Feeding Young Horses

Q – I have a young horse I’m looking to start into work. What should I be feeding him?

A – By the time you’re starting to get your youngster into work, the majority of his growth should be behind him. That said, he is likely still growing and, therefore, his nutrient requirements are going to reflect those needed for both growth and exercise. The National Research Council’s Nutrient Requirements of Horses (2007) recommends that horses 24 months of age be fed to reflect both of these needs. Once a horse reaches three years of age, while he may still be growing, these nutrient needs are not outlined specifically. The NRC uses daily rate of gain in its equations for calculating the nutrient requirements of growing horses, and by three years of age and older, the rate of gain is so small (about 0.2 kg/day decreasing to 0.01kg/day until maturity), the requirements are often very comparable to a mature (non-growing) horse.

In general, all classes of nutrients will be increased for a horse at work to reflect increased needs for energy (expressed as Mcal/day – or “megacalories” per day; where1 kcal = 1 calorie and 1000 kcal = 1 Mcal), protein and some minerals (most notably calcium and phosphorus, and the electrolytes sodium, potassium and chloride). A growing horse will have additional needs to support the development of the skeleton and body tissue to increase his overall size and weight. As mentioned, the NRC uses the horse’s average daily gain to reflect these increases in needs, because how fast a horse is growing will reflect his nutrient requirements.

The needs of a growing horse are different from a mature horse, especially with respect to protein, calcium and phosphorus. Protein needs are increased to support the development of body tissue. The amino acid (one of the building blocks of protein) that is particularly important for growing horses is lysine. This amino acid is found, in limited amounts, in most horse feeds (such as hay and cereal grains) and, therefore, feeds such as soybean meal (which is an excellent source of both protein and lysine) should be included in diets formulated for growing horses. Calcium and phosphorus needs increase to support bone remodeling that occurs with exercise. These nutrients are important to help the growing horse’s skeleton develop, as are other minerals such as zinc and copper. Thus, if you compare a 24-month-old growing horse (even with a relatively slow rate of gain) to a mature horse in Table 1 (no work), you will note that even for a smaller body weight (24 months), a growing horse has higher energy, protein, lysine, calcium and phosphorus requirements.

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When a growing horse is put into work, the largest increase in nutrient requirements is going to be dietary energy, as fuel will be needed for the muscles to work. There will be additional small increases in protein requirements as well (to support the growth and development of added muscle), but these needs are easily met with increased feed intake (which is needed to meet the increased calorie requirements). Also, because any horse that works is going to sweat, electrolytes will need to be replaced (potassium, sodium and chloride). As reflected in Table 1, there are not increases in calcium and phosphorus fora 24-month-old horse, comparing no work with work (despite significant bone remodeling that occurs with exercise). This is because the calcium and phosphorus requirements for a growing horse are already quite high, and would accommodate any increased need resulting from exercise.

To meet these needs, owners should look for high-quality forage sources, such as hays that include some alfalfa or other legume. Forage should be fed at a rate of 1 – 2% of body weight, depending on the forage quality. This will provide ample energy, protein and calcium for the horse. Next, horse owners should look for a commercially available concentrate (grain mix) that is formulated for growing horses (to ensure it has the added soybean meal for lysine, and copper and zinc). Typical growing horse rations will have approximately 14-16% crude protein, about 0.8% calcium and 0.5% phosphorus and between 50-80 ppm copper and 100-200 ppm zinc. This concentrate should be fed in amounts recommended by the manufacturer, depending on the rest of the diet (hay quality and any other supplements that may be fed). The horse owner should keep a close eye on the horse’s body condition score (the 1-9 Henneke scale that assesses body fatcoverage) to ensure the horse is maintaining a good condition. Young horses do tend to be fairly lean (in the 4-5 range). I don’t like to see higher body conditions in young horses, as that puts extra strain on the growing bones and joints, and may predispose them to metabolic or developmental problems. (See the November/December issue for more on Equine Metabolic Syndrome and other obesity related conditions).

As with any exercise training program, young horses need to be introduced to work slowly to ensure their muscles, bones, joints, ligaments and tendons are strong enough to handle the increasing workload. As such, increases in nutrient needs will also increase slowly, and horse owners should work closely with a nutritionist and/or their veterinarian who has a strong background in nutrition, to ensure they are meeting their horse’s needs sufficiently.