The laboratory opossum, Monodelphis domestica, serves as a critical marsupial model in biomedical research. Proper feeding approaches are essential for promoting animal growth and wellbeing. In this study, we systematically evaluated food scattering and potential food contamination from feces across 4 feeding methods: direct placement of food pellets on bedding and using 3 different types of containers. We conducted timed daily observations of food scattering and marking behaviors in 22 animals, capturing images by photograph at specific intervals over the course of a week. Body weight was measured before and after the trial. Our findings revealed that the containers did not prevent food scattering behaviors, as evidenced by comparable survival curves for food scattering across all methods (P > 0.05, log-rank test). Although the paper tray and ceramic dish delayed the occurrence of food marking by feces, indicated by a significant extension in the time to marking events (P = 0.009 and P < 0.001, respectively), these containers introduced new animal welfare concerns. The paper tray increased bleeding incidents in digits and paw pads nearly 8-fold (P = 0.0002), presumably due to sharp edges. The ceramic dish was associated with urine marking, and small but statistically significant weight loss (0.7%, P < 0.05). By 144 h, all cages showed food contamination regardless of the feeding method. The results suggest that containers provide minimal benefit in preventing food contamination, and some types of containers may pose health risks. Therefore, we propose that placing food pellets directly on the bedding, a practice used for 45 y of laboratory opossum maintenance, is acceptable for promoting optimal health and operational efficiency for this species. Our results fill a significant gap in care practices and offer insights into optimal colony management for this important research model.Abstract
Monodelphis maintenance cage setup before and after USDA inspection. (A) Setup of an opossum maintenance cage, with opossum food placed directly on the bedding at one corner of the cage (approved by IACUC). (B) Modification of the opossum maintenance cage in response to USDA concerns, by adding a paper tray as the food container. (C and D) Top view of the opossum maintenance cage demonstrating the paper tray with opossum chow inside, without (C) and with (D) the wire bar top.
Increase of Monodelphis bleeding incidence after switching to paper tray as feeding container. (A) Plot of the number of bleeding reports between January 2023 and February 2024. The total incidence of bleeding is represented by the blue line/dots. Bleeding from known causes, such as aggression/fighting following the pairing of breeders, is indicated by the orange line/dots. Bleeding from unknown causes, such as dried blood found in the cage, is shown in green. (B) Photo showing an opossum placing its paw on the edge of a paper tray.
Design of food contamination and marking behavior experiments to test 4 feeding containers. (A) Behavior experiment design. A total of 22 animals were enrolled in this study and housed individually. Following each cage change, food contamination, by scattering and marking behaviors, was observed at multiple time points: 0, 0.5, 1, 2, 4, 24, 48, 72, 96, 120, 144, and 168 h. (B) Cartoon illustrations depict 2 ways of food contamination: food scattering (top panel), the opossum moves the food pellets and hides them under the bedding, where they can come into contact with feces; food marking (bottom panel), the opossum defecates or urinates directly onto the food pellets or inside the food containers. (C) Top view and side view of 3 food types of food containers tested: paper tray, weighing boat, and ceramic dish (from left to right). (D) Cage setting for the 4 treatment groups: 1) food placed on the bedding, 2) food placed inside the weighing boat, 3) food placed inside the paper tray, and 4) food placed inside the ceramic dish.
Characterization of food scattering behavior in opossum maintenance cages under 4 different feeding approaches. (A) Two photographs of the same opossum, taken consecutively, demonstrate examples of opossum food scattering/hiding behaviors. (B) Estimated survival probability (inverse probability of food scattering events) using ceramic dish (green), paper tray (blue), weighing boat (orange), and no container (red). Statistical significance was determined using a log rank test (ns, not significant with P > 0.05). The shaded bands in the graph represent 95% confidence intervals.
Characterization of food marking behavior in opossum maintenance cages under 4 different feeding approaches. (A–D) Examples of fecal marking contaminations using no container (A), weighing boat (B), paper tray (C), and ceramic dish (D). Contamination levels 2 and 4 are shown. (E and F) Observations of food marking in the ceramic dish container revealed caked food at the bottom of the dish (E) caused by urine marking, and accumulation of fecal piles near the dish (F). (G) Estimated survival probability (inverse probability of food-marking events) using ceramic dish (green), paper tray (blue), weighing boat (orange), and no container (red). Statistical significance was determined using a log rank test (*, P ≤ 0.05; †, P ≤ 0.01; ‡, P ≤ 0.001; §, P ≤ 0.0001; +, P ≤ 0.005; ×, P ≤ 0.0005). The shaded bands represent 95% confidence intervals.
Survival curves demonstrating time to food contamination by food scattering or marking under 4 different feeding approaches. Estimated survival probability (inverse probability of food scattering or marking events) using ceramic dish (green), paper tray (blue), weighing boat (orange), and no container (red). Statistical significance was determined using a log rank test (*, P ≤ 0.05; †, P ≤ 0.01; ‡, P ≤ 0.001; §, P ≤ 0.0001; +, P ≤ 0.005; ×, P ≤ 0.0005). The shaded bands represent 95% confidence intervals.
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