Handout_Goat_Urolithiasis_KarinMueller.pdf

Urolithiasis in the goat Karin Mueller MVSc DCHP DECBHM MRCVS Surgical treatment section first published in the GVS Journal (2015, 31: 67 – 71). Reprinted with kind permission of the Goat Veterinary Society. Castrated males are most at risk, because of a narrower urethra due to lack of testosterone...

Urolithiasis in the goat Karin Mueller MVSc DCHP DECBHM MRCVS Surgical treatment section first published in the GVS Journal (2015, 31: 67 – 71). Reprinted with kind permission of the Goat Veterinary Society. Castrated males are most at risk, because of a narrower urethra due to lack of testosterone (and males because the urethra is longer than in females). Predisposing factors include rations rich in concentrates (2.5% of BW dry matter intake for two months or more), alfalfa (high calcium content), or pasture with high levels of silica, oxalate or oestrogens. It may also be caused by high levels of magnesium in milk replacers, and Vitamin A deficiency may possibly play a role. Contributing factors are ‘nidus formation’ - organic material as the core of the calculus, e.g. epithelial cells or necrotic tissue after local infection. Low salt contents of diet and restricted access to water favour precipitation of solutes. Types of calculi in ruminants are: Clover pasture Calcium carbonate Extensive pasture Silica Feedlot / Fattening Phosphates (Calcium, Magnesium, Ammonium) Common sites for the calculus to lodge are the sigmoid flexure or the urethral process. The goat shows abdominal discomfort (e.g. arched back, colic, shortened stride). There is dysuria or stranguria, producing no or only a few drops of urine. Sometimes crystals are present on preputial hair or the inner thigh. Digital rectal examination reveals pulsation or spasms of the urethra. A distended bladder may be palpable through the abdominal wall in young, thin goats. Rupture of the urinary bladder or urethra may occur after about 48 hours. This results in sudden relief of pain and, in the case of urethral rupture, ventral subcutaneous fluid swelling, cellulitis and possibly toxaemia. Bladder rupture results in ascites, uraemia, anorexia and depression. Uraemia is present on bloods. An increased serum phosphate level above 2.9 mmol/l is associated with a poor prognosis in cattle. A creatinine concentration in peritoneal fluid 1.5 – 2 x times higher than serum levels indicates an uroperitoneum. Calcium-containing stones (e.g. calcium-oxalate, ca-carbonate, silicate) can be detected on radiography, but ultrasonography is often easier to perform. The various abnormalities it can detect, depending on the stage of disease, are a distended bladder, the calculus if lodged in the externally accessible part of the urethra, free peritoneal fluid, or subcutaneous fluid accumulation (Scott, 2000). The management plan consists of:  Restore patent urethra  Manage pain  Correct dehydration & electrolyte imbalance  Restore urine pH  Prevent infection  Herd control Treatment options Pain, considerable electrolyte disturbances and onset of hydronephrosis 48 hours mean that prompt treatment is required. In small ruminants, 17% - 55% long-term recovery after urethrostomy, and 88% after cystotomy are reported. Supportive treatment Regardless of method chosen to restore a patent urethra, the goat should receive intravenous fluids at maintenance rate once urinary output is established, and maximum water intake should be encouraged (including adding salt to the diet – see below). NSAID are best avoided for pain relief until normal kidney function is restored. Butorphanol can be used under the cascade for analgesia in the meantime. Antibiosis is indicated. Medical treatment  Passing a urinary catheter in the male goat is impossible because of the urethral process, sigmoid flexure and urethral diverticulum.  A smooth muscle relaxant (like xylazine, clenbuterol, Buscopan, acepromazine. Note: all constitute off-datasheet use) may be tried. The animal is placed onto concrete or shavings to monitor urine output. Xylazine increases urine output, so if not successful, prompt surgical treatment is required.  Ultrasound-guided cystocentesis and lavage with Walpole’s solution (effective against struvites) has been described (Janke et al., 2009). Removal of urethral process This is worthwhile regardless of further approach, either to cure or to prevent other calculi becoming lodged at this point. With the goat on its haunches, the penis is exteriorised, and the process cut with sharp scissors as close to the glans penis as possible. Urethrotomy This is a salvage procedure to allow urination while the animal recovers from the effects of urolithiasis, such as uraemia, prior to slaughter. I may be carried out under light sedation and caudal epidural anaesthesia or local infiltration. The author prefers the perineal approach, and for this places the patient into sternal recumbency with flexed hindlegs and the backend slightly overhanging the operating table’s edge. Alternatively, the patient may be placed into either left or right lateral recumbency, with the uppermost hindleg elevated. After tying the tail away and clipping and surgical preparation, a 5 – 8 cm long skin incision is made midline in the perineum. The centre point of the incision should coincide with the most caudal point of the perineum (i.e. where it begins to slope cranio-ventrally). After incision of the fascia, blunt dissection is used to part the retractor penis muscles. If the penis cannot be visualised, it can be identified by palpation as a firm tubular structure of about small-finger thickness. A curved pair of artery forceps is pushed underneath the penis and, using blunt and sharp dissection staying close to the penis, it is freed around its entirety to gain some movability. The penis is cut at right-angle near the ventral margin of the skin wound. The aim is to have the stump just ventral to the most caudal point of the perineum, to avoid urine scalding. But not too ventral to avoid irritation from hindleg movements. Using 3 to 4-metric suture material on a cutting needle, the penile stump is fixed to the skin by a figure-of-eight suture (through skin on one side, then through corpus cavernosum and skin on the other side, then tied off underneath the stump). Great care must be taken not to include the urethra (which lies dorsally in the reflected stump) in this suture. If pressure application is not sufficient to arrest haemorrhage, the dorsal penile artery is ligated. The skin incision is closed in a routine manner. Aftercare consists of fly-repellent, ointments such as Vaseline to reduce the risk of urinary scalding, and the supportive treatment described above. The author typically makes no attempt to exteriorise the distal portion of the dissected penis. Some surgeons prefer to spatulate the urethra over a length of a centimetre or so, suturing the mucosa to the skin. The author uses this technique if there is marked oedema around the urethra. An alternative to above technique, which may provide longer survival, is urethrostomy. The approach is the same, but instead of cutting through the penis, the surgeon dissects onto the urethra and sutures it to the skin to create a stoma (Van Metre, 2004). Tube cystotomy This procedure, described by Cockcroft (1993) is useful in patients where reproductive function or long-term survival are desirable, for example a breeding buck or pet animal. The procedure may be carried out under GA, lumbo-sacral epidural anaesthesia, or sedation and local infiltration, with the animal in right lateral recumbency. The site is clipped and surgically prepared. An incision long enough to allow passage of the surgeon’s hand is made in the caudoventral left flank, just above to and roughly following the knee-fold. If the urinary bladder can be exteriorised, an absorbable purse-string suture is placed, a stab incision made in the centre of this suture into the bladder, and a Foley catheter passed into the ventral bladder, close to the apex. If the bladder cannot be exteriorised, a Steinman pin is placed into the Foley catheter, the bladder grasped intra-abdominally with one hand, and the catheter pushed blindly into the ventral bladder. The cuff of the Foley catheter is inflated with saline and pulled against the bladder wall. The catheter end is passed out through a stab incision two to three centimetres away from the surgical incision. The catheter is secured with a butterfly-tape anchored with skin sutures. The abdominal wound is closed in a routine manner. Using the Foley catheter, the bladder is lavaged several times with sterile saline. Retrograde lavage via a catheter placed into the distal urethra can also be tried. Continuous urine passage is allowed through the Foley catheter for the first few days. Supportive therapy is given during this time (such as anti-inflammatories, antibiotics, ammonium chloride, smooth muscle relaxants). The bladder may also be flushed with Walpole’s solution (50 - 200 ml of a 1:10 Walpole: water dilution, retained in the bladder for 30-60 minutes by blocking the catheter). After a few days, the catheter is blocked for trial periods of several hours, and the animal observed for normal urination. Once normal urination has been established for 24-48 hours, the Foley catheter is removed. Notes on suture material: Poliglecaprone 25 (Monocryl) and Catgut are poor choices, as they get absorbed rapidly or unpredictably when in contact with urine. Polyglactin 910 (Vicryl), polyglycolic acid (Dexon) and polydioxanone (PDS) are good choices. Salvage slaughter Uraemia is likely present at the time clinical signs are detected, making the animal unfit for human consumption. Prevention & Control  Ensure Calcium : Phosphorus ratio is at least 1.2 : 1 in ration.  Adequate water intake can be helped by adding 4% salt to ration. Salt also prevents silica calculus formation. Plus basic husbandry of providing readily accessible, clean water.  Ammonium chloride at 100-200mg/kg BW bid (or 0.5% to 1% of ration dry matter) prevents phosphate calculi. o This salt is bitter, i.e. must be mixed with moist feed or molasses. o In fattening kids, 0.5% ammonium chloride is routinely added to concentrates, plus <1% sodium chloride. o In small animals, prolonged use of acidifying agents causes skeletal decalcification. Therefore continuous use of ammonium chloride may not be appropriate for breeding or pet animals. References & Further reading Cockcroft P.D. (1993). Dissolution of obstructive urethral uroliths in a ram. Veterinary Record, 132 (19): 486. Janke J.J., Osterstock J. B., Washburn K.E., Bissett W.T., Roussel Jr A.J., Hooper R.N. (2009). Use of Walpole’s solution for treatment of goats with urolithiasis: 25 cases (2001-2006). Journal American Veterinary Medical Association, 234:249–252 Scott P. (2000). Ultrasonography of the urinary tract in male sheep with urethral obstruction. In Practice, 22: 329-333 Van Metre D.C. (2004). Urolithiasis. Chapter 19.2 in: Farm Animal Surgery, by S.L. Fubini & N.G. Ducharme. Saunders. Van Metre D.C. & Fubini S.L (2006). Ovine and Caprine Urolithiasis: Another Piece of the Puzzle. Veterinary Surgery, 35:413–416