We need to feed another few billion mouths in the coming decades, and that's just humans. U.S. cats and dogs already account for at least 150 million more (slightly stinkier) maws, according to the U.S. Census.
So environmentally speaking, feeding animals by-products isn’t a bad way to go.
The article “Nutritional Sustainability of Pet Foods,” published in the journal Advances in Nutrition, explores the eco-aspects of providing for our companion animals.
The authors — including Kelly Swanson, associate professor of comparative animal nutrition at the University of Illinois at Urbana-Champaign, along with scientists from pet food supplier The Nutro Company — note, “Rather than competing with humans for food, pet foods based on by-products actually lighten the environmental burden of the human food system.”
The word “by-product” isn’t synonymous with pink slime. Broken kernels of rice, the authors also note, are among the hundreds of by-products used by the pet food industry. Their use lightens the carbon and water footprints of the food system at large.