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Varied cages and aggression
295 Psychological Wellbeing of Captive Laboratory Primates. Noyes Publications, Park Ridge, N J, pp. 75-88.
Varied cages and aggression R.B. Jones .4FRC Institute o.fAnimal Physiology and Genetics Research, Roslin, EH25 9PS, Uh"
(Accepted 3 July 1991 )
Dear Sir, McGregor and Ayling ( 1990 ) reported that aggressive behaviour appeared sooner when male mice from established groups reared in the standard, relatively barren laboratory cages were briefly translocated in pairs to cages containing additional food and water sources and a number of unfamiliar objects rather than to cages whose contents were similar to those of their home environment. They then claimed that these results have "obvious implications for the welfare of captive mice". However, the experimental design does not warrant their subsequent conclusions: firstly, that providing "more varied and natural" cages may facilitate aggression and, secondly, that the stark environment of a standard laboratory holding cage will retard aggressive behaviour and is, therefore, not necessarily unsatisfactory. Of greater concern is the retrograde effect that such unsubstantiated statements could have on the growing and laudable tendency to provide more complex, enriched and natural environments for laboratory and farm animals. Of course, the animals' responses to increased environmental complexity must always be carefully monitored but the desirable consequences of environmental enrichment are becoming well documented (Markowitz, 1982; Chamove, 1989 ). I will outline some of the obstacles to a meaningful interpretation of the findings of McGregor and Ayling (1990) in terms of environmental impoverishment or enrichment. Firstly, no records of pre-test aggression between the members of each translocated pair, or of their positions in the social hierarchy of the established group were presented. Secondly, whilst I sympathise with the authors' ethical decision to terminate each test upon the first indication of a presumed aggressive posture, their argument is weakened by the absence of measures of sniffing, tail-rattling, biting and submission. For instance, it could be argued that the aggressive tendencies induced by translocation to a complex environment may have dissipated rapidly and that the expression of aggressive intent may not have escalated into actual fighting.
296
Thirdly, exposure to a novel environment or a clean cage alone can elicit fighting between animals which had previously coexisted peacefully (Archer, 1976). Indeed, the translocated mice in McGregor and Ayling's study were more active and "excitable" and this may, in turn, have increased the likelihood of violation of individual distance. Furthermore, olfaction is an important regulator of social behaviour in mice and the absence of any aggressioninhibiting effect of a familiar colony odour may have further confounded the results. A balanced design incorporating translocation between similar, moreand less-complex cages is absolutely essential to provide adequate control for the potential effects of novelty per se. It is commonly recognised that environmental enrichment involves increasing the complexity of the young animal's home environment by the regular introduction of unfamiliar stimuli, often over a lengthy period or even permanently. Conversely, the procedure used by McGregor and Ayling ( 1990 ) allowed them only to examine the effects of social disruption and brief exposure to novel places and objects, and not those of environmental enrichment or impoverishment. In conclusion, it is worth noting some of the beneficial effects of environmental enrichment. Not only has this procedure been reported to improve learning, memory, social affiliation, growth and reproductive performance but also to reduce emotionality and the occurrence of abnormal and often undesirable behaviours, such as overeating, stereotypies, withdrawal and aggression, in many zoo, farm and laboratory animals (Markowitz, 1982; Chamove, 1989; Jones, 1989; Schaeffer et al., 1990).
REFERENCES Archer, J., 1976. The organization of aggression and fear in vertebrates. In: P.P.G. Bateson and P.H. Klopfer (Editors), Perspectives in Ethology, Volume 2. Plenum, New York, pp. 231298. Chamove, A.S., 1989. Environmental enrichment: a review. Anim. Technol., 40 155-178. Jones, R.B., 1989. Development and alleviation of fear. In: J.M. Faure and A.D. Mills (Editors). Proc. Third European Symposium on Poultry Welfare, 11-14 June, 1989 World's Poultry Science Association, Tours, pp, 123-136. Markowitz, H., 1982. Behavioral Enrichment in the Zoo. Van Nostrand Reinhold, New York. McGregor, P.K. and Ayling, S.J., 1990. Varied cages result in more aggression in male CFLP mice. Appl. Anim. Behav. Sci., 26:277-281. Schaeffer, A.L., Salomons, M.O., Tong, A.K.W., Sather, A.P. and Lepage, P., 1990. The effect of environment enrichment on aggression in newly weaned pigs. Appl. Anita. Behav. Sci., 27: 41-52.
Varied cages and aggression R.B. Jones .4FRC Institute o.fAnimal Physiology and Genetics Research, Roslin, EH25 9PS, Uh"
(Accepted 3 July 1991 )
Dear Sir, McGregor and Ayling ( 1990 ) reported that aggressive behaviour appeared sooner when male mice from established groups reared in the standard, relatively barren laboratory cages were briefly translocated in pairs to cages containing additional food and water sources and a number of unfamiliar objects rather than to cages whose contents were similar to those of their home environment. They then claimed that these results have "obvious implications for the welfare of captive mice". However, the experimental design does not warrant their subsequent conclusions: firstly, that providing "more varied and natural" cages may facilitate aggression and, secondly, that the stark environment of a standard laboratory holding cage will retard aggressive behaviour and is, therefore, not necessarily unsatisfactory. Of greater concern is the retrograde effect that such unsubstantiated statements could have on the growing and laudable tendency to provide more complex, enriched and natural environments for laboratory and farm animals. Of course, the animals' responses to increased environmental complexity must always be carefully monitored but the desirable consequences of environmental enrichment are becoming well documented (Markowitz, 1982; Chamove, 1989 ). I will outline some of the obstacles to a meaningful interpretation of the findings of McGregor and Ayling (1990) in terms of environmental impoverishment or enrichment. Firstly, no records of pre-test aggression between the members of each translocated pair, or of their positions in the social hierarchy of the established group were presented. Secondly, whilst I sympathise with the authors' ethical decision to terminate each test upon the first indication of a presumed aggressive posture, their argument is weakened by the absence of measures of sniffing, tail-rattling, biting and submission. For instance, it could be argued that the aggressive tendencies induced by translocation to a complex environment may have dissipated rapidly and that the expression of aggressive intent may not have escalated into actual fighting.
296
Thirdly, exposure to a novel environment or a clean cage alone can elicit fighting between animals which had previously coexisted peacefully (Archer, 1976). Indeed, the translocated mice in McGregor and Ayling's study were more active and "excitable" and this may, in turn, have increased the likelihood of violation of individual distance. Furthermore, olfaction is an important regulator of social behaviour in mice and the absence of any aggressioninhibiting effect of a familiar colony odour may have further confounded the results. A balanced design incorporating translocation between similar, moreand less-complex cages is absolutely essential to provide adequate control for the potential effects of novelty per se. It is commonly recognised that environmental enrichment involves increasing the complexity of the young animal's home environment by the regular introduction of unfamiliar stimuli, often over a lengthy period or even permanently. Conversely, the procedure used by McGregor and Ayling ( 1990 ) allowed them only to examine the effects of social disruption and brief exposure to novel places and objects, and not those of environmental enrichment or impoverishment. In conclusion, it is worth noting some of the beneficial effects of environmental enrichment. Not only has this procedure been reported to improve learning, memory, social affiliation, growth and reproductive performance but also to reduce emotionality and the occurrence of abnormal and often undesirable behaviours, such as overeating, stereotypies, withdrawal and aggression, in many zoo, farm and laboratory animals (Markowitz, 1982; Chamove, 1989; Jones, 1989; Schaeffer et al., 1990).
REFERENCES Archer, J., 1976. The organization of aggression and fear in vertebrates. In: P.P.G. Bateson and P.H. Klopfer (Editors), Perspectives in Ethology, Volume 2. Plenum, New York, pp. 231298. Chamove, A.S., 1989. Environmental enrichment: a review. Anim. Technol., 40 155-178. Jones, R.B., 1989. Development and alleviation of fear. In: J.M. Faure and A.D. Mills (Editors). Proc. Third European Symposium on Poultry Welfare, 11-14 June, 1989 World's Poultry Science Association, Tours, pp, 123-136. Markowitz, H., 1982. Behavioral Enrichment in the Zoo. Van Nostrand Reinhold, New York. McGregor, P.K. and Ayling, S.J., 1990. Varied cages result in more aggression in male CFLP mice. Appl. Anim. Behav. Sci., 26:277-281. Schaeffer, A.L., Salomons, M.O., Tong, A.K.W., Sather, A.P. and Lepage, P., 1990. The effect of environment enrichment on aggression in newly weaned pigs. Appl. Anita. Behav. Sci., 27: 41-52.