Vegan feline diets: appendices

After extensively searching the biomedical literature, I can confirm that at least one study does exist demonstrating a disease of malnutrition, namely hypokalaemic polymyopathy (a muscular disease caused by low potassium levels), in cats fed a vegetarian diet. However, this diet was deliberately formulated to be nutritionally inadequate. The study abstract is provided below. I have been unable to locate any other studies demonstrating diseases of malnutrition in cats or dogs maintained on vegetarian diets. Despite the popular belief that vegetarian diets are inevitably harmful for companion animals, there are, to my knowledge, no studies that have been able to demonstrate this when nutritionally complete and reasonably balanced vegetarian diets are used.

Leon A, Bain SA, Levick WR (1992). Hypokalaemic episodic polymyopathy in cats fed a vegetarian diet. Aust Vet J 69(10), 249-254.

A previously undocumented hypokalaemic condition with a cyclical nature, comprising acute bouts of polymyopathy followed by spontaneous recoveries, is described in the cat. Cats being fed a high protein vegetarian diet developed recurrent episodes of polymyopathy, characterised by ventroflexion of the head and neck, stiff forelimb gait, lateral head-resting and generalised muscle weakness. Plasma potassium concentrations (mean +/- standard deviation) were reduced from 3.28 +/- 0.33 mmol/l at the beginning of the experiment to 2.45 +/- 0.24 mmol/l during bouts of myopathy. This hypokalaemia was associated with increased creatine kinase activities indicative of muscle damage, and decreased urinary potassium concentrations, and was caused by insufficient dietary potassium. Cats that received the same diet supplemented with potassium did not develop hypokalaemic polymyopathy. Spontaneous recoveries of affected cats were not associated consistently with increases in plasma potassium concentrations. Plasma taurine concentrations decreased and glutamic acid increased markedly in all cats fed the experimental diet. There was no evidence of thiamin deficiency associated with the high glutamic acid intake. Veterinarians should be aware that hypokalaemic cats, and in particular those on potassium-deficient diets, may show cyclical disease with episodes of polymyopathy recurring after periods of spontaneous clinical recovery. This condition in cats may be a useful animal model for familial hypokalaemic periodic paralysis in humans.

A previously undocumented hypokalaemic condition with a cyclical nature, comprising acute bouts of polymyopathy followed by spontaneous recoveries, is described in the cat. Cats being fed a high protein vegetarian diet developed recurrent episodes of polymyopathy, characterised by ventroflexion of the head and neck, stiff forelimb gait, lateral head-resting and generalised muscle weakness. Plasma potassium concentrations (mean +/- standard deviation) were reduced from 3.28 +/- 0.33 mmol/l at the beginning of the experiment to 2.45 +/- 0.24 mmol/l during bouts of myopathy. This hypokalaemia was associated with increased creatine kinase activities indicative of muscle damage, and decreased urinary potassium concentrations, and was caused by insufficient dietary potassium. Cats that received the same diet supplemented with potassium did not develop hypokalaemic polymyopathy. Spontaneous recoveries of affected cats were not associated consistently with increases in plasma potassium concentrations. Plasma taurine concentrations decreased and glutamic acid increased markedly in all cats fed the experimental diet. There was no evidence of thiamin deficiency associated with the high glutamic acid intake. Veterinarians should be aware that hypokalaemic cats, and in particular those on potassium-deficient diets, may show cyclical disease with episodes of polymyopathy recurring after periods of spontaneous clinical recovery. This condition in cats may be a useful animal model for familial hypokalaemic periodic paralysis in humans.

The following nutrients are of particular importance to cats maintained on vegetarian diets, as they are scarce in the plant material available in the cat’s natural environment, and are naturally sourced from small mammals, birds and insects. Regardless of the ingredients used, diets should be complete and reasonably balanced with respect to all essential nutrients, or disease is likely to result, sooner or later. This may be achieved by adding a vegetarian nutritional supplement to a home-made diet (recipes are available from some suppliers of supplements), or by feeding a nutritionally complete commercial diet. Ideally this should be certified as meeting the nutritional standards of the Association of American Feed Control Officials (AAFCO), or equivalent national authority.

Protein and amino acids

Cats are biochemically dependent on protein as a primary energy source, and consequently have a very high dietary protein requirement. Of the 23 different amino acids, 11 are considered essential in the cat’s diet (Gillen 2003). The following require alternative supplementation if quality meat is not provided:

Taurine
This sulfur-containing beta amino acid occurs at low levels in plant material. For reasons of economy commercial pet food manufacturers have for many years used synthetic, rather than animal, sources of taurine. The same source is used by vegetarian pet food manufacturers.

Taurine is particularly required by cats for several reasons (Baker & Czarnecki-Maulden 1991, Blood & Studdert 1988, Gray et al. 2004, National Research Council 1986, Palackal et al. 1986, Peden 1999):

• Taurine synthesis occurs in the liver at a relatively low rate in cats.
• Unlike other species, cats are unable to synthesise taurine from amino acids cysteine and methionine.
• Within the intestinal lumen, microbial degradation further increases taurine loss.
• Most mammals make bile salts (as taurocholic acid) from both taurine and glycine, however cats can only use taurine for taurocholic acid synthesis.
• Feline taurine deficiency can result in multiple organ system dysfunction, the effects of which have been described by numerous investigators. Effects include generalised retinal atrophy, developmental deficits of the visual cortex and cerebellum, dilated cardiomyopathy, reproductive failure and thromboembolism. Normal growth, immune and neurological function are all dependent on adequate taurine levels.

Typical retinal degeneration (atrophy of the rods and cones) in adult cats or older kittens causes only partial loss of vision, except in advanced cases. Without a dietary source of taurine, cats exhibit evidence of retinal changes in as little as three months. These changes become extensive within six months and total blindness may take two years to develop. If treated with supplementary taurine in time, degeneration is reversible.

The entry of calcium into the myocardium in order to trigger each heart beat is regulated by taurine. Deficiency results in cardiomyopathy. Cats with this degenerative disease typically live only a few days to weeks after diagnosis, with death resulting from myocardial flaccidity and impaired pumping ability.

Methionine and cysteine
These sulfur-containing amino acids are less available in plant material, and are required in greater quantities by cats because they are highly utilised as gluconeogenic substrates (allowing the creation of glucose – a universal cellular energy source), in addition to cysteines roles in hair and felinine (an amino acid of unknown function) synthesis (Blood & Studdert 1988, Zoran 2002). Cats are unable to synthesise or conserve methionine, and deficiency can result in poor growth and dermatitis (an inflammatory skin condition) (Gray et al. 2004).

Arginine
Arginine is found in low levels in plant material, and cats are unable to synthesise its precursors. Arginine is an essential amino acid in the feline diet due to its function in the urea cycle. Deficiency can lead to hyperammonemia and hepatic encephalopathy, poor growth and rapid loss of body mass (National Research Council 1986).

Lysine
Lysine is required by cats and is normally limited in the diet when grain is the only major protein source. This essential amino acid is important in the formation of collagen, fibrin and keratin; hence deficiencies would result in skin and connective tissue deficits (MacDonald et al. 1984, Blood & Studdert 1988).

Arachidonic acid

This essential fatty acid found primarily in meat. Unlike dogs, cats lack the enzyme delta 6 desaturase and are consequently unable to synthesise arachidonic acid from linoleic acid (National Research Council, 1986). Arachidonate is crucial for the biosynthesis of some prostaglandins, which have a variety of potent biological activities of a hormonal or regulatory nature. Arachidonate deficiency results in listlessness, reduced feed conversion efficiency and poor growth, enlarged, fatty livers, mild mineralisation and fatty infiltration of the kidneys, dry hair coat, scaly skin and dandruff, inflammatory skin lesions, immune suppression and, paradoxically, higher lymphocyte production. Cats lacking dietary arachidonate can experience prolonged bleeding times due to delayed and weak platelet aggregation. The most sensitive indicator of arachidonate deficiency is reproductive failure in female cats (MacDonald et al. 1984).

Vitamins

Vitamin A
Unlike some other species, cats are unable to synthesize vitamin A (retinol) from beta-carotene in the intestinal mucosa, hence retinol must be provided pre-formed in a cat’s diet (Gray et al. 2004). Deficiency can lead to blindness, dermatological lesions, secondary infections, and reproductive problems (National Research Council 1986).

Fish liver oils supplied vitamin A until 1941 when war orders banned fishing vessels from the Pacific, and chemists learned to synthesise it out of necessity. By 1966, production of synthetic vitamin A totalled over 830 tons in the USA (Peden 1999).

B Vitamins
B vitamins are not conserved in cats (Gray et al. 2004). Cobalamin (a cobalt-containing complex common to all B12 vitamins) is produced by microbes and is scarce in plants. Deficiency may result in poor growth and neuropathies (Kirk et al. 2000). Commercial production of vitamin B12 uses the synthesising ability of bacteria such as streptomycetes.

Niacin (a water soluble B complex vitamin) is less available in plant tissue, and unlike some other species, cats are unable to synthesise significant levels of niacin from tryptophan. Deficiency manifests in diarrhoea, anorexia, weight loss, weakness and apathy. Thick saliva with a foul odour is characteristic, as well as ulceration of the upper palate. An association with respiratory disease is common, contributing to early death (MacDonald 1984, Blood & Studdert 1988).

Pyridoxine (Vitamin B6) is a component of transaminases, and is needed in relatively high quantities by cats due to their increased protein catabolism (Gray et al. 2004). Deficiency manifests as cardiac dilatation, congestion, deterioration of the peripheral nerves, convulsive seizures, and irreversible kidney lesions (National Research Council 1986, 26).

Other nutrients

Additional nutrients that must be supplied in the correct proportions but which are of less concern in vegetarian animal diets include overall energy, carbohydrates, L-carnitine, calcium, phosphorus, magnesium, iron, copper, zinc, selenium, potassium, sodium, chlorine, iodine, vitamins C, D, E, thiamin (vit. B1), riboflavin (vit. B2), pantothenic acid, folic acid, biotin, choline, linoleic acid, and water (Peden 1999).

See also the associated debate about vegetarian feline diets in the J Amer Vet Med Assoc, 2005.

A study by Gray and colleagues (2004) clearly illustrates the need for sound quality control procedures during manufacturing. Two commercially available vegetarian cat foods were subjected to blind (i.e. labels removed) nutritional analysis by Woodson-Tenent Laboratories. Diet A (Vegecat KibbleMix) was prepared according to company instructions, using vegetable oil, flour, tomato paste, and the supplied powdered dietary supplement for adult cats. Diet B (Evolution canned diet for adult cats) required no additional preparation.

The laboratory results were compared to Association of American Feed Control Officials (AAFCO) nutrient profiles for the maintenance of adult cats. The Committee on Animal Nutrition, reporting to the Board of Agriculture within the National Research Council (NRC), has developed nutrient requirement standards for at least fifteen specific species of animals. AAFCO historically used the NRC recommendations, but in 1993 began publishing its own expanded nutrient requirements. These are now widely recognised as the required nutritional standards for animal feeds.

The results of Gray et al.’s study are listed in Table 1.

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                                 Vegecat (%)     Evolution (%)     AAFCO nutritional requirements (%)
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  Protein                         29.29                    25.40                              26
  Crude fat                      9.17                    15.33                                9
  Tryptophan                  0.35                       0.29                                0.16
  Methionine                   0.47                      0.33                                 0.62
  Threonine                     0.90                      0.84                                 0.73
  Valine                            1.16                      1.02                                 0.62
  Isoleucine                     1.03                       0.91                                0.52
  Leucine                         1.80                       1.53                                1.25
  Phenylalanine              1.33                       1.09                               0.42
  Lysine, total                   0.71                       1.20                               0.83
  Histidine                         0.52                       0.47                               0.31
  Arginine                         0.95                       1.49                                1.04
  Taurine                           0.02                     <0.04                               0.10
  Linoleic acid                  1.55                       3.72                                0.50
  Arachadonic acid       <0.01                     <0.02                                0.02
  Calcium                          0.80                       0.06                                0.60
  Phosphorus                   0.54                       0.28                                0.50
  Selenium                        7 ppm                    0.48 ppm                       0.1 ppm
  Niacin                            75.07 mg/kg         39.97 mg/kg                 60 mg/kg
  Retinol (Vit A)      618631 IU/kg          <1599 IU/kg                  5000 IU/kg
  Pyroxidine                       3.28 mg/kg           2.91 mg/kg                   4 mg/kg
  Cobalamin                      0.31 mg/kg           0.02 mg/kg                   0.02 mg/kg
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Table 1: Nutritional content of two vegan feline diets
All values represent dry matter (DM) proportions – i.e. after the water content has been removed.

While both brands claimed nutritional completeness on their labels, as Table 1 demonstrates, both were in fact deficient in certain amino acids, trace minerals, vitamins, and arachidonic acid. The Evolution diet was also deficient in overall protein content.

Protein
The Evolution diet was just barely deficient at 25.4 %, while the vegecat diet was adequate at 29.29 %. The AAFCO requirement was 26 %. The study authors suggest that the AAFCO level may be inadequate (Gray et al. 2004). While unable to substantiate this suggestion, they cited the protein levels of Hill’s Pet Nutrition diets for comparison: 33.5 % protein DM for a feline maintenance diet, and 28.3 % protein DM for cats with renal failure (Hill’s Pet Nutrition 2003). High protein diets have been used or suggested to control signs of diabetes mellitus (Frank et al. 2001), inflammatory bowel disease (Zoran 2002) and to reduce obesity (Hannah 1999). On the other hand, the excessive protein levels found in some meat-based commercial brands predispose to chronic renal disease. DiBartola et al. (1993) demonstrated renal lesions in an alarming 56% (5/9) of cats exclusively fed a meat-based commercial diet containing 40% DM protein for two years.

Amino acids
Both brands were deficient in taurine; the vegecat diet contained 0.02% and the Evolution diet contained less than 0.04%. The AAFCO requirement was 0.10%. Both brands were deficient in methionine; the vegecat diet had 0.47% and the Evolution diet contained 0.33%. The AAFCO requirement was 0.62%. Lysine and arginine were deficient in the vegecat diet at 0.71% and 0.95%, respectively. The AAFCO requirements were 0.83% and 1.04%.

Arachidonic acid
Arachidonic acid was deficient in both diets as well; the vegecat diet contained less than 0.01% and the Evolution diet contained less than 0.02%. The AAFCO requirement was 0.02%. The vegecat diet utilised a species of seaweed, Ascophyllum nodosum, as an arachidonic acid source. The deficiency detected could be due to variations in arachidonic acid concentration between batches of seaweed. Available light and nutrients during seaweed growth and age at harvest may all affect nutrient availability (Peden 2004).

Vitamins
The Evolution diet was deficient in several B vitamins as well. Niacin was inadequate at 39.97 mg/kg and cobalamin was marginal at 0.02 mg/kg. The AAFCO requirements were 60 mg/kg and 0.02 mg/kg respectively. Both were deficient in pyroxidine; the vegecat diet contained 3.28 mg/kg and the Evolution diet contained 2.91 mg/kg. The AAFCO requirement was 4 mg/kg. The Evolution diet was also deficient in retinol (vitamin A) at less than 1599 IU/kg. The AAFCO requirement was 5000 IU/kg.

Minerals
The Evolution diet was deficient in calcium (0.06%) and phosphorus (0.28%). The AAFCO requirements were 0.60% and 0.50% respectively. The Ca:P ratio was 0.21, as compared to an ideal of 1:1 to 2:1. A low ratio places cats at risk of nutritional secondary hyperparathyroidism and consequent loss of bone density. Interestingly, the vegecat diet selenium levels of 7 ppm greatly exceeded the AAFCO requirement of 0.10 ppm. Selenium toxicosis has not been demonstrated in cats, although levels greater than 5 mg/kg are toxic to many other species (National Research Council 1986).

Manufacturer response: Evolution Diet

In response to these results, Eric Weisman, Evolution Diet CEO (2004) stated, “We have ten to twenty thousand healthy and long living dogs, cats and ferrets living on the Evolution Diet. … Major animal sanctuaries use our products and stand behind them. These sanctuaries use our products because they have lower rates of illness and mortality when their animals are placed on our foods.” Clearly, if their diets were consistently inadequate, nutritional diseases would result instead, at least for any animals maintained on these diets long-term. The population of affected animals, at least in big sanctuaries, would be so large it would probably be unmissable, and these sanctuaries would subsequently report this to the manufacturer, and change diets. Yet this has not occurred.

Given that Gray et al.’s study illustrated that one tested Evolution Diet sample failed to meet the AAFCO nutrient profiles for maintenance of adult cats, one or more of the following possibilities must be true:

• The sample tested was nutritionally inadequate, but the great majority of samples sold and used are adequate. This may have resulted from a formulation error at the factory or from degradation over time of an old sample. However, it is unlikely that an old sample would have been retained for testing.

• The laboratory results were significantly in error for several nutrients tested. However, given a professional, accredited laboratory was used, and that the samples were tested blind to prevent bias, this seems very unlikely.

• The AAFCO cat food nutrient profiles for the maintenance of adult cats are highly conservative, and, although Evolution Diet pet food does not meet the AAFCO requirements, it does meet the actual the nutrient requirements for the maintenance of the great majority of adult cats. However, this also seems unlikely. Even if only 10% of cats required the nutrient levels specified by AAFCO, given that “ten to twenty thousand healthy and long living dogs, cats and ferrets [live] on the Evolution Diet” (Weisman 2004), this would have resulted in a minimum of several hundred cats showing signs of nutritional deficiency following chronic feeding on the Evolution Diet. An affected population this large would most probably be detected, yet it has not been.

Hence the most likely possibility is that the sample tested was nutritionally inadequate, but the great majority of samples sold and used are adequate, and that a formulation error occurred at the factory.

Manufacturer response: Harbingers of a New Age

James Peden, of Harbingers of a New Age (2004), stated in relation to their Vegecat KibbleMix:

Overall
“We were frankly shocked by the analysis of the kibble made from Vegecat KibbleMix. I talked with our mixing personnel about the report and tried to understand how such a situation could have occurred. I’m convinced that this particular batch of Vegecat KibbleMix was made improperly, and have stressed to our personnel the importance of paying attention to the mixing process and if any errors are made to notify me immediately rather than pass on incorrectly mixed product.
…
We will reformulate our products in light of these unsettling facts, and submit to a lab for analysis
…
The fact that we’ve supported so many healthy vegan cats for so many years indicates that this particular batch was an isolated incident. But still, this is very alarming and requires our immediate attention.
…
Probably this was a one-time event, and never happened again.
…
It is so unfortunate that Tina [Tina Gray, study author] analyzed an atypical batch of KibbleMix. … It probably only affected 14 pounds total, since that is the small amount we make per batch by hand!
…
One more thing we plan on doing soon. We have a larger facility that we are moving into for mixing, and it will make it possible to keep our raw ingredients and premixes better isolated and organized.”

Protein
“One note about the protein. In our directions we state that any wheat flour can be used. We will change that to read only whole wheat or bread flour. That adds 1% protein over the results that Tina achieved, since Tina used all purpose flour.”

Taurine and selenium
“We don’t even add selenium to the kibble formulation. The taurine that we obtain is crystalline and assays at 98.5% purity.
…
[The mixing person] brought to my attention what must have happened. He mistakenly picked up the Vegecat Micro-Mix container instead of the Vegecat KibbleMix MACRO. That substitution would have resulted in grossly elevated selenium levels as well as a complete lack of taurine, since only the MACRO contains the taurine, and not the Vegecat Micro-Mix.

It’s a relief to me to know what happened, and why the values are so off. What I’m going to do is put color coding on the containers that will match color coding on the wall charts.”

Amino acids and vitamins
”We depend to a large extent upon a food yeast for vitamins and amino acids. Apparently the nutrient profiles that we have for that raw material are in error. What we plan to do is add additional methionine, as well as add lysine, arginine, and pyroxidine (B6) to make up for the deficiency. We will add a preformed source of arachadonic acid, instead of depending upon the kelp to meet that requirement.

The excessive amounts of B12 and Vit A are alarming, and again I’ve stressed the importance of paying attention to the mixing process.”

As with the Evolution Diet, the same three possibilities exist to account for both Gray et al.’s study results, and the large existing population of healthy cats maintained on Vegecat KibbleMix. Once again, the most likely possibility is that the sample tested was nutritionally inadequate, but the great majority of samples sold and used are adequate, and that a formulation error occurred at the factory. This hypothesis was confirmed and the error corrected by the company.

The steps described to rectify the nutritional inadequacies identified by Gray and colleagues are reassuring. As with Evolution Diet cat food, ultimate confirmation would be provided by repeatable independent laboratory analyses. Unfortunately however, I’m not aware of any such confirmatory results.

Conclusions

Gray et al.’s 2004 study illustrates the need for good quality control during production to ensure that feed products consistently meet the nutritional requirements specified by authorities such as AAFCO, and intended by their manufacturers. It is entirely feasible that repeated independent laboratory analyses of a range of commercial brands, both vegetarian and meat-based, would similarly demonstrate nutritional inadequacies, and also inconsistency of nutritional content over time.

Such findings in no way negate the ability of well formulated vegetarian or meat-based diets to meet all the nutritional requirements of the animals for which they are intended. They simply demonstrate the consequences of inadequate quality control, and the need for sound quality control systems during manufacture, including regular laboratory nutritional analyses.

References

• DiBartola SP, Buffington CA, Chew DJ, McLoughlin MA, Sparks RA. Development of chronic renal disease in cats fed a commercial diet. J Am Vet Med Assoc 1993; 202(5): 744-751.
• Frank G, Anderson W, Pazak H, et al. Use of a high-protein diet in the management of feline diabetes mellitus. Vet Ther 2001; 2: 238-246.
• Gray CM, Sellon RK, Freeman LM. Nutritional adequacy of two vegan diets for cats. J Am Vet Med Assoc 2004; 225(11): 1670-1675.
• Hannah S. Role of dietary protein in weight management. Compend Contin Educ Pract Vet 1999; 21: 32-33.
• Hill’s Pet Nutrition. http://www.hillspet.com/index.jsp, accessed 21 Oct. 2003.
• Weisman E. Personal communication to Andrew Knight re: Evolution Diet vegan pet food. 24 Feb. 2004.
• Peden J. Personal communication to Andrew Knight re: feline vegetarian diets and Harbingers of a New Age vegan pet food. 24 Feb. 2004.
• Zoran DL. The carnivore connection to nutrition in cats. J Am Vet Med Assoc 2002: 1559-1567.