Effects of dietary boron on mineral balance in sheep

Eighteen Hampshire crossbred wethers (45kg) were used in a completely randomized experiment (20-day adjustment to basal, 11-day treatment and collection) to test the effects of supplemental boron (B) on fecal and urinary excretion, % digestion (apparent absorption), and % retention of Ca, Mg, K, and P. Supplemental B intakes of 75 (Trt 2) and 200 (Trt 3) mg/d were achieved by adding sodium borate to the corn silage-soybean meal basal ration, Trt 1 (B intake of 30 mg/d). When regressed against day, Ca digestion and retention tended to follow quadratic patterns for all treatments, decreasing until days 5 and 6 for supplemented and control groups, respectively, then increasing through the end of the trial. Significant fit to the quardatic response was observed for Ca digestion (P less than .05) in Trts 1 and 3, urinary excretion (P less than .06) in Trts 2 and 3, and retention (P less than .02) in Trts 1 and 3. Calcium digestion (apparent absorption) and retention, although negative, tended to be higher for Trts 2 and 3 on days 8 and 9, and was significantly higher (P less than .10) on days 10 and 11. Over the entire trial, Ca digestion was increased (P less than .10) by B at each level, and Ca retention was greater (P less than .10) for Trts 2 and 3. There were no significant effects of B on Mg urinary excretion or digestion, but Trts 3 increased (P less than .10) Mg retention over the entire trial. No significant pattern of Mg excretion over time was observed. No significant effects of B on K or P excretion were observed. Mean % B retention over treatments decreased each day, from 60.1 on day 1 to 32.1 on day 11. Absolute B retention (mg) was greater at higher levels of B intake. Although some effects of B on macro-mineral excretion were observed, these data indicate that the effects of B may be more pronounced in studies of longer duration.