is used until the penis can be grasped. The retractor penis muscles can often be confused for the penis. The retractor penis muscles are pink, soft, and identifiable as two separate components versus the firm penis which is covered in white tunica albuginea [21]. Once the penis is grasped, firm traction is used to pull the penis caudodorsally toward the skin incision, while the retractor penis muscles can be reflected or sharply dissected. Caudal traction and dissection are performed until a 6‐cm segment of penis can be exteriorized without tension [21]. If substantial subcutaneous urine accumulation has occurred, the penis can separate from the preputial attachments, allowing exteriorization of the entire penis [4]. The dorsal penile artery and vein are identified and ligated approximately 5 cm distal to the dorsal aspect of the skin incision [21]. The penis is transected distal to this ligature. However, removal of the distal penis requires substantial dissection of the preputial attachments in cases with urethral obstruction but absence of urethral rupture. In these cases, the dorsal penile vasculature should remain intact and be blunted dissected and reflected from the penis.
Once the penis is transected, it is turned over 180° with the urethra now oriented dorsally. A horizontal mattress pattern using a monofilament non‐absorbable suture is made through the corpus cavernosum to secure the penile stump to the skin [4, 21]. Caution should be used to not incorporate the urethra; a retrograde polypropylene catheter may be placed to ensure inadvertent urethral involvement is avoided (Figure 20.8). To assist with prevention of urine scald, the stump should extend 2–3‐cm from the skin incision [21]. Spatulation of the urethra is optional (Figure 20.8). If performed, the urethra is incised from the distal aspect of the penile stump to the proximal aspect of the incision. The urethral mucosa and tunica albuginea are sutured to the skin using an absorbable 2–0 monofilament suture in a simple continuous or interrupted pattern. Spatulation of the urethra is performed to decrease the rapidity of urethral stricture formation [21]. The skin remaining proximal and distal to the urethrostomy site is closed in a routine fashion.
Figure 20.8 Perineal urethrostomy showing spatulation of the urethra and use of polypropylene catheter to assist with urethra location during suturing.
For individuals with a urethral rupture, subcutaneous skin incisions should be made as/if needed to drain any subcutaneous urine accumulation. Individuals with uroabdomen should have abdominal drainage of urine performed.
Potential complications from this procedure include postoperative hemorrhage from the corpus cavernosum of the penile stump and hemorrhage from repeated trauma to the penile stump. A securely fitted urethral catheter can be placed to put pressure on the corpus spongiosum to assist with hemorrhaging. Other common complications include urine scald, urethral stricture, and reobstruction with blood or calculi.
Other Procedures
Other treatment methods include laser lithotripsy, basket catheter urolith retrieval, and bladder marsupialization. Laser lithotripsy and basket catheter urolith retrieval will only be briefly mentioned here due to their limited use at referral institutions. Bladder marsupialization is only briefly mentioned due to the high complication rate in bovines.
Removal of urethroliths via laser lithotripsy has been reported in the literature for steers, goats, and pot‐bellied pigs [35, 36]. An endoscope and laser fiber can be passed retrograde or normograde through an ischial urethrotomy [35]. Once the urethrolith is identified, the fiber is fired in a pulsatile fashion on the stone until fragmented enough to clear the urethra.
Basket catherization involves inserting a basket catheter into the urethral orifice and manipulating the instrument past the urethrolith. The instrument is opened, the urethrolith is maneuvered within the basket, and the catheter is removed. One report states a 55% successful urethrolith removal in calves [37] and another report successfully treated a bull with basket catherization while maintaining fertility [38].
Bladder marsupialization is often used in small ruminants as a last resort procedure with recurrent episodes of urethral obstruction. This procedure can also be utilized for detrusor muscle atony of the bladder. The apex of the bladder mucosa is sutured to the skin, allowing constant drainage of urine from the bladder. Numerous complications associated with this procedure include urine scald, bladder mucosa prolapse, stoma stricture, cystitis, and ascending pyelonephritis [12, 24, 25, 39]. It is not recommended for cattle. One study reported a mortality rate of 77% within two weeks of surgery [2]. Another study performed bladder marsupialization 12 hours after experimental induction of the urethral obstruction; of the six calves included in the study, one calf died and the remaining five calves had stoma stricture within three weeks postoperatively [40]. A novel procedure involving vesiculopreputial anastomosis has been described in small ruminants with a 50% success rate at six months postoperatively [41].
Prevention
The most important aspect of urolithiasis prevention is dietary modification. Ideally, the urolith(s) should be submitted to a laboratory for urolith analysis to determine composition. In the absence of this information, gross appearance of the urolith and ration evaluation should assist in figuring out the likely calculi involved. For phosphate calculi, excessive dietary phosphorus should be avoided, and rations should be adjusted to contain a calcium to phosphorus ratio of 1.5–2 : 1 and dietary magnesium should be less than 0.2%. Grain and alfalfa feeding should be reduced. For individuals fed a total mixed ration, roughage content should be evaluated. The primary excretion of phosphorus in ruminants is saliva, not urine. Therefore, if roughage is increased in the ration, rumination increases and salivary excretion of phosphorus is increased while solute in the urine is decreased. For silica uroliths, avoidance of at‐risk pastures and feedstuffs is recommended. High‐risk pastures can be used to graze female cattle instead of bulls and steers.
Adequate water consumption is critical in the prevention of urolithiasis. Ensuring access and availability to good quality water sources should be evaluated. If quality water sources are available, addition of sodium chloride to the ration should be considered to increase water consumption, ultimately creating dilute urine. According to Hawkins, sodium chloride has an effect of displacing magnesium and phosphorus from nucleation centers and thus preventing crystal development and urolith formation [1]. Silica uroliths form predominantly in the last 60 days before weaning; therefore a heavily salted creep feed is recommended for calves in the prevention of siliceous uroliths [4, 27, 42]. Sodium chloride can be fed up to 3–5% of the daily dry matter intake; this level of salt should be gradually increased to this level [4, 27].
Alternatively, reduction in urine pH can be attempted by feeding ammonium chloride at 0.5–1% of dry matter intake in a ration, which may help prevent apatite, struvite, and carbonate uroliths [27]. Feeding a DCAD ration can also be used to lower urinary pH in cattle. Silica urolith formation is not affected by urine pH. Caution should be used with long‐term use; reduced bone mineral density has been reported in mature ewes fed anionic salts long term [43].
As previously discussed, urethral diameter is testosterone dependent. Delaying castration would result in a larger urethral diameter. According to Hawkins [1], a calf castrated at seven months of age could pass a urolith 13% greater in diameter and a bull could pass a urolith 44% greater in diameter than a calf castrated when one month old. While the evidence exists that delaying castration increases urethral diameter, the welfare consequences of delaying castration should be considered prior to implementation. Dietary modification and water consumption would be better areas of focus for prevention.
References
1 1 Hawkins, W. (1965). Experimental production and