Professor Raubenheimer added that it would be misplaced to think we can maintain current pet populations. A large dog's environmental paw-print is about the equivalent of an SUV driven for two years. Some environmentally-conscious pet owners are trying novel ways to reduce their animals' consumption of meat. But it can be a "tragic trade-off", a Sydney University lecturer and veterinarian Dr Anne Fawcett said. In one case, Dr Fawcett couldn't work out why a sick dog wouldn't eat until she discovered the animal's "well meaning and very loving owner" was sprinkling peas on the top of the pet's food to reduce its consumption of meat. "Let's take the peas away," she recommended. A study by Professor Greg Okin from UCLA found American dogs and cats consume about a third of the animal-derived energy (or meat) that humans do.

Loading The research published in PLOS One said meat-based diets require more land, energy and water and have greater environmental consequences - including erosion and waste (dogs and cats produce about a third of the faeces produced by humans) - than vegetarian diets. Pet ownership is growing around the world, including in the United States and in rapidly developing countries like China. According to the RSPCA there an estimated 4.8 million pet dogs in Australia; 20 dogs for every 100 people, and about 3.9 million pet cats (16 cats for every 100 people). But Professor Okin said "these consumers of agricultural products are rarely included in calculations of the environmental impact of dietary choices". At the same time, a major report this year by Eat-Lancet Commission called for meat to be almost entirely eliminated from human diets if we are to feed the world's population of around 10 billion by 2050.

Professor Okin's research said if just a quarter of US pet food was suitable for human consumption, it would be enough to feed meat to five million Americans a year. Despite the benefits of animal companionship should we reduce the number of pets? Is it Time to Eat the Dog (as the controversial New Zealand book of that name asked in 2009 when they compared the ecological footprint of different pets) or is it time for pets to eat vegetables? The Sydney University forum heard it may be possible in the future to develop vegan diets for cats and dogs, or find new sources of animal protein like bugs. But because cats are carnivores, vegan substitutes currently for sale don't provide all their nutritional needs. That meant other changes needed to be made, said Professor Raubenheimer. "In the short term, we need to think about the number of pets we have, the size of these pets, and also the species," he said. That could mean thinking about whether it was necessary to have carnivorous animals like dogs and cats as pets.

"We are going to get nowhere ... if we say that everyone should stop eating meat. Everyone is not going to stop eating meat," Professor Raubenheimer said. "But we might begin by cutting down on the amount of meat we eat. That would have significant benefits: for the environment, for animal welfare and, for many people, also their health." "And the same with pets. If you say, 'you shouldn't be having pets, you shouldn't be having cats,' we are not going to get anywhere. Instead we need to think about how many pets, and whether you really need a replacement when your pet dies." So what pet is best for the environment? Some panellists talked about smaller animals like rabbits and lizards, and others that don't eat meat. Yet there was consensus they don't provide the same level of companionship. We need to think about how many pets, and whether you really need a replacement when your pet dies. Professor David Raubenheimer Chickens may be the answer. Thinking about them is what prompted Professor Okin, who said he likes cats and dogs, to do his research. "I was thinking how cool it is that chickens are vegetarian and make protein for us to eat, whereas many other pets eat a lot of protein from meat,” he said. “And that got me thinking — how much meat do our pets eat?”