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nonsteroidal anti-inflammatory drug (NSAID) long term is a clue that the cause of haemorrhage may be NSAID-induced ulcers in the urinary bladder (Aleman et al. 2011) or that the haemorrhage is caused by NSAID-induced necrosis of the renal medullary crest (Read 1983; Behm and Berg 1987). Haematuria may be the primary presenting sign of a horse with cantharidin toxicosis (i.e. blister beetle toxicosis) (Schumacher 2007), although horses with haematuria caused by cantharidin toxicosis usually display signs of abdominal pain or endotoxaemia by the time they have developed haemorrhagic cystitis. Palpating the bladder per rectum may provide a clue or


adefinitive answer as to the cause of haematuria. A cystolith can usually be palpated per rectum, especially if the bladder contains little urine, and the probability of palpating a cystolith is enhanced when the hand is inserted no further than wrist deep, to the level of the neck of the bladder, where a cystolith is most likely to lodge (Duesterdieck-Zellmer 2007). Normally, the ureters cannot be palpated per rectum, but a ureter enlarged by the presence of an ureterolith might be detected. A cystic neoplasm may be mistaken for a cystolith during palpation of the bladder, but a cystic neoplasm feels less firm than a cystolith (Traub-Dargatz 1998). In a retrospective study of horses diagnosed with renal cell carcinoma, a large, smooth or irregular kidney or an intra- abdominal mass, not recognised at the time as being a neoplastic kidney, was found during examination of the abdomen per rectum in the majority of affected horses (Wise et al. 2009). Detecting a prominent exostosis on the pubic bone during transrectal palpation of the abdomen of a horse with a history of exercise-induced haematuria might indicate that haematuria is the result of repetitive damage to the bladder by the protuberance (Rebsamen et al. 2012). The site from which the haemorrhage emanates can


usually be identified during endoscopic examination of the lower portion of the urinary tract. A 100 cm long (or longer), 12 mm diameter (or preferably smaller) endoscope is used to cystoscopically examine a male horse. The horse can be induced to protrude its penis by administering a tranquiliser or a sedative or by anaesthetising its pudendal nerves, at the level of the ischium, or the penis can be manually extracted from the preputial cavity, provided that the horse is amendable to this manipulation. The cavernosal spaces of the CSP, which surrounds the


urethra, become prominent when air is introduced into the urethra of a male horse, as the endoscope is advanced proximally (Schott and Varner 1997). The prominent cavernosal spaces may be mistaken for inflamed mucosa, or even haemorrhage, leading to an inappropriate diagnosis of primary urethritis. The occurrence of primary urethritis, however, is not well-documented in the horse (Table 1). A longitudinal rent, or tear, on the convex surface of the


urethra can sometimes be found at the level of the ischium during urethroscopic examination of a gelding with haematuria (Fig 1) (Schumacher 2007; Madron et al. 2013). The site of the rent can be readily confirmed during urethroscopy by pressing on the urethra percutaneously, with a finger, at level of the ischium. A urethral rent should be suspected as the cause of haematuria of a gelding even when no rent is observed during urethroscopy, if the results of examination have eliminated all other possible sites of haemorrhage (Glass et al. 2016). Urolithiasis, primary cystitis (Fig 2) (Smith et al. 2016), mucosal ulceration associated with chronic administration of a NSAID


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(Aleman et al. 2011), exercise-induced mucosal erosions in the bladder (Schott 2002), cystic neoplasia (Fischer et al. 1985; Patterson-Kane et al. 2000; Hurcombe et al. 2008; Serena et al. 2009; Busechian et al. 2016) and polypoid cystitis (Rosales et al. 2019) can be identified during cystoscopy. Immuno- histochemical examination of endoscopically obtained tissue from a cystic carcinoma can identify whether the neoplastic cells express COX-2 receptors, thereby determining if treating the horse with a COX-2 selective NSAID might be effective (Lisowski et al. 2015; Busechian et al. 2016). The slit-like ureteral orifices can be found during


cystoscopy at the 10 and 2 o’clock positions in the trigone region of the bladder, about 2 cm from the urethral opening. They can be difficult to locate but can be found by watching for spurts of urine discharging asynchronously from the orifices, about once every minute from each orifice (Schott et al. 1990; Carr 2003). The kidney or ureter can be identified as the source of haemorrhage when discharge from a ureteral orifice is bloody. Bloody urine for cytological examination and bacterial culture can be aspirated through sterile polyethylene tubing advanced from the biopsy port of a sterilised endoscope through the ureteral opening (Fig 3). Ultrasonographic examination of the kidneys should be


considered if lesions of the upper portion of the urinary tract are thought to be the likely cause of haematuria, based on history, results of palpation of the kidneys performed per rectum or endoscopically observing blood emanating from a ureter. The kidneys are typically examined ultrasonographically transcutaneously using a real-time B-mode ultrasound scanner with a 3- to 5-MHz curvilinear transducer. Increased echogenicity of the renal papilla and echogenic debris within the renal pelvis found during ultrasonographic examination of the kidneys support a diagnosis of renal medullary necrosis, typically caused by long-term administration of a NSAID, as a cause of haematuria (Reef 1998). A hyperechoic structure that causes distal acoustic shadowing within the renal pelvis, seen during ultrasonographic examination, can be presumed to be a renal calculus (Juzwiak et al. 1988). Ultrasonographic examination of the kidneys for a nephrolith


or other disease of the upper portion of the urinary tract is warranted when a urolith is found in the bladder or urethra (Mair and Holt 1994; Schott 2002). In one study, one or more nephroliths were found in four of 68 horses that had a urolith in the bladder or urethra (Laverty et al. 1992). In another study, five equids with recurrent urolithiasis of the bladder or urethra were found to have nephrolithiasis or pyelonephritis, indicating that a cystolith or urethrolith may, for some horses, be the consequence of renal disease (Schott 2002). A hypoechoic-to- anechoic focal mass caused by Halicephalobus gingivalis larvae was found in the renal medulla during ultrasonographic examination of a kidney of a donkey (Schmitz and Chaffin 2004). Renal biopsy may be indicated when a renal mass is found during ultrasonographic examination or during palpation of the abdomen per rectumof a horsewith haematuria. Horses with pyelonephritis have ultrasonographic renal


changes that include decreased length, increased echogenicity, abnormal outline of the kidney, loss of corti- comedullary distinction, pyelectasia and focal hypoechoic or hyperechoic cortical defects (Kisthardt et al. 1999). These same ultrasonographic changes may also be seen in horses with idiopathic renal haematuria. Pyelonephritis and idiopathic renal haematuria may be the same disease, because the clinical findings, signalment (most horses are Arabian) and


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