colloids will precipitate [7]. Uroliths that precipitate in alkaline urine include struvite, calcium phosphate, and calcium carbonate [4]. Urine pH has no effect on the calculogenesis of silica uroliths [3, 4].
Inadequate body water balance is a significant risk factor in the occurrence of urolithiasis. Dehydration results in increased solute concentration in the urine, providing more scaffold and calculogenesis opportunities. Seasonality can occur, with an increase of cases seen when decreased water consumption occurs. During the summer, palatable water sources and drought can result in decreased water intake. During times of extreme cold, voluntary decreased intake may occur. Herd outbreaks of urolithiasis can even occur if available palatable water sources are extreme.
The narrow, long, and tortuous male ruminant urethral anatomy contributes to the occurrence of urinary obstruction in cattle. The most common site for urethral obstruction in bulls and steers is the distal sigmoid flexure. Occurrence at the ischial arch is less commonly reported [8]. While urolithiasis is seen in castrated and intact males, obstruction tends to be most common in steers due to the narrower urethral diameter from the absence of testosterone. Early castration has been shown to result in decreased urethral diameter and increased incidence of urolithiasis [9, 10]. Steers greater than eight months of age are the most commonly presented for disease [9]. Because of the effect of castration on urethral diameter, some authors suggest delaying castration until six months of age [1]; however, ethical considerations and castration complications at this weight should be considered before implementation of this recommendation.
Other commonly cited implications for urolith formation include hypovitaminosis A, hypervitaminosis D, and estrogenic intake [1, 4, 8]. However, true evidentiary support in the literature is lacking. Hypovitaminosis A occurs when cattle are fed poor quality hay and silage stored for prolonged periods. Hypervitaminosis D is commonly a result of feeding error during ration mixing. Diethylstilbestrol implantation and estrogen intake are hypothesized to result in hypertrophic effect on seminal vesicles, urethras, and bulbourethral glands, thus increasing the risk for urolithiasis [1, 8, 10].
Clinical Signs
Clinical signs associated with urolithiasis vary based on the location and duration of the obstruction. Common clinical signs include listlessness, anorexia, colic, tail switching, posturing, vocalization (more common in goats), and dehydration. Less common signs include rectal prolapse associated with tenesmus. For urolithiasis associated with phosphate calculi, stones can be appreciated on the preputial hairs (Figure 20.1). For cases with a single obstructive urolith, careful palpation of the urethra along the length of the penis might assist with location of the urolith.
Figure 20.1 Urethral calculi visible on preputial hairs.
Acute urethral obstruction is commonly associated with acute colic symptoms such as bruxism, repeated stretching, treading of feet, and kicking of the abdomen in bulls and steers. In addition to the previously mentioned clinical signs, palpation of the preputial orifice and preputial hairs is dry, indicating no urine passage. Upon rectal palpation, affected individuals will have an enlarged urinary bladder and palpable urethral pulsations. Individuals with a partial urethral obstruction show signs of discomfort as well as dribbling of urine, stranguria, and hematuria. If a complete obstruction is left untreated for 48 hours or longer, a urethral rupture or bladder rupture will occur and signs of colic typically cease. If a urethral rupture occurs, subcutaneous edema develops along the ventral abdomen that can extend from the scrotum to the sternum, but especially in the preputial region (Figure 20.2). Severe necrosis and sloughing of these tissues can occur if left untreated. With bladder rupture, bilaterally symmetric ventral abdominal distention will occur (“waterbelly”). With bladder rupture, a palpable fluid wave will also be present. Upon rectal palpation, free abdominal fluid will be appreciable and a small partially filled urinary bladder. Bulls with uroabdomen may also develop a hydrocele. Owners typically report the colic associated with a complete urethral obstruction, then improvement for 24–48 hours, after which they notice the abdominal distention and worsening depression again. Dehydration is also severe (≥10%) with bladder rupture, due to osmotic pull of fluid from the vascular space into the abdomen. Individuals afflicted with ureteroliths and nephroliths will experience similar clinical signs as those listed above. A ureterolith and hydroureter may be palpable per rectum, but often definitive diagnosis of ureteroliths and nephroliths does not occur antemortem.
Figure 20.2 Subcutaneous peripenile swelling typically extends from the base of the scrotum cranially and involves the entire ventrum.
Diagnosis
Urolithiasis can typically be diagnosed utilizing historical data and clinical signs. Additionally, rectal palpation and careful palpation of the penis can typically locate the site of obstruction and the presence or absence of a urethral or bladder rupture. For feedlot steers or economically constrained cases, treatment is implemented based on physical examination. However, for valuable individuals a complete diagnostic picture includes a complete blood count (CBC), biochemistry profile, and ultrasound.
The abnormalities observed with a CBC will typically coincide with the severity and duration of disease. Typical findings include a neutrophilia and possible hemoconcentration depending on the degree of dehydration. Cases with urethral rupture may have increased fibrinogen with excessive subcutaneous tissue necrosis. Common biochemical abnormalities include azotemia, hyponatremia, and hypochloremia. In ruminants, potassium can be normal or elevated in individuals with obstructive urolithiasis. When hyperkalemia is present, the degree of elevation is typically mild. One study experimentally induced uroabdomen and demonstrated increased salivary potassium excretion, possibly explaining the less severe hyperkalemia observed in ruminants with urolithiasis [11]. In small ruminants, Ewoldt et al. found individuals with no free abdominal fluid and a serum potassium less than 5.2 meq/l more likely to survive [12]. Individuals with urolithiasis may have a metabolic alkalosis, acidosis, or normal blood pH. When acidosis occurs, individuals are often severely dehydrated and suffering from lactic acidosis [13]. With prolonged obstructions, hyperphosphatemia and hypomagnesemia can occur and concerns of secondary renal failure should be considered. One study stated the best prognostic indicator was excessive serum phosphate being associated with increased likelihood of death [14]. In absence of hydronephrosis, 48 hours of fluid diuresis should be administered before diagnosing an individual in secondary renal failure. In individuals with uroabdomen, the degree of azotemia, hyponatremia, hypochloremia, and hyperkalemia can be severe due to the osmotic gradient across the abdominal wall pulling sodium and chloride into the abdomen, potassium and blood urea nitrogen intravascularly, with creatinine staying mostly intra‐abdominally, since it diffuses at a slower rate being a larger molecule.
If available, ultrasound can be used to assist with assessment of the urinary tract. Ultrasonography can be used transcutaneously or transrectally to assess the integrity and location of uroliths. Additionally, ultrasonography can assist with diagnosing the presence of cystoliths, ureteroliths, or nephroliths. Cystoliths usually have a sandy debris appearance that is hyperechoic with a rough, irregular surface that casts acoustic shadows [15]. Ureteroliths and nephroliths are often difficult to diagnose antemortem, but are hyperechoic half‐moon‐shaped or round calculi that cast acoustic shadows through deeper tissues [15]. Ureteroliths may also be diagnosed via rectal examination if hydroureter is associated with the condition. Prior to surgical intervention,
