Vets are like Dr.s if a mainstream major corporation sends them literature and gives them a HUGE discount on retailing a product they do it.
IMHO it's all about the money!
I wouldn't donate a bag of SD to the animal shelter.
I prefer TOTW, or BB now that they have a grainless wilderness flavor...although I feed Raw and BARf in model prey it's not for everyone.
Try here--->
http://www.dogfoodadvisor.com