Comparison of Neutral Fat and Free Fatty Acids in High Lipid-Low Carbohydrate Diets for the Growing Chicken

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Abstract
Three experiments were conducted with day-old chicks a) to determine if they require an exogenous source of carbohydrate when fed diets high in lipids, and b) to study the comparative nutritional properties of soybean oil (SO) and soybean oil fatty acids (SOFA). Semipurified diets based on isolated soybean protein were used. The reference high carbohydrate diet supplied in percentage of metabolizable calories: glucose, 45; protein, 32; and SO, 23. For the high lipid diets, both glucose and SO were equicalorically replaced with the lipid under study; supplemental carbohydrate added to these diets replaced an equicaloric amount of lipid. Diets supplying the non-protein calories as SO permitted growth nearly equal to the high carbohydrate controls; addition of 3% glycerol or up to 6% glucose calories did not improve it. In contrast, chicks fed the high SOFA diet grew slowly and developed foot dermatitis and beak deformities. This syndrome was not prevented by feeding the fatty acids as the methyl or ethyl esters. The supplementation of these diets with 6% glucose markedly improved growth but did not prevent the development of the foot and beak abnormalities. The high So diet induced moderate ketonemia; the high SOFA diet induced hypoglycemia and severe ketonemia, which were prevented completely by the supplementation with 6% glucose. β-Hydroxybutyric acid is the major ketone substance in the ketonemic chick. Apparent lipid absorbability was of the order of 90% for all diets except those containing the ethyl esters of SOFA in which absorbability was approximately 80%.