Influence of magnesium, water, and sodium chloride on urolithiasis in veal calves

Forty veal calves were fed milk replacers containing differing concentrations of Mg in a 16-w study. The concentrations were .1% (basal), .3%, .6% Mg, and .6% Mg plus 2% NaCl. The four groups were further subdivided into two groups fed reconstituted milk replacer at 14 or 17.9% DM. Weight gain was greater at the two lower concentrations of Mg. Calves fed .6% Mg or .6% Mg plus NaCl excreted significantly more Mg than calves fed .1 or .3% magnesium. The low water group (17.9% DM) excreted a more concentrated urine relative to Mg, Ca, and P than did the high water group (14% DM). No urethral obstructions were observed. Seventy percent of calves at .6% Mg and 30% of calves at .6% Mg plus NaCl had stones in their kidneys consisting primarily of calcium apatite and secondarily of struvite. Added NaCl reduced kidney and bladder calculi formation. When high amounts of water were fed, added NaCl prevented calculi formation completely. All calves fed the NRC level of .1% Mg performed normally.