The Dog

Introduction to Canine Nutrition and Feeding

Deciding what, when and how to feed your dog can be a challenging task. Canine nutrition is a highly debated topic in the dog world and can easily become polarized. With a variety of food options available and the potential consequences of using them, it can be difficult to determine the best approach for your dog. Factors such as convenience, veterinary and health concerns, performance, availability, individual preference and more can all affect our dietary decision-making for our dogs.

In this chapter, we will explore the evolutionary history of domestic dogs and its impact on their nutritional ecology. We will examine the digestive anatomy, physiology and feeding behavior of dogs to understand their nutritional needs and preferences. As the caregiver/owner/partner/handler of your dog, your role in making nutritional choices for them is crucial. By understanding the fundamentals of canine nutrition and considering key factors, you can make informed decisions about what to feed your dog(s).

Even dogs of the same breed have individual nutritional requirements.

In nutrition, a ‘one size fits all’ approach is rarely effective. Each individual animal is unique and requires a tailored approach to their dietary needs. While nutritional guidelines provide evidence-based starting points for formulating diets, it is important to consider the individuality of each animal. When feeding dogs, the person(s) caring for the dog must take into account the individual needs of the dog in front of them.

Factors such as breed/type, size, activity level, health status and taste preferences all impact dietary choices for dogs. For example, even within a group of dogs of the same breed and closely related, there may be differences in age, bodyweight and activity level that require subtle adjustments to their diets based on their individual needs.

Nutritional individuality is a crucial concept in supporting the long-term health and well-being of our dogs.

Food Choices for Our Dogs

The variety of dog food options available in pet shops, supermarkets and online retailers can be overwhelming. While this variety offers the potential to find a suitable option for your individual dog and living situation, the abundance of choice can also be problematic. The selection is not limited to the form and flavor of the food, but also includes factors such as manufacturer, marketing claims and nutritional support and guidance. The range of ingredients and formulations further increases the options available. Terms such as ‘natural’ and ‘superfood’ are commonly used in pet food marketing, despite having little defined meaning.

A number of overlapping factors affect the diet choices we make for our dogs.

When considering dietary choices for our dogs, it is helpful to take into account several distinct groups of influencing factors: animal (dog) factors, food factors, human factors and environmental factors. While these factors can be viewed separately, they overlap and all impact the choices we make when feeding our dogs.

Animal factors relate to the digestion and dietary needs of the dog. Food factors include the nutrients and their bioavailability in the food. Human factors encompass the choices we make and our lifestyles that affect our dogs’ diets. Environmental factors include considerations of sustainability and the ability to source chosen foodstuffs.

The Nutritional Ecology of the Domestic Dog

The domestic dog (Canis lupus familiaris) was one of the first species that humans domesticated and is one of the most commonly kept domestic species globally. Dogs are our companions, work colleagues, family members, therapists and exercise partners, and fulfil a whole host of other roles, both for and with us. Exploring our dogs’ ancestry, their relationship with related species and what they have evolved to eat helps us understand what they prefer to eat, what they need to eat and what we choose to feed them. Let’s explore the biology of our dogs that is relevant to their nutrition and feeding.

Nutritional ecology is the scientific understanding of how an animal relates to its environment through food and nutrition provided by that food. For our dogs, this means understanding their evolution, their nutritional requirements and the links between nutrition and health, wellbeing, reproduction and performance. These are essential points when thinking about making the best choices for what we choose to feed our own dogs.

The Ancestral Dog and a Common ‘Wolf-Like’ Ancestor

The domestic dog (Canis lupus familiaris) is one of the first species to be domesticated by humans and is one of the most commonly kept domestic species worldwide. Dogs serve as companions, work colleagues, family members, therapists and exercise partners, among other roles. Understanding their ancestry, relationship with related species and dietary evolution can help us understand their dietary preferences and needs.

Nutritional ecology is the study of how an animal relates to its environment through the food and nutrition it obtains. For dogs, this means understanding their evolution, nutritional requirements and the links between nutrition and health, well-being, reproduction and performance. These are important considerations when making informed choices about what to feed our dogs.

Our dogs evolved from a common wolf-like ancestor to produce the diversity in dogs we see today.

The Origin of the Domestic Dog

Over thousands of years, dogs have shared our environment, living spaces and diet. While dogs and grey wolves are closely related at the genetic level, there are subtle genetic differences that mean dogs are not wolves and direct comparisons are scientifically inaccurate. These genetic changes have affected the physical appearance, metabolism, behavior and nutritional requirements of dogs. The exact origins of dogs are still debated, but evidence shows that intensive selection has occurred over the years of domestication through both natural and artificial means.

Dogs and humans have a deep evolutionary past and show convergent evolution, with both species evolving together and developing shared traits and abilities that are mutually beneficial. This has had interesting consequences for dogs, including their ability to recognize and respond to our facial expressions and gestures. Anatomical changes in dogs, such as alterations to their eye muscles, allow them to adopt ‘puppy dog eyes’ in their interactions with us. But what does this mean for the diet of our dogs? How does their evolutionary history impact how we feed them?

The Dog – a Carnivore?

Over thousands of years, dogs have shared our environment, living spaces and diet. While dogs and grey wolves are closely related at the genetic level, there are subtle genetic differences that mean dogs are not wolves and direct comparisons are scientifically inaccurate. Dogs are classified as carnivores based on their diet and zoological classification. However, defining dogs as carnivores from a dietary perspective is an oversimplification. In a zoological sense, dogs are correctly classified as carnivores or more specifically, carnivorans, as members of the order Carnivora.

The order Carnivora includes almost 300 distinct species with biological characteristics that support the consumption of animal tissues. Members of the Carnivora include ‘dog-like’ carnivorans such as bears, dogs and weasels; ‘cat-like’ carnivorans such as felids, hyenas and mongooses; and aquatic carnivorans such as seals and walruses. These animals have a wide geographical distribution and diverse dietary intake.

A simple representation of the order Carnivora, to which dogs belong.

Characteristics of the Carnivorans

All carnivorans have a defining physical characteristic called the carnassial apparatus, regardless of whether their diet is carnivorous, omnivorous or mostly herbivorous. The carnassial apparatus consists of a modified fourth premolar tooth in the upper jaw and the first molar in the lower jaw that function like a pair of scissors to shear through flesh.

Carnivoran jaws have limited lateral or side-to-side movement, enhancing the strength and functionality of the vertical shearing motion of the carnassial apparatus. This also means that dogs are unable to chew food in the same way as animals such as horses or sheep. This limits the amount of mechanical processing of food in the mouth and explains why dogs often gulp or gorge their food.

The carnassial apparatus in a canid skull consists of the upper premolar overlapping the lower molar. The location of the carnassial apparatus is circled in each image. In image A, the jaws are opened to show the overlapping teeth. In image B, the jaws are closed to show the positioning of the teeth in a closed mouth. In image C, the location of the carnassial apparatus is shown in relation to the skull and other dentition.

Carnivore species have strong attachments of jaw muscles to the skull, useful for catching and dispatching prey and processing food. While not as essential in dogs as in ancestral or related species, dogs still have significant jaw strength, although this varies with differences in skull and jaw shape and size.

Carnivorans that consume a diet rich in animal-derived tissues, such as obligate carnivores like cats, generally have fewer teeth than those with a more mixed dietary intake, such as dogs. Bears and dogs have modifications to their premolars and molars that support the grinding and processing of plant material, while species with insect- or fish-based diets have distinct dental adaptations.

Dogs retain many characteristics of carnivorans and are correctly classified as carnivores based on zoology and anatomy. However, their diet means that calling them carnivores from a nutritional perspective is less clear-cut.

The Diet of Carnivorans

Many carnivorans rely on the consumption of animal tissues to obtain essential nutrients that cannot be obtained from plant or other sources. For example, the domestic cat (Felis catus) is an obligate carnivore that requires animal tissues in its diet to supply pre-formed vitamin A, arachidonic acid and the amino acid taurine, among other key nutrients. A dietary deficiency in any of these nutrients can have serious consequences for obligate carnivores.

In contrast, dogs can synthesize vitamin A and arachidonic acid from plant precursor compounds and have a lower dietary requirement for taurine than cats. Dogs are capable of synthesizing taurine if enough precursor substances are provided in their diet, although taurine in dog diets has recently attracted attention. As a result, dogs are commonly described as omnivorous or opportunistic/facultative carnivores.

The spectrum of carnivory ranges from hypercarnivorous, true/obligate carnivores to species that have a plant-based diet. The domestic dog has evolved to survive on a diet consisting of mixed plant and animal-derived material and is often described as an opportunistic/facultative carnivore or as an omnivore.

Carnivorans have adapted to alternative dietary ingredients. Predatory carnivorans may consume the partially digested gut contents of herbivore prey, while others scavenge and occasionally actively seek out plant and fungal matter to eat. The dietary spectrum of carnivorans ranges from ‘true’ carnivory to a plant-based diet. The giant panda has evolved dental and digestive adaptations to support its specialized diet of bamboo, while seals and other aquatic species have teeth adapted for a diet mostly consisting of fish. Dogs have also developed genetic changes that support a dietary intake of mixed animal and plant material, including the ability to digest starch carbohydrate thanks to the presence of amylase enzymes.

Genes encoding proteins involved in digestion and metabolism appear to have rapidly evolved as dogs developed, supporting the role of diet in domestication. Research suggests that different dog breeds have varying capabilities to digest starch, further emphasizing the importance of nutritional individuality when feeding our dogs.

The Dog – a Canid

While dogs are classified as carnivores, like other members of the order Carnivora, they have additional physical and biological characteristics indicating a mixed diet. The ‘dog-like’ carnivorans include several families of related species. Dogs belong to the family Canidae, which includes three subfamilies: Hesperocyoninae and Borophaginae, both now extinct, and Caninae. Members of the Caninae subfamily, referred to as canines, include wolves, jackals, foxes, domestic dogs and other ‘dog-like’ species. Caninae members have a diverse range of diets, with some being hypercarnivorous and consuming mostly animal-derived material while others are hypocarnivorous and specialize in other dietary ingredients such as plants and insects.

The family Canidae, the dog-like carnivorans, includes three subfamilies: Hesperocyoninae and Borophaginae, both now extinct and existing only in the fossil record, and Caninae. Dogs belong to the subfamily Caninae.

Canids range from opportunistic scavengers to omnivores to general carnivores, with many showing substantial dietary flexibility. Some species scavenge or hunt individually, while others exhibit group hunting or scavenging behaviors. Feral dogs have been recorded group-hunting medium-sized prey and in rare cases, humans have been hunted by dogs. Due to their wide dietary adaptations, dogs and their canid relatives are naturally found on every continent except Antarctica, where domestic dogs are banned due to concerns about disease transmission to resident species.

Smaller canids tend to be hypocarnivorous or even omnivorous, with diets often consisting of up to 70% animal-sourced material and the remainder consisting of seeds, fruit, plants and sometimes insects. Dietary flexibility is a distinct survival advantage for any species, especially in the face of seasonal or environmental changes. This may partly account for the success of dogs. The extinction of many large hypercarnivorous species, such as the dire wolf (Canis dirus), is considered linked to their dependence on prey species. When prey abundance declined, the ability of dependent species to survive also declined.

The Diet of Dogs

Dogs are a highly successful species due to the development of skills, characteristics and behaviors that we find useful and appealing, as well as their dietary flexibility. The domestic dog has evolved as an opportunistic scavenger with a taste preference for animal-derived material. This preference is evident in the use of food rewards in training. However, dogs also retain many scavenger-like characteristics and can be opportunistic in acquiring food and consuming material that may not be appealing to human sensibilities.

The way dogs eat, what they eat, the structure of their digestive system and its function all descend from their evolutionary ancestry. This is important to consider when thinking about the nutrition of our modern dogs. We must also remember that domestication and selective breeding have resulted in significant changes in the domestic dog that are relevant when considering their nutrition and how best to provide it.

Digestive Anatomy and Physiology of the Dog

Digestive anatomy refers to the organs and structures that make up the digestive system, while physiology refers to how the system functions. In biology, structure and function are closely linked. By examining the anatomy and physiology of the dog’s digestive system, we can understand how it works to support the digestion of food from start to finish.

The Digestive Process

Digestion has four stages, all supported by the anatomy and physiology of the digestive system. The first stage is ingestion, where food is consumed and mechanically processed in the mouth with the aid of the dog’s teeth. The second stage is digestion, where ingested food is broken down and processed to release nutrients and make them available to the body through mechanical and chemical processes. Once digestion has begun, absorption occurs, where the products of digestion are absorbed from the digestive system and transported throughout the body. The final stage is elimination, where any undigested or unabsorbed material, along with waste and indigestible matter, is excreted as feces.

The digestive process in dogs involves four stages. The first stage is ingestion, where food is consumed via the mouth. The second stage is digestion, where food is broken down and processed in the stomach and small intestine. The third stage is absorption, where nutrients liberated by digestion are absorbed in the small intestine. The fourth and final stage is elimination, where indigestible material and waste are excreted as feces.

Mechanical and Chemical Digestive Processes

Mechanical digestion starts in the mouth where food is altered in shape and size by shearing, crushing and grinding. This increases the surface area of ingested material for later digestive processes. However, dogs have limited ability to chew and mechanical processing is restricted to some shearing and tearing of material. This means that the time spent eating by the average dog is short and characterized by rapid ingestion of food.

Some dogs are prone to consuming indigestible foreign bodies that are not altered in shape or size by mechanical processing. These are described as ‘dietary indiscretions’ and occasionally require surgical intervention.

Chemical digestion is where secretions from tissues and organs along the digestive tract break down nutrients. This process is termed hydrolysis and is helped by specialized substances called enzymes. Enzymes are biological catalysts that work to speed up reactions and are critical for normal metabolic and digestive functioning. There are a number of different enzymes involved in digestion, each specifically breaking down an individual nutrient into smaller end products, suitable for absorption.

Examples of enzymes involved in the dog’s digestive system, the nutrients they digest and end products produced

The Digestive System

Digestion starts in the mouth and ends with the elimination of feces. The transit time for material from being eaten to elimination is rapid, typically taking between six and twelve hours. The digestive system is a short, simple tube that runs from mouth to anus and involves a number of different structures, tissues and organs. It has intimate links to other body systems.

The health of the digestive system and the population of microorganisms that live within it, the microbiome, can have significant effects on the rest of the body, from the immune system to the nervous system. While most research currently focuses on the human microbiome and its impact, we are learning about the role of the canine microbiome in our dogs’ health and wellbeing.

The Mouth

Digestion starts in the mouth and ends with the elimination of feces. The transit time for material from being eaten to elimination is rapid, typically taking between six and twelve hours. The digestive system is a short, simple tube that runs from mouth to anus and involves a number of different structures, tissues and organs. It has intimate links to other body systems.

The health of the digestive system and the population of microorganisms that live within it, the microbiome, can have significant effects on the rest of the body, from the immune system to the nervous system. While most research currently focuses on the human microbiome and its impact, we are learning about the role of the canine microbiome in our dogs’ health and wellbeing.

Saliva

Dogs have several salivary glands that secrete saliva in response to stimuli. Major salivary glands are found around the jaw and base of the ears. Minor glands are found in the mouth and around the tongue. Saliva production varies based on diet and other factors.

Saliva is key in the early stages of digestion. It acts as a lubricant, aiding chewing and swallowing. It also contains substances that have antibacterial effects. However, canine saliva also contains allergens that humans may react to and can contain bacteria potentially dangerous to humans.

Unlike many other species, dogs have negligible digestive enzymes in their saliva. Saliva enhances taste by solubilizing water-soluble components of food that are detected by the olfactory system and taste buds. Dogs can detect compounds commonly found in animal-derived tissues, meaning there is a dietary choice preference for foods rich in these substances, aided by smell and taste.

Taste Buds

Dogs have a limited number of taste buds on their tongue and in their mouth. The number of taste buds is often quoted as around 1,700. This is fewer than seen in grazing animals, where an enhanced ability to detect different tastes is important in the selection of safe material to eat.

Dogs do not show an increased preference for saltiness like many grazing species. But dogs can detect specific flavors, including sweetness, and appear to prefer sweet to bitter tastes. This could be why dogs sometimes select sweet plant material to eat and their occasional ingestion of sweet human foods, such as chocolate. Interestingly, cats appear unable to detect sweet flavors, further supporting their dietary classification as obligate carnivores, in contrast to the more omnivorous dog.

Dogs have taste receptors that detect sweetness which might account for their interest in potentially dangerous human foods such as chocolate. It is important to note that chocolate can be harmful to dogs and should not be consumed by them.

Dentition

Dogs have enlarged canines, a carnassial apparatus and more teeth than many obligate carnivores. For example, the domestic cat has thirty teeth, while the dog has forty-two. This increased number of teeth is associated with subtle changes suggesting a gradual move away from a hypercarnivorous diet and towards alternative dietary components.

The significant alterations in skull shape and size in many dog breeds have altered the position of teeth and, in some cases, created dental overcrowding issues. This is nutritionally important as some dogs may be limited in their ability to ingest and process food. Brachycephalic dogs that have significantly shortened muzzles may struggle to eat from narrow food bowls or to process food easily because of their tooth positioning. Bite force is also related to the size and shape of the skull, jaws and bodyweight. Consequently, what might be suitable for one breed to eat might be less than ideal for another.

Chang the tone to professional: Brachycephalic dogs such as bulldogs and pugs have shortened muzzles.

Dolichocephalic dogs such as the borzoi have elongated muzzles.

Skull shape and size will affect a dog’s bite force and tooth positioning. 1, Brachycephalic dogs have shortened muzzles and often have altered tooth positions. 2, Mesocephalic (or mesaticephalic) dogs have moderate muzzle lengths and are more reminiscent of ancestral dog-types. 3, Dolichocephalic types have very elongated muzzles that may also affect tooth position.

The Oesophagus

Ingested material leaves the mouth and moves to the stomach via the esophagus, which has a muscular structure that supports rapid swallowing. The movement from mouth to stomach takes seconds. Mucus helps to lubricate the esophagus and aids swallowing. Food travels down the esophagus and enters the stomach through the cardiac sphincter, a tight ring of muscle that controls entry to and exit from the stomach.

The Stomach

The dog’s stomach is small and simple in relation to their body size but is capable of significant expansion and can function as a food store. This means that dogs can consume large quantities of food in short periods of time. Chemical digestive processes to break down dietary protein start in the stomach, although most digestion occurs in the small intestine.

In the stomach, food mixes with gastric secretions, including digestive enzymes and hydrochloric acid. This means that the stomach contents are highly acidic, which promotes digestion and can help to protect dogs from potentially pathogenic microorganisms. The stomach regularly contracts, mixing its contents and preparing them for release into the small intestine via the muscular pyloric sphincter.

The activity of the stomach is controlled by hormones and the nervous system. A number of factors can affect its physiology. Anxiety, fear, illness and stress can affect how the stomach and the rest of the digestive system work. Food characteristics can also affect how the stomach processes its contents and empties.

The Small Intestine

The small intestine is divided into three regions: the duodenum, jejunum, and ileum. It is responsible for most carbohydrate and fat digestion, as well as the continued digestion of proteins. Peristalsis helps move food along and mucus lubricates and protects the lining. Digestive secretions from the pancreas and other glands contain enzymes to digest fats, proteins, and carbohydrates. The pancreas also secretes bicarbonate salts to neutralize acidic food and create a suitable pH for enzyme function. The liver produces bile, stored in the gallbladder and released when needed, to emulsify dietary fat for digestion and absorption by lipase enzymes.

Nutrient Absorption in the Small Intestine

Digestion is completed in the small intestine where nutrients are absorbed through cells lining its surface. The surface area is increased by villi and microvilli projections. Vitamins and minerals are also absorbed here and transported to the liver and other tissues via the blood and lymphatic systems. Nutrient absorption occurs via different processes, some passive and others active. Vitamin B12 requires intrinsic factor for absorption. If the small intestine is damaged or inflamed, normal digestion and absorption can be affected.

The small intestine has a significant microbial population that helps exclude disease-causing organisms and produces beneficial substances such as short-chain fatty acids. Microbiome health can be supported by including prebiotic fibers like MOS and FOS in the dog’s diet. The microbiome also synthesizes vitamin K and B vitamins. Indigestible materials continue through the small intestine to the large intestine.

The Caecum

The small intestine joins the large intestine at the ileocecal valve. The caecum is a blind pouch where microbial digestion occurs in some species. In carnivores and omnivores, the caecum is smaller and there is less reliance on microbial fermentation. However, dogs have a larger caecum than cats and some fiber digestion occurs. The microbial population contributes to the microbiome and animal health. Microbial digestion produces compounds that give feces its color and smell. Sudden dietary changes or poor-quality ingredients can cause excess gas production and offensive smells. Dietary changes should occur slowly to minimize impact on the microbiome.

The Large Intestine (Colon)

The caecum is continuous with the large intestine or colon, which leads to the rectum and anus. The dog’s colon is short but resorbs water and electrolytes from digested material. Unlike the small intestine, the colon has no villi or microvilli and absorption is passive. Inflammation or irritation of the colon can affect water and electrolyte resorption, resulting in loose stools or diarrhea. In these cases, it is important to ensure adequate hydration and provide electrolytes if necessary.

Faecal Output from the Digestive System

Material that reaches the rectum is eliminated as feces. The amount, consistency, color, texture, and smell are affected by the dog’s diet and health. Frequency of defecation is affected by diet quantity and quality. Diets high in indigestible fiber result in larger feces than more digestible diets. Faecal monitoring is a simple daily health check and faecal scoring charts can record quality. Significant and persistent changes in faecal output should be investigated to identify and manage any health issues.

Healthy ‘Poop’

Normal dog feces are formed and sausage-like with surface cracks. Small and hard feces can indicate constipation while liquid consistency indicates digestive disturbance. Time of defecation can impact consistency. The color and consistency can indicate dietary ingredients. White, crumbly feces can indicate high levels of bone or bonemeal. Poultry-rich diets produce lighter, yellow-colored feces than beef or lamb-rich diets. Very dark, tar-like feces can indicate intestinal bleeding and should be investigated by a veterinarian.

White, chalky, crumbly dog ‘poop’ is a sign of lots of bone or other minerals in the diet.

What a Dog Needs and What a Dog Wants from their Food

Dogs need food to survive and thrive. Nutrition is a controllable variable that can significantly impact their health, wellbeing, and lifespan. A nutritionally balanced and appropriate diet is important. When choosing food for our dogs, we must consider their ancestry, biology, digestive anatomy and physiology, preferences, and nutritional needs to support their activity level and lifestyle. The diet should supply the necessary nutrients in the appropriate forms and amounts.

Nutrient Supply

Food supplies energy to our dogs through macronutrients such as protein, carbohydrate, and fat. It also supplies micronutrients like vitamins and minerals that are essential for normal bodily function. A complete and balanced diet supplies all nutrients in the correct amount and form to avoid potential risks of nutritional inadequacy through excess or deficiency.

Food as Enrichment and Reward

Beyond basic nutrition, food can also be environmentally enriching and used to support training and behavior management as rewards. Food-activity toys or devices can encourage movement and problem-solving, providing stimulation and promoting preferable behaviors.

Food Safety

Food safety is important for our dogs. Food should not be contaminated by bacteria, pathogenic organisms, toxic substances or problematic items. However, the scavenging behavior of dogs can lead to the consumption of harmful food and other materials.

Food Acceptability and Palatability

Food must be acceptable and palatable to our dogs. A well-formulated diet is of no value if the dog will not eat it. Some dogs may dislike new foods or ingredients based on palatability or prior experience. Food refusal or reticence may also be a way for dogs to influence our behavior around food provision.

Food can be enriching for our dogs. Cow hooves stuffed with mashed potato and vegetables make for a tasty treat.

Summary

• The domestic dog has evolved as an opportunistic scavenger with diverse dietary habits.
• Dogs have the digestive anatomy, physiology and dentition of a carnivore, as well as a dietary preference for animal derived material but can digest starch and eat a wide range of dietary material.
• We make dietary choices for our dogs based on key influencing factors relating to the dog, the food, the humans (us) and the environment.
• Digestion has four stages – ingestion, digestion, absorption and elimination – our dogs have specific adaptions to support these stages.
• Dogs need a diet that is nutritionally adequate, safe, palatable and acceptable – we make choices based on our needs and those of our dogs.