Cage effects on levels of stress in female rats during lactation

Abstract

High stress levels over long periods of time have been found to have a negative impact on the welfare of laboratory animals by disrupting biological functioning, causing illnesses, and abnormal, stereotypical behaviours. Prolonged stress can also lead to reduced validity of data and increase the need for repetitions of experiments; thus leading to more animals being used in vivisection overall. A minimum level of welfare must be obtained in a laboratory environment to ensure the animals the best quality of life as possible and improve quality of data. Environmental enrichment is commonly used in laboratory environments to improve the welfare of the experimental animals. In this study a non-invasive method of enzyme immunoassay analysis was used to investigate faecal corticosterone metabolite levels of female Sprague-Dawley rats in enriched and standard cages. Faecal samples were collected throughout pregnancy, lactation and a predicted period of weaning conflict (days 14 to 21 of lactation), in order to compare stress levels of females in the two cage types. Observations of female and pup behaviour were performed during lactation to compare differences between cage types. No overall effect of cage type was found on corticosterone metabolite level throughout lactation. However, females in the enriched cages had higher corticosterone metabolite levels on day 18 of gestation and lactation than the females in the standard cages, which potentially indicates that these females were more stressed by certain aspects of the cage design. There was no difference in corticosterone metabolite levels during the predicted weaning conflict between the two cage types. Females in both cage types showed a decrease in corticosterone metabolite level during the predicted weaning conflict, showing that either the weaning conflict is not a significant stressor to the females, or that the weaning conflict in Sprague-Dawley rats does not occur when we predicted. On day 18 of lactation, females in the enriched cages made more use of the second level feature of their cages as the activity behaviour of their pups increased. This suggests that females make use of the upper level in order to avoid their demanding pups during weaning. Cage type had an effect on maternal behaviours: suckling, retrieval and pup-licking and sniffing, possibly due to the differences in activity levels of females and pups during observations. The females in the standard cages were seen to be much more active, and did not suckle their pups as much as the enriched females. However there was no difference in weight gain of pups throughout lactation, suggesting that conditions during observations had an effect on the activity and suckling behaviour of females and pups in both cage types.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Reinmar Hager (Supervisor) & Matthew Cobb (Supervisor)