Trends in companion animal nutrition often mirror trends in human nutrition, reflecting the desire of pet owners to feed diets that they consider healthy and beneficial for the well-being of their pets.1–3 The number of people choosing to eat a plant-based diet and adopting a vegan lifestyle has been steadily increasing as individuals seek a lifestyle that they perceive to be healthier and with less impact on animals and the environment.4–6 It has been suggested that eliminating meat from the diet is more prevalent among pet owners than for the general public.7–9 Many of these meat-avoiding individuals have a moral dilemma regarding the husbandry of carnivorous pets: they avoid animal products in their own diet, but they live with pets that rely on nutritional sustenance from products derived from other animals.7
Interest in, and availability of, plant-based diets are growing in popularity in the North American pet food market,10,11 but there are little data to support the benefits of feeding plant-based diets to omnivorous and carnivorous pets. For dogs, most essential nutrients can be obtained from plant sources.12 However, dogs evolved while eating an omnivorous diet that was high in animal tissues,13 which leads to concerns about whether plant-based diets can completely satisfy the nutritional requirements of dogs. Few studies have been conducted to examine the nutritional sufficiency of plant-based diets. Investigators of published studies14–17,a simply evaluated the content of some nutrients in plant-based diets or evaluated a limited number of health variables in dogs fed plant-based diets.
The purpose of the information reported here was to address nutrients of concern when formulating plant-based diets and how to satisfy nutrient requirements of dogs without the use of animal-derived ingredients. It was intended to assist veterinarians when evaluating plant-based diets and providing guidance to pet owners who wish to feed their dogs such diets.
Nutritional Requirements of Dogs
Domesticated dogs (Canis lupus familiaris) are descended from wolves (Canis lupus) and have coexisted with humans for 10,000 to 30,000 years.18,19 Dogs and wolves are both canids (family Canidae of the order Carnivora).20 This taxonomic nomenclature is misleading because the order Carnivora also contains obligate carnivores such as the family Felidae (eg, cats, cheetahs, and lions) and herbivores such as the family Ailuropodidae (eg, pandas).19 The diet of wolves can vary drastically, ranging from a diet consisting almost completely of prey animals to one containing up to 50% plant matter, which makes them true omnivores or facultative carnivores.13,21,22 Wolves are naturally omnivorous in the wild, and the domestication of dogs in coevolution with humans has resulted in further evolutionary adaptation to diets with a higher plant content.23 Ancestors of domesticated dogs began to live in close association with humans during the early agricultural revolution, and they scavenged from refuse and waste near human settlements. As humans adopted a less nomadic lifestyle and began cultivating crops, their early dump sites would have included food waste and feces rich in starches.24 Indeed, differences in the genome of domesticated dogs and wolves indicate that dog ancestors adapted from a mainly carnivorous diet to one richer in starch as they began to rely on human settlements as sources of nutrition.13,23
Current understanding of the nutritional requirements of dogs has been determined through decades of research, such as studies and reports issued by the National Research Council of the National Academies of Sciences.25 On the basis of this information, nutrient profiles published for use by the pet food industry, such as those developed by the AAFCO26 and FEDIAF,27 are used to define the nutritional adequacy of pet diets appropriate for various life stages. These life stages include maintenance of adult dogs, growth of puppies, and reproduction and lactation. In comparison with maintenance requirements for adult dogs, puppies have increased requirements for many nutrients to support organ development, muscle synthesis, and skeletal growth. Growing puppies are at greater risk of nutritional insufficiencies than are adult dogs, and appropriate nutrition is critical for healthy development. In particular, puppies require higher concentrations of dietary fats, protein, and essential minerals as well as provision of calcium and phosphorus within a strict ratio.28 Inappropriate dietary management of puppies, particularly those of large and giant breeds, can result in irreversible deformities and compromise quality of life.29–32 It is likely more difficult to meet the higher nutrient requirements of puppies, compared with nutrient requirements of adult dogs, when feeding a diet devoid of animal ingredients.
Nutrients of Concern in Strictly Plant-Based Diets
Macronutrients and micronutrients
Essential macronutrients for dogs (ie, protein and fat) can be found in both plant and animal ingredients. However, micronutrients pose a greater challenge when formulating a complete and balanced food for dogs. No single ingredient, regardless of whether it is of plant or animal origin, is replete in all the essential nutrients in sufficient quantities or proportions. All the essential nutrients can be obtained from nonanimal sources. Compared with animal-derived ingredients, plant-based ingredients may be scarce or poor sources of some nutrients. As such, commercial dog foods typically contain, at a minimum, additional vitamins and minerals, which may be from synthetic or plant-derived sources.
Of greatest concern for strictly plant-based diets is the sufficiency of essential AAs and nutrients that are primarily derived from animal ingredients. These include lysine; the sulfur-containing AAs methionine, cysteine, and taurine; the omega-3 PUFA DHA; and vitamins A, B12, and D.12,15,33 Some minerals, namely calcium, phosphorus, potassium, and zinc, are found in low concentrations in most plant-based ingredients12,15 and can be deficient in diets that are not formulated or supplemented appropriately. However, these minerals are available as supplement-type products from nonanimal sources. Both animal- and plant-based diets often rely on supplementation of minerals to be nutritionally complete and balanced. As long as diets are supplemented with appropriate amounts of minerals, the provision of adequate quantities of minerals without the use of animal products is not a concern; thus, mineral supplementation of plant-based diets will not be discussed further.
Most diets are also supplemented with vitamins. Although nonanimal sources of most vitamins exist, vitamins A, B12, and D are traditionally obtained from animal sources.
Protein and essential AAs
Although protein can readily be found in many plant ingredients, the protein content of strictly plant-based diets should be closely monitored. Dietary protein provides both nonessential and essential AAs. Essential AAs cannot be synthesized within the body and must be obtained from the diet in adequate amounts to maintain life, promote healthy growth, or support gestation and lactation. In comparison, nonessential AAs may be produced by the body as required, provided adequate precursors are available. Both nonessential and essential AAs may be used to synthesize proteins within the body, act as functional metabolites, or be catabolized as energy. The essential AAs for dogs are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.25
The total quantity of protein in a diet is important, but the quality or biological value of the protein must also be considered.34 The biological value of protein is considered primarily to be a function of digestibility and constituent AA content and describes the ability of the protein ingredient to provide essential AAs to the subject consuming the diet.35 Other characteristics of an ingredient can affect the biological value of protein, including the source and processing practices. Animal tissues typically contain proteins of high biological value; often all 10 essential AAs are provided in sufficient quantities with high digestibility. In contrast, the biological value of plant proteins for pet foods has been questioned because their AA profiles may be incomplete, particularly with methionine or lysine being limiting AAs.12,15,17 When compared with animal-derived proteins, plant-derived proteins may have lower digestibility because of the presence of poorly digestible structural carbohydrates. In addition, plant-derived proteins may require more processing to mitigate antinutritional factors that impact palatability, digestibility, and utilization of nutrients.34,36 However, a number of plant-based protein ingredients have been proposed for use in companion animal diets.36–38
Protein content differs among plant sources, although some plant sources of protein contain total protein and sulfur-containing AAs in quantities comparable to those of animal sources of protein commonly used in conventional pet foods39–48 (Table 1). In addition to the essential AAs, taurine content must also be considered in diets for dogs. Taurine, a β-aminosulfonic acid, is not considered essential for all dogs because it can be endogenously synthesized when there are adequate amounts of sulfur-containing AAs in the diet.25–27 However, taurine may be considered conditionally essential in some circumstances, particularly for breeds that may be susceptible to taurine-deficient health conditions.49,50 Taurine is not incorporated into protein in the body. Instead, it is involved in fetal development, growth, neuromodulation, vision, heart function, and antioxidation reactions.25 Dogs have obligatory conjugation of bile acids with taurine, which leads to high losses through fecal excretion.49,50 This is exacerbated by diets high in fermentable fiber, which may result in enhanced bile acid excretion and microbial degradation of taurine-conjugated bile acids.51 Dogs consuming plant-based diets may be at increased risk of taurine deficiency because taurine is absent in plants other than algae, and plant-based diets replete with protein may be marginal in precursor sulfur-containing AAs.25 Furthermore, the high fiber content of most plant ingredients may also increase taurine loss.52 Taurine deficiency may manifest clinically as nonspecific signs (eg, lethargy and anorexia) or as a more specific condition (dilated cardiomyopathy).50 Therefore, it is crucial that plant-based diets formulated for dogs contain sufficient quantities of methionine and cysteine to support sulfur-containing AA metabolism as well as taurine synthesis. To ensure adequate dietary intake of sulfur-containing AAs with plant-based diets, the addition of methionine and taurine is recommended. Nonanimal sources of these nutrients are readily available, their bioavailabilities have been determined, and they are already used by animal feed industries.53,54
Common sources of proteins for dog foods.
| Sulfur-containing AAs (g/100 g of product)* | |||||
|---|---|---|---|---|---|
| Source | Product | Total protein (g/100 g of product)* | Methionine | Cysteine | Reference |
| Plant | |||||
| Pearled barley | 10 | 0.2 | 0.2 | 39 | |
| Chickpeas | 17 | 0.2 | 0.2 | 40 | |
| Corn | |||||
| Distillers' grains | 29 | 0.5 | 0.5 | 41 | |
| Germ meal | 20 | 0.6 | 0.4 | 41 | |
| Gluten meal | 60 | 1.9 | 1.1 | 41 | |
| Lentils | 25 | 0.2 | 0.2 | 40 | |
| Oats | |||||
| Groats | 11 | 0.2 | 0.4 | 39 | |
| Flour | 12 | 0 | 0 | 39 | |
| Peas | |||||
| Protein concentrate | 49 | 0.5 | 0.6 | 42 | |
| Whole dried | 23 | 0.2 | 0.2 | 40 | |
| Soy | |||||
| Meal | 48 | 0.7 | 0.7 | 41 | |
| Protein concentrate | 76 | 1.1 | 0.8 | 43 | |
| Whole beans | 43 | 0.6 | 0.7 | 40 | |
| Sunflower meal | 49 | 0.8 | 0.8 | 42 | |
| Brewer's yeast | 59 | 1.3 | 1.3 | 44 | |
| Animal | |||||
| Cattle | |||||
| By-product meal | 52 | 0.4 | 0.4 | 45 | |
| Sheep | |||||
| Lamb meal | 59 | 0.8 | 0.8 | 46 | |
| Pigs | |||||
| Meat-and-bone meal | 53 | 0.7 | 0.5 | 47 | |
| Blood meal | 89 | 1.0 | 1.0 | 47 | |
| Poultry | |||||
| Chicken by-product meal | 53 | 0.9 | 0.9 | 41 | |
| Chicken meal | 66 | 1.0 | 1.7 | 46 | |
| Duck meal | 61 | 1.2 | 0.6 | 46 | |
| Mechanically separated chicken meat | 15 | 0.3 | 0.1 | 48 | |
| Poultry by-product meal | 69 | 0.8 | 0.5 | 45 | |
| Poultry meal | 63 | 1.3 | 0.6 | 48 | |
| Deer | |||||
| Venison meal | 59 | 0.7 | 0.5 | 46 | |
As-fed basis.
Few studies have been conducted to evaluate the total protein or AA content (or both) of plant-based dog foods. However, it has been found that diets were replete and met industry requirements for those nutrients.15,a Although single plant-derived ingredients do not provide proteins that meet all essential AA requirements for dogs, complementary proteins may be used to meet these requirements. By combining plant-derived proteins with complementary AA profiles, a complete AA profile is created.55 Use of complementary proteins can be illustrated by use of the Liebig barrel (Figure 1).
Schematic depiction of complementary proteins by use of the Liebig barrel to demonstrate fulfillment of AA requirements. The barrel on the left depicts an incomplete protein profile, whereas the barrel on the right indicates the use of complementary proteins to form a complete AA profile. Arg = Arginine. His = Histidine. Ile = Isoleucine. Leu = Leucine. Lys = Lysine. Met = Methionine. Phe = Phenylalanine. Thr = Threonine. Trp = Tryptophan. Val = Valine.
Citation: Journal of the American Veterinary Medical Association 253, 11; 10.2460/javma.253.11.1425
Neither the total protein nor AA content is of concern when a plant-based diet is appropriately formulated, although the issue of digestibility of plant-derived protein must be addressed. Plant-based diets may have a higher fiber content than diets containing animal ingredients, thus reducing both total digestibility and protein digestibility.15,34 Soy, a common plant protein source in pet foods, has total digestibility that is demonstrably similar to that of animal sources of protein.56–58 Rice and potato proteins, canola, sunflower and peanut meals, and protein fractions of low-fiber cereal products (eg, barley, corn, flour, and wheat) are well digested by dogs.36,59 Protein-rich plant-based ingredients reportedly have digestibility similar to that of animal-derived ingredients. However, the protein content, AA content, and digestibility of commercial plant-based diets, with the exception of 2 vegetarian therapeutic diets,b,c have not been widely reported. Although the protein and AA content of plant-based diets do not appear to be adversely affected when animal-based ingredients are not used, careful formulation is required to provide complementary AAs to achieve an AA profile that meets the nutritional requirements of dogs and ensures adequate quantities of essential AAs are available to the animals.
Fatty acids
Certain omega-3 and omega-6 PUFAs are essential fatty acids required by the body for critical cellular structure and physiologic functions.25,60 For adult nonreproductive (males as well as females that are not pregnant or lactating) dogs, α-linolenic acid is the only essential omega-3 PUFA required to maintain health, and linoleic acid is the only essential omega-6 PUFA.25 Other longer-chain omega-3 PUFAs (eicosapentaenoic acid and DHA) can be synthesized in small but sufficient quantities from α-linolenic acid and are not considered essential for adult nonreproductive dogs. However, puppies require direct provision of dietary DHA during growth because this essential PUFA selectively accumulates within developing nervous tissues.61 Therefore, DHA must be provided in diets formulated to support gestation, lactation, and growth.25–27 Terrestrial plants can be rich sources of α-linolenic acid, but they are not a major source of DHA. Until recently, fish oil was the only concentrated dietary source of DHA used commercially.62 It is known that many species of algae contain high amounts of DHA, and these ingredients can be included in food formulations.63 Thus, plant-based foods can be formulated to meet the essential fatty acid requirements of dogs, even during gestation, lactation, and growth, through the inclusion of marine plant products.
Vitamin A
Vitamin A (retinol) is a fat-soluble vitamin found exclusively in animal tissues. It is essential for healthy cell division and differentiation.64 Many plants contain precursor provitamin A carotenoids that omnivorous animals such as dogs can metabolize to form active vitamin A.65 On the other hand, obligate carnivores such as cats cannot use carotenoids and require dietary provision of preformed vitamin A.66,67 Inclusion of vegetables rich in β-carotene can be used to formulate canine diets that contain adequate precursors for vitamin A metabolism. Furthermore, synthetic vitamin A analogs, in the form of retinyl esters, can also be added to plant-based diets.64
Vitamin B12
The vitamin B complex includes a number of essential nutrients, such as thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), biotin (vitamin B7), folate (vitamin B9), and cobalamin (vitamin B12). In general, the B vitamins are enzymatic cofactors and precursors required for many metabolic processes throughout the body.
Of the B vitamins, only cobalamin is not found in plant materials. Cobalamin is produced only by microbes in soil or fermented organic substances and in specific parts of the gastrointestinal tract of animals.25 In some animals, cobalamin is synthesized by gastrointestinal microbes and is then absorbed and distributed to the tissues, where it plays a role as a cofactor in metabolic reactions. Thus, animal tissues can be a rich source of vitamin B12. However, although the gastrointestinal tract of dogs contains the necessary flora for cobalamin synthesis, it occurs caudal to the site of absorption and thus cannot be used by canids. Therefore, dietary inclusion of cobalamin is required.25 The dietary source of cobalamin in pet foods has historically been from animal products, but most commercial pet foods currently may also contain bioavailable synthetically derived cobalamin produced from microbial fermentation.25 The addition of synthetic cobalamin to plant-based diets thus fulfills the dietary requirement for dogs.
Vitamin D
Vitamin D is the precursor to the hormone calcitriol, which critically influences calcium homeostasis and bone metabolism.68,69 It is important to have a sufficient amount of vitamin D for proper skeletal mineralization, particularly in highly metabolically active growing bones of juvenile dogs. Without provision of adequate vitamin D, dysfunction of bone mineralization can occur despite meeting established requirements for dietary calcium and phosphorus.69
There are 3 potential sources of vitamin D: dietary vitamin D as ergocalciferol (vitamin D2), dietary vitamin D as cholecalciferol (vitamin D3), and endogenous synthesis in the skin when exposed to UV light.70 Whereas most animals are capable of synthesizing vitamin D in their skin with adequate exposure to sunlight or UV radiation, dogs have high enzymatic catabolism of vitamin D precursors that results in negligible conversion to vitamin D3.69,70 Thus, dogs have a strict dietary requirement for vitamin D.
Differences in physiologic activity between vitamin D2 and vitamin D3 have been documented in other species, with most animals able to use vitamin D3 with greater efficiency.25 For example, in both carnivorous cats and omnivorous humans, vitamin D2 was found to have less influence than vitamin D3 on the concentration of the main vitamin D metabolite calcidiol.71,72,d Dogs may be capable of using vitamin D2 with an efficiency equal to cholecalciferol as a dietary source of vitamin D73,e; however, this finding has not been confirmed, and recommendations for the inclusion of vitamin D2 in diets formulated for dogs currently do not exist.
The form of vitamin D is of paramount interest when formulating plant-based diets because vitamin D2 is derived from fungi and yeasts, whereas vitamin D3 has traditionally been derived from animal products, particularly fish oils or sheep lanolin. However, vitamin D3 has also been isolated from plants and is biologically active in animals.74,75 Plant tissue or cell cultures from species of terrestrial flowering plants and grasses from the Solanaceae, Cucurbitaceae, Fabaceae, and Poaceae families as well as microalgae and lichens may provide a source of plant-derived vitamin D3 for fortification of plant-based pet foods.74–76 Although commercial preparations of plant-sourced vitamin D3 exist in the nutritional supplement market for humans, such products do not appear to have been adopted for use by the pet food industry. Thus, it would appear that vitamin D may currently be the nutrient of most concern in plant-based diets for dogs. A prudent recommendation to pet owners feeding their dogs a plant-based diet may be to monitor serum calcidiol concentrations as an indication of vitamin D status.
Commercial Plant-Based Diets for Dogs
In accordance with the current understanding of pet nutrition, the importance of nutrients, not ingredients, is emphasized. Thus, evaluation of the nutritional sufficiency of a plant-based diet should be based on the same criteria as diets that include animal-derived ingredients. In North America, a diet must be formulated to meet AAFCO nutrient recommendations or pass a feeding trial conducted in accordance with an AAFCO protocol for that diet to have a statement indicating it is complete and balanced for a given life stage.26 Many consider feeding trials to be superior to simply being formulated to meet a specific nutrient profile because nutrient bioavailability may be affected by processing and the nutritional content of a consumed diet may differ from the expected nutritional profile of a diet formulation.56
A large criticism of plant-based diets is that there is little evidence to substantiate claims of nutritional sufficiency because, to the authors' knowledge, no plant-based diets have been evaluated in a feeding trial conducted in accordance with an AAFCO protocol. However, this is not a criticism exclusive to plant-based diets. As revealed by the nutrition statement on the packaging, most of the diets sold by the top commercial manufacturers are formulated to meet the AAFCO requirements of the specific life stage of animals but have not been evaluated via feeding trials. Furthermore, feeding trials performed in accordance with AAFCO protocols require only a small sample size, a short duration, and few outcome measures that strongly correlate with nutritional adequacy.26
Although a feeding trial may be used to substantiate claims of nutritional adequacy, it is by no means widely adopted throughout the industry. For diets that have been formulated to a specific nutrient profile but that have not been substantiated with a feeding trial, additional evidence to support the nutritional statement may be achieved through testing of the final product (eg, dietary nutrient analysis and digestibility testing; Supplementary Table S1, available at avmajournals.avma.org/doi/suppl/10.2460/javma.253.11.1425). Companies do not typically include this information on dog food packaging or on their websites. Therefore, interested veterinarians and pet owners are encouraged to contact companies to discuss the qualifications and credentials of the diet formulator, quality assurance and quality control measures for diet manufacturing, and types of tests performed on the finished product.77
Home-prepared Plant-Based Diets for Dogs
Since the concept of complete and balanced diets was introduced into the pet food industry nearly 50 years ago, the practice of feeding commercial diets has commonly been the main method of feeding pet dogs.78,79 However, trends in companion animal nutrition often mirror trends in human nutrition, and a growing number of pet owners currently appear to prefer home-prepared diets over processed commercial diets for their dogs.80,f Home-prepared diets are recognized as being at high risk for nutritional imbalances and insufficiencies when not properly formulated, and feeding such diets may result in adverse health effects.3,81,82 Whereas home-prepared diets made with animal ingredients are often nutritionally imbalanced and insufficient in some nutrients, particularly vitamins and minerals, they may be replete in protein and AAs because they contain complete protein sources.83,84 Considering the aforementioned challenges regarding essential nutrients found primarily in animal ingredients, home-prepared plant-based diets are at least as likely to have vitamin and mineral imbalances and insufficiencies as home-prepared animal-based diets. In addition, they are also likely to be insufficient in sulfur-containing AAs and may not provide adequate amounts of total protein. From an infectious disease perspective, home-prepared plant-based diets do have an advantage over raw home-prepared animal-based diets in that there is an absence of uncooked meat with associated pathogenic organisms and the potential for infectious disease and antimicrobial resistance.85–87
It is challenging to properly formulate home-prepared diets, and a plant-based home-prepared diet should be fed to a dog only when the diet has been formulated by an experienced veterinary or animal nutritionist. The veterinary literature contains numerous examples of adverse health outcomes associated with improperly formulated home-prepared diets,29,31,32,88 and pet owners are advised to scrutinize the formulators of home-prepared diets and commercial pet foods with the same standards.77 Thus, it is recommended that all dogs fed a home-prepared diet, regardless of ingredients, be considered high-risk patients and be examined by a veterinarian at least biannually to monitor health and wellness.3 Veterinarians can quickly assess the suitability of a home-prepared diet using resources such as checklists to identify likely nutritional inadequacies.37 When it appears that a diet is unlikely to meet the nutritional requirements of the pet to which it is being fed, veterinarians are encouraged to advise pet owners to transition their pets to a suitable commercial diet, which may be determined by use of World Small Animal Veterinary Association recommendations.77 Alternatively, pet owners may be referred to a veterinarian who is board certified in veterinary nutritiong,h for evaluation of the diet.
Clinical Summary
Dogs have dietary requirements for energy and essential nutrients, but they do not have a recognized requirement for animal-derived ingredients per se. In accordance with the current understanding of pet nutrition, any diet that meets or exceeds the minimum nutrient requirements of a dog for a specific life stage would be considered nutritionally sufficient for that animal, regardless of ingredients. However, special care must be taken when formulating plant-based diets to ensure that all nutrient requirements are met, particularly requirements for concentrations of total protein, methionine, taurine, DHA, and vitamins A, B12, and D because these nutrients are typically obtained from animal-based ingredients. An additional consideration for dogs fed plant-based diets may be to evaluate vitamin D status to ensure the dietary ergocalciferol content is adequate to maintain serum 25-hydroxyvitamin D concentrations. Dogs fed home-prepared plant-based diets are at similar risk of nutrient imbalances and deficiencies as dogs fed any other home-prepared diets. Thus, it is recommended that a pet owner who wants to feed a home-prepared plant-based diet use a recipe formulated by a qualified veterinary or animal nutritionist and that dogs fed a home-prepared diet be considered as high-risk animals and be routinely examined by a veterinarian.
Acknowledgments
Financial support for Dr. Dodd was provided by a Mitacs Accelerate grant in partnership with Petcurean Pet Nutrition.
Dr. Dodd has received grants in association with pet food companies that produce or distribute plant-based dog foods and has engaged in paid industry internships. Dr. Adolphe is a paid employee of PPN Limited Partnership (Petcurean). Dr. Verbrugghe is the Royal Canin Veterinary Diets Endowed Chair in Canine and Feline Clinical Nutrition at the Ontario Veterinary College.
ABBREVIATIONS
| AA | Amino acid |
| AAFCO | Association of American Feed Control Officials |
| DHA | Docosahexaenoic acid |
| FEDIAF | European Pet Food Industry Federation |
| PUFA | Polyunsaturated fatty acid |
Footnotes
Semp PH. Vegan nutrition of dogs and cats. Master's thesis, Veterinary University of Vienna, Vienna, Austria, 2014.
Vegetarian, Royal Canin, St Charles, Mo.
HA-Hypoallergenic, Nestlé Purina PetCare Co, St Louis, Mo.
Delaney SJ. Serum ionized calcium, 25-hydroxyvitamin D, and parathyroid hormone in two dogs fed a homemade diet fortified with vitamin D2 (abstr). J Anim Physiol Anim Nutr 2015;99:818–819.
Wilson L, Tripkovic L, Hart K, et al. Mechanisms for differences in the efficacy of vitamin D2 and vitamin D3: assessment of post-supplementation decline in vitamin D status in the D2-D3 study (abstr), in Proceedings. Annu Conf Nutr Soc 2016;75:E116.
Dodd SAS, Cave NJ, Adolphe JL, et al. Changes in pet feeding practices over the past decade (abstr), in Proceedings. Am Coll Vet Intern Med Forum 2018;894.
Directory of Diplomates of the American College of Veterinary Nutrition. Available at: www.acvn.org/directory/. Accessed Jun 6, 2018.
Directory of Diplomates of the European College of Veterinary and Comparative Nutrition. Available at: ebvs.eu/specialists/find-a-specialist?collegeId=407&countryId=0&specialistTitleId=14. Accessed Jun 6, 2018.
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