With one major pet supply chain removing all Chinese-made dog and cat treats from its outlets, and a second planning to do so by March, the question of what has actually caused illness and 1,000 deaths of dogs and cats in this country since 2007 remains.  The Food and Drug Administration targeted the Chinese-made treats and continues to investigate, but tests have not confirmed any connection.  Dr. Mike Foss of Hood River’s Alpine Veterinary says it appears to be a renal toxin, but determining the actual chemical has been difficult.  He adds even animal food that is made here can tend to include some foreign-made ingredients, primarily vitamin and mineral supplements.  Petco announced Monday it was removing all remaining Chinese-made dog and cat treats from its shelves and website, and PetSmart plans to do so by March.