Boron content of plasma and urine as indicators of boron intake in cattle.

Yearling beef heifers were offered drinking water (0.8 mg of B/L of water) to which 0, 15, 30, 60, or 120 mg of B/L of water was added for 10-day periods. Feed and water consumption were unaffected by treatments. There were no overt signs of toxicosis. Increased B ingestion increased plasma and urine B concentrations. The percentage of renally filtered B that was excreted was increased with the 30, 60, and 120 mg of B/L of water treatments, and B clearance exceeded endogenous creatinine clearance with these treatments. Ingesting increased amounts of B was associated with decreased plasma PO4(-3) concentration and increased renal clearance and urinary excretion of PO4(-3). The B status of cattle can be predicted from plasma or urine B concentrations. Results indicated that prediction can be made from the B/creatinine ratio of urine. With an induced urine sample, the equation for predicting B ingestion is Y = -67.79 + 976.74X - 141.91X2 (r = 0.96; Syx = 121.57) where Y is B in milligrams per 100 kg of body weight per day, and X is the ratio of urine B (mg/L of urine) to creatinine (mg/L of urine).