The National Research Council (NRC) of the U.S. National Academy of Sciences is the leading provider of nutrient recommendations for dogs and cats. These form the basis for the Association of American Feed Control Official’s (AAFCO) nutrient profiles. AAFCO, in turn, provides mechanisms for developing and implementing uniform laws, regulations, standards and enforcement policies pertaining to such diets [ 28 ].

Other countries and regions have frequently developed their own nutritional guidelines based on country-specific legislation (e.g., Regulation (EC) No 767/2009 for Europe [ 29 ]) and with reference to AAFCO guidelines (e.g., the European Pet Food Industry (FEDIAF) on feeding trials [ 30 31 ]; the Working Group on the Labelling and Advertising of Pet Food in Canada on ingredient labelling [ 32 ]). The World Small Animal Veterinary Association (WSAVA) similarly provides global nutritional assessment guidelines [ 33 ].

Companion animal diets may be accompanied by labelling claims that they are nutritionally complete and balanced. There are two recognised methods of substantiating such claims, and within the U.S., the label’s nutritional adequacy statement must specify the method used [ 34 ]. The first method is to formulate the diet to meet AAFCO Dog and Cat Food Nutrient Profiles. The second method (which is considered the gold standard) [ 35 ], is to conduct a feeding trial for the specified life stage, using AAFCO-approved protocols. Upon successful completion of an appropriate feeding trial, the pet food is exempt from requirements to formulate it to meet nutrient profiles [ 36 ]. If nutritional claims cannot be substantiated using either method, the product must be clearly labelled as a snack, treat, or dietary supplement, or must contain a statement that indicates it is “intended for intermittent or supplemental feeding only” [ 34 ].

Such standards are intended to ensure that companion animal diets are nutritionally sound and that their nutritional content is accurately understood by consumers. However, a number of studies have raised concerns about the nutritional adequacy of vegetarian or vegan companion animal diets.

Most recently, Kanakubo and colleagues examined 13 dry and 11 canned vegetarian diets for dogs and cats that were sold in all or most of the United States. Crude protein (CP) and amino acid (AA) concentrations were compared with AAFCO Dog and Cat Food Nutrient Profiles. Minimum CP concentrations for the specified species and life stages were met by 23 diets; the remaining diet passed appropriate AAFCO feeding trials. However, 25% (6/24) diets did not meet all AA minimum requirements.

3.2. Company Responses

Twelve companies based in the U.S. and internationally supplied the 24 diets examined. In late 2015, we contacted all of these companies by email. We inquired whether they had any additional data or information relevant to the conclusions of Kanakubo and colleagues [ 37 ]. In particular, we asked whether companies could supply any evidence (e.g., studies by external independent laboratories or internal assessments) to verify the nutritional adequacy of their products. We also inquired about any steps taken during the manufacturing process to ensure that diets are nutritionally adequate, and consistent over time.

An initial email inquiry was followed by an additional email to non-responders after one month. Five companies (Ami, Evolution Diet Pet Food, Purely for Pets, Big Heart Pet Brands, Central Garden and Petco) failed to respond to either inquiry. An additional company (Natural Balance Pet Foods) declined to provide comments. Responses from the remaining six companies varied substantially.

Some of these six asserted that their products were nutritionally adequate. Royal Canine, for example, asserted that, “Canine vegetarian dry and wet diets are formulated to meet the nutritional levels established by the AAFCO Dog Food Nutrient Profiles for maintenance”.

Similarly, Purina Nestle asserted that, “The nutritional adequacy of our products is fundamental. We ensure this through formulation, feeding trials, and strict manufacturing processes. We meet or exceed every major food quality and safety standard, including those issued by the FDA, USDA, AAFCO and FEDIAF”.

V-dog asserted that their diet is “formulated to meet or exceed the nutritional levels established by the AAFCO Dog Food Nutrient Profiles for adult maintenance”. They even supplied the ingredient lists for their products and a nutritional breakdown. They also asserted that “Our production facility has staffed animal nutrition experts and veterinarians that conduct regular tests on the kibble post production to ensure its nutritional adequacy. We obtained our kibble’s guaranteed analysis from an external lab and our regular nutrition and quality tests are performed by our production facility on a regular basis”. They stated that they had not performed feeding trials, however “we’ve been in business for over 11 years and have seen thousands of dogs thrive into their golden years on the v-dog kibble”.

PetGuard asserted that, “In addition to independent laboratory tests for determining the level of vitamins, minerals and nutrients in our finished diets, we conduct home feeding studies to determine the performance of our diets in an actual home environment. It is an ongoing program for our dog and cat foods. The only compensation these pet parents receive for completing health and behavioural forms six times per year—and submitting the yearly veterinarian check-up report—is the foods themselves. Canned, kibble, treats or snacks, all are evaluated. We have done this for the past 20 years and are confident and pleased with our data that shows our diets perform, as a single source diet should, for the long term health and long life of our study group’s companions (average 16 years for canines and 18 years for felines)”.

No company provided details of independent laboratory verification of the nutritional content of their diets. PetGuard also stated that, “Our data is proprietary and we will not be able to share it with you. In a very competitive environment—where innovation and creativity comes from hard work, study, and technical manufacturing breakthroughs—discretion is necessary”.

Clearly, few companies asserted that they had used feeding trials or independent laboratory verification of nutritional composition. Evanger’s Dog and Cat Food Company provided some insights into the possible reasons for this: “Many brands send their foods to third-party laboratories to make sure they meet their guaranteed analyses, which typically doesn’t include the complete AAFCO breakdown as that would cost a few thousand dollars more—and no one makes that in profit on a batch of food. This is why manufacturers rely on help from their vitamin and mineral premix suppliers for help when formulated ( sic ) the food. They would assist in the inclusion rates and the knowledgeable ones would even provide degradation results for the age and processing of certain vitamins”.

In one case (Wysong), the company admitted that its product was unlikely to be nutritionally complete: “Wysong does not advocate the singular feeding of VeganTM to carnivores such as dogs and cats. … It is designed for intermittent feeding or as a base to add different meats for sensitivities and allergies”. They further asserted their philosophical opposition to the concept of attempting to produce a single, nutritionally complete diet: “Complete knowledge of nutrition does not exist … and therefore “completeness” is misleading. … With that in mind, Wysong seeks to formulate and educate for optimal, not “adequate” nutrition and encourages pet owners to rotate, vary, and enhance the diet”.