Canine Nutrition E-Book

Jacqueline Boyd

• Herausgeber: The Crowood Press
• Kategorie: Lebensstil
• Sprache: Englisch

Veröffentlichungsjahr: 2023

Beschreibung

Explore the world of canine nutrition and learn about feeding your dog with science, sense and sensibility.Canine nutrition is easily one of the most debated topics in the dog world. Canine Nutrition: Food, Feeding and Function aims to help canine caregivers navigate the world of dog food and feeding, and is an essential guide for anyone who lives with dogs and wants to understand more. With a strong grounding in canine and nutritional science, this book introduces the key concepts and foundation knowledge of what dogs need nutritionally. It considers how our relationships with our dogs and our decision-making influences what and how we feed them, and how we can best meet their needs, as well as our own. Practical approaches to supporting canine health, wellbeing and activity through nutrition are examined in a clear and accessible way throughout, whilst also acknowledging the variety of food options that are available to canine caregivers. This is all achieved with a firm evidence base in canine nutritional science.

Leseprobe

First published in 2023 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

[email protected]

www.crowood.com

This e-book first published in 2023

© Jacqueline Boyd 2023

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 0 7198 4184 2

Cover photo of cocker spaniel Byrbwll Nugget by Andrew Robinson

Acknowledgements

This book could not have been written without the help and support of so many friends, family, colleagues, students and clients – two- and four-legged! You have all continually supported me, shouted at me (when needed), taught me, inspired me and understood when I said I couldn’t do something because I was ‘chained to my desk’.

Special thanks to my mum and dad for always supporting me and absolutely (mostly!) allowing me to indulge in my animal-related passions from an early age – I can never thank you enough.

Big hugs to my bestie Sarah who has always been my cheerleader and has the best skill of saying the right thing to make me feel less of an imposter at the right time (I don’t think you even know you do it!).

Special spaniel snogs to Hannah – for just being the perfect pal always!

To everyone at Crowood for their help, support, guidance, and confidence – I will be eternally grateful for this opportunity.

Finally, to my little cocker spaniel team, past and present. Every single one of you has inspired me and made me a better person, scientist, teacher and canine caregiver. Not a day goes by when you don’t make me think ‘I wonder…’ and off I go exploring another avenue of canine science. You have also been constant companions during long hours at the computer, made me get up for walks, runs and cups of tea. You have even been brilliant models for photos! You are the best.

Photographs all by the author except for the following: Andrew Robinson of Whaupley Gundogs: pp.49, 66, 126 and 136; Adam Scott: pp.87 and 124; Pixabay/congerdesign: p.86; Pixabay/jagdprinzessin: p.88; Pixabay/Jeanette 1980: p.20 (bottom); Pixabay/Julie C: p.2; Pixabay/No-longer-here: pp.54 and 84; Pixabay/Rebecca Scholz: p.10; Pixabay/Viola: p.62 (bottom); Unsplash/Hermes Rivera: p.20 (top left); Unsplash/Natalie Spehner: p.48; and Unsplash/Ayla Verschueren: p.89.

Cover design by Sergey Tsvetkov

Contents

Introduction

Part One: Navigating Nutrition: The Essentials of Canine Nutrition

1 The Dog

2 The Caregiver

3 The Food

4 The World of Dog Food

Part Two: How Nutrition Works: The Nutritional Needs of the Domestic Dog

5 Energy

6 Canines and Carbohydrates

7 Proteins: The Building-Blocks of the Body

8 Fat: Is it Your Dog’s Friend?

9 Vitamins and Minerals

Part Three: Feeding for Function: Applying Canine Nutrition Knowledge in the Real World

10 How to Feed

11 Critical Canine Nutrition

12 Feeding for Life Stage

13 Feeding for Health

14 Feeding for Activity and Performance

Conclusion

Bibliography and Further Reading

Index

Introduction

The Domestic Dog

The dog is one of the earliest domesticated species and one of our most commonly kept companion animals. For thousands of years, we have shared our environment, living spaces, diet and sometimes even our beds with them. Dogs have become an integral part of human society around the world. Some dogs exist in a feral, semi-feral or pariah state, their degree of integration with human community and culture varying depending on culture, religion and social status. These dogs survive with a level of dependence on humans for their nutrition, largely by scavenging human waste and left-overs. They demonstrate feeding strategies and preferences based on food availability.

Let’s look forward into the world of canine nutrition and feeding.

Conversely, the domestic dog that lives as a companion, working colleague, assistance/therapy animal or in the myriad of other roles that dogs find themselves in, is typically entirely dependent upon their human caregiver(s) for their complete nutritional provision, care, management and wellbeing. These dogs are typically cared for in a way to support them ‘thriving’, not just ‘surviving’, and nutrition is a significant part of that. ‘You are what you eat’ is an oft-quoted adage, highlighting the importance of nutrition in overall health, and while it can sometimes over-simplify the relationship between food and the animal eating the food, there is little doubt that diet can play a significant role in supporting health, activity and promoting longevity.

Feeding Our Dogs

What and how we feed our dogs is easily one of the most debated and discussed subjects by canine enthusiasts around the world. As dogs have become increasingly recognised and described as family members, and the humanisation of dogs has become more common, dietary choices made by caregivers have become more diverse and increasingly humanised. Added to this is a multibillion-dollar international industry in the form of pet food production, distribution and marketing. Consequently, canine nutrition and feeding have significant human and commercial interest.

In animal nutrition, we refer to the animal feed industry, while the food industry is that which produces and supplies products for human consumption. The food and feed industries are linked. The feed industry benefits from by-products from the food industry, and supplies animal-derived products back into the food industry for human consumption. When it comes to our pets, however, we have humanised the terms we use, referring to ‘pet food’ and ‘dog food’. To avoid confusion, in this book, the term ‘food’ will be used when talking about what we feed our dogs and what they choose to eat, while acknowledging that the pet food industry is a significant (and growing) part of the global animal feed industry. The term ‘diet’ will also be used for the food we feed to our dogs, not necessarily indicating any restriction of food for weight control – the more typical ‘human’ use of the term.

Why This Book?

The concept for this book first took root when I was lecturing degree-level, animal science students. We were exploring nutrition fundamentals and examining the nutritional requirements and feeding standards for the domestic dog. In that discussion, ‘the human factor’ was mentioned and we considered the impact that we have on dietary choices for dogs in our care.

In a class of undergraduate students, well versed in critical analysis and assessing scientific evidence, it was clear that the biases, beliefs, traditions, the approaches taken to feeding their own dogs and how they would advise others, varied significantly. Some felt that domestic dogs should be fed like wolves. Others felt that sustainability and ethical considerations meant that companion dogs should be fed vegetarian or vegan diets. The diversity of views in that class was a microcosm of the wider, global dog-caregiver community.

I realised a slightly different approach was needed to how I both taught and advised canine nutrition. Yes, science and an evidence base were essential to ensure that what was being fed would supply the nutrients needed in a suitable amount and form. However, there was a significant variable that had both dramatic and subtle impacts – the human(s). Luckily, I also have more than a passing interest in anthrozoology – the science that explores the interactions between humans and non-human animals. Combining nutritional science with the science of human – animal interactions has underpinned much of my nutrition work since.

By examining how we view our dogs and our relationships with them, and exploring the diversity of those relationships, we can start to understand the choices and decisions made by individuals for their dogs. Combined with knowledge and understanding of the dogs’ nutritional needs, we can start to make logical, rational and appropriate dietary choices – ones that are mutually acceptable and beneficial. It can also help us have confidence in our own decisions and support others who might seek advice with compassion and respect.

But, in exploring canine nutrition and feeding, identifying fact from fiction can be difficult and, for some, a source of much stress. Who to trust? What is safe? What does my dog really need? What is the best diet for my dog? These are all valid and frequent questions when it comes to feeding our dogs.

Feeding Our Dogs with Science, Sense and Sensibility

A golden rule in animal nutrition is to always ‘feed the animal in front of you’. I now add to that, ‘and ensure that whatever you feed that animal, also meets with the human needs’. This does not mean sacrificing an evidence-based and well-formulated diet for an animal to suit the whims and desires of their human caregiver. It is about balancing the needs of both parties and finding the ‘best fit’ – like so many other things in life, nutrition is a compromise, but it can be a good compromise!

This book aims to explore how to meet this nutritional ‘best fit’ for dog and human. If you are interested in how to navigate the world of canine nutrition, and how to make effective, evidence-based choices that support your dog’s health, wellbeing, longevity and activity level, then this book is for you.

We will explore the essentials of canine nutrition through the biology of the dog, their nutritional requirements and how these differ in different circumstances and situations. We will examine some of the hot topics in the dog world and consider how what we feed our dogs can impact on the environmental challenges the world faces, all with an evidence base. In order to enhance accessibility and readability, references have not been referred to explicitly within the text. However, where information has come from a key scientific resource, the full reference information is available at the end of the book, should you wish to access the original, primary material to learn even more.

This book is not intended to tell you there is one single way to feed your dog(s), nor will it vilify different options, ingredients, diet types or pit commercially produced dog food against ‘natural’ or home-prepared diets. Instead, we will examine current evidence and apply that to how we might best feed our dogs for our individual circumstances and situations. The majority of dogs eat a mixed diet through their lifetime. Situations change, economics alter, ingredient availability changes and a host of other variables affect the food and feed industries. Being able to be responsive, dynamic and informed about how to make decisions can then become a useful skill. This book will help you do exactly that, no matter what your budget or situation is.

I am hugely privileged to share my life with my own dogs and want to make the world a better place for dogs and their people. Thanks for joining me on this part of my mission and I hope that this book will help shape your knowledge, understanding and application of nutritional science to the benefit of you and your dog(s). Whether you live with one dog or many, occasionally care for others’ dogs or are just interested in learning more, let’s go for a walk into the world of feeding the domestic dog.

PART ONE

Navigating Nutrition: The Essentials of Canine Nutrition

CHAPTER

1

The Dog

Introduction to Canine Nutrition and Feeding

Deciding what, when and how to feed your dog can be difficult. Canine nutrition is easily one of the most debated subjects in the dog world and a topic that can easily become polarised. Everyone who has ever cared for a dog will have experienced the variety of food options available, as well as the varied consequences and the results of using them. Some people swear by particular food types, forms, ingredients and even manufacturers. Others will have had to vary approaches and explore alternatives because of convenience, veterinary and health concerns, performance, availability, individual preference and a range of other factors that affect our dietary decision-making for our dogs.

In this chapter, we are going to explore the evolutionary history of our domestic dogs and what that means for their nutritional ecology – essentially, where our dogs have come from and how that affects what and how we feed them. We will consider the digestive anatomy, physiology and feeding behaviour of dogs and examine what a dog needs, and even wants, from their food. The role of you, your dog’s caregiver/owner/partner/handler is also important, because you make the decision as to what to buy and feed your dog(s). This will help us to understand the fundamentals of canine nutrition and to identify key factors to consider when we make nutritional choices for our dogs.

Even dogs of the same breed have individual nutritional requirements.

An Individual Approach to Feeding

The reality is that in nutrition a ‘one size fits all’ approach rarely works – an individual approach needs to be taken. Nutritional guidelines are available and are wonderful, evidence-based starting points in formulating diets, but every individual animal is unique and nutritional individuality is important. When feeding dogs, an individual approach is as much about the person(s) caring for the dog, as it is about the dog itself. We must feed the animal in front of us and fully acknowledge that nutritional individuality. This is why nutrition can be sometimes a tricky subject – what works fantastically for one dog (and their person), may not work for another.

Our dogs should affect the choices we make – breed/type, size, activity level, health status and even their own taste preferences, will all impact on the dietary choices made. For example, my own dogs are all the same breed, and several are closely related, but my little ‘family group’ (I avoid the term pack as they do not function as a pack in the biological sense of the word) range in age, bodyweight and activity level. Consequently, while to the untrained eye they will all look very similar and there might be an assumption that they are all fed the same, there are subtle amends made for each, based on their individual needs. Nutritional individuality is an important concept for supporting a long, healthy life for our dogs.

Food Choices for Our Dogs

Wander down the aisle of any pet shop, pet section in your supermarket or even search your favourite online retailer for ‘dog food’ and you could well be overwhelmed by the variety of options on offer. On one hand, this variety means that selecting an option to suit your individual dog and living situation should be easy. However, a significant problem comes when there is too much choice. Choice is not even just in the form and flavour of food that is available to feed our dogs. It comes from manufacturer, marketing claims and even nutritional support and guidance. Ingredients and different formulations increase choice further. Terms such as ‘natural’ and ‘superfood’ are common parlance in pet foods now, despite having little defined clarity of meaning.

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

When looking at dietary choices for our dogs, it is useful to consider distinct groups of influencing factors:

• Animal (dog) factors

• Food factors

• Human factors

• Environmental factors

While these factors can be viewed as distinct from each other, they overlap and all impact on the choices we make in feeding our dogs.

Animal factors relate to how an animal digests its food and what it eats. Food factors include nutrients and their bioavailability. Human factors are the choices we make and lifestyles we lead that impact on our dogs’ diets. Environmental factors include aspects of sustainability, as well as the ability to source chosen foodstuff.

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 evolved from a common wolf-like ancestor – a now extinct population of wolves and ancestors to the modern grey wolf (Canis lupus). The early ‘proto-dogs’ were domesticated by living beside, and with, human populations, benefitting from human waste and left-overs, including excess food that we couldn’t effectively use because of our own digestive and metabolic limitations. Archaeological evidence also indicates that early dogs were fed prepared diets, reflecting distinct roles in society. The preparation of specific dog food is thus not just a modern concept.

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 (estimates range from 200,000 to 15,000 years), dogs have shared our environment, our living spaces and our diet. This means that while the modern dog and the grey wolf are closely related at the genetic level, there are subtle genetic differences meaning that dogs are not wolves – direct comparisons are scientifically inaccurate. These genetic changes have affected the physical appearance, metabolism, behaviour and nutritional requirements of our dogs. The exact origins of dogs are still under intense debate, but evidence shows that intensive selection has occurred over the years of domestication. This selection has been both natural and artificial – natural selection occurring where individual animals had some advantage that supported survival and reproduction. This means that their genetics were more likely to be passed to future generations. Artificial selection is where humans deliberately selected individual animals from which to breed. These individuals had characteristics, such as appearance, size, behaviour, docility or trainability, considered useful, so there was a desire to keep those traits in subsequent offspring.

Dogs and humans have a deep evolutionary past. Dogs and humans show convergent evolution – two species evolving together over time and developing shared traits and abilities that are mutually beneficial. This has had some interesting consequences for the domestic dog, including their ability to recognise and respond to our facial expressions and pointing gestures. Dogs have developed anatomical changes, including alterations to their eye muscles, not seen in wolves, meaning that they are more able to adopt ‘puppy dog eyes’ in their interactions with us – a significant benefit to the human–dog relationship, especially when it comes to feeding them. But what does this mean about the diet of our dogs? What does the evolutionary history of dogs mean for how we feed them?

The Dog – a Carnivore?

Dogs are described as carnivores, referring to diet and their zoological classification. However, defining dogs as carnivores from a dietary perspective is an over-simplification. In a zoological sense, dogs are quite correctly called carnivores or, more specifically, carnivorans – they are members of the order Carnivora.

The order Carnivora is a large group of animals, including almost 300 distinct species that have biological characteristics that support the consumption of animal tissues – carnivore translates as ‘flesh-eating’. Members of the Carnivora include the ‘dog-like’ carnivorans, such as bears, dogs and weasels; the ‘cat-like’ carnivorans, such as felids, hyaena and mongooses; and the aquatic carnivorans, such as seals and walruses. These animals show a wide geographical distribution and diverse dietary intake.

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

Characteristics of the Carnivorans

The carnivorans all have a defining physical characteristic called the carnassial apparatus, irrespective of whether their diet is carnivorous, omnivorous (mixed plant and animal material) or mostly herbivorous. The carnassial apparatus is a modified fourth premolar tooth in the upper jaw and the first molar in the lower jaw. These teeth overlap and function like a pair of scissors to shear through flesh.

The carnivoran jaws are limited in their ability for lateral or side-to-side movement, meaning that the carnassial apparatus has enhanced strength and functionality in its vertical shearing motion. This also means that our dogs are not able 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 will often gulp or gorge their food.

The carnassial apparatus in a canid skull. Note that the dentition is not complete, but the location of the carnassial apparatus is circled in each image. A, Jaws opened to show the upper premolar overlapping the lower molar. B, Jaws closed to show how the teeth are positioned in a closed mouth. C, Location of the carnassial apparatus in relation to the skull and other dentition.

There are strong attachments of jaw muscles to the skull in carnivore species. This is useful for catching and dispatching prey animals, as well as the processing of material for eating. While this is not as essential in our dogs as in ancestral or other related species, dogs do have significant jaw strength, although this is affected by differences in skull and jaw shape and size.

A general trend is that the carnivorans that consume a diet rich in animal-derived tissues, such as the true or obligate carnivores (e.g. cats), have fewer teeth in total than those with a more mixed dietary intake, such as the dog. Bears and dogs appear to have modifications to their premolars and molars that support an increased amount of grinding and processing of plant material, while those species that have an insect- or fish-based diet have distinct dental adaptations.

Our dogs retain many of the characteristics of carnivorans and it is correct to call them carnivores based on zoology and anatomy. However, the diet of dogs does mean that calling them carnivores from a nutrition perspective is less clearcut.

The Diet of Carnivorans

Many carnivorans are dependent on the consumption of animal tissues to supply essential nutrients that cannot be obtained from plant or other sources. The domestic cat (Felis catus) is a true or obligate carnivore, for example. In contrast to dogs, cats require animal tissues in their diet to supply pre-formed vitamin A, arachidonic acid and the amino acid taurine, in addition to other key nutrients. A dietary deficiency in any of these nutrients can be catastrophic for obligate carnivores.

Conversely, dogs can synthesise vitamin A and arachidonic acid from plant precursor compounds, and their need for a dietary supply of taurine appears to be less than cats. Indeed, dogs are capable of synthesising taurine if enough precursor substances are provided in the diet, although lately, taurine in dog diets has attracted attention. Consequently, dogs are commonly described as omnivorous or opportunistic/facultative carnivores.

The spectrum of carnivory, from the 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 also adapted to alternative dietary ingredients. Predatory carnivorans are known to consume the partially digested gut contents of herbivore prey, while others scavenge and occasionally actively seek out plant and fungal matter to eat. Carnivorans demonstrate a dietary spectrum that ranges from ‘true’ carnivory through to a plant-based diet. The giant panda has a highly specialised diet of bamboo and has evolved certain dental and digestive adaptions to deal with this foodstuff. Seals and other aquatic species have teeth that are 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. A notable adaptation is the ability to digest starch carbohydrate, thanks to the presence of amylase enzymes that aid the breakdown of starch in the digestive tract. This means that dogs, unlike wolves, are able to thrive on a starch-rich diet, providing the starch is appropriately cooked.

In fact, genes that encode proteins involved in digestion and metabolism appear to have rapidly evolved as dogs developed, strongly supporting a role of diet in domestication. Research suggests that different dog breeds have different capabilities to digest starch. These findings further add to our understanding of the importance of nutritional individuality when feeding our dogs.

The Dog – a Canid

So, while the dog is classified as a carnivore, in common with other members of the order Carnivora, dogs have additional physical and other biological characteristics indicating a mixed diet is consumed. The ‘dog-like’ carnivorans include a number of families of related species. Dogs belong to the family Canidae, which includes three subfamilies, two of which are now extinct – the Hesperocyoninae and the Borophaginae. The third is the Caninae subfamily, members of which are referred to as canines and include wolves, jackals, foxes, the domestic dog and other ‘dog-like’ species. Caninae members have a diverse range of diets – some are hypercarnivorous and animal-derived material is the majority of their dietary intake. Others are hypocarnivorous and specialise in other dietary ingredients, such as plants and insects.

A simplified representation of the subfamily members of the family Canidae, the dog-like carnivorans. Two subfamilies are now extinct and exist only in the fossil record. Dogs belong to the subfamily Caninae.

Broadly, canids range from opportunistic scavengers, to omnivores, to general carnivores, with many showing substantial dietary flexibility. Some species will scavenge or hunt individually, while others show group hunting or scavenging behaviours. Feral dogs have been recorded as group-hunting medium-sized prey. In some rare but slightly disturbing cases, humans have been hunted by dogs. Because of their wide dietary adaptations, dogs and their canid relatives are naturally found on every continent, with the exception of Antarctica. Indeed, domestic dogs are banned from Antarctica for fears that they could introduce and transmit diseases to other resident species.

Smaller canids tend to be hypocarnivorous or even omnivorous, with their diets often consisting of up to 70 per cent animal-sourced material and the remainder consisting of seeds, fruit, plants and sometimes insects. Being able to be flexible in the food consumed is a distinct survival advantage for any species, especially where there may be significant seasonal or other environmental changes. This could well in part account for the success of the dog. The extinction of many large hypercarnivorous species, such as the dire wolf (Canis dirus), is considered linked to their dependence on prey species. When the abundance of prey species fell, the ability of species dependent on them for food to survive also fell.

The Diet of Dogs

Dogs are a highly successful species, thanks to the development of skills, characteristics and behaviours that we like and find useful, as well as their dietary flexibility. The domestic dog that we know and love, has evolved as an opportunistic scavenger, with a taste preference for animal-derived material. This preference for animal-tissue will come as no surprise to anyone who uses food rewards in training. However, our dogs also retain many scavenger-like characteristics and can be opportunists in how they acquire food, as well as the material they choose to consume – some of which is less than appealing to human sensitivities.

How our dogs eat, what they eat, the structure of their digestive system and how it functions, all descend from their evolutionary ancestry. It is useful to think about this when considering the nutrition of our own, modern dogs. We also have to remember that domestication and selective breeding has meant there are some significant changes in the domestic dog that are also relevant when considering their nutrition and how we can best provide it.

Digestive Anatomy and Physiology of the Dog

Digestive anatomy refers to the organs and structures that comprise the digestive system. Physiology is how the system works. In biology, structure and function are closely linked, so examining structure (anatomy) and physiology (function) means we can consider the digestive system of the dog from start to finish and how it works to support the digestion of food.

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, initially, mechanically processed in the mouth with the aid of the dog’s teeth. The next stage is digestion, where the food ingested is broken down and processed to liberate nutrients and make them available to the body. Digestion is achieved by mechanical and chemical processes. Once digestion has begun, the process of absorption occurs, where the products of digestion are absorbed from the digestive system and transported around the body. The final stage is elimination, where any material that has not been digested or absorbed, plus waste and indigestible matter, is excreted as faeces.

The digestive process in the dog. 1, Ingestion of food via the mouth. 2, Digestion of food begins in the stomach and continues in the small intestine. 3, Absorption of the nutrients liberated by digestion in the small intestine. 4, Elimination of indigestible material and waste as faeces.

Mechanical and Chemical Digestive Processes

Mechanical digestion begins in the mouth when the teeth alter the shape and size of ingested food particles by shearing, crushing and grinding. This reduces the size of food for ease of swallowing and 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, rather than prolonged grinding and chewing, as seen in other species. This also means that the time spent eating by the average dog is short and characterised by rapid ingestion of food. Mechanical digestion is aided by muscular contractions (peristalsis) of the digestive system that moves food along the digestive tract, mixing it with various secretions during its digestive journey.

Unfortunately, some dogs are prone to consuming, intentionally or accidentally, indigestible foreign bodies that are not altered in shape or size by mechanical processing. Examples include stones, large pieces of bone, toys, clothing or household items. These are described as ‘dietary indiscretions’ and occasionally require surgical intervention to remove the offending item and to prevent severe damage to the dog’s digestive system.

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 specialised 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. These enzymes are released from digestive organs and tissues at various points along the length of the digestive system.

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

Enzyme

Nutrient targeted

End product of enzymatic digestion

Amylase

Carbohydrate – starch amylose

Glucose

Sucrase

Carbohydrate – sucrose

Fructose and glucose

Maltase

Carbohydrate – maltose

Glucose

Lactase

Carbohydrate – lactose

Glucose and galactose

Lipase

Lipid/fat

Glycerol, free fatty acids, monoglycerides, diglycerides

Trypsin

Protein

Polypeptides, individual amino acids

Pepsin

Protein

Polypeptides, individual amino acids

Peptidases

Protein – peptides

Dipeptides, individual amino acids

Chymotrypsin

Protein

Polypeptides, individual amino acids

The Digestive System

Digestion starts in the mouth and ends with the elimination of faeces. The transit time for material from being eaten to elimination is rapid, typically taking between six and twelve hours. The digestive system (sometimes called the alimentary canal or gastrointestinal tract) 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. An important recognition is that the health of the digestive system and the population of microorganisms that live within it, the microbiome, can all 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 how it differs between individuals and its impact, we are learning about the role of the canine microbiome in our dogs’ health and wellbeing.

The Mouth