They also contain a protein called avidin which decreases the absorption of biotin which is very important in your dog's growth and coat health. (dachshund-owner-guide.com)
While this is true, there is plenty of biotin in egg yolks to make up for the amount of avidin in the whites. (petfoodtalk.com)
This is due to a constituent called avidin which is destroyed by cooking. (whfoods.org)