Apples are a fine food for your dog. Apples are filled with nutrients, water and fiber for your dog to eat and benefit from. However, in humans, apples are known for causing constipation. Apples may also cause constipation in dogs as well - but remember that every dog is different and react to certain foods differently. If you want to feed apple to your dog, remove the seeds first, see if they enjoy a bite-sized chunk of apple, then wait and see if constipation develops within the subsequent 12-24 hours. If no constipation, apple sauce without added sugar can be a "sometimes" treat, but apple juice is likely too high in sugar to cause anything but extra bacterial growth under the gums and around the teeth.