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When assuming a species-typical tripodal posture, female Mongolian gerbils most often rest on their left forepaws and hold their right forelimbs aloft; male gerbils most often do the reverse. This experiment examined effects of gonadectomy, both in infancy and in adulthood, on the sexually dimorphic asymmetry in forelimb use by Mongolian gerbils when maintaining a tripodal stance. In adulthood, both male and female gerbils that had been gonadectomized at birth reversed their forelimb use while in a tripodal stance: Gonadectomized males used their forelimbs as did sham-operated females, and gonadectomized females used their forelimbs as did sham-operated males. Gonadectomy in adulthood abolished the sexual dimorphism in forelimb use seen in sham-operated subjects. It was concluded that gonadal hormones have organizational as well as possible activational effects on adult patterns of forelimb use by gerbils

Adult. --- Adulthood. --- Asymmetries. --- Asymmetry. --- Birth. --- Congenital adrenal-hyperplasia. --- Experiment. --- Female mongolian gerbils. --- Female. --- Females. --- Gerbil. --- Gerbils. --- Handedness. --- Hormone. --- Hormones. --- Male. --- Males. --- Mongolian gerbil. --- Mongolian gerbils. --- Mongolian-gerbil. --- Pattern. --- Patterns. --- Paw preference. --- Positions. --- Posture. --- Rat. --- Sexual dimorphism. --- Sexual. --- Testosterone levels. --- Time.

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Aggression in group-housed male mice is known to be influenced by both cage size and group size. However, the interdependency of these two parameters has not been studied yet. In this study, the level of aggression in groups of three, five, or eight male BALB/c mice housed in cages with a floor size of either 80 or 125 cm(2)/animal was estimated weekly after cage cleaning for a period of 14 weeks. Furthermore, urine corticosterone levels, food and water intake, body weight, and number of wounds were measured weekly. At the end of the experiment, tyrosine hydroxylase (TH) activity, testosterone levels, and weight of spleen, thymus, testes, and seminal vesicles were determined. Results indicate a moderate increase of intermale aggression in larger cages when compared to the smaller cages. Aggression in soups of eight animals was considerably higher than in groups of three animals. The increase of agonistic behavior was observed both in dominant and subordinate animals. Physiological parameters indicate differences in stress levels between dominant and subordinate animals. It is concluded that aggressive behavior in group-housed male BALB/c mice is best prevented by housing the animals in small groups of three to five animals, while decreasing floor size per animal may be used as a temporary solution to decrease high levels of aggression in an existing social group. (C) 2001 Elsevier Science Inc. All rights reserved

Activity. --- Aggression. --- Aggressive-behavior. --- Aggressive. --- Agonistic. --- Animal. --- Animals. --- Behavior. --- Body weight. --- Body-weight. --- Cage size. --- Cage. --- Cleaning. --- Corticosterone. --- Crowding. --- Experiment. --- Floor. --- Food. --- Group size. --- Group. --- House mice. --- Housing. --- Increase. --- Laboratory mice. --- Level. --- Male-mice. --- Male. --- Mice. --- Modulation. --- Mus-musculus. --- Parameters. --- Physiological. --- Size. --- Social-behavior. --- Social. --- Stress. --- Testosterone levels. --- Testosterone. --- Time. --- Tyrosine. --- Urine. --- Weight. --- Welfare.

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'Environmental enrichment' is often considered to improve captive animal welfare. However, some studies using male mice, Mus musculus, indicate that increasing cage complexity, increases aggression. Limited evidence suggests that enrichment differs in ifs effects on behaviour and physiology between strains; but behaviour also differs between strains in non-enriched environments. Differ ences in enrichment type, evaluation methods, and strains used, have caused difficulty in interpreting the efficacy of environmental enrichment in improving welfare. Using enrichment suitable for commercial laboratories (nesting material and a Perspex tunnel), we physiological responses among males of six strains housed in iron-enriched standard polypropylene cages with those housed in 'enriched' cages. Outbred ICR(CD-1) and TO mice, and inbred BALB/c mice were more aggressive than C57BL/6, CBA/Ca and DBA/2 mice, which exhibited low levels of aggression typical of most inbred strains. Enrichment did not significantly affect aggression levels. Animals in enriched cages spent more time investigating the internal cage environment, eating and drinking, and in stereotypic behaviour patterns, although levels differed between strains. The greatest increase in stereotypy levels (bar-related stereotypies,pies) with enrichment was found in DBA/2 mice. Higher testosterone levels were maintained over the study, period ill mice housed in enriched cages, and in more aggressive strains. IgG levels were also higher in mice housed in enriched cages, and in the outbred strains ICR(CD-1) and TO compared with inbred strains. The relationship between aggression, testosterone and 'enrichment' suggests, that increasing complexity in laboratory cages may increase a naturally, selected territorial response in some strains. The implications for strain-specific welfare are discussed

Aggression. --- Aggressive-behavior. --- Aggressive. --- Animal welfare,behaviour,enrichment,mice,physiology,strain differences. --- Animal welfare. --- Animal-welfare. --- Animal. --- Animals. --- Babesia-microti. --- Behaviour. --- Cage. --- Design. --- Drinking. --- Enriched. --- Enrichment. --- Environment. --- Environmental enrichment. --- Environments. --- Hormonal responses. --- Immunity costs. --- Inbred strains. --- Increase. --- Increases. --- Laboratory cages. --- Laboratory mice. --- Laboratory. --- Level. --- Male house mice. --- Male-mice. --- Male. --- Males. --- Method. --- Mice. --- Mus musculus. --- Mus-musculus. --- Musculus. --- Nesting material. --- Pattern. --- Patterns. --- Physiological-responses. --- Physiological. --- Physiology. --- Resistance. --- Response. --- Responses. --- Social-organization. --- Stereotypic behaviour. --- Stereotypic. --- Stereotypies. --- Stereotypy. --- Testosterone levels. --- Testosterone. --- Time. --- Welfare.