to maintain weight provides almost 150% of an adult horse’s protein requirement.
It is often said that adult horses need a 10% protein diet (or 10% protein grain). The horse’s protein need is actually in grams/day and depends on body weight, sex, level of activity, pregnancy, etc.. The protein percentage alone is meaningless. What matters is how many grams of protein the horse gets, which depends on both percentage and how much of it the horse eats. One kilogram (2.2 lbs) of a 10% protein hay provides 100 grams of protein while 10 kg of the same 10% protein hay yields 1000 grams of protein.
The % protein in the grain is particularly irrelevant since hay always provides a significant, if not major, proportion of the dietary protein. An average size horse needing 750 grams/day of protein would get only 227 grams of protein from 5 lbs of a 10% protein feed. That’s quite a gap.
To make up the additional 525 or so grams of protein from hay would take 11.5 pounds of a 10% hay, or 23 pounds of a 5% protein hay, etc. If you fed only half as much, the horse would get half as much protein.
Protein is a critically important part of your horse’s dietary needs. Too little is definitely a problem but there are no health threatening problems related to too much. If you are having issues with your horse, don’t blame protein.
Eleanor Kellon, VMD