See the pet food industry article on website link below.I don't know what to believe on how to get truth in labeling. Pork is cheaper than venison, usually. At the very least, not cleaning the equipment from the last batch could contaminate things. The ingredients in at least two of the foods described come up on google, being possibly Merrick Harvest Moon canned dog food with the mislabeled poultry/game bird ingredient list and possibly Dogswell Nutrisca which had gluten in the supposedly gluten free formulas.

http://www.petfoodindustry.com/Are_your_petfood_labels_accurate_.html
Quoting article to pet food makers:
"The need for increased attention to identifying animal proteins and grains was highlighted in a recent survey of 21 commercial dog foods performed by our laboratory in Florida. Ten of the foods were purchased in local grocery stores and 11 were purchased in local specialty pet stores. Five of the foods were chosen specifically because they claimed to be gluten-free, while the remainder was an equal mix of large and small brands.

All the products were tested for the presence of beef, pork, poultry, turkey, sheep, horse and deer content using the US Department of Agriculture protocol, which is a qualitative enzyme-linked immunosorbent assay (ELISA) method that can detect both muscle and organ tissue from the designated species. The samples were also tested for gluten using a quantitative ELISA. The test results were then compared to the ingredient label on the package.

Importers and producers will bear more responsibility for verifying the safety and authenticity of proteins and grain products.
We found eight foods that tested positive for an animal protein not listed on the ingredient label: two instances of undeclared beef/sheep, five of pork and one of deer. Conversely, in two instances, foods claiming to contain venison tested negative for deer content but positive for beef, sheep or pork. Two foods used a general term, meat and bone meal, rather than listing a specific protein source. Both of these foods tested positive only for pork content, but these were not considered instances of mislabeling.


A recent survey of 21 commercial dog foods showed 12 instances of mislabeling in 10 of the products tested (two foods had more than one labeling issue).Twelve of the 21 foods tested listed no gluten source (wheat, rye, barley or related grains) in their ingredient list, and five were specifically labeled as gluten-free or grain-free. Five of the 12 foods with no listed gluten source, including two of those foods promoted as gluten- or grain-free, tested positive for gluten at greater than 80 ppm. This level is far above FDA’s proposed limit of 20 ppm for gluten-free labeling in human foods.

Overall, there were 12 instances of mislabeling in 10 of the dog foods tested; two foods had more than one labeling issue (Table 1). As in the human food industry, this type of mislabeling is typically not intentional on the part of the manufacturer. Rather, it is most often the result of mistakes during formulation or the receipt of mislabeled product from a supplier.