small ruminant Urolithiasis

08 سبتمبر 2020
small ruminant Urolithiasis

Overview

The urinary tract contains the kidneys, ureters (small channels that pump urine from the kidneys into the intestine), the intestine and the urethra (the tube that takes urine from the bladder and out of the animal). Urolithiasis — the accumulation of "blocks" or mucous, protein, and mineral concretions in the urinary tract — is a common problem in small male ruminants and a challenging problem for owners and veterinarians

The urolith composition (also called "urinary stones" or "calculi") varies with the area of the country where the animal lives. Calcium apatite and phosphatic calculi (e.g., calcium hydrogen phosphate dihydrate, and magnesium ammonium phosphate or struvite) are the most popular uroliths. There are also occasional sightings of silicate and calcium carbonate uroliths

Urethral obstruction caused by uroliths is highly common seen in high-grain, low-roughage diets of show or pet goats and lambs. Diets rich in grain, phosphorus, and magnesium and low in roughage (hay or new grass) and calcium can raise the likelihood of urolith production of phosphates. Naturally a ruminant outputs phosphorus from its body by excreting it into saliva and then pushing out the faeces (manure) into it. High grain, low roughage diets limit the production of saliva, so the kidneys must extract excess phosphorus from the blood and then excrete it into the urine. The urinary phosphorus levels get too elevated as foods are so rich in phosphorus, and the phosphorus settles and combines into stone-like pellets which might be too big to move. These uroliths greatly increase the risk with the urinary tract infection, and may lead to life-threatening urethra obstruction. Some sheep breeds (for example, Texel and Scottish Blackface) may be predisposed to forming stones because they tend to excrete phosphorus through the urinary tract rather than through saliva and faeces

Signs and symptoms 

Early clinical signs include

  • Blood in the urine
  • Straining to urinate
  • Decreased urine production
  • Painful urination
  • Prolonged urination
  • Dribbling urine
  • Tail flagging
  • Abdominal pain (stretching out all four limbs, kicking at the abdomen, looking at the side)

Late clinical signs include

  • Loss of appetite
  • Lethargy (apparent depression)
  • Abdominal swelling (from a ruptured bladder)
  • Swelling around the prepuce (the skin covering the penis)

Once the animal is severely ill, they may lay on their side and not get up, and may eventually seizure or die suddenly.

Diagnostics 

Your veterinarian will do a medical checkup. Abnormal symptoms can include heart rate changes, fast breathing, and likely a large bladder. If the bladder has ruptured into the belly, often a fluid pulse may be sensed ("balloted") as pressure is applied on one side of the abdomen

Most uroliths in small ruminants locate in "urethral process" or "vermiform appendage" — a narrow tube-like expansion of the skin and urethra at the tip of the penis; the second most frequent location is in the "distal sigmoid flexure" — an S-shaped curve in the lower half of the penis Uroliths stuck in the urethral phase can frequently be felt during physical exam. Blood samples will show elevated amounts of blood urea nitrogen (BUN), creatinine, and potassium that are usually excreted into the urine as contaminants build up. Significant variations in blood tests can involve elevated muscle enzyme concentrations, and low sodium and chloride concentrations. Acid can also build up in the stream of blood. Uroliths are usually identified with abdominal ultrasound. Ultrasound will distend the bladder and probably the urethra (overfilled with fluid), and the stones can also be seen. On radiographs (x-rays) certain uroliths are visible and can be used to estimate the number and position of stones. Special contrast tests can be carried out using x-rays to assess if the bladder has ruptured

Treatment 

Typically, surgery is required to remove uroliths or to alleviate blockage. Also, farm management activities should be checked to decide whether diet or other factors may raise the risk of urolithiasis in the herd

  • Urethral Process Amputation

The urethral process is a very small , thin tube-like structure on the tip of the penis, which is the most frequent place for uroliths to be obstructed because of its position and size. "Amputation" or removal of this process with a scalpel blade can permit uroliths to move through this process, but recurrence of obstruction is likely , especially if uroliths still occur higher up in the urethra. If this is the case, additional surgical procedures are needed

  • Perineal Urethrostomy

The urethra and the associated tissues can be easily seen in the sheep and goats' back end ("perineum") 2-3 inches just below anus and behind the rear legs. In this region, where uroliths obstruct the penis or when the urethra has split downstream from this area, a new opening can be created to allow the animal to urinate like a female.Often this operation is conducted under extreme sedation with regional anaesthesia (nerve blocks), but it is also administered under general anaesthesia in important animals or dogs. An incision is made into the skin and through the urethra, and the new opening of the urethra is then sewn to the skin. Then the animal urinates downwards and backwards rather than upward

  • Tube Cystostomy

Urine must be redirected away from the urethra in animals with urethral obstruction or tear to allow swelling to subside and tissues to recover. tube  Cystostomy involves inserting a rubber intestine through the bladder surgically and removing the tube through the wall of the abdomen next to the prepuce. This operation is undertaken in combination with amputation of the urethral process and the detachment of uroliths from the bladder by surgical technique. If the urethra swelling has healed, any uroliths which have not been removed through surgery frequently travel into either the urethra or the channel in the urine. When the animal is cured it is possible to remove the tube

While sedation and local nerve blocks can be done using a tube cystostomy, general anaesthesia is also used. This requires optimum sterile treatment and time to extract uroliths from the bladder, or patch them if they have ruptured, which helps the surgeon to clean the abdomen completely before inserting the tube. Once the tube is in place, to allow urine excretion, it can be attached to the sterile collection system or covered with a single-way valve

  • Prepubic Cystostomy

For animals who have strict (narrowed) perineal urethrostomy sites and subsequent re-obstruction, a permanent opening between the bladder and the wall of the abdomen near the prepuce may be made. This operation is often called a "marsupialisation" of the bladder

  • Urethral Translocation

This difficult technique involves connecting the urethra to the lower half of the penis or prepuce inside the abdomen. A ruptured urethra (or failed urethrostomy) can be attempted "by-pass"

Advanced urethral surgeries can require advanced training due to potential complications, particularly when the patient is a valued breeding animal or beloved pet. Your veterinarian will recommend / refer you with an ACVS board-certified veterinary surgeon who is trained with these procedures to the proper facility

Aftercare and outcome 

  • Urethral Process Amputation:Usually minimal to no aftercare with excellent outcome if the blockage was only localized to the urethral process
  • Perineal Urethrostomy: Daily evaluation of the site to ensure that the newly created hole remains open and has not strictured (closure of the hole) down in some animals. Also, the animal can no longer be used for breeding since semen does not pass through the penis
  • Tube cystostomy: The tube is kept in the animal until urine is seen dripping from the prepuce for 48 hours. Then, the tube is clamped and urination is monitored. If the animal can urinate, is not painful, and is able to empty its bladder, the tube is removed. If the animal can only partially urinate and continues to retain urine, the tube is left unobstructed for 5 to 7 more days and the process is repeated. On average, a tube cystostomy is removed 10 to 14 days after surgery. The main complication with a tube cystotomy is the risk of reobstruction following removal of the tube. Also, early removal (less than 5 days after placement) or accidental obstruction of the tube could result in leakage of urine into the abdomen
  • Prepubic Cystostomy: Urine will leak constantly from this hole, and may irritate the skin (“urine scald”), particularly if the skin around the new opening is not shaved and cleaned frequently. Development of chronic urinary tract infections. Therefore, this procedure is considered one of the “last resort” treatment for pet animals. In addition, the permanent cystostomy can become strictured and obstructed, requiring a second and sometimes a third surgical procedure
  • Urethral Translocation: This also is a “last resort” procedure for pet animals. Complications include loss of bladder tone and function “neurogenic bladder atony”, with pooling of urine in the bladder and subsequent development of chronic cystitis (bladder infection)

Breeding males should be physically resting for 1-2 weeks following amputations in the urethral phase and 2 months after other urethral procedures to reduce the chance of surgical complications

Prevention of urolithiasis never involves feeding horse grain to small ruminants as the diet is not adequately balanced for them and thus increases the risk of urolith formation. All show animals to be fed with a relatively high grain diet should have salt (sodium chloride) added to the ration at a rate of 2 to 5 per cent (alternatively, ammonium chloride may be used at a rate of 0.5 to 1 per cent) to increase urine formation or acidify urine. Calcium-rich diets can reduce the amount of phosphorus absorbed; owners should always talk to their veterinarians before adding any supplements to the feed

Refrance 

https://www.acvs.org/large-animal/urolithiasis-small-ruminants

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