The importance of amino acids and where to find them in the equine diet

Protein is essential for maintaining health and sustaining life. It is found in every cell and tissue in the body. Protein is a vital component of muscle, skin, hooves and hair but is also required to perform nearly every bodily function including, but not limited to: growth and repair, cell renewal, fluid balance, blood clotting, cellular transport and hormone, enzyme and neurotransmitter synthesis. 

Protein itself is, however, pretty useless to the horse. It is the amino acids or the “building blocks” of protein that are the important part. 

Protein is made up of very (very) long chains of amino acids - imagine them like a length of beads on a string where each bead represents a single amino acid. Horses cannot make use of protein in this form so digestive juices and enzymes in the stomach and small intestine, break the long chain down into shorter chains that can be absorbed and utilised. Amino acids can be used singularly or more often, in conjunction with other amino acids, to perform essential bodily functions.

There are around 20 amino acids which can be classified in two separate groups – 10 are essential amino acids which need to be supplied by the equine diet and the rest are considered non-essential amino acids, as the horse can produce these themselves. Amino acids are usually easily identifiable as they end in “-ine” e.g. lysine, arginine and leucine, but there are some exceptions to this rule: tryptophan, glutamic acid and aspartate / aspartic acid.

Of the essential amino acids, some are also known as limiting amino acids which means their own availability and supply limits how much of the other amino acids can be absorbed and utilised. If the diet does not supply sufficient levels of the limiting amino acids, then even if the other amino acids are present abundantly, the horse will not be able to make use of them. This can lead to deficiencies which may present as muscle loss, weak hooves, fatigue or slow recovery times and susceptibility to illness.

The three main limiting amino acids in order are lysine, methionine and threonine. Protein quality is judged by the range of amino acids present but also how much of the essential and the limiting amino acids it supplies. A feed ingredient may be high in protein but, if it is not high in essential and limiting amino acids, then its protein is considered poor quality.

Forage protein is considered higher quality protein than cereal protein because of this assessment – the protein in forage may be lower in some cases but its range of amino acids and levels of limiting amino acids are much higher. Grass protein is good but legume protein – from lucerne and sainfoin – is even better because the levels of limiting amino acids are higher still.

Whilst beneficial for gut health, providing a varied forage diet helps increase the range and total level of amino acids our horses will consume. High protein and higher nutrition forages can be used for poor doers or those lacking muscle tone, whilst using forages naturally lower in digestible energy but still supplying quality protein - high in these essential and limiting amino acids - ensures our better doers can lose weight but maintain, or even build muscle, and maintain good overall health.

If you want to discuss protein intake in your horse’s diet, please contact the Simple System Feed Line on 01728 604 008 or complete our advice request form.