By Llinos Owen MSc, BSc (Hons), FDSc, Dodson & Horrell Nutritional Advisor.
Protein is a vital nutrient necessary for the growth and repair of cells and body tissues. Protein is made up of chains of amino acids, hence why they are often called the building blocks of protein. When protein is ingested, the chain of amino acids is broken down in the stomach and small intestines into individual amino acids. These individual amino acids are then absorbed into the bloodstream and travel to sites where they are needed for normal function, growth, and repair of tissues such as muscles, hair and hoof. There are 22 different amino acids required for protein synthesis in the body; the horse can synthesise 12 of these and are called “non-essential amino acids”. However there are 10 amino acids that the horse cannot synthesise in the body, these are called “essential amino acids” and must be provided in the diet.
Lysine is the main essential amino acid that is deficient in a forage-based diet, followed by Threonine and Methionine. These are known as “limiting” amino acids because if they are not received in adequate amounts in the diet, protein synthesis will be limited which can have a negative impact on the growth and repair of tissues.
Providing good quality protein will provide these essential amino acids which will support protein synthesis. The daily protein requirement for a mature adult horse of 500kg weight 630g per day at a maintenance level, this increases linearly with workload. Typical light work feeds that contain 10% crude protein or less will be adequate for those in light work up progressing up to medium work. For horses in medium work upwards a 12% feed is more suitable.
Typical crude protein values found in hay is 4-12% and 9-15% in haylage, values will vary according to stage of plant growth and level of fertiliser used. Having your forage analysed will give you a more accurate understanding of your horse’s daily protein intake and help you identify the most appropriate feed.
Even the best quality hay is often deficient in one or more of the three limiting essential amino acids discussed above and so these must be included in the horse’s diet via feed, balancers or supplements. Legumes such as alfalfa, soya, peas, beans and linseed are high-quality protein sources often incorporated in fortified horse feeds providing these essential amino acids.