"What most people feed their pets is largely dictated by big business - companies that have the financial muscle to pay for advertisements in the press, and also on TV. One pet food manufacturer in the UK spends around £35 million each year on advertising alone to tell you that its food is the best (this figure doesn't include PR or sponsorship)."
"But big business influence stretches further than advertising, through sponsorship of veterinary and research establishments. Ask a vet how he was trained in pet nutrition, and he will usually admit that, if he received any nutritional training at all, an employee of a petfood company was wheeled in to do the teaching - for maybe two days. Then, once qualified, vets are 'educated' by visiting sales reps, and the 'food' they stock in their practices is often the 'food' with the biggest margin. Veterinary nurses are also fooled into thinking they are learning about nutrition when they go on pet food manufacturers' sponsored 'training' courses."