The effects of witnessing managemental procedures during the light versus the dark phase of the light cycle on behaviour, performance and welfare of laboratory rats

Abstract Research has indicated that witnessing managemental procedures are stressful to laboratory rats. Yet there has been little investigation into whether the time of witnessing these procedures affects behaviour and welfare in these animals. Ninety-six rats, representing two batches, were used in this study. Forty-eight of them were housed, in groups of four, in either light phase witnessing group (LPWG) ( n  = 6) or dark phase witnessing group (DPWG) ( n  = 6) for five consecutive weeks. The remaining 48 rats were exposed to the managemental procedures (e.g. weighing, cage cleaning, restraint and vehicle injection) in either the light or the dark phase of the light/dark cycle, and were also housed in groups of four. At the beginning of the 5th week of the housing period, behaviour for all cages was sampled over the 1st 4 h of both the light and dark phases of the light/dark cycle. Physiological (e.g. body weight) and pathological (e.g. thymus and spleen weight) measures were collected at the end of the 5th week of the housing period. Principal component analyses yielded six factors, four of which revealed significant treatment differences. For the first, loaded positively on the body weight of animals, and negatively on relative weight of the adrenal gland, rats of the DPWG scored higher than those of the LPWG ( P P P P