Protein is the most expensive ingredient in a diet. Equine nutritionists are trained with the same mindset as nutritionists working with other livestock. Cost is a consideration; return for the investment. This often results in recommendations being the minimum you can get away with rather than the optimum for health and performance.
For example, recommendations for broodmares are focused on getting a live foal on the ground but there is convincing research the current guidelines need adjustment. In a series of studies published 1997 and 1998, Van Niekerk and Van Niekirk found mares receiving quality protein (higher total protein and essential amino acids) ovulated sooner in the spring transition, had higher progesterone in early pregnancy and lower rates of early loss. Foals from mares fed recommended levels of protein were 25% smaller at weaning than mares on a higher protein intake. Tanner et al 2014 found weanlings fed the recommended level of crude protein and lysine incorporated less protein into their tissues than those fed at a higher protein intake.
With exercising horses, the prevailing wisdom is often that higher protein intakes may actually be harmful but Oliveira et al 2015 have solid data to the contrary. Horses in eventing training fed 2.25 grams of crude protein/kg of body weight showed improved nitrogen absorption, more absorbed nitrogen retained as protein and even improved fiber digestibility. The current recommendation (NRC Nutrient Requirements of Horses 2007) is only 1.72 grams crude protein/kg of body weight for horses in heavy exercise, a 31% difference.
Since we know very little about the horse’s dietary requirements for essential amino acids, it’s quite possible the same effects could be achieved simply by increasing intake of key amino acids (the building blocks of protein) rather than large increases in protein across the board. However, we only have good information for a few of the 10 to 12 essential amino acids and wouldn’t really know where to start.
When the horse absorbs protein, it is first broken down into amino acids which are then reassembled into proteins inside the body. In addition to building muscle, protein/amino acids are needed for the framework of bone, tendons, ligaments, enzymes and hormones. Creatine, which stores high energy in muscles, is a protein. Carnitine is needed to carry fats into the mitochondria to be burned and its metabolite, acetyl-L-carnitine, is a critical regulator of energy generation. Carnitine synthesis requires lysine and methionine. Glutathione, the major antioxidant in muscle, is a protein. The list goes on.
How do current diets measure up to the higher, probably more optimal, protein intake? A 500 kg (1100 lb) horse eating 10 kg (22 lb) of an 11.25% protein hay would meet the higher protein intake for heavy work but since you would need to feed considerably more hay on a hay only diet (close to 30 lb) the hay would only have to be about 8% protein. Any good hay would likely meet this crude protein requirement. Ironically, if you feed grain and less hay your deficit is probably larger because a lb of grain contains 2 to 3 times the calories but not 2 to 3 times the protein.
The only way to know precisely how your horse’s diet measures up would be a formal diet analysis. As a rule of thumb, to close the gap on what could be as much as a 30% deficit in protein intake try adding 50 grams of protein (e.g. 100 g of a 50% protein supplement) from a mixture of flax seed (about 30% protein), soy and whey protein plus a supplement of L-lysine, L-methionine and L-threonine (10-5-2.5 g), especially if you are seeing an indication your horse’s muscle function could be better. This includes issues with muscle bulk, speed, endurance, topline definition or muscle soreness – all very common complaints with active horses.
Eleanor Kellon, VMD