I own a 10-year-old Quarter Horse gelding currently in occasional work with the thought of ramping up to moderate work in the coming weeks. He weighs about 1,200 lb (545 kg) and is in fleshy body condition (a score of 7). I feed him 1 lb (0.45) of soybean meal, 2 oz of a commercial mineral supplement, and 700 IU of vitamin E. He has free-choice grass hay that contains some timothy and a salt block. He has all-day, year-round access to pasture, and it is plentiful during the growing season. Am I feeding him enough protein? Are his calcium and phosphorus intakes sufficient? He is overweight, especially fleshy over the ribs and tailhead, but he has a hay belly. He is not muscular or filled out over the topline. Is this just due to lack of exercise or is this a dietary deficiency?
Because your hay has not been tested, I used average values to represent the grass hay being fed. The estimated current diet is meeting all of the required nutrient levels and providing calcium and phosphorus (Ca:P) at an appropriate 2:1 ratio. Even though soybean meal tends to have more phosphorus than calcium, this is counteracted by (1) feeding a forage-based diet with the correct Ca:P ratio of at least 1:1; (2) offering a mineral supplement that contains added calcium; and (3) feeding only a small amount of soybean meal (1 lb or 0.45 kg).
Many factors are involved in the calculation of protein requirements, including digestibility of protein, amino acid content of protein, the protein to energy ratio of the diet, and age and life stage of the horse. The National Research Council (NRC) in Nutrient Requirements of Horses (2007) and optimized recommendations provided by Kentucky Equine Research (KER) have factored into their calculations the differences in protein digestibility of feedstuffs, such as forages, cereal grains, and protein supplements.
Mature horses, both idle and working, have relatively low protein requirements compared to other life stages. The NRC provides the following equation for calculating crude protein (CP) requirements for a mature, idle horse: body weight (BW) x 1.26 g CP/kg BW/d. For your gelding, this would be approximately 545 kg BW x 1.26 = 687 g.
The estimated diet of 18 lb (8.2 kg) free-choice grass hay, 1 lb (0.45 kg) soybean meal, and 2 oz mineral supplement is providing about two-thirds more protein than his dietary needs. The grass hay alone meets the protein requirement of a mature horse based on a value of 9.5% protein and 0.77 Mcal/lb of digestible energy.
Excessive protein levels may increase water requirements, urea production, and ammonia production. Stall sanitation may become an issue for horses that excrete excessive urine.
Hay quality can have a huge impact on the nutrient value of forage. As hay matures and becomes more stemmy, the quality of nutrition decreases. This can be a concern for horses maintained on this type of forage program year-round, if not supplemented accordingly. The quality of the protein source is a key factor in meeting the horse’s amino acid requirements; high-quality protein sources are those that contain an assortment of amino acids which approximate the needs of the horse. Soybean meal is considered the gold standard.
Commercial ration balancers have been developed to provide horses with relatively low energy demands a source of concentrated nutrition to prevent marginal dietary deficiencies when maintained on pasture or hay-only diets. Ration balancers provide good-quality protein, macrominerals, trace minerals, and vitamins at the appropriate levels to complement forages of unknown quality when fed at 1-2 lb (0.45-0.9 kg) per day.
Based on your current program, I’d recommend switching to a balancer pellet that has been formulated to provide proper nutrition when fed in combination with pasture or hay. Follow the feeding recommendations provided by the manufacturer.
The addition of regular exercise will help your gelding return to moderate body condition, which will be better for long-term health. Exercise is thought to delay onset of metabolic disease, a problem that affects many chronically overweight horses.
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