Effects of level of dietary protein and exercise on growth rates of horses.

Rates of growth were measured in two-year-old (Experiment 1) and nine-month-old (Experiment 2) horses fed high (12 or 14 per cent) or low (6 or 8 per cent) crude protein diets with one of two levels of exercise (0 or 12 km trotting per day at 12 km/h). In the non-exercised horses feed intakes and growth rates were greater on the high than on the low protein diets. Exercise increased feed intakes and growth rates of horses on the low but not the high protein diets, so that in the exercised groups there were no significant differences in feed intakes or growth rates between the horses on the two dietary protein levels. Exercise increased the apparent digestibility of dry matter, energy and crude protein. There were no differences in skeletal characteristics caused by either dietary protein level or exercise. These results suggest that the growing horse, if exercised regularly, may be given a diet of lower protein concentration than currently recommended without significant reduction in growth rate.