Inflammatory response, growth, and thyroid hormone concentrations are affected by long-term boron supplementation in gilts

An experiment was conducted to determine the long-term effects of dietary b oron (B) on growth performance, immune function, and plasma and serum chara cteristics in gilts. Fifty weanling gilts were allotted to 10 pens based on weaning weight and litter origin. Pens were randomly assigned to receive o ne of two dietary treatments. Treatments consisted of a bas al diet low in B (control) and the basal diet supplemented with 5 mg B/kg diet as sodium b erate. Gilts remained on their respective experimental diets and with their penmates throughout the nursery, growing, and finishing phases. The B conc entration of the basal. diet was 0.98, 2.1, and 2.2 mg/kg diet during the n ursery, growing, and finishing phases, respectively. At the end of each pro duction phase, animals were weighed and feed consumption was determined to assess growth performance variables. In addition, blood samples were obtain ed from three randomly selected gilts per pen at the completion of each pha se. Boron had no affect (P > 0.58) on growth performance during the nursery phase, but gilts receiving supplemental B had increased (P < 0.05) ADG at the end of the finishing phase and over the entire growing-finishing period . Serum concentrations of triiodothyronine (T-3) tended (P < 0.07) to be re duced by dietary B at the end of the nursery phase, but serum thyroxine (T- 4) was not affected (P = 0.46) by B. At the completion of the growing phase , supplemental B decreased (P < 0.05) the concentrations of T-3 and T-4 in the serum. In addition, serum concentrations of total cholesterol and the a ctivity of alkaline phosphatase were increased (P < 0.05) by dietary B at t he end of the growing phase. Serum concentrations of urea N tended (P < 0.0 9) to be increased by B at the end of the growing phase. Beginning at d 95 of the experimental period, measures of immune function were assessed in ra ndomly selected gilts. Boron decreased (P < 0.05) the inflammatory response to an intradermal injection of phytohemagglutinin. Boron did not affect (P > 0.30) the blastogenic response of isolated lymphocytes to mitogen stimul ation or the humoral immune response against a sheep red blood cell suspens ion. Results indicate that B may affect serum thyroid hormone concentration s, the inflammatory response, and growth in pigs.