Urolithiasis is one of the most common urogenital conditions amongst small ruminant species.1-3 Males are particularly predisposed to this condition due to the narrow anatomy of the male urethra in combination with the presence of a sigmoid flexure.1 In addition, geographic location/associated pastures, diet composition and early neutering procedures have all been recognised as potential risk factors to the development of urolithiasis in ovine and caprine species.1,4 Obstructive urolithiasis frequently presents as an emergency and is associated with significant pain, compromised animal welfare, high mortality rates and subsequent production and financial losses on the behalf of the producer.1
In mid-February 2020, a sheep producer in Southern Tablelands of New South Wales reported sudden death in a mob of Border Leicester rams less than 18 months of age (Figure 1). The producer had reported that 6/33 (18%) of the ram lambs had died suddenly and a number of the remaining mob had some degree of staggers and/or drooping ears.
The mob was grazed on a native perennial pasture of predominantly cocksfoot and was supplemented with ewe/lamb pellets. It was not known what brand of pellets were being fed. [Common ingredients incorporated in ewe/lamb pellets include; barley, wheat, rice, sorghum, legumes, vegetable oil, limestone, salt, dicalcium phosphate and mineral mixes. Average values for this type of ration; 15% crude protein, 2.5% crude fat, 9% fibre, 11.76MJ energy, 1.6% calcium, 0.45% phosphorous]. The mob had access to clean water troughs. They were up-to-date on both vaccinations and worming prevention.
Upon presentation, some of the ram lambs were staggering, had drooped ear carriage and lacked a normal level of alertness. The physical examination findings from one ram are presented in Table 1.
|Body Condition score (0-5)||3.5|
|Estimated weight (kg)||50kg|
|Respiratory Rate (Breaths per minute)||40|
|Heart Rate (Beats per minute)||100|
|Clinical signs||Haematuria, hindlimb weakness, staggers|
There was haematuria from the pizzle, but no evidence of physical trauma, nor any straining to urinate (Figure 2). The ram had hindlimb ataxia and difficulty supporting its own weight but could walk if pushed.
A urine dipstick test was performed revealing marked haematuria, marked proteinuria and an alkaline urine pH. The test was negative for both ketones and glucose.
The producer elected to humanely euthanase a ram in order to investigate the cause of the mob's morbidity and mortality. There were no lesions or abnormalities noted in the integument or musculoskeletal systems.
Presentation of the thoracic cavity was within normal limits. There was no significant fluid accumulation and normal negative pressure was noted upon diaphragmatic puncture.
There were no lesions or ulcerations present on the tongue or within the oral cavity. The trachea had a normal post-mortem appearance. All lungs lobes were pale pink in colour and appeared normal in presentation. There was no evidence of lesions, contusions and no areas of consolidation. The heart was of a normal size, with a normal amount of pericardial fat present and no external abnormalities noted. Upon incision there was no evidence of enlarged chambers or valvular abnormalities.
A normal amount of pericardial fluid was present.
The abdominal cavity contained a moderate amount of serosanguinous fluid. There was a small focal area of pallor on the diaphragmatic surface of the right lobe of the liver. This lobe had slightly rounded margins. The peripheral margin of the left lobe was angular but had marginal linear areas of pale discolouration. The gall bladder was moderately distended with no superficial abnormalities. No liver fluke were present in the gall bladder or the bile duct. The spleen and intestinal lymph nodes were unremarkable in appearance.
All components of the gastrointestinal tract were normal in colour and presentation.
The urogenital tract appeared grossly abnormal. The bladder was markedly distended with prominent serosal vasculature and a dark purple to red discolouration of the dorsal half surrounding the region of ureteral attachment (Figure 3).
The retroperitoneal space had a marked accumulation of fluid. This fluid was a serosanguinous red-brown colour and surrounded the kidneys tracking the passage of the ureter to the bladder. There was a focally extensive area of dark purple to red haemorrhage present dorsal to the bladder. The reflected abdominal musculature appeared to have multifocal, irregular round areas of dark red to brown haemorrhagic contusions. There was a normal amount of retroperitoneal fat present.
Both left and right kidneys were moderately grossly enlarged. On the external surface there was an area of well demarcated, irregular, multifocal coalescing, dark purple capsular haemorrhage, as well as a moderate amount of subcapsular oedema (Figure 4).
There was a generalised loss of renal architecture with an absence of distinct medullary renal pyramids, in addition to parenchymal losses at the apical portion of the pyramids. The kidneys showed poor corticomedullary demarcation. The cortex had multifocal, petechial haemorrhages, as well as larger, focal areas of haemorrhage and necrosis. The renal pelvis was pale white in colour and had generalised, multifocal, petechial haemorrhages present. The ureteral entrance appeared distended (Figure 5). The path of the ureter to the bladder was markedly distended along the entire length and it was dark brown red in colour.
The mucosal surface of the bladder appeared inflamed with generalised, multifocal, small round ulcerations that reached the depth of the muscularis layer (Figure 6). Additionally, there was a number small, round, uroliths in the trigone of the bladder obstructing the urethra.
The above clinical and post-mortem findings are consistent with a diagnosis of urolithiasis. The uroliths within the bladder caused physical damage and ulceration to the bladder mucosal surface, further contributing to the presence of haematuria. The accumulation of uroliths around the trigone obstructed the urethra, leading to an accumulation of urine in the bladder and increasing retrograde pressure to the kidneys via the ureters. The sequelae of this obstruction was marked distension of the both the bladder and ureters (hydroureters), causing tissue compromise, rupture, haemorrhage, oedema and subsequent leakage of urine into the retroperitoneal space.2 Additionally, the increased back pressure also caused a degree of haemorrhage and pressure necrosis within the renal parenchyma2 and further accounted for the changes observed on the urine dipstick. It is likely that the focal lesion in the liver and mild hepatic changes identified were incidental in nature.
Urolithiasis in small ruminants is a multifactorial condition.5 The core aspect of this disorder relates to body water balance and dietary mineral intake.5 Uroliths are solid aggregations composed of a matrix of inorganic and organic materials that form when the urine is in a supersaturated solution.5 Saturation of urine is directly linked to water intake and rate of renal excretion.5 Additional factors that may predispose to the formation of uroliths include urine pH, dietary mineral composition of pasture and grain sources (specifically related to the calcium: phosphorous [Ca:P] ratio), intermittent feeding, vitamin A deficiencies (linked to uroepithelium metaplasia), hypothesised genetic predispositions, as well as early castration that limits complete urethral maturation and widening.4,5
In this particular case the most likely cause of the urolithiasis in these young rams was a calcium: phosphorus dietary imbalance. This imbalance was likely caused by a combination of high pellet consumption and the composition of the cocksfoot pasture. Recent rainfall following a period of drought conditions contributed to the presence of short green pick, a young rapidly growing pasture, which typically has a higher phosphorous profile compared to more mature-staged plants.6 Furthermore, cocksfoot pasture tends to have a mineral profile higher in phosphorus than calcium, with concentrations focused particularly in the base and middle portions of the plant.7 One study also found that consumption of cocksfoot pasture tends to result in greater mineral retention compared to other pasture types.7 Although this research was not explicitly conducted in the ovine, there is potential for extrapolation and further research.
The normal pathway of phosphorus excretion involves elimination via saliva and faeces.8 However, when there is a mineral imbalance, excess phosphorus starts to involve the renal excretory pathway.8 Decreased saliva production due to increased grain and reduced roughage intake further exacerbates the amount of phosphorous required to be removed via the kidneys and predisposes to solid precipitates forming in the urine.8
Decreased water intake was not found to be a major contributing component in this case. However, the potential role of decreased water intake should be considered in similar presenting cases. Decreased consumption may be related to the water quality, palatability, temperature or general accessibility.2 Thus, an important component of initial investigations should involve assessment of water quality. The presence of algae, detritus, flocculant material or high salinity may affect the taste.9 Furthermore, the relative distance between water troughs and how far animals need to travel to access them may also impact on consumption.2 Seasonal changes to the temperature of water within troughs can also impact overall consumption.2
There are two broad approaches to the treatment of urolithiasis in small ruminants, surgical or conservative management. Selection of treatment type depends on a number of factors. Consideration for the disease state, the cost of the treatments, the likelihood of reoccurrence, associated complications, the economic status of the farmer, the individual value and purpose of the animals would all be influential in the decision-making process in determining a viable treatment approach.2 In addition to treatment of affected animals, it is also crucial to develop a management plan to minimise and prevent future reoccurrence.
In this particular case the producer was focused on conservative management and preventative flock health for the ram lambs, as surgery was not an option on practical grounds. Ammonium chloride at 1.5% dry matter intake (DMI) was added to the feed pellets as the mainstay treatment and preventative action implemented in this case,2 with recommended doses varying from 0.5-2% DMI2,4 or 200mg/kg.5 Ammonium chloride is an anionic salt and acts to solubilise stones and sediments, whist concurrently acidifying the urine to prevent further urolith formation.5,10 Additionally, it has diuretic effects to promote urine excretion and indirectly influences water intake.2 Due to the addition of salt to the diet, it is critical that the farmer has sufficient, readily accessible water sources available to the flock.2,10 In this case, a conservative management approach alone through dietary correction was highly successful with no further deaths reported in the mob and resolution of all clinical signs within four weeks post dietary change.
However, there are a number of alternative preventative measures that may be considered appropriate depending on the circumstances of a particular flock. These include; increasing the forage and decreasing the grain component of the diet as this change further contributes to improved water intake as well as increases saliva production to aid in phosphorous excretion.2,5 Provision of feed/pasture access on an ad libitum basis rather than intermittent feeding with the latter causing a sudden production of ruminal volatile fatty acids that have a subsequent osmotic effect, shunting water to the rumen and causing a temporary concentration of urine.2,5,10 Ensuring sufficient trough access with clean, palatable water within a normal temperature range.2,5,9-11 A Ca:P ratio of 2:1 is another critical preventative component, with the phosphorous dietary component not exceeding 0.6% of the total ration.2,4 If the dietary mineral imbalance is due to excess phosphorus, the addition of calcium (calcium carbonate, calcium chloride or calcium sulfate)10 to the diet can also assist in preventing urolith formation, as calcium acts by competing with phosphorous for intestinal absorption and matrix binding sites.2,5 It is also important to consider the balance of other mineral constituents in the diet ration of the animal. Especially magnesium, potassium, sodium, silica, as not only can these interact with the calcium and phosphorus, but excessive amounts can predispose to the formation of different types of uroliths. Delaying castration in companion sheep facilitates complete maturation of the urethra due to the influence of testosterone and minimises the anatomical risks associated with early castration.2,5,10
Surgical options may be more viable in circumstances where the individual stud ram is highly valuable or where the animal is a companion pet. There are a multitude of surgical approaches. Urethrostomy is one surgical option, which can be performed at any level of perineum. However, this procedure is commonly associated with the formation of strictures, recurrence of obstruction and urine scalding and thus is not recommended for breeding rams.2
Another surgical approach mentioned in the literature is urethrotomy. Similarly, this procedure also has a number of associated complications including strictures and fibrosis surrounding the area of surgical closure.3 Formation of fibrotic attachments may further impede the erectional capacity and thus has a guarded prognosis for future breeding purposes.3 Other surgical options that may also be considered include; a cystotomy with antegrade hydropulsion, tube cystotomy, vermiform appendage/urethral process or penile amputation and bladder marsupialisation (salvage procedure).2,5,10
Prior to undertaking a surgical option, the less invasive intermediate option of retrograde catheterisation and urohydropulsion may be considered for individuals of high economic or companion value.2 Although this method does not have as many associated complications as the surgical alternatives, it does have a very low reported success amongst small ruminants. This finding is mainly attributed to the anatomical feature of the urethral recess, which is prone to lodging of the catheter.2
Overall surgical options are theoretically viable, however the reality is they often provide less than ideal outcomes with numerous complications, a high risk of re-obstruction and they are costly to perform, particularly when dealing with a herd or flock of animals. Furthermore, surgical procedures are complicated by the presence of a rupture at any level of the urogenital tract and these cases are reported to be more difficult to surgically close.3