True or false: Weanlings, which are growing like weeds as they begin their transition from foal to adult horse, need high-carbohydrate grain-based concentrates and restricted protein to avoid developmental orthopedic disease (DOD) and support speedy growth rates.

False! In fact, high carbohydrate diets in young, growing horses could contribute to DOD, whereas protein does not. Young horses expected to mature at 500 to 600 kilograms (1,000-1,200 pounds) gain up to 1.0 kilogram (2.2 pounds) per day in the first year of life, which makes careful nutritional balance critical for healthy growth.

Sarah Ralston, VMD, PhD, Dipl. ACVN, of the Department of Animal Sciences at Rutgers, the State University of New Jersey, in New Brunswick, separated fact from fiction pertaining to growing weanlings’ dietary needs in her presentation at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.

Weanlings require sufficient protein, energy, and balanced minerals to support proper skeletal and soft tissue development as they grow. The faster the growth rate, the more critical nutritional balance becomes. In the past, excess protein was thought to cause DOD, but it turns out that high protein does not actually cause of abnormal growth. Rations with high levels of carbohydrates and improperly balanced minerals are the more likely culprit, said Ralston.

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In fact, researchers revealed in repeated studies that low-carbohydrate, forage-based rations containing little to no carbohydrate-rich grains were more efficient for rapidly growing weanlings than traditional high-grain rations, when both were balanced for mineral content. So Ralston conducted a study from 2004 to 2008 in which she compared rapidly growing draft-crossbred weanlings with free access to forage-based, total mixed ration (TMR) cubes to those consuming a traditional 50/50 forage/grain concentrate ration in recommended amounts

Across all years, protein content ranged from 11% to 18% and was consistently slightly higher in the TMR rations. The high-grain rations’ nonstructural carbohydrate content (NSC, starch and sugar) was from15.5 to 20%, whereas the TMR rations’ was less than 16%, dipping as low as 6.5% in the last year. Other nutrient concentrations were similar between the two rations. The TMR weanlings had higher average daily gains across all five years compared to the high-grain-fed weanlings, which gained weight at the predicted rate. There were no differences in the incidence of DOD between the groups in any of the years, and the researchers observed only very mild DOD in both groups.

Take-Home Message

A low-carbohydrate, forage-based TMR ration fed free choice to weanling draft-cross horses supported rapid growth rates at or above National Research Council predictions without harmful DOD. All-forage rations that are properly balanced for protein and mineral content are a viable option for growing weanlings, said Ralston.