May 12, 1992 - (Woody CleaL 8/15, supplied by IFFA-Credo. Broekman, Someren, The Netherlands). Room lighting, temperature and humidity were kept.
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L,7boratory Animals (1993) 27, 270-272
Whisker trimming behaviour in A2G mice is not prevented by offering means of withdrawal from it F. A. R. VAN DEN BROEKI, C. M. OMTZIGTI & A. C. BEY~EN2 'Laboratory Animals Centre, Agricultural University, PO Box 8921, 6700 EV Wageningen and 2Department of Laboratory Animal Science, State University, PO Box 80.166, 3508 TD Utrecht, The Netherlands
Summary In group-housed laboratory mice whisker trimming (removal of vibrissae) occurs occasionally, but in the A2G strain it is seen almost invariably. We have tested the hypothesis that whisker trimming in A2G mice is not prevented by offering the possibility to withdraw from it. Pairs of male or female mice showing absence of whiskers and/or absence of nasal fur were separated by placing in their cage either one or two wire screens with a 10 mm mesh. Unlike the single screen, the two screens, which were 10 mm apart from each other, excluded nose to mouth contact. After five weeks, whiskers had regrown in mice separated by the double screen, whereas in the pairs separated by the single screen whiskers remained in part absent. This suggests that 2 mice involved in whisker trimming, either actively or passively, co-operate in this behaviour. Keywords: Whisker trimming; Vibrissae; A2G mice
In general, whisker trimming (removal of vibrissae) occurs only occasionally in laboratory mice, and may be considered as a form of abnormal behaviour. In the AlG strain, however, it is seen almost invariably (Strozik & Festing, 1981). It has been suggested that in groups of male mice only the dominant trims (Rheinhardt & Militzer, 1979; Strozik & Festing, 1981). This could relate to the submissive mouse not being in Correspondence to: Dr FAR van den Broek. Received 12 May 1992; accepted 26 November 1992
a position to retract from the dominant trimmer. However, female (Strozik & Festing, 1981) and male (own observations) A2G mice trim each other, indicating that social ranking alone does not determine whether a mouse actively trims or is being trimmed. It could be suggested that whisker trimming is a form of aberrant behaviour developed to cope with inadequate housing conditions. Whisker trimming would in this respect be equivalent to some mouth-based anomalous syndromes in farm animals (Sambraus, 1985). It could further be suggested that trimming as well as being trimffii~dis mutually acceptable to A2G mice, which could imply that whisker trimming is not prevented by offering a possibility to withdraw from it. In the present experiment this implication was put to the test. Materials and methods Weanling A2G/Ola/Hsd mice, bred in-house from animals purchased from Harlan CPB, Zeist, The Netherlands, were housed in same sex pairs in MacroLon II cages (225 x 160x 140mm), with a layer of sawdust as bedding material (Woody CleaL 8/15, supplied by IFFA-Credo Broekman, Someren, The Netherlands). Room lighting, temperature and humidity were kept controlled (12 h light/dark cycle; 20-22°C, 40-600/0). Clean cages with fresh bedding were introduced once a week. When nasal alopecia was evident in the animals to be tested (n = 42), the cages were divided into 2 parts of equal size by a wire screen. At that time tt.e animals were aged 14-15 weeks. One mouse of each pair was kept on either side of the screen. For animals in the test group a
Whisker trimming in mice
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"Males n = 8; females n", 14.
mice whiskers had regrown. This could be expected, as 5 weeks suffice for complete regrowth (Ibrahim & Wright, 1975). The damage of vibrissae (score 2) in certain mice may have been caused by autogrooming or by rubbing the nose against the wire screen while thrusting it through (Litterst, 1974). Housing of the test mice was designed to offer the possibility to withdraw from being trimmed by cage mates. To be trimmed, a mouse had to actively seek contact with its cage mate. In males, but not in the females, final scores of the test mice were significantly lower than initial scores, indicating that there was partial regrowth of whiskers. Final scores of the test mice were significantly higher than those of the control mice. This experiment suggests that whisker trimming is reduced, but not prevented by offering the possibility of withdrawal from it. We have observed that mice housed in groups are often trimmed while sleeping. This was not possible after introduction of the screen, which explains the fall of scores in the test mice. It has been reported that in groups of male mice one animal remains intact (Rheinhardt & Militzer, 1979; Strozik & Festing, 1981). This was explained by the supposition that only dominant mice trim whiskers. Table I shows that the distributions of initial and final scores in males and females were similar. This indicates that in both sexes there can be mutual whisker trimming. Whisker trimming is a behaviour that requires the co-operation of 2 mice. Separation of the mice by a single wire screen reduced, but did not eliminate whisker trimming. Possibly the two mice involved in whisker trimming both profit from this behaviour, which could relate to release of endorphins. If whisker trimming can be proven to be a means of coping with inadequate housing conditions, this behaviour
bMales n = 14; females n = 6.
might be an indicator
+Significantly different from initial distribution (P
