This might help, too.
RAWHIDES, COW HOOVES, AND PIGS' EARS
Rawhides, cow hooves, and pigs' ears can also be dangerous for several reasons:
1. If they are swallowed whole or in large chunks, rawhide chews can lodge in the throat and cause choking, or a large piece may be swallowed, scraping and irritating the throat and esophagus, and, once in the stomach or intestinal tract, a large piece of rawhide can also create a physical obstruction.
2. In some countries, an arsenic-based preservative is used in the processing of rawhide toys. If you do purchase these products, stick to brands processed in the U.S.
3. The FDA says that there is a risk of Salmonella accociated with dog chew products made from pork or beef-derived materials: refer to the FDA advisory or call 1-888-INFO-FDA.
Cow hooves are even more dangerous than rawhides. They are hard enough that a dog can actually break a tooth on one. They can also be chewed up into sharp fragments that can cause a partial intestinal obstruction. Partial obstructions are often difficult to diagnose until the point at which the fragment is ready to perforate the wall of the bowel from pressure against the sharp edges. If perforation has occured, the infection that ensues from leakage of intestinal contents can be fatal.
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Symptoms of salmonella poisoning include gastrointestinal upset, vomiting, diarrhea, depression, a high temperature, and loss of appetite and listlessness.