Mastitis is one of the costliest diseases for the U.S. Dairy Industry, and management decisions that may affect mastitis risk are considered carefully. One such decision is the choice of a bedding substrate that helps keep cows clean and comfortable. Maintaining good udder hygene does reduce mastitis risk. Several bedding options are available, and each has advantages and disadvantages. Separated manure solids (SMS) have been used as a dairy cow bedding substrate for many years. Some farms have used SMS successfully, meaning the transition to manure solids bedding did not increase mastitis and/or reduce milk quality. Other herds experienced increased mastitis around the time they switched to manure solids, and attributed this to bedding. Much research has been done to help the industry understand best management practices for use of this organic bedding substrate, but consensus still lacks on if and how SMS should be used.