Aggression in male mice often leads to injury and death, making social housing difficult. We tested whether (1) small group size, (2) early age of allocation to a group decreases aggression and 3) manipulation increases aggression in male mice. A 14wk study was performed to assess the following conditions in male CD-1/ICR mice: group size (1, 2, or 3), age at grouping (5 or 7wks), and manipulation (daily scruffing or minimal weekly handling). Wounds, body weights, food consumption, nest scores, sucrose consumption, fecal corticosterone and blood for hematology were collected. At the end of the study, mice were euthanized and pelted to assess wounding with the pelt aggression lesion scale (PALS). No signs of acute or chronic stress were observed in any of the groups. Trio housed mice showed less bite wounds than pair housed mice. In general, mice in larger groups ate less but weighed more. Individually housed mice, however, had high nest scores, low body weights, and increased sucrose and food consumption. These results suggest that even when nesting material is provided, individual mice may be experiencing thermal stress. Based on this data, CD-1 mice can successfully be housed for up to 14wks and groups of 3 may be the best for reducing even minor levels of aggression (i.e. wounding).

In the development of cancer therapeutics, no suitable replacements for the use of animals that are capable of modeling such complex disease processes are currently available. In orthotopic models, surgery is often required to access the target organ for tumor cell inoculation. Historically analgesics have been withheld in such models in light of potential effects on tumor development. The current study evaluated the effect of the opioid buprenorphine on tumor growth of a human ovarian cancer cell line (OVCAR5 OT luc2 mCherry). Female CB17 SCID mice (n = 150) underwent surgery for orthotopic inoculation and were assigned to 1 of 3 treatment groups: vehicle control, 1 dose of buprenorphine, or 2 doses of buprenorphine administered perioperatively. Bioluminescence imaging revealed no significant difference on tumor engraftment rate or growth between control and analgesia-treated groups. These data demonstrate that acute, perioperative analgesia with buprenorphine did not alter tumor growth. Although further research is needed to evaluate potential effects of buprenorphine in other cell lines and mouse strains, the justification for withholding analgesia and the potential influence of pain and stress due to insufficient analgesia in these models should be considered thoroughly.