Obstructive urolithiasis means the formation of calculi in the urinary tract with subsequent urinary blockage by uroliths (Emerick 1988, Payne 1989, Radostits et al. 2000). It appears to affect equally both sexes, but urinary blockage is an important problem only in males. Steers are most commonly affected by the obstructive form of the disease because of the anatomical conformation of their urinary tract (Emerick 1988, Larson 1996, Radostits et al. 2000). Urinary calculi formation usually results from a combination of physiologic, nutritional and management factors. It is mainly attributed to excessive or imbalanced intake of minerals (McIntosh 1978, Larson 1996, Radostits et al. 2000). These circumstances occur especially in feedlots with fattening cattle receiving rations high in cereal grains and oil meals. These feedstuffs contain phosphorus and magnesium in excess, but relatively low levels of calcium and potassium, predisposing to occurrence of the disease (Payne 1989, Radostits et al. 2000). A calcium-phosphorus imbalance results in high urinary phosphate excretion which is an important factor in the genesis of phosphate calculi (Radostits et al. 2000). Numerous additional factors have been incriminated as contributing causes for the development of phosphate calculi with resultant obstructive urolithiasis in cattle. These include heavy concentrate-low roughage diets, limited water intake, deprivation of water or dehydration, urine alkalinity, mineralized artesian water, alkaline water supplies, excess of sodium bicarbonate in the diet, vitamin imbalances e. g. hipovitaminosis A and hypervitaminosis D, and high-protein rations (Emerick 1988, Larson 1996, Radostits et al. 2000). Less frequent types of uroliths include those composed of silica, carbonates or oxalates (Larson 1996). Livestock grazing in areas in which pasture plants contain large quantities of oxalate, estrogens or silica are prone to develop these types of calculi (Radostits et al. 2000). Urolithiasis in castrated beef cattle associated with diethylstilbestrol implants was reported in only one single occasion (Clotilde et al. 1980).
The formation of urinary calculi results when inorganic or organic urinary solutes are precipitated out of solution as crystals or amorphous deposits (Radostits et al. 2000). The mucoprotein which may act as a cementing agent favoring the formation of calculi may be increased in the urine of feeder steers fed heavy concentrate-low roughage rations or pelleted rations (Radostits et al. 2000). Deficiencies in several macromolecules that inhibit crystallization of matrix in urine have also been suggested as a contributory factor to calculogenesis (Griffin 1998, Atmani & Khan 1999). Uroliths have been linked to nanobacterial infection but dietary factors influence their progression (Ciftcioglu et al. 1999).
Fatality rate of urolithiasis in male cattle due to rupture of the urethra or urinary bladder and the economic impact of this condition has been extensively reported in field and slaughterhouse studies developed in many countries (Gasthuys et al. 1993, Radostits et al. 2000). Occurrence of calculi has been associated with lower weight gain and lighter carcasses (Huntington & Emerick 1984). Similar information is not available for brazilian feedlot cattle herds. Obstructive urolithiasis has been infrequently reported in beef cattle in south-eastern and central Brazil (Lemos & Silveira 2002). Relevant data concerning composition of basal diet, mineral constitution of urinary calculi and influence of the disease on weight gain and carcass characteristics at slaughter are not available (Clotide et al. 1980, Vianna et al. 1984, Salvador et al. 1999, Lemos & Silveira 2002). Effective prevention measures of this metabolic disorder in these areas rely on knowledge of the major causative factors of the disorder and the circumstances in which they occur.
The present report describes additional cases of obstructive urolithiasis that occurred as a single outbreak in a beef feedlot in southern Brazil and highlights the importance of appropriate nutrition for the prevention of urolithiasis in feedlots.