By Professor Andrew Knight, Adjunct Professor (Animal Welfare), Murdoch University and Griffith University, Visiting Lecturer, University of Winchester

This article was originally published in The Conversation on 30 December 2024

At least a quarter of all human-generated greenhouse gas emissions to date can be traced to the livestock industry. Vast tracts are used to grow feed crops and to graze the world’s 92 billion cows, pigs, chickens and other animals slaughtered each year. This hunger for land means livestock farming is a leading cause of deforestation, as well as a significant drain on freshwater.

A global transition towards plant-based diets is urgently needed. But should this include our pets?

Researchers have struggled to determine how pet food affects the planet as there is not much data on what goes into it. Fortunately, a report published in 2020 detailed over 500 ingredients used by the pet food industry in the US – a country with more pets than any other.

I calculated the environmental impact of meat-based pet food based on this information. Then I asked what would happen if the entire world population of pet dogs and cats ate plant-based alternatives instead.

The results (published in Regenerative Farming and Sustainable Diets) shatter the assumption that it is just people who need to change their diets for the sake of the environment.

Vegan diets have massive climate and environmental benefits

If the world’s pet dogs were transitioned onto nutritious diets which excluded all animal products, it would save greenhouse gas emissions equivalent to 0.57 gigatonnes (1 gigatonne is 1 billion tonnes) of CO₂ a year – much more than the UK emitted in 2023 (0.38 gigatonnes) – and liberate an area of land larger than Mexico, potentially for habitat restoration which would boost carbon capture and biodiversity.

And what if the calories fed to animals meant for slaughter were instead used to create plant-based foods for pets? Most of the plant-based calories fed to livestock animals are lost during conversion to meat, milk or eggs. This is highly inefficient. A similar quantity of plant-based calories could feed many millions more people. In fact, a nutritious vegan diet for every pet dog would save enough calories to feed 450 million people – more than the entire EU population. At least six billion land-based “food animals” would also be spared from slaughter annually.

Pet cats eat one billion land-based food animals annually, and vast numbers of fish. Feeding them nutritious vegan diets instead would eliminate greenhouse gas emissions equivalent to 0.09 gigatonnes of CO₂ – more than New Zealand’s annual emissions (with its very large methane-emitting dairy industry) – and would save an area of land larger than Germany. Seventy million additional people could also be fed using the food energy savings – more than the entire UK population.

Around 75% of the animal-based ingredients of pet food are byproducts of making food for humans. These byproducts include ears, snouts and internal organs, and are usually considered inedible by people. Some are sold cheaply to pet food manufacturers, and it’s long been assumed that this lowers its environmental impact by curbing the number of livestock animals that need to be killed.

However, my research using additional meat industry data demonstrates the opposite. I found that a smaller proportion of carcasses are used to make byproducts than meat. This increases the number of carcasses required to produce the same quantity of pet food ingredients. Demand for byproducts from the pet food industry actually increases the number of livestock animals killed. More livestock means more land, water and waste, including the greenhouse gas emissions heating Earth’s climate to dangerous levels.

Are vegan diets safe for pets?

Dogs are biologically omnivorous, and cats carnivorous. This means that they would naturally hunt and kill a variety of small mammals, birds and insects to obtain the nutrients needed for survival.

Of course, this is of little relevance to modern domesticated dogs and cats that normally eat commercial diets. Almost 50% of these diets comprise plant materials like grains, soy, fruits and vegetables. These are mixed with body parts from species dogs and cats would never naturally hunt (consider fish in cat food), and chemical flavourants, colourants and preservatives. The product, such as dry kibble, is fed at predictable times daily, and bears little resemblance to the natural diet of an ancestral dog or cat.

What dogs, cats, and indeed all species actually need is a set of nutrients including certain amino acids, vitamins and minerals, as well as macronutrients such as protein and carbohydrates. There is no biological requirement for meat. Provided manufacturers ensure all necessary nutrients are added, in the right proportions, modern commercial vegan diets are normally nutritionally sound.

By late 2024, 11 studies in dogs, three in cats, and one systematic review covering both had all demonstrated that dogs and cats thrive on modern vegan or vegetarian diets. Certain health benefits appear consistent across the research, such as a reduction in obesity and of conditions that may be triggered by animal-sourced allergens, like itchy skin and ears and gastrointestinal problems.

But do these naturally carnivorous animals (or omnivorous, in the case of dogs), actually enjoy vegan diets? Apparently so, according to a detailed analysis of their feeding behaviour. Dr Liam Satchell and I studied every known indicator of enjoyment, including jumping, barking, purring, licking, sniffing and salivating in 2,308 dogs and 1,135 cats. This was the largest study of its kind, and we found that, on average, pets seemed to enjoy vegan meals as much as meaty ones.

To address climate change and nature loss, UN secretary-general Antonio Guterres has said action is needed “on all fronts: everything, everywhere, all at once”. This certainly includes the livestock sector, which feeds not only us but our pets.

Fortunately, we can do this while providing a nutritious diet for the animals we love. To safeguard pet health, all diets, including vegan diets, should be manufactured by reputable pet food companies which carefully formulate their food to be nutritionally sound.

Can pets be vegan? Here’s how much it would help the planet