Oxalate urinary calculi in beef steers.

Hereford X Angus steers (10/treatment) were fed 90% concentrate diets containing 0.3%, 0.6%, 0.9%, or 1.2% of calcium for 92 days (trial 1) or 114 days (trial 2). Ground limestone was the supplemental calcium source. At slaughter, 12 of 20 steers fed 0.3% calcium had calculi in the urinary bladder or kidneys, compared with 5 of 20 fed 0.6% calcium, 5 of 20 fed 0.9% calcium, and 4 of 20 fed 1.2% calcium. Analyses of calculi indicated they were oxalate calculi. During the first 49 days of trial 2, plasma hydroxyproline concentrations were higher (P less than 0.10) for steers fed 0.3% calcium than for steers fed higher calcium concentrations. Increased bone resorption in steers fed concentrations of 0.3% calcium, resulting in increased plasma hydroxyproline, an oxalate precursor, was indicated as a source of oxalate in calculi and as an explanation of lower occurrence of calculi in steers fed higher concentrations of calcium.