Castration, Testosterone Replacement Therapy and Spacing Patterns in Laboratory Mice ( Mus Musculus )

15 animals in each group of Swiss-Webster male mice (Alus musculus) were either castrated on Day 1, on Day 50, or received sham operations on Day 1, or on Day 50. Five mice from each group were paired with five mice from each other group and tested for inter-male aggressiveness. The sum of attacks for all groups suggested that early and late castration suppressed attacks, and exogenous testosterone propionate increased attacks in the Late Castrates, but not the Early Castrates. Locations of attacks by animals in this experiment were not equally distributed over the experimental apparatus. Before injections (testosterone replacement or distilled water) the Early Shams and Late Shams attacked Early and Late Castrates in the castrates' experimental space. After injections, Early Shams, Late Shams, and Late Castrates attacked Early Castrates in their experimental space. Attacks did not occur in the attacking animals' experimental space.