Methionine hydroxy analog (free acid) reduces avian kidney damage and urolithiasis induced by excess dietary calcium.
Urinary acidification previously was shown to be an effective treatment for calcium-induced urolithiasis in domestic fowl, but diuresis caused by the acidifying agent (ammonium chloride) was an undesirable side effect. Because supplemental dietary methionine reportedly acidifies mammalian urine, an experiment was conducted to evaluate the efficacy of the free acid form of methionine hydroxy analog (MHA) as an acidifying agent for treating avian urolithiasis. From 5 to 17 wk of age, immature Single Comb White Leghorns were fed diets containing normal calcium (1%) or high calcium (3.5%). Diets were supplemented with 0, 0.3 or 0.6% MHA. Relative to birds fed the normal calcium diets, birds fed the high calcium diet without added MHA were in a state of metabolic alkalosis and excreted more alkaline urine containing high levels of calcium. Birds fed the high calcium diet without MHA also had significantly higher kidney asymmetry ratios, a higher incidence of gross kidney damage, and a higher incidence of urolith formation when compared with birds fed normal calcium diets. When compared with the high calcium diet without MHA, the high calcium diet supplemented with 0.6% MHA significantly acidified the urine without causing detectable metabolic acidosis, significantly reduced kidney asymmetry and gross kidney damage, and reduced the incidence of urolith formation without increasing water consumption or urine flow. These data demonstrate that MHA effectively prevents calcium-induced kidney damage in domestic fowl without causing undesirable side effects. MHA did increase both fractional and absolute calcium excretion during calcium loading.