ecomes about the same in cows, heifers, bulls,

ecomes an important clinical disease of castrated male ruminants when calculi cause urinary tract obstruction, usually obstruction of the urethra. Urethral obstruction is characterized, clinically by complete retention of urine, frequent unsuccessful attempts to urinate and distension of the bladder. Urethral perforation and rupture of the bladder can be sequelae. Mortality is high in cases of urethral obstruction and treatment is surgical. As a result, prevention is important to limit losses from urolithiasis. ETIOLOGY Urinary calculi, or uroliths, form when inorganic and organic urinary solutes are precipitated out of solution. The precipitates occur as crystals or as amorphous , deposits’. Calculi form over a long period by a gradual accumulation of precipitate around a nidus. An organic matrix is an integral part of most types of calculus. Several factors affect the rate of urolith formation, including conditions that affect the concentration of specific solutes in urine, the ease with which solutes are precipitated out of solution, the provision of a nidus and the tendency to concretion of precipitates. These are presented under Epidemiology. Factors that contribute to the clinical syndrome of obstructive urolithiasis are dealt with separately. EPIDEMIOLOGY Species affected Urolithiasis occurs in all ruminant species but is of greatest economic importance in feeder steers and wethers (castrated lambs) being fed heavy concentrate rations, and animals on range pasture in particular problem areas. These range areas are associated with the presence of pasture plants containing large quantities of oxalate, estrogens, or silica. When cattle graze pasture containing plants with high levels of silica, uroliths occur in animals of all ages and sexes.1 The prevalence of uroliths is about the same in cows, heifers, bulls, and steers grazing on the same pasture and they may even occur in newbom calves. Females and bulls usually pass the calculi and obstructive urolithiasis is primarily a problem in castrated male animals. Obstructive urolithiasis is the most common urinary tract disease in breeding rams and goats.2 There are three main groups of factors that contribute to urolithiasis: o Those that favor the development of a nidus about which precipitation and concretion can occur o Those that facilitate precipitation of solutes on to the nidus