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Protein can be a confusing topic for horse owners, and understandably so - horses don’t necessarily have a protein requirement, but rather a requirement for amino acids, which make up protein!
Common crude protein value recommendations follow the following guidelines:
Mature horses: 8-10%
Lactation or older horses: 12-14%
Growing horses: 14-16%
However, as horses have a requirement for amino acids, not crude protein, the protein quality is more important than the %CP - the amount of protein provided does not matter if the required amino acids are not provided.
ESSENTIAL AMINO ACIDS
Lysine
Methionine
Threonine
Arginine
Histidine
Isoleucine
Leucine
Phenylalanine
Tryptophan
Valine
If one amino acid is limited (present in less than adequate amounts; “limiting amino acid”), or if one is over-supplemented and prevents other amino acids from being absorbed, protein synthesis will also be limited (NRC, 2007). Supplementing just 1 amino acid without a detailed analysis of the horse’s diet can only further disturb amino acid balance, and as a result, disturbed protein synthesis.
Some amino acids cannot be produced in adequate amounts in the body, and thus are essential in the adult horse’s diet. As hay and pasture often contain limited levels of certain amino acids, especially lysine, methionine and threonine, it’s incredibly important that other areas of the diets contain quality proteins to provide amino acids.
Grass-based diets often are limiting in lysine and threonine, especially if it is a mature cut. When feeding a low-quality protein forage, supplementation with a high-quality source is recommended so as to ensure amino acid requirements can be met (NRC, 2007). Soybean, alfalfa, canola and flax are commonly used to increase protein in the diet, as legumes and cereals have higher protein content than grasses (Novak, Shoveller and Warren, 2008).
SIGNS YOUR HORSE NEEDS HIGHER QUALITY PROTEIN
Signs of insufficient amino acid provision in the diet include weight loss (despite adequate energy intake), poor topline development (which can contribute to poor performance), reduced feed intake, and poor hair growth, milk production and hoof growth.
Topline is assessed across the back, croup and loins, and while it can be considered during body condition scoring, can help speak to the amino acid balance of your horse’s diet. This is why palpating your horse while body condition and topline scoring is important to distinguish between fat deposition and muscle.
If your horse appears to be below ideal condition and you’re not happy with their topline, but they have fat deposition at body condition score points, amino acid balance may need to be corrected. Check the protein sources in your horse’s current feedstuffs, and consider using a ration balancer or commercial feed that contains high quality protein ingredients such as soybean meal. Additionally, adding alfalfa hay or hay cubes can help increase protein in the diet, as well as topdress feeds containing soybean meal or flax.
HOW MUCH TO ADD?
Of course, factors such as your horse’s requirements (ie exercise, growth, lactation, etc), hay and current diet will impact how much you’ll want to supplement, but we’ll provide some numbers to help you get an idea!
Requirement for 500 kg Mature Horse at Maint. | Mature Grass Hay fed at 2% BW DM (10 kg). | High quality Mixed Hay fed at 2% BW DM (10 kg). | 1 kg Alfalfa Pellets | 1 kg 30% Protein Ration Balancer | |
Protein (g) | 630 g | 630 g | 870 g | +170 g | +280 g |
Lysine (g) | 26 g | 26.8 g | 38.6 g | +7.5 g | +6.84 g |
Methionine (g) | 7.3 g | 9 g | 12.18 g | +2.16 g | +1.85 g |
Threonine (g) | 16.8 | 24.8 g | 34.2 g | +6.6 g | +3.7 g |
Example for a 500 kg mature horse at moderate exercise.
Requirement for 500 kg Mature Horse at Moderate Exercise. | Mature Grass Hay fed at 2% BW DM (10 kg). | High-quality Mixed Hay fed at 2% BW DM (10 kg). | 1 kg Alfalfa Pellets ($1.55) | 1 kg 30% Protein Ration Balancer ($1.74) | |
Protein (g) | 768 g | 630 g | 870 g | +170 g | +280 g |
Lysine (g) | 33 g | 26.8 g | 38.6 g | +7.5 g | +6.84 g |
Methionine (g) | 8.9 g | 9 g | 12.18 g | +2.16 g | +1.85 g |
Threonine (g) | 20.45 g | 24.8 g | 34.2 g | +6.6 g | +3.7 g |
*Remember that unless feeding a concentrated vitamin/mineral product to cover vit/min requirements, make sure to follow feeding rates when using bagged feeds such as ration balancers to ensure your horse is getting enough vit/min.
It’s important to remember that when feeding protein to your horse, the goal is not to provide the highest quantity of protein that you can, but rather, provide quality protein that will contribute to the amino acid pool available to the horse.
The effects of excess protein in horses has not received much research focus, despite protein being commonly overfed to horses (Woodward et al, 2011;NRC, 2007).
Concerns regarding excess protein include:
Lower blood pH at rest & during exercise.have
Increased calcium and phosphorus losses.
Will bypass foregut digestion and reach the hindgut, where it will be fermented.
Increased water losses as excess protein is excreted in urine, as urea.
Increased metabolic heat production, may impact thermoregulation.
As is often the case with nutrition, quality > quantity! Need help with the protein in your horse's diet? Let's connect!
References
NRC, 2007. Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press 2007.
Hammer, C. 2010. Feedstuffs for Horses. North Dakota Extension Service. Fargo, ND. 2010.
Mok, CH., Urschel, KL. 2020. Amino acid requirements in horses. Asian-Australas J Anim Sci 33(5):679-695.
Novak, S., Shoveller, AK., Warren, LK. 2008. Nutrition and Feeding Management for Horse Owners. Alberta Agriculture and Rural Development. 1-123.
NRC, 2007. Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press 2007.
Woodward, AD., Nielsen, BD., Liesman, J., Lavin, T., Trottier, NL. 2011. Protein quality and utilization of timothy, oat-supplemented timothy, and alfalfa at differing harvest maturities in exercised Arabian horses. Journal of Animal Science 89(12): 4081-4092.
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