Apples

Safe for Dogs to Eat?

Yes. Only in moderation!
Health Benefits of Apples:

Apples are a wonderful source of particular nutrients, such as Vitamin A and Vitamin C. These vitamins help to support eye health, bone growth, and immune system response. Unlike humans, however, dogs can manufacture their own vitamin C within their bodies. The quick moving digestive systems that dogs have will put a limit on the nutritional benefits that a dog might receive from apples.
Apples also serve to help freshen a dog’s breath, especially for puppies and older dogs that have bad breath that is less than desirable for most owners. Giving a dog a slice of fresh apple before going on car rides might help the owner to avoid the dog breath aroma in close quarters.
In addition to the other two benefits, apples can help to clean teeth as well. The outer layer of the apple, the skin, is quite fibrous. It is fairly difficult to chew, which means the dog will continue to chew while the peel scrapes against the teeth and gums inside of the dog’s mouth. It will help to remove plaque, thus helping to prevent tartar. Jonathan apples are probably best for this, as they have tough, thick skins.
Things to Remember:

A dog should never ingest apple seeds due to toxicity. All seeds must be removed from the apple before it is fed to a dog, or the animal could become very ill over time. The seeds contain small traces of cyanide which could become deadly if they are consumed regularly or in large amounts. If your dog eats a seed or two on rare occasion, do not panic; just ensure to remove them all next time.
Apples should not be a staple in a canine’s diet either, as they do not provide the nutrition a dog needs. Instead, the dog should be fed a balanced formula that provides complete nutrition. There are also high amounts of sugars in apples, which could put a dog at risk of diabetes if it ingests large amounts of them regularly. In addition, diabetic dogs should steer clear of apples.
What Too Many Apples Can Do to a Dog:

Naturally, too much of any one particular food will cause problems with a dog’s health. In the case of apples, you will witness some hallmark symptoms of an improper diet. These symptoms include: upset stomach, digestive issues, diarrhea, malnutrition, and even diabetes. While apples can supply a dog with a few key nutrients, they are not a good source of healthy fats, proteins, or varying vitamins and minerals. Diabetes is also a possibility after eating many apples over a long period of time. Warning symptoms of diabetes include excessive thirst and urination.