In this paper the question is posed whether it is not only better for the animal to be happy, but whether its state of mind may also have the potential to influence the scientific results derived from it. To ensure good science, the animal should have a normal physiology and behaviour, apart from specific adverse effects under investigation. There is a growing body of evidence from a wide variety of sources to show that animals whose well-being is compromised are often physiologically and immunologically abnormal and that experiments using them may reach unreliable conclusions. On scientific, as well as ethical grounds, therefore, the psychological well-being of laboratory animals should be an important concern for veterinarians, animal technicians and scientists.
Starting with 4 pairs of marmosets, 204 young were successfully reared during 6 years. They were kept in family groups of 2- 10. Litter size varied from 1-4; singletons (2%), twins (35%), triplets (55%), and quadruplets (8%). The mean annual increase of weaned young was 3.24 per pair. The median interbirth interval was 154 days. Of 46 pairs of marmosets, 8 failed to produce young. Approximately 11% of young born were stillborn and a further 32% of all young born died within 3 weeks; perinatal mortality is largely a result of the failure of parents to rear more than 2 young. In only 2 of 68 triplet births did the parents rear the young unaided. 53% of young born were males but differential mortality reduced the final sex ratio for live young to 50-5% males. Females did not accept and rear the young after caesarian section. The linear regression of the growth curve for 5-17 months (where y = weight in grams and x = months) could be expressed as y = 16.6x + 163.6. The data form 4 marmoset colonies are compared and the relative efficiency of breeding methods discussed.
The playful behaviour of laboratory rats (Rattus norvegicus) was investigated in litters of five individuals with the mother present; parallel observations were made on mice (Mus musculus). Seven mixed litters containing four young rats and a young mouse fostered at birth were also observed.
Solitary play was recorded in both species and took a similar form but social play was only observed in rats. In rats, solitary play frequently preceeded social play.
The behavioural elements involved in the social play of Rattus norvegicus were described, and the majority of these were the playful equivalent of adult agonistic behaviour elements. These social play elements were found to be organized into definite sequences which differed from those of adult aggression. Each behavioural element was found to act as a social releaser.
Young mice did not respond playfully to social play from a rat litter mate; mice were less attractive to rats as playmates in comparison with fellow rats.
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