We often find that vets have questions about when to recommend prescription hepatic diets, so here's a quick overview - I hope it's helpful.
What commercial hepatic diets are available in Australia and New Zealand?
In Australia and New Zealand, the two main options for dogs are Hill's Prescription Diet l/d canned and dry, and Royal Canin Hepatic canned and dry. Let's do a quick comparison of the dry diets (the canned diets are very similar):
Hill's Prescription Diet l/d dry diet:
14% calories from protein
47% calories from fat
Copper: 1.1 mg per 1000 kcal ME
Royal Canin Hepatic dry diet:
15.7% calories from protein
38.2% calories from fat
Copper: 0.77 mg per 1000 kcal ME
As you can see, both diets are quite similar. Both are high in fat to help with weight maintenance, both are copper-restricted, and both are low in protein. Both canned diets are high in moisture, which may help to reduce the risk of ammonium urate urolithiasis secondary to reduced hepatic function.
What is available for a cat with a portosystemic shunt?
Not much, unfortunately - although cases are quite rare, so it makes sense that commercial options are limited. Hill's previously manufactured l/d feline, although that was discontinued some time ago. A low protein, prescription renal diet is likely the best option for an adult cat - growing kittens with a shunt may need a properly formulated, home-prepared therapeutic diet.
When should I recommend a prescription hepatic diet for a pet?
This is the most important question. Too often we see dogs referred to us because they have a mild elevation in liver enzymes and they won't eat a prescription hepatic diet.
To summarise, there are only really two indications to prescribe a hepatic diet:
1) Hepatic encephalopathy
These prescription diets are very low in protein - unnecessarily low, for dogs with elevated liver enzymes, or even dogs with portosystemic vascular anomalies (with no clinical signs of hepatic encephalopathy).
Generally speaking, dogs with liver disease should be fed as much protein as they will tolerate, without becoming clinically encephalopathic. Sufficient protein in the diet helps to preserve lean muscle mass, which decreases liberation of ammonia from tissue catabolism and lowers the risk of hepatic encephalopathy developing. Providing adequate protein is also important as there may be impaired protein synthesis by the liver.
A moderate protein prescription diet (for example, Hill's Prescription Diet i/d) or a maintenance diet is likely to be much more appropriate for most dogs with an undiagnosed hepatopathy, chronic hepatitis, or vascular anomalies (not encephalopathic).
2) Copper-associated hepatopathy
These diets are copper-restricted, so they are obviously the most appropriate choice for dogs with copper-associated hepatopathy. How restricted is copper in these diets? Let's compare the copper content to both AAFCO and NRC requirements/recommendations:
AAFCO minimum requirement for copper (adult maintenance) = 1.83 mg per 1000 kcal ME
AAFCO minimum requirement for copper (growth/reproduction) = 3.1 mg per 1000 kcal ME
NRC recommended allowance (adult dogs) = 1.5 mg per 1000 kcal ME
NRC recommended allowance (growth) = 2.7 mg per 1000 kcal ME
Hill's Prescription Diet l/d dry diet = 1.1 mg per 1000 kcal ME
Royal Canin Hepatic dry diet = 0.77 mg per 1000 kcal ME
So, as you can see, these diets are actually quite copper-restricted - well below the NRC recommended allowance for both adults and puppies. What this means is that if these diets are prescribed unnecessarily, there's potential to cause copper deficiency with long-term use - just something to keep in mind.
Are these diets formulated for growth?
Many portosystemic shunts are diagnosed in growing pups, so it makes sense that hepatic diets meet the requirements for growth.
Both Hill's Prescription Diet l/d canned and dry diets can be fed to growing pups (although very young large or giant breed pups may be better suited to a homemade diet), however Royal Canin Hepatic is not formulated for growth.