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THERAPEUTIC NUTRITION

Useful information about the needs of cats and dogs with nutritionally sensitive health conditions.

Hepatic Disorders

Portosystemic Shunts and Hepatic Encephalopathy

A portosystemic shunt allows portal blood to bypass the liver. The liver does not receive the nutrition it needs, resulting in liver atrophy. Nutrients and other compounds absorbed from the intestines do not undergo hepatic metabolism or detoxification and instead travel directly into the systemic circulation. Compounds, e.g., ammonia derived from the nitrogen in protein and normally detoxified to urea in the liver, as well as bacteria, endotoxins, and aromatic amino acids, cause adverse effects on other systems in the body:1,2

red generic liver icon
  • Due to effects of these compounds on the brain, portosystemic shunts are the main cause of hepatic encephalopathy (HE), causing signs such as lethargy, seizures, ataxia, and changes in behavior. In cats, ptyalism and copper-colored irises are common signs. 
  • Vague gastrointestinal signs, e.g., vomiting and diarrhea, may be seen. 
  • Elevated levels of ammonia and uric acid in the urine may result in urate urolithiasis. 

Shunts may be either congenital or acquired. Congenital portosystemic shunts are more common in dogs than cats. Their prevalence has been reported at 0.02-0.6% in dogs and 0.02-0.1% in cats.1 In dogs, congenital shunts are more common in purebreds, e.g., Irish Wolfhounds, Golden Retrievers, Yorkshire Terriers, and Maltese.1,3 In cats, congenital shunts occur more often in domestic shorthairs.2 Pets with congenital shunts are often small in stature with low body condition scores. Congenital shunts most commonly occur as one vessel in an individual pet, while acquired shunts are usually comprised of numerous vessels.4 Acquired shunts may develop in any pet secondary to chronic liver disease or liver damage (e.g., aflatoxin poisoning) with fibrosis resulting in portal hypertension.4,5

Surgical ligation of a congenital shunt is generally the treatment of choice. However, some pets with congenital shunts are poor surgical candidates, the owners decline surgery, or surgery is not fully successful. In these cases, in pets prior to surgery, and in pets with acquired shunts, targeted nutrition may be utilized as part of management.3,6

Key Messages

  • Diet can be used to help manage associated clinical signs, especially of HE, and improve quality of life:3
    • A balanced protein intake is key to reduce the risk of hyperammonemia. A diet containing a moderate level of highly digestible, high biologic value protein is recommended.7,8 Avoid excess restriction of protein to preserve lean body mass and to prevent cachexia,9 which is associated with diminished immune function, increased morbidity, and shorter life span.10 
      • Hepatic stores of glycogen are lower in pets with portosystemic shunts, leading to an increased utilization of amino acids for energy.11,12 If protein intake is insufficient, muscle protein is catabolized at a high rate.12 Muscle wasting in turn can potentiate hyperammonemia since muscle becomes the primary site of ammonia detoxification with a portosystemic shunt.9
      • Start with a level of 2.1-2.5 g protein/kg body weight/day for dogs and 4 g protein/kg body weight/day for cats in the diet. Provided that the pet shows no signs of HE, gradually increase the level of protein in 0.3-0.5 g/kg increments to the maximum level the pet will tolerate.13,14
      • In dogs, the protein source may be important. Non-meat protein sources, such as soy, are better tolerated in dogs with portosystemic shunts at risk for hepatic encephalopathy.6,7
      • Consult with a veterinary nutritionist if a homemade diet is elected to ensure individual amino acid requirements are met.15
    • Lactulose and prebiotics, e.g., pectin or chicory root, lower the intestinal pH (due to production of short chain fatty acids), which helps reduce ammonia absorption from the gastrointestinal tract. In an acidic environment, ammonia converts to ammonium, which is not absorbed and is excreted in the feces. An acidic environment also promotes the growth of non-urease producing bacteria, e.g., Lactobacillus, which decreases production of ammonia.12
    • Probiotics may also promote the growth of non-urease producing bacteria.14,15
    • Since zinc is a cofactor for several enzymes involved in detoxification of ammonia, increased dietary levels of zinc may help reduce the risk of hyperammonemia. Zinc is also an antioxidant.14
    • Supplementation of fish oil, a source of the long chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, may reduce inflammation which, in turn, may reduce the risk of HE.8
    • Ammonia is produced during digestion of food. Small, frequent meals should be fed to reduce the level of the post-prandial ammonia burden.8
    • To help prevent recurrence of urate urolithiasis, adding water to the diet may increase total water intake, increase urine volume, and decrease urine specific gravity. A more dilute urine contains a lower concentration of urolith precursors. A higher urine volume may also increase frequency of urination, helping eliminate precursors before they can form uroliths.16
  • Regularly reassess weight, body condition, and muscle condition.
conversation starter background image

“We want to reduce the chance that your pet will show clinical signs of [his/her] portosystemic shunt. We can do this by feeding a diet containing just the right level of protein–not too much and not too little. We’ll start with a diet moderate in protein (particularly limiting meat-based protein sources) but will gradually increase or decrease the protein level to find the diet that best supports your pet’s health and quality of life.”

Related Tools and Content:

The Purina Body Condition System

The Purina Body Condition System is an easy and practical tool for assessing a pet's body composition.​

View Brief 1 min to 5 min

How to Perform a Body Condition Assessment - Cat

Assess a cat's Body Condition Score in just 3 simple steps.​

View Video 1 min to 5 min

How to Perform a Body Condition Assessment - Dog

Assess a dog's Body Condition Score in just 3 simple steps.​

View Video 1 min to 5 min

Use Muscle Condition Scoring to Detect Muscle Loss in Patients

Muscle condition scoring is a hands-on method for evaluating lean body mass that can be used as part of nutritional assessments.

View Brief 1 min to 5 min

Cachexia in Dogs and Cats

Cachexia is the loss of lean body mass and body weight that occurs with disease, and targeted nutrition can help address this adverse condition.

View Brief 1 min to 5 min

Hydration in Pets

The water needs of pets should not be overlooked.

View Brief 1 min to 5 min

To Share With Pet Owner:

Evaluating Your Cat’s Body Condition

Assess your cat's Body Condition in just 3 simple steps.​

View Video 1 min to 5 min

Evaluating Your Dog’s Body Condition

Assess your dog's Body Condition in just 3 simple steps.​

View Video 1 min to 5 min

References

  1. Paepe, D., Haers, H., Vermote, K., Saunders, J., Risselada, M., & Daminet, S. (2007). Portosystemic shunts in dogs and cats: Definition, epidemiology and clinical signs of congenital portosystemic shunts. Vlaams Diergeneeskundig Tijdschrift, 76, 234–240.
  2. Tivers, M., & Lipscomb, V. (2011). Congenital portosystemic shunts in cats: Investigation, diagnosis and stabilisation. Journal of Feline Medicine and Surgery, 13, 173–184. doi: 10.1016/j.jfms.2011.01.010 
  3. Van den Bossche, L., & van Steenbeek, F. G. (2016). Canine congenital portosystemic shunts: Disconnections dissected. The Veterinary Journal, 211, 14–20. doi: 10.1016/j.tvjl.2015.09.025
  4. Berent, A. C., & Tobias, K. M. (2009). Portosystemic vascular anomalies. Veterinary Clinics of North America: Small Animal Practice, 39(3), 513–541. doi: 10.1016/j.cvsm.2009.02.004
  5. Cullen, J. M. (2009). Summary of the World Small Animal Veterinary Association standardization committee guide to classification of liver disease in dogs and cats. Veterinary Clinics of North America: Small Animal Practice, 39(3), 395–418. doi: 10.1016/j.cvsm.2009.02.003
  6. Proot, S., Biourge, V., Teske, E., & Rothuizen, J. (2009). Soy protein isolate versus meat-based low-protein diet for dogs with congenital portosystemic shunts. Journal of Veterinary Internal Medicine, 23, 794–800. doi: 10.1111/j.1939-1676.2009.0327.x
  7. Lidbury, J. A., Cook, A. K., & Steiner, J. M. (2016). Hepatic encephalopathy in dogs and cats. Journal of Veterinary Emergency and Critical Care, 26(4), 471–487. doi: 10.1111/vec.12473
  8. Gow, A. G. (2017). Hepatic encephalopathy. Veterinary Clinics of North America: Small Animal Practice, 47, 585–599. doi: 10.1016/j.cvsm.2016.11.008
  9. Stern, R. A., & Mozdziak, P. E. (2019). Differential ammonia metabolism and toxicity between avian and mammalian species, and effect of ammonia on skeletal muscle: A comparative review. Journal of Animal Physiology and Animal Nutrition, 103(3), 774–785. doi: 10.1111/jpn.13080
  10. Freeman, L. M. (2012). Cachexia and sarcopenia: Emerging syndromes of importance in dogs and cats. Journal of Veterinary Internal Medicine, 26, 3–17. doi: 10.1111/j.1939-1676.2011.00838.x
  11. Nichols, R. (2021). Hypoglycemia in patients without diabetes mellitus. In D. Bruyette (Ed.), Clinical small animal internal medicine (pp. 103–111). John Wiley & Sons, Inc. doi: 10.1002/9781119501237.ch13
  12. Center, S. A. (1998). Nutritional support for dogs and cats with hepatobiliary disease. Journal of Nutrition, 128(12 Suppl), 2733S–2746S. doi: 10.1093/jn/128.12.2733S
  13. Webster, C. R. L., Center, S. A., Cullen, J. M., Penninck, D. G., Richter, K. P., Twedt, D. C., & Watson, P. J. (2019). ACVIM consensus statement on the diagnosis and treatment of chronic hepatitis in dogs. Journal of Veterinary Internal Medicine, 33(3), 1173–1200. doi: 10.1111/jvim.15467
  14. Salgado, M., & Cortes, Y. (2013). Hepatic encephalopathy: Diagnosis and treatment. Compendium on Continuing Education for the Practicing Veterinarian, 35(6), E1–E9.
  15. Norton, R. D., Lenox, C. E., Manino, P., & Vulgamott, J. C. (2015). Nutritional considerations for dogs and cats with liver disease. Journal of American Animal Hospital Association, 52(1), 1–7. doi: 10.5326.JAAHA-MS-6292R2
  16. Queau, Y. (2019). Nutritional management of urolithiasis. Veterinary Clinics of North America: Small Animal Practice, 49, 175–186. doi: 10.1016/j.cvsm.2018.10.004