Wet dog food is worse for the environment than dry kibble, scientists say

Want to make your dog the next Pet-a Thunberg? Try replacing their wet food with dry kibble.

A new study has found that feeding your dog wet food contributes almost seven times more carbon dioxide per year than dry food.

Scientists from the University of Sao Paulo in Brazil assessed the environmental impacts of commercially available and homemade pet foods for dogs and cats.

They found that owners are able to make their pet’s diet more sustainable by switching to kibble and biscuits, without compromising nutritional value.

“Food production is responsible for nearly a quarter of environmental impact and therefore its importance to sustainability should not be overlooked,” the authors write.

“Wet diets, although indicated as a strategy to increase the palatability and water intake of cats and dogs at higher risk of developing urolithiasis, are those that have the greatest impact on the environment.”

Scientists from the University of Sao Paulo in Brazil assessed the environmental impacts of commercially available and homemade pet food for dogs and cats (stock image)

Estimated carbon dioxide equivalent emissions (left) and land use (right) per 1000 kcal of dog diets by diet type.  Cc: Homemade diets commercially available, Cs: Homemade diets prepared by the owner, S: Dry diets and U: Wet diets

Estimated carbon dioxide equivalent emissions (left) and land use (right) per 1000 kcal of dog diets by diet type. Cc: Homemade diets commercially available, Cs: Homemade diets prepared by the owner, S: Dry diets and U: Wet diets

Estimated sulfur dioxide (left) and phosphate (right) emissions per 1000 kcal of dog diets by diet type.  Sulfur dioxide can damage plants, while phosphates can lead to harmful algal blooms that disrupt marine ecosystems.  Cc: Homemade diets commercially available, Cs: Homemade diets prepared by the owner, S: Dry diets and U: Wet diets

Estimated sulfur dioxide (left) and phosphate (right) emissions per 1000 kcal of dog diets by diet type. Sulfur dioxide can damage plants, while phosphates can lead to harmful algal blooms that disrupt marine ecosystems. Cc: Homemade diets commercially available, Cs: Homemade diets prepared by the owner, S: Dry diets and U: Wet diets

WHY ARE INGREDIENTS OF ANIMAL ORIGIN HARMFUL FOR THE ENVIRONMENT?

Food products of animal origin harm the environment in different ways.

Cows, pigs and other farm animals release huge amounts of methane into the atmosphere, which is a greenhouse gas and contributes to global warming.

Raising livestock also means converting forests to agricultural land, which means that CO2-absorbing trees are cut down, further contributing to climate change.

Factory farms and growing crops also require huge amounts of water, with 542 liters of water used to produce a single chicken breast.

On top of that, nitrogen-based fertilizer used on crops adds to nitrous oxide emissions. Nitrous oxide is about 300 times more effective at trapping heat in the atmosphere. These fertilizers can also end up in rivers, contributing to pollution.

Keeping a pet dog or cat is hugely popular around the world, with around ten million dogs and 11 million cats in the UK alone, according to the charity PDSA.

In Brazil, where the study was based, there are around 52 million dogs, and the researchers wanted to find out how much of an impact their diet had on the environment.

They assessed the greenhouse gas emissions, land use and water use of ingredients in the diets of 618 dogs and 320 cats.

These included kibble and wet food from three Brazilian pet food retailers, as well as “homemade” products that were either made by companies or prepared at home by owners.

The nutritional value and calorie content of the different diets were also assessed for the study, published today in Scientific reports.

Researchers have found that wet dog and cat food diets have a higher overall impact on the environment than kibble or homemade diets.

They calculated that a 22-pound (10 kg) dog consuming an average of 534 calories per day from wet food would be responsible for 6,541 kg of carbon emissions per year.

For dry foods, however, they would provide only 828.37 kg of carbon dioxide, almost seven times less.

In terms of nutritional value, dry diets provided the highest number of calories per gram, although wet and homemade foods provided higher amounts of protein.

British Veterinary Association Senior Vice President Justine Shotton added: “There is no nutritional difference between wet and dry pet food.

“In some cases, a vet may recommend one over the other for specific reasons, such as urinary issues and specific types of allergies.

“The British Veterinary Association advises your vet to first make any changes to your pet’s normal diet to ensure they remain nutritionally balanced.”

In wet diets, researchers found that 89% of calories came from animal ingredients, such as poultry meal and fat, but that was only 45% in dry diets.

These animal sources likely contribute to its greater environmental impact and suggest replacing them with protein from insects, e.g. mealworms.

While a plant-based diet would also reduce environmental impact, dogs and cats are carnivores and have different nutritional needs than humans.

The article points out that feeding pets a vegan diet “could pose risks,” but adding synthetic amino acids is a potential solution.

In terms of nutritional value, dry diets provided the highest number of calories per gram, although wet and homemade foods provided higher amounts of protein (stock image)

In terms of nutritional value, dry diets provided the highest number of calories per gram, although wet and homemade foods provided higher amounts of protein (stock image)

However, in 2020 scientists discovered that the dry pet food industry needed land twice the size of the UK to make a sufficient supply.

It also produces 106 million tons of carbon dioxide per year, making the industry dirtier than the Philippines.

This suggests that while kibble is still a greener alternative to wet food, the environmental footprint of the industry as a whole is far from negligible.

In fact, pet food contributes about one-ninth of carbon dioxide every year, because the the aviation industry.

Dr Peter Alexander, co-author of this study from the University of Edinburgh, said: “This is a subject that has been previously overlooked, but we have shown that companion animals and the way they feed must be considered alongside other actions to reduce climate change and biodiversity loss.

Dogs on a raw food diet may shed antibiotic-resistant bacteria that could be passed to humans

Dogs fed raw meat are more likely to shed antibiotic resistant bacteria Escherichia coli (E. coli) in their feces, veterinarians have warned.

Previous research showed that it is also possible that E. Coli is transmitted from dogs to their human owners through normal daily interaction.

Researchers from the University of Bristol suggest that pet owners who feed their dogs raw should take extra care when cleaning up their messes.

They also suggest that the fad diet is not the safest choice for a domestic dog for this reason.

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