Abstract: [Objective] The effect of high diatery magnesium on urolithiasis in feedlot wethers compared with high potassium and phosphate under the chinese traditional feeding style with cotton seed meal and rice straw diet. [Method] Eighteen wethers aged from 3-4 months were randomly allotted to three groups, as group A, B, C feeding for three months with cotton seed meal and rice straw diet comprised of P 0.40％ ,K 1.24％, Mg 0.32% respectively. From the third month, KH2PO4 and K2HPO4 was provided to goats in group B by drinking water and so did MgO to goats in group C,. goats in group A still drink tap water, which means dietary P, K in group B was added up to 1.74% and 0.75%, and dietary Mg in group C to 0.56%. Blood and urine samples were collected to analyze the concentration of P, K, Mg, Ca ion, and the activity product of potassium magnesium phosphate was calculated to evaluate the supersaturation of urine before and after urolith formation. The composition of urinary sediments and stones was studied by chemical qualitative analysis，X-ray diffraction, X-ray energy dispersive spectrometry (EDS) and fourier transform infrared (FTIR) spectroscopy. [Result] The urolithiasis was found on day 5-8 in all 6 goats of group C after drinking water contains MgO, one urolithiasis case was found in group B and C on day 25,28 of the third month respectively. Synthetical analysis showed that the chemical composition of urinary stones and urinary sedimental crystals was potassium magnesiumphosphate and magnesium ammonium phosphate. P, K, Mg ion concentrations of urine decreased significantly, so did activity product of potassium magnesium phosphate. [Conclusion] High dietary levels of magnesium is a more important factor of urolithiasis in wethers compared with feeding with high P, K diets containing, and the effect of magnesium induced urolithiasis might be associated with the change of inhibitory activity of some inhibitor in urine.

Key words: urolithiasis, cotton seed meal, magnesium, phosphorus, potassium, goat