Protein in the horse's diet - what you need to know

http://www.horses-and-horse-information.com/articles/0698protein.shtml

Protein is one of the most misunderstood topics in the equine nutrition world – does my horse need more protein? Is too much bad? Feed companies do not always help by listing feeds by total protein content by percentage (often listed as CP% - crude protein percent), suggesting a certain percent is needed, or that more is always better. Better understanding this important nutrient requires a brief dip into biochemistry (I know, not everyone’s fave…), but it will be worth your while!

Firstly, we need to understand exactly what protein does in the body. While everyone knows that protein is important for building muscles, it actually has a role in regulating almost every process in the body. Proteins are found in all cells and are the most common, and varied, type of biological molecule. 

Enzymes, hormones, antibodies, muscle fibres, the lens of the eye, keratin in the hoof and many other substances are all proteins. Proteins can have a regulatory function, such as an enzyme or hormone which regulates a physiological process, or have a structural function, such as keratin or muscle proteins, which provide protection, connection and strength.

How can one molecule do so many things? Proteins are made from smaller “building blocks” - the amino acids. There are 20 commonly found amino acids, which have different biochemical properties. Proteins are built by joining anywhere between 100 and several thousand amino acids. The final structure and function of the end protein is determined by which amino acids are used, in what order, and how they interact with each other. Amino acids can attract or repel each other within the chain, causing the protein to fold and twist, which creates different functions in the body.​

As the body builds each protein from scratch, it is important that we have the right amino acids available. Some of these can actually be produced by the horse, but there 10 that must be in the diet – the essential amino acids. The two most important amino acids to consider in the horses diet as lysine and methionine – they are known as “limiting amino acids”, because without enough of them, correct proteins cannot be built, no matter how much of the other amino acids are present.

This leads us to the idea of protein quality (and ends the biochemistry lesson!). Good quality protein has all 10 essential amino acids, in the right proportions to synthesise all the proteins needed in the body. Grass, and grass hays, are generally quite low in lysine and methionine, but many common horse feeds such as cereal grains, beet pulp, flaxseed meal and legumes such as lucerne or soybean meal contain higher amounts. Scientific research (NRC) has so far only determined the exact requirements for lysine in the horse, however Dr Juliet Getty recommends a ratio of 3:1 lysine:methionine. Lucerne, flaxseed meal and soybean meals all fall nicely into this balance, and are feeds to consider for adding good quality protein.

Photo: Dave Taylor

​While total protein is usually easily met
(or exceeded) in the average horse, the important amino acids may not be if the diet is predominantly lower quality grass or hay, but this can be solved by careful addition of good quality protein sources.

But what about these percentages of crude protein the feed manufacturers list on the back of the bag? 10, 14, 16% are commonly seen, but the truth is, a mature horse in light work only needs 700g of protein in his diet. This works out to be as low as 6-7% of his total feed intake. As even the lowest quality grass and hays have protein levels around 8%, and lucerne hay around 20%, most horses are consuming more than enough protein. Horses in heavy work need a little more, but this is easily provided by the concentrates they consume to provide additional energy, so there is no need to add high protein feed. Lactating mares need the most of any class of horse, up to 14% of their total intake, which makes sense as they are busy producing all the milk proteins the foal needs

If most diets actually contain excess protein – is this a bad thing? Should you be trying to reduce the protein levels in the diet? The short answer is no, but it depends! Generally, excess protein is well tolerated by healthy horses, and the excess amino acids are metabolised into energy sources (this is not a particularly efficient way of producing energy however, so protein should not be fed to increase condition or energy levels).​

​This metabolism occurs in the liver, and excess nitrogen is excreted through the kidneys – so only horses with liver or kidney problems may experience issues from too much protein. Urination is also increased, which can lead to dehydration if not enough water is provided, and can also create increased ammonia fumes in stabled situations, which can cause respiratory irritation. So while excess protein isn't usually damaging to the horse, it’s not necessary and may put extra strain on the body.

​Find more articles here, and check out the Facebook page for more interesting, informative links and articles from Integral Equine Nutrition.

Need more help?