DIETARY BORON MODIFIES THE EFFECTS OF VITAMIN-D-3 NUTRITION ON INDEXES OF ENERGY SUBSTRATE UTILIZATION AND MINERAL METABOLISM IN THE CHICK

An experiment was designed to test part of the hypothesis that physiol ogic amounts of dietary boron enhence utilization of or, alternatively , compensate for, inadequate concentrations of active vitamin D metabo lites to normalize energy substrate utilization and mineral metabolism . Day-old cockerel chicks were fed a ground corn, high-protein casein, corn oil-based diet (less than or equal to 0.18 mg B/kg) supplemented with physiologic amounts of boron (as orthoboric acid) at 0 (non-PSB) or 1.4 (PSB) mg/kg and vitamin D-3 (as vitamin D-3 powder in corn end osperm carrier) at 3.13 (inadequate, IVD) or 15.6 (adequate, AVD) mu g /kg. After 26 days, IVD decreased food consumption and plasma calcium concentrations and increased plasma concentrations of glucose, beta-hy droxybutyrate, triglycerides, triiodothyronine, cholesterol, and alkal ine phosphatase activity. In the IVD chicks, PSB returned plasma gluco se and triglycerides to concentrations exhibited by the AVD chicks and increased food consumption in both IVD and AVD chicks. Histologic fin dings suggested that PSB enhanced maturation of the growth plate. A ni nefold increase in dietary boron yielded only a twofold increase in pl asma boron concentration and no increase in femur boron concentration, which suggests that boron is under homeostatic control. The findings suggest that boron acts on at least three separate metabolic sites bec ause it compensates for perturbations in energy substrate utilization induced by vitamin D-3 deficiency, enhances major mineral content in b one, and, independently of vitamin D-3, enhances some indices of growt h cartilage maturation.