How much protein is enough for my three Arabian mares?

Hoof Nutrition Intelligence is a twice-a-month web segment that is designed to add to the education of footcare professionals when it comes to effectively feeding the hoof. The goal of this web-exclusive feature is to zero in on specific areas of hoof nutrition and avoid broad-based articles that simply look at the overall equine feeding situation.

Below you will find Part 2 of the latest question and answer installment that you can share with your footcare clients.

Q: How much protein is enough for my three Arabian mares?

By Eleanor M. Kellon, VMD

A: Protein is the most expensive ingredient in a horse’s diet. Equine nutritionists are trained with the same mindset as nutritionists working with other livestock; cost is a consideration, as well as the return on investment. This often results in recommendations being the minimum you can get away with rather than what is ideal for health and performance.

For example, recommendations for broodmares are focused on getting a live foal on the ground, but there is convincing research that points to the current guidelines needing to be adjusted. With exercising horses, the prevailing wisdom is often that higher protein intakes may actually be harmful, but there is solid data to the contrary.

When the horse absorbs protein, it’s first broken down into amino acids, which are then reassembled into proteins inside the body. In addition to building muscle, protein and 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 ideal, protein intake? 

1 A 1,100 pound horse eating  (22 pounds daily of an 11.25% protein hay) would meet the higher protein intake for heavy work.

2 However, since you would need to feed considerably more hay on a hay-only diet (close to 30 pounds per day), the hay would only have to be about 8% protein. Any good hay would likely meet this crude protein requirement. 

3 Ironically, if you feed grain and less hay, your deficit is probably larger because a pound of grain contains two or three times the calories, but not two or three  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 (100 grams 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 that 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.

Since we know very little about the horse's dietary requirements for essential amino acids, it's possible the same effects could be achieved simply by increasing the intake of key amino acids (the building blocks of protein) rather than adding large increases in protein. 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.

Recommendations for broodmares are focused on simply getting a live foal on the ground, but there is convincing research that the current guidelines need adjustment. In a series of studies published in 1997 and 1998, Van Niekerk 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 in 2014 studies 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 in 2015 studies had solid data to the contrary. Horses in eventing training fed 2.25 grams of crude protein per kilogram 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 per kilogram of body weight for horses in heavy exercise, which represents a 31% difference.

Eleanor Kellon is the staff veterinary specialist for Uckele Health & Nutrition. She is an established authority in the field of equine nutrition for over 30 years, and a founding member and leader of the Equine Cushings and Insulin Resistance (ECIR) group, whose mission is to improve the welfare of horses with metabolic disorders via integration of research and real-life clinical experience. Prevention of laminitis is the ultimate goal. For more information visit www.ecirhorse.org.

Click here to read part 1 of the March 1, 2020 installment of Hoof Nutrition Intelligence: How does calcium affect the hoof horn when white line disease is a concern? Click here to read more installments of Hoof Nutrition Intelligence.