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How important is protein for horses?

How important is protein for horses?

Protein is an essential nutrient in your horse’s diet that serves a multitude of roles in the body:

  1. Musculoskeletal growth and repair
  2. Healthy skin, coat and hooves
  3. Cardiovascular and immune health
  4. Mineral and nutrient absorption

It is a major component necessary for the formation of muscles, skin, tendons, blood vessels, organs, bone, hair and hoof. It is not only important in building cells and repairing tissues, but also aids in regulating many of the bodies’ systems and functions. For example, proteins form antibodies to combat invading bacteria and viruses; they make up enzymes and some hormones; they build nucleoproteins such as DNA; they carry oxygen throughout the body and they participate in muscle activity. After water, the major constituent of the body is protein. In fact, eighty percent of the horse’s fat free, moisture free body composition is protein.

 What is protein?

Protein is a long chain molecule made up of amino acids. In total, there are 22 different amino acids needed for protein synthesis in the body and these are divided into two groups – essential and non-essential amino acids. The ‘essential’ amino acids (arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) must be provided in the diet. Of these lysine is the most important as it is the first limiting amino acid. This means, if your horse’s diet is low in lysine, then it doesn’t matter how much protein they’re fed, the amount of lysine will dictate how much protein will be available for the horse to utilise.

Non-essential amino acids do not have to be supplied by the diet, as they can be synthesised by microorganisms in the horse’s caecum and anterior portion of the large colon and by metabolic processes in the body.


Is all protein the same?

All protein is not the same; the source and quality of protein are the most important in the diet. Protein quality is determined by the type and amount of amino acid it contains and the digestibility of the protein source. Soyabean meal has the highest biological value and has a 48% protein content on an as fed basis. Forages and grain horse feed are naturally lower in lysine and methionine, whereas soya is naturally high.

All Connolly’s RED MILLS horse feed include soya as a protein source for optimum growth and performance of your horses. Linseed, sunflower seed meal, and alfalfa are also good sources of protein for the horse.


Protein requirements

Protein is required by all ages of horses, but the amount and quality required depends on the horse’s age and physiological status. Young, growing horses and broodmares need the most and the best protein, followed by horses in higher levels of work. Some young horses can tolerate more protein and can use it to grow muscle, but many breeds of easy-keeping horses do poorly on excess amounts of protein when young. Horses recovering from illness or injury or older horses can also have increased protein requirements.

Protein deficiency

If a horse is deficient in protein, it will negatively affect not only the growth and development of a young horse, but the strength and recovery of your athlete or the overall health of your pensioner. Protein deficiency can result in:

  • Poor skeletal development
  • Poor coat / hooves
  • Reduced immunity
  • Lengthened recovery time
  • Poor semen quality
  • Reduced milk production
  • Ill thrift

Too much protein

If enough protein is good – then more must be better? No! The horse, like all mammals, cannot store protein for use in the future and can only use certain amounts of protein. Any excess will be metabolised and excreted in urine as nitrogen, this is why overfeeding protein can potentially be problematic – if stables are deep-littered, the build up of strong-smelling ammonia from the urine, can irritate the horses airways and potentially cause respiratory problems.

In addition, excess protein can potentially reduce blood pH and this may have a detrimental affect on performance. So, feeding excess protein, besides being expensive, could be detrimental to the horse’s overall health and performance.

Don’t confuse protein with energy

There is a common misconception that protein content of a feed is representative of the energy or the power of a feed. This is because performance feeds, such as racehorse feeds, tend to be higher in protein than say, leisure feeds. However, protein is a poor energy source for the horse and will only be utilised in the absence of any other options (such as starvation). Performance horse and stud feeds tend to be higher in protein because growing horses, broodmares in late gestation and horses in hard work or competition have higher protein requirements to support muscle development, growth and repair.

Feeds have been traditionally categorised by protein content rather than starch content. Consequently, it is understandable that when a high protein (and high starch) feed is being fed, protein has mistakenly been blamed for problems such as such as laminitis, epiphysitis, excitability and colic. Research has shown that high starch diets and the imbalance or deficiency of other nutrients, such as minerals, are contributing factors to muscle related problems, digestive problems and bone and soft tissue developmental problems in horses – not protein.


All horses require protein – it is absolutely necessary for the body to survive – but the amount and quality of protein needed vary considerably among the different life stages of horses and the use of the horse. A surplus is equally undesirable as a deficiency, so a delicate balance is required between feeding enough to ensure the best results whilst not providing excessive levels that may cause problems.

If you have any questions about horse feed please check our Horse Care Range or get in touch with our expert team.

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