Effect of Dietary Boron on Immune Function and Disease Resistance to Bovine Herpesvirus Type-1 in Growing Steers

Abstract

Two experiments were conducted to examine the effects of dietary boron (B) on immune response and physiological responses to a viral disease challenge in growing steers. In experiment 1, 36 Angus and Angus x Simmental cross steers with an initial average body weight (BW) of 284 kg were fed one of three dietary treatments: 1) control (no supplemental B), 2) 5 mg supplemental B⁄kg DM, and 3) 15 mg supplemental B⁄kg DM from Na2B4O7 for 47 d. The control diet analyzed 13.3 mg B⁄kg DM. On d 34 of the study steers were inoculated intranasally with bovine herpevirus type-1 (BHV-1). Supplementation of dietary B increased (P < 0.01) plasma B concentration in a dose responsive manner. The change in DMI from d 0 (pre-inoculation) differed (P < 0.05) on d 1 and 2 among the control steers and those supplemented with 15 mg B⁄kg DM, due to an increase in DMI in control steers. The rectal temperature change from pre-inoculation values for steers supplemented with 15 mg B⁄kg DM tended (P < 0.10) to be less on d 6 and was less (P < 0.01) on d 7 and 8 post challenge than steers supplemented with 5 mg B⁄kg DM. On d 8 steers consuming the control diet had a greater decrease (P < 0.05) in rectal temperature change relative to d 0 when compared to steers supplemented with 5 mg B⁄kg DM. Inoculation of BHV-1 increased (P < 0.01) plasma concentrations of acute phase proteins by d 4 post challenge relative to d 0 values. Inoculation of BHV-1 decreased (P < 0.01) plasma IFN-γ concentrations on d 4, and increased (P < 0.01) plasma concentrations of TNF-α on d 2 post inoculation and d 4 TNF-α concentrations were lower(P < 0.01) than d 0 concentrations. ii

In experiment 2, 36 Angus and Angus x Simmental cross steers with an initial average body weight (BW) of 269 kg were used to determine the effect of dietary B on immune response. Steers were fed one of three dietary treatments: 1) control (no supplemental B), 2) 5 mg supplemental B⁄kg DM, and 3) 50 mg supplemental B⁄kg DM from sodium borate (Na2B4O7 · 5H2O) for 78 d. The control diet analyzed 10.2 mg B⁄kg DM. Supplementation of dietary B increased (P < 0.01) plasma B concentration in a dose responsive manner. Also, supplemental B tended (P = 0.12) to increase the blastogenic response of B-lymphocytes to pokeweed mitogen, but did not affect proliferation of T-lymphocytes when stimulated with concanavalin A or phytohaemagglutinin (PHA). Furthermore, specific anti-PRBC IgG titers tended to be affected by a treatment x day interaction (P = 0.07). Boron supplemented steers had greater (P < 0.05) IgG titers than controls on d 7 but not on d 14 or 21 post-injection. Specific anti-PRBC IgM titers were not affected by dietary B. Dietary B did not affect skinfold thickness following PHA injection. Boron supplemented steers tended (P = 0.12) to have greater ADFI than control steers. Average daily gain and G:F was not affected during the study.

Supplementation of dietary B had minimal effects on immune responses and disease resistance in growing steers. Lack of a significant effect of B was likely due to the B content in the basal diet. The basal diets containing 13.3 and 10.2 mg B⁄kg DM seemed to provide optimal physiological responses.