Prof Andrew Knight’s studies on the benefits of a plant-based diet in our pets are both fascinating and gamechanging for the way we need to view our pet’s health and nutrition.

We are so thankful that with his careful published research, we finally have the scientific proof that we need that proves that plant-based diets are as healthy if not healthier for our pets than meat-based, from his 2016 published article that you can read here.

We then have to commend Prof Andrew Knight for his second extensive study and published paper (read it here), by far the largest of its kind, that surveyed 4,060 dog and cat owners in 2021 with the following results:

– Plant-based pet foods appear to be enjoyed as much as meat-based diets.
– Study shows no difference for animals between plant-based and meat-based diets.
– Plant-based pet foods do not compromise animal welfare, provided other determinants of welfare, such as nutritional requirements, are adequately provided

Prof Andrew Knight and colleagues (Huang E, Rai N, Brown H) published a groundbreaking research paper on the 13th April 2022 that stated from the findings of 2639 dogs, that “the pooled evidence to date indicates that the healthiest and least hazardous dietary choices for dogs, are nutritionally sound vegan diets.”

All the information below is available to read on Prof Knight’s own website Sustainable Pet Food, but we have included sections which we found particularly interesting from his published works and intense research and we thought we’d share them with you as you do your own research –

Incidence of health problems
Infections
Overview
The most common health problem was infections of all kinds. 11.7% (35/300) suffered some type of infection, with ear infections being the most common (16), followed by urinary tract infections (eight), eye infections (six), and other miscellaneous infections (seven). There was an inverse relationship between length of time as a vegan or vegetarian and incidence of infections:

· No dog who had been vegan for four or more years or vegetarian for more than 5.2 years contracted ear, urinary tract, eye or other infections.
· No dog who had been vegan for more than 3.5 years had an ear infection.
· No dog who had been vegetarian for more than four years had a urinary tract infection.

Urinary Tract Infections
2.7% (8/300) dogs had a history of urinary tract infections, of which six were female and two male. According to a veterinarian contacted by PETA, this figure is somewhat higher than the expected rate of infection (about 1%).

The excretion of the nitrogenous waste products of protein catabolism results in the acidic urine of carnivores. Vegetarian diets with typically decreased protein contents may result in urinary alkalinisation, which increases the risk of urinary stones, which may result in partial or complete urinary obstruction. Alterations in bacterial flora, with increased possibility of urinary infections, may also result (see ‘Urinary Alkalinisation’ below).

Skin problems
The second most common health problem observed after infections was skin ailments, which also constitute the most common illnesses of dogs overall. 11.3% (34/300) suffered from some form of skin irritation (hot spots, flea allergy, dermatitis, etc.), but eight of these were considered to be minor.

Arthritis
The third-ranking health problem was arthritis, with 7.3% (22/300) suffering from this condition. Seven of the 22 dogs had arthritis related to old injuries, such as broken bones. Of the remaining 15 dogs, 13 were 10 years old or older, so the arthritis may have been age-related.

Benign growths
4.7% (14/300) had apparently benign growths, tumours, warts, or cysts, which appeared unrelated to time spent on a vegetarian diet.

Heart problems
4.0% (12/300) had heart problems, and seven of the 12 had died as a result of those problems. Five of the dogs who died of heart problems were 13 to 15 years of age, i.e. elderly. However, the trend for heart disease was the opposite of that for infections, i.e., there was a direct correlation between heart disease and length of time as a vegan or vegetarian: all dogs with heart disease had been vegan for at least four years or vegetarian for at least 10 years.

The most common and serious cardiac disease was dilated cardiomyopathy (DCM). Five dogs (aged five, nine and older), all of whom had been vegan for at least four years, had DCM, which results in myocardial (heart muscle) flaccidity and impaired pumping ability. This potentially fatal disease of the heart muscle normally affects about 2% of all dogs, appearing mostly in large and giant breeds. A small percentage of these lack sufficient cardiac levels of the amino acid L-Carnitine. The amino acid taurine, which dogs, unlike cats, are able to synthesise, regulates the entry of calcium into the myocardium in order to trigger each heart beat. Deficiency may also result in cardiomyopathy (heart muscle disease).

However, recovery is possible with taurine or L-carnitine supplementation. Of the five dogs with DCM, three recovered by taking supplements of either L-carnitine or taurine. Prevention appears possible through regular supplementation with these two amino acids, e.g. via a nutritionally complete vegetarian canine supplement.

Body weight
A low 3.7% (11/300) were considered by their guardians to be overweight. However, all 11 of these dogs were nevertheless described as in good to excellent health or energetic. The decreased protein and fat levels and increased dietary fibre of vegetarian diets are all effective in promoting a healthier weight.

Digestive problems
3% (10) were identified as having digestive problems. Of these, nine were seven years or older, which may have been related to a general decline in digestive enzyme secretion with age, and which is often treatable with enzyme supplementation.

Hypothyroidism
2.7% (8/300) had hypothyroidism, a decrease in serum thyroid hormone levels. However, no dog who had been vegan for more than three years had hypothyroidism, and no dog who had been vegetarian for more than four years suffered from it.

Vision or hearing deficits
2.7% (8/300) were deaf or had hearing loss, but seven of the eight were 13 years old or older. Similarly, seven dogs (2.3%) were blind or had vision loss, but six of the seven were 13 years old or older. Age-related hearing and vision loss is unfortunately normal. The younger blind dog was a collie with congenital blindness.

Cancer
A low 2.7% (8/300) had cancer. Of these eight, six were 9 years old or older, with the other two being seven years old. The incidence of cancer normally rises with age. The inverse correlation between duration of vegan or vegetarian diet and cancer incidence may have been significant: no dog who had been vegan for more than five years and no dog who had been vegetarian for more than 5.5 years had cancer.

Specific foods
Nutritional yeast and garlic
Dogs eating nutritional yeast and/or garlic did seem to fare somewhat better than the rest of the dogs. 81.6% (102/125) of the dogs eating nutritional yeast were in good to excellent health, compared to 72.6% of those who did not. 83.3% (70/84) of dogs eating garlic were in good to excellent health, compared to 80% of those who did not. Dogs eating either nutritional yeast or garlic also had a much higher incidence of good or improved coats—44% for nutritional yeast eaters and 47.6% for garlic eaters, compared to only 22.9% of dogs not eating nutritional yeast and 17.8% of dogs not eating garlic.

Soy foods
The only other specific food item that seemed significant was soy food products. Since all the commercial vegetarian dog foods eaten contained soy, very few dogs had no soy products in their diets—only 13% (39/300). However, these 39 dogs were in substantially better health than the others. 89.7% (35/39) of the dogs who ate no soy products were in good to excellent health, compared to 74.3% of dogs who ate soy products. Also, the incidence of skin problems was much lower in the dogs who didn’t eat soy—only 5.1% (2/39) had skin problems compared with 10.7% of those who ate soy products. Some dogs are allergic to soy, which may cause skin reactions. Dogs who did not eat soy products relied heavily on grains (oats, rice, bread, and pasta), legumes (chick peas, lentils, split peas, and beans), vegetables, potatoes, and sunflower seeds.

Conclusions
Although tests for statistical significance were not performed, the results suggest that:

• The longer a dog remains on a vegetarian or vegan diet, the greater the likelihood of overall good to excellent health.
• Veganism is more beneficial than vegetarianism.
• The longer a dog remains on a vegetarian or vegan diet, the less likely he or she is to get cancer, infections, hypothyroidism, or suffer from obesity.
• A vegetarian diet may increase urinary alkalinisation, with its consequent potential for urinary stones, blockages and infections; hence regular urine pH monitoring and correction of alkalinisation is important (see below).
• The longer a dog remains on a vegetarian or vegan diet without supplementation of L-carnitine or taurine, the greater the likelihood of dilated cardiomyopathy or other cardiac disease, particularly in large or giant breeds.
• Nutritional yeast and garlic appear beneficial to overall health and coat condition.
• Dogs without soy foods in their diet appear healthier than those who eat soy, which is known to cause skin and other reactions in dogs allergic to it.

Cataract resolution
John Grauer of New York described cataract resolution in his 16 year dog Simone: “A couple years ago, she had cataracts — her eyes were cloudy and dull. Recently, I have been giving her some of my own food (pea soup, tomatoes, cabbage, etc.). I always noticed that after giving her vegetables, her eyes would turn a deeper color brown. Finally, I began to realize that her eyes were not turning color, rather, the cataracts were going away! I haven’t been to my vet in a while, but when I go again, I will ask him to look at her eyes. Now they are bright and clear, as far as I can tell. Actually, I think what did the trick was the cabbage. Simone eats cabbage like there is no tomorrow. She eats it raw, cooked, the cores, and any old part of a cabbage. She always wants it, even after she has had her regular dinner! To me, it is kind of funny to see a dog eating cabbage, but that is what she likes (I like it too).” (Peden 1999).

Urinary acidifiers
Struvite requiring 7.0 or higher to crystallise (Gillen 2003). Accordingly, acidifying urine via dietary modification can decrease struvite occurrence and aid urolith dissolution. Urine may be acidified in several ways.

Asparagus, peas, brown rice, oats, lentils, garbanzos, corn, Brussels sprouts, lamb’s quarters (the herb Chenopodium album, also known as pigweed), most nuts (except almonds, coconuts and macadamia nuts), grains (not millet), and wheat gluten (used in kibble recipes) may be included in vegetarian dog food, and are all urinary acidifiers (Peden 1999).

Vitamins are also of benefit. Vitamin C (ascorbic acid) is a urinary acidifier. Tablets may be pulverised or ascorbic acid powder may be used. The BSAVA (British Small Animal Veterinary Association) Small Animal Formulary (drug handbook) recommends a dosage of 50-80 mg/kg every 24 hours for cats and dogs (Tennant 2003). pH buffering negates their effectiveness, so unbuffered Vitamin C should be used. If other urine acidifiers are also used, doses may be decreased.

Methionine is particularly effective in preventing struvite formation. Methionine is metabolised into sulfuric acid which is a powerful urinary acidifier. Additionally, sulfate displaces phosphate from the magnesium-ammonium-phosphate complex, preventing struvite formation. The BSAVA Small Animal Formulary recommends a dosage of 200 – 1,000 mg/dog every 8 hours (Tennant 2003). The dosage should be adjusted to maintain urine pH at or below 6.5. Excessive methionine levels can result in metabolic acidosis with consequent loss of bony calcium and electrolyte imbalances (Peden 2003). Methionine should not be used in young animals nor those with kidney or severe liver disease (Tennant 2003).

Sodium bisulfate is a particularly powerful urinary acidifier, and is added to some vegetarian pet nutritional supplements (Peden 2004). Ammonium chloride is also a powerful urinary acidifier, but may decrease palatability. In his ‘5-minute (veterinary) consult drug formulary,’ Papich (2004) recommends a dosage of 100 mg/kg every 12 hours.

Prevention
Dogs are less predisposed to urolithiasis and related urinary problems than cats, and although adverse health consequences are unlikely, those consequences may nevertheless include fatal blockage of the urinary system, particularly for males; and painful urinary tract infections. Hence urinary pH and dietary magnesium concentrations should be monitored.

I recommend that to provide a good level of safety urinary pH levels of both males and females are checked before implementing any dietary change, to establish a baseline, and weekly thereafter whilst transitioning to a vegetarian diet, and then monthly, for life, even once diet and pH levels appear to have stabilised. Levels should be checked more frequently during any dietary, environmental or other changes with the potential to result in destabilisation, or at the first sign of any urinary abnormalities developing. Urine can be collected from dogs using containers such as foil baking trays. pH test strips are also available from veterinarians, although pH meters provide the most accurate results.

Gillen (2003) describes three steps, in increasing order of magnitude, that may be taken to rectify urinary alkalinisation, if detected. He applies these steps to cats, but the general principles are also applicable to dogs:

1. For minor cases, he states that enzyme supplements which include methionine, vitamin C, and/or cranberry extract will be sufficient. These limit both urinary alkalinisation and inflammation. They also aid digestion, and can result in increased vitality.

2. For moderate cases, Gillen states that vegetarian nutritional supplements with added sodium bisulfate may be sufficient.

3. For severe cases Gillen recommends methionine pills.

Information copied from Prof Andrew Knight’s research as published on his Sustainable Pet Info website