An Equine Nutrition Blog by Madeline Boast, MSc. Equine Nutrition.
Protein is one of 6 nutrient classes that horses have a requirement for. It is a major component of body tissues. Along with being a core component of tissues, proteins are also heavily involved in enzymes, hormones, and antibodies.
Proteins are long chains of amino acids, there are 21 amino acids that join in a multitude of combinations to form proteins. In equine nutrition, we divide the amino acids into essential and non-essential. The essential amino acids are those that the horse cannot produce and therefore must be supplied in the diet. They include: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Unfortunately, the individual requirements for each amino acid have not been elucidated for horses except for lysine. More research is required to be able to understand the exact dietary requirements for individual amino acids.
Now that we have established a basic understanding of protein in the equine diet, let’s discuss which horses have a higher requirement for protein in their diet.
A horse’s requirement for protein depends on their physiological state as well as workload. Typically, horses do not have high protein requirements. In fact, most of the time their protein requirement can be met with quality forage as long as the protein levels in the forage are adequate. That being said, occasionally, protein in the forage will not be adequate and an additional source must be added to the nutrition program – again this highlights the importance of a hay analysis.
Growing horses, pregnant mares, lactating mares, and horses under a moderate to heavy exercise regime will probably need additional protein. Mares in late gestation and those in the first three months of lactation have the highest requirements. Best practice for these horses would be to first have them on a protein-rich forage such as legume-based hay, then add additional protein as needed.
Although this sounds simple, there is one more factor to consider. Not only do you need to ensure your horse has adequate protein in their diet, but it must also be high quality.
Protein quality has to do with the amino acid composition of that ingredient as well as the digestibility. High quality protein provides essential amino acids in the correct proportions, whereas lower quality protein may be inadequate at providing essential amino acids or have poor digestibility. Therefore, when curating a diet for a horse that has increased protein requirements ensuring you are adding a good quality protein can make a significant difference in their nutritional well-being.
When comparing feedstuffs based on protein quality a general rule is that legume hay has a better protein profile than grass hay or pasture. Additionally, many cereal grains (barley, corn, oats) are considered to have low quality protein. Typically, soybean meal is the go-to high quality protein source for horses as it provides a high percentage of lysine.
When evaluating your horse’s diet for protein a hay analysis should ALWAYS be done. This way a nutrition program can be built around the forage. After the hay analysis, if a nutritionist determines your horse needs an additional source of protein added they will either recommend a single ingredient such as soybean meal or add a balanced complete feed. When shopping for a complete feed it pays off to do your research not only on protein content but also on protein quality!! When supplementing protein, it is important to know the level to which to supplement as there are complications both with protein deficiency and with excess protein.
Research suggests that protein deficiency in the horse is less common when compared to the excess protein being provided. However, there are still negative health consequences associated. Symptoms of protein deficiency in mature horses are muscle loss, weight loss, inadequate feed intake, and poor growth of hooves and hair. In addition to the previously listed symptoms, pregnant mares may experience fetal loss as well as poor milk production if they are deficient in protein. In young horses, a decrease in growth is seen when protein is lacking in the diet. If you have a nutritionist complete a hay analysis, they will be able to determine if an additional protein source should be added to the diet.
When a horse is supplied with excess dietary protein that protein will be broken down and excreted from the body as urea in the urine. When there is additional urea to be excreted, the horse may experience an increase in water loss. When more water is lost, the water intake requirement of that horse will increase. This could be problematic for horses under intense exercise who may already struggle with hydration.
Research has shown that when high protein diets are given to exercising horses it interferes with the acid-base balance in their body. Additionally, when horses urinate more and have a higher urea content in the urine it negatively impacts the air quality in the barn and can lead to respiratory problems down the road.
A study using Arabian horses under training has suggested that improving protein quality but decreasing protein quantity in the diet is a good option. This way you can ensure a working horse is not deficient in important amino acids such as lysine but avoid the undesired effects of greatly oversupplying protein.
Another problematic consequence of oversupplying protein is that the increased urea can lead to earlier fatigue during exercise. Another concern related to exercise is heat. When a horse is using protein for energy, they produce more body heat which increases sweating and therefore increases the risk of dehydration in working horses.
A final area that is important to highlight is the environmental impact of providing excess protein in livestock nutrition. Unfortunately, the equine sector does not have the same published parameters on nitrogen and urea excretion as other livestock sectors, but it is well documented that when too much protein is fed, there is an increase in nitrogen released in the urine. This negatively impacts both air quality and groundwater. Plus, protein shouldn’t be wasted! It is an expensive feed ingredient.
To conclude, all of this highlights the need for precision in ration formation. Stop guessing with your horse’s nutrition! Have a hay analysis done and get an equine nutritionist to balance the diet to your forage analysis.
If you have any questions, please reach out to Madeline at balancedbaynutrition@gmail.com
By: Madeline Boast, MSc. Equine Nutrition
About the author:
Madeline Boast completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids – from miniature ponies to competing thoroughbreds. Through Balanced Bay she designs customized balanced nutrition plans that prioritize equine well-being. This includes diets for optimal performance as well as solving complex nutritional issues and everything in between. For additional information see www.balancedbay.ca .
References:
Graham-Thiers, P. M., Kronfeld, D. S., Kline, K. A., Sklan, D. J., & Harris, P. A. (2003). Dietary protein and fat effects on protein status in Arabian horses during interval training and repeated sprints. Journal of Equine Veterinary Science, 23(12), 554-559.
Loos, C. M., McLeod, K. R., Stratton, S. C., van Doorn, D. A., Kalmar, I. D., Vanzant, E. S., & Urschel, K. L. (2020). Pathways regulating equine skeletal muscle protein synthesis respond in a dose-dependent manner to graded levels of protein intake. Journal of Animal Science, 98(9), skaa268.
National Research Council. 2007. Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press. https://doi.org/10.17226/11653.
Tanner, S. L., Wagner, A. L., Digianantonio, R. N., Harris, P. A., Sylvester, J. T., & Urschel, K. L. (2014). Dietary crude protein intake influences rates of whole-body protein synthesis in weanling horses. The Veterinary Journal, 202(2), 236-243.