Protein – how much does your horse need?

Protein is probably one of the most misunderstood nutrients in the horses’ diet. Often thought of as an energy source, in reality protein mainly provides structure along with other key functions within the horse’s body.  Protein is vital for correct body function, so it is important to know how much your horse needs on a daily basis to provide the right amount for optimal health and performance.

What is Protein?

All tissues in the body are made of protein, along with enzymes, hormones and antibodies. Protein is a major body constituent and is present in hooves, skin, hair and muscle, making up around 15% of the horse’s body mass.

Protein is made up of chains of amino acids – the ‘Building Blocks’ of protein, so the horses’ individual requirement is actually for amino acids. There are 21 amino acids that are a part of protein in mammals¹ and 10 of these are known as ‘essential’, with lysine considered to be the most critical. These ‘essential’ amino acids need to be provided in the diet as the horse either cannot synthesise them at all or cannot synthesise them in large enough quantities to meet their demand.

When your horse consumes protein it is broken down in the small intestine by enzymes called proteases. The proteases break down the long chain of amino acids into individual amino acids which are then released and absorbed into the bloodstream. The amino acids are then re-synthesised into protein as needed for maintenance and growth but this is not an efficient process, resulting in protein losses and a continual need for dietary protein to replace those loses.

Not all proteins are created equal

Many different proteins can be synthesised according to different combinations of amino acids in the chain, but all the required amino acids need to be present at the same time to make a specific protein. Certain amino acids, however, always need to be present in order to build protein or synthesis is limited and these are known as ‘limiting’ amino acids, namely, Lysine, Threonine and Methionine. Lysine is the first limiting amino acid as its supply normally runs out first, so it is important that dietary protein contains good levels of lysine but also adequate levels of threonine and methionine for correct protein synthesis.

Dietary protein quality is defined by how well it is digested in the small intestine and by how closely the individual proportions of amino acids contained within match the proportions required by the horse’s tissues². Overall protein quality is greatly improved by good levels of lysine.

The protein content of feeds is expressed as Crude Protein (CP) because it is difficult to say exactly how much is well digested and as yet there is insufficient data to be able to clarify Digestible Protein (DP) for the horse³. Currently, the actual DP of a particular feed is considered to be about 2-5% less than the CP stated³.

Sources of Protein for horses

Good sources of dietary protein for horses include:

  • Fresh Grass, chop or pellets
  • Good quality hay and haylage
  • Wholesome Balancers
  • Alfalfa chop or pellets
  • Linseed meal
  • Peas
  • Chia seeds

How Much Protein does a horse need?

Protein requirements, in line with the protein content of feeds, are also expressed as CP. In general to fulfil protein requirement, horses need around 8-12% protein according to type but this can be higher, for example, for foals and lactating mares. The table below gives a guide of the percentage protein required by different classes of horses.

Table 1Daily % Protein recommendations for different types of horses⁴

ClassificationProtein Level %
Nursing foal, 2-4 months (needs above milk)16
Weanling at 4 months14.5
Weanling at 6 months14.5
Yearling (12 months)12.5
2 year old (24 months)11
Mature horse maintenance (idle)8
Mature horse in light work (e.g. pleasure riding)10
Mature horse in moderate work (e.g. jumping)10.5
Mature horse in intense work (e.g. racing, polo, endurance)11.5
Elderly horse12
Stallion in breeding season10
Pregnant mare – first nine months8
Pregnant mare – 9th and 10th months10
Pregnant mare – 11th month11
Lactating mare – first 3 months13
Lactating mare – from 3rd month on11

Too Much Protein?

Too much protein in a horse’s diet is often blamed for causing excitability and excess energy, but this is actually a myth. Protein can be used as an energy source but this is normally only when the horse is not receiving enough energy from the diet. Protein fed in excess of requirement results in 2 waste products: Urea and Ammonia, which then have to be excreted via the kidneys. Ammonia produces a strong smell after exiting the body in urine and can often be smelt in stables if the horse is receiving too much protein. Ammonia in the stable can also cause irritation to the respiratory tract.  The process of excreting urea and ammonia results in an increase in urine output which can put a strain on the kidneys, and consequently the horse will have an increased need for water. Therefore, it is best to avoid feeding too much protein because of the potential to cause certain health problems.

Top Tips

  • Feed the best quality protein you can by providing you horse with a wholesome and nutritious diet
  • Look out for feeds containing Lysine and ideally Methionine and Threonine, which indicates good protein quality, such as Smart Balance and Smart Linseed.
  • Consider your horses’ type and workload to deliver the correct amount of protein for peak health and performance.
  1. Urshel, K.L. and Lawrence, Laurie M. (2013) Amino Acids and Protein. In: Geor, R., Harris, P., Coenen, M., eds., (2013) Equine Applied and Clinical Nutrition. China: Saunders Elsevier, pp. 113-132.
  2. Frape, D. (2010) Utilisation of the Products of Dietary Energy and Protein. In: Frape, D. (2010) Equine Nutrition and Feeding. Chicester: Wiley-Blackwell, pp. 21-36.
  3. National Research Council of the National Academies (2008) Proteins and Amino Acids. In: Nutrient Requirements of Horses, 6th Edition. Washington, DC: The National Academies Press, pp. 54-68.
  4. Lewis, Lon D. (1996) Equine Nutritional Requirement Tables. In: Lewis, Lon, D (1996) Feeding and Care of the Horse. Chicester: Wiley-Blackwell, pp. 411-418.

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