EFFECT OF FEED AND ENVIRONMENTAL ENRICHMENT ON DEVELOPMENT OF STEREOTYPIC WIRE-GNAWING IN LABORATORY MICE

At 21 days of age, 16 pairs of male laboratory mice of the ICR strain were weaned and allocated to four treatment groups in a 2 x 2 factoria l design matched for genetic background (litter) and body weight. Fact or one was the hardness of the food pellets with a significant 2.5-fol d difference between soft and hard feed. Factor two was the environmen t, with half of the mice being kept in barren standard cages, while th e other half were additionally provided with a cardboard tube. Subject s were videotaped during the full 12-h dark period on three occasions: 3 days after weaning, when stereotypies start to develop (24 days), a t an early stage of stereotypy development (34 days), and when adult w ith fully established stereotypies (80 days). Since feed hardness had no effect on time spent feeding, the absence of an effect of the feedi ng treatment on stereotypic wire-gnawing remains inconclusive with res pect to the role of feeding motivation in the development of this ster eotypy. The interaction between the development of feeding and wire-gn awing, respectively, does not, however, suggest a strong relationship. In contrast, enrichment significantly reduced stereotypic wire-gnawin g in adults by 40% (F= 4.47, df = 1,26, p < 0.05), presumably as a con sequence of the cover provided by the cardboard tubes. This is substan tiated by observations that the tubes were used as a place to retreat upon disturbance as well as for resting. As a consequence, when adult the mice showed more resting (F = 6.46, df = 1,26, p < 0.05) and less grooming ( F = 9.79, df = 1,26, p < 0.01) in cages containing them, su ggesting that mice with access to a cardboard tube land hence shelter) perceived a greater level of security in these cages. Cardboard tubes therefore provide a simple means of environmental enrichment to reduc e the development of abnormal behaviours in laboratory mice and may th us be beneficial in terms of their well-being. (C) 1998 Elsevier Scien ce B.V. All rights reserved.