Breeding Mouse colonies tend to be very labor intensive and are discouraged for the production of commercially available strains of mice. The cost of breeding mice for research use far outweigh the cost of purchasing from commercial vendors. Also, it is very difficult to maintain the genetic heterozygosity required for outbred mice in small colonies and to prevent subline divergence when breeding inbred mice. For strains not available commercially or in instances where neonatal or fetal animals are required, breeding colonies are maintained Investigators requiring the establishment of breeding colonies should consult with the Animal Care Unit to assure proper management of the colonies. Breeding animals have different nutritional requirements, which if not provided, will have a detrimental effect on reproductive