Dietary carbohydrates and fat influence radiographic bone mineral content of growing foals

Hydrolyzable carbohydrate intake in horse diets mag become excessive when r apidly growing pastures are supplemented with grain-based concentrates. The substitution of fat and fiber for hydrolyzable carbohydrate in concentrate s has been explored in exercising horses but not in young, growing horses. Our objective was to compare bone development in foals that were fed pastur e and concentrates rich in sugar and starch (corn, molasses) or fat and fib er (corn oil, beet pulp, soybean hulls, oat straw). Forty foals were examin ed, 20 each in 1994 and 1995. In each year, 10 mares and their foals were f ed a corn and molasses supplement (SS) and 10 others were fed a corn oil an d fiber supplement (FF). The concentrates were formulated to be isocaloric and isonitrogenous, and mineral content was balanced to complement the past ures and meet or exceed NRC requirements. Dorsopalmar radiographs were take n of the left third metacarpal monthly from birth to weaning and then every other month until 1 yr of age. Bone density was estimated using imaging so ftware and an aluminum stepwedge. Radiographic examination indicated differ ences in medial, lateral, and central bone mineral content of the metacarpa l III. Bone mineral content increased with age, and a plateau was observed during winter. Bone mineral content was lower in weanlings and yearlings fe d the FF supplement than in those fed SS. Subjective clinical leg evaluatio ns indicated differences in physitis, joint effusion, and angular and flexu ral limb deformities in response to age, and possibly to season. Regression analysis indicated positive relationships between bone mineral content and body weight, age, and body measurements. Nutrient and chemical interaction s, such as the binding of calcium by fat and fiber, may alter the availabil ity of elements necessary for bone development.