Horse nutrition update: FEED INTERNATIONAL, AUGUST 1996

Balancing

protein and energy

with stage of development and level of activity

by Domenick Castaldo, PhD

Researchers fairly well have discovered the nutrient requirements for horses in several stages of development and activity (NRC, 1989). In general, adult horses can utilise higher concentrations of forage than growing horses. However, protein requirements range from 9.6 in stallions to 14.5% for weanlings.

Also, young horses require a higher calcium-to-phosphorus ratio than older equines. Pregnant and lactating mares require higher concentrations of vitamins A and D and working horses require more thiamine. Thiamine is an essential co-factor in the biological conversion of carbohydrate to metabolic energy (see Table, Nutritional Requirements).

Better approach to protein and energy

According to Ott (1999), who compared the new report with previous National Research Council (USA) reports, between 1961 and 1989, the published crude protein requirements have been increasing steadily for mares in late gestation and early lactation. The digestible energy recommendation for mares in late gestation has increased while the digestible energy recommendations for early lactation has fallen. For growing horses, the NRS has been raising its protein and energy recommendations.

Research has expanded the NRC definitions. A proper evaluation of a horse feed begins with a determination of the horse's metabolic energy needs (Pagan, 1995). The energy requirements can be calculated from various equations that are based on a horse's body weight and class - for example, weanling or moderately working animals. Once the energy requirement is known, the other nutrients can be determined based on a specified forage-to-concentrate ratio.

Although the horse is a hindgut fermenter, microbes contribute little to the amino acid requirements of the horse (Hintz and Cymbaluk, 1994). Lysine is the first-limiting amino acid in most horse feeds. The addition of .1% threonine to a feed containing .2% lysine may improve muscle growth (Hintz and Cymbaluk, 1994). Researchers also have suggested that .5% taurine in grain-based pregnant and lactating mare feed may improve foal performance. However, other horse nutritionists caution not to overfeed protein. Feeding excess protein is not only expensive in terms of feed costs, it can result in depressed growth. Overfeeding of young horses can cause them to founder, develop colic, or become fat which can result in developmental orthopedic disease (DOD).

Working horses and those engaged in competition require high amounts of energy. Fat is the most de