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Aspects of Stress in Man and Animals

adjusted according to the number of mice in each group. At 8 weeks the heaviest male and female were selected to enter the next generation. A cyclical mating programme was used to minimize in-breeding effects. Early results showed that breeding floor areas of 600 cm2 or more impaired infantile growth and survival and it was shown that survival was directly related to cage size. Female mice bred in cages of 150 cm2 lost approximately 20% of their litters whilst corresponding animals in cages of 1350 cm2 suffered an 80% offspring mortality. A reversal of cage conditions for the same breeding females for the next litters simply reversed the mortality figures so it was possible to obtain high or low infantile mortality by placing the female in a large or small cage. Assessments of maternal behaviour were also conducted and the results showed that females with smaller breeding areas produced the highest maternal scores. The offspring mortality in large cages was invariably due to a failure of the female to nurse the young and mammary development was inhibited. However, post-weaning growth was not affected by floor area. The results therefore suggested that the effect of floor area was maximal during the parturient and nursing periods. Furthermore, cross-fostering of young at birth showed that the viability of the young was unaffected by conditions in utero. Such data therefore emphasize the importance of space and illustrate the sensitivity of the dam during the post-partum period. It is important to note that the mouse is less productive when available space is increased which contradicts the opinion that restricted space leads to a reduction in performance. A possible interpretation of these results suggests there may be an optimum spatial requirement and increases or decreases lead to changes in reproductive efficiency. Although only spatial effects were studied, there are now indications that when group size is introduced as another variable, interaction effects begin to emerge. In the dairy industry the resultant effect of increasing the size of the herd and reducing floor area per cow has been a suppression of cestrus. Work in the UK and USA suggests that optimum group size is between 70 and 100 cows at present day floor area allowances of 80-100 sq ft (7.4-9.3 m2) per cow. Some herds exceeding these numbers during the housed winter period have reported a decline in behavioural aestrus, which means that artificial insemination is delayed and there is a subsequent loss of milk production. Other work at Bristol with battery housed hens shows that they too reflect the effects of group size and floor area allowances by altering not only egg output but also the composition of the egg. This paper has attempted to give some indication of the attitudes of man towards stress in domestic animals. Man's attitude and ability is important because he has to decide whether an animal is stressed and we still rely heavily on subjective measures of assessment as knowledge of behaviour patterns under different management systems is very inadequate, although information is now coming forward. Much additional work is now in progress featuring the adrenal gland and corticosteroid levels although in terms of an onthe-spot appraisal of stress the behaviour and/or the reproductive performance of the animal is and probably will remain for a considerable time the most important means of assessment of stress in domestic animals.