Apple seeds are not harmful to dogs when ingested in small amounts, according to DogSupplies.com. However, apple seeds contain a form of cyanide that is toxic to humans and animals when ingested in large quantities.
Eating one or two apple seeds is considered harmless to dogs, but consuming small amounts of apple seeds over time can lead to a build-up of poison in the dog's system. Therefore, dog owners should core apples prior to feeding to prevent gradual toxicity.
Apples contain high amounts of vitamin C, omega-3 fatty acids and fiber. Omega-3 fatty acids help to promote a shiny coat, while vitamin C is believed to minimize the risk of hip dysplasia in large and purebred dogs.