They are hypoallergenic: they do not contain any element that triggers canine allergies. They do not contain cereals or gluten. When chewed, the horn breaks down into small grains generating a gritty effect that rubs against tartar and plaque, as if it were a toothbrush. No calorie content. Dogs should always be provided with clean, fresh water. They are hypoallergenic: they do not contain any elements that trigger canine allergies. They do not contain cereals or gluten. When chewed, the horn breaks down into small grains generating a sandy effect that rubs against tartar and plaque, as if it were a toothbrush. No calcium content. Size S (15-39 gr) Size M (40-75 gr) Size L (76-150 gr) Size XL (151-225 gr)