Abstract
Cortisol (the end product of activity in the hypothalamic pituitary adrenal [HPA] axis) has been traditionally used as a major physiological index of stress across the mammalian taxa. Inherent in many welfare studies is the assumption that cortisol provides an objective, quantifiable measure of the subjective feelings of an animal. The HPA axis, however, is involved in many physiological processes in addition to the stress response. The broad goal of the current study was to assess factors in addition to stress that trigger a HPA response in captive ring-tailed lemurs, Lemur catta.Specifically there were five aims to the current research. First was to biologically and immunologically validate an enzyme immunoassay (EIA) to quantify levels of cortisol in L catta urine and faeces. This goal included developing a method to extract cortisol from L. catta faeces. Second, as HPA function is closely linked to animal behaviour, the behaviour patterns of captive L catta were assessed in relation to institution of residence, time of day and sex. Third, factors considered to influence activity in the HPA axis of captive animals were considered. These factors were institution of residence, sex and different aspects of behaviour. Fourth, as dominance status has been shown to influence cortisol production in wild L catta, the current study assessed if a similar relationship existed in captivity. Fifth, due to the potential for visitor presence to influence captive animals, the impact of increasing visitor numbers on captive L catta behaviour and HPA function was investigated.
Subjects comprised 40 captive adult L. catta residing in five stable social groups in different institutions. A total of 767 hours of behavioural data were collected and 903 faecal samples and 208 urine samples were obtained from which levels of excreted glucocorticoid were quantified.
A successful method was developed to extract cortisol from L. catta faeces. ElAs were immunologically and biologically validated to measure cortisol in the urine and faeces of L. catta. Behaviour was shown to be modified by the institution in which subjects were housed, by sex and by time of day. The following factors modified HPA function in captive L. catta: institution in which subjects were housed and behaviour. Specific behaviours associated with cortisol production were time spent inside, time spent engaged in locomotion and percentage of agonistic attacks initiated. Intersex, female intrasex and male intrasex dominance hierarchies existed in the captive groups studied. This result differs from wild studies where only strict female dominance occurs. The relationship between dominance rank and cortisol levels varied between institutions of residence. In all but one study group, there was no relationship between dominance rank and cortisol levels. In the group where a relationship was observed, the most dominant individuals exhibited highest cortisol levels. Finally, visitor numbers were demonstrated to impact captive L. catta behaviour and HPA function. Visitor numbers were associated with a change in the following behaviours: time spent alone; time spent engaged in locomotion and time spent grooming with other group members. In general, cortisol levels decreased as visitor numbers increased.
Although the present results do not negate the use of cortisol as a welfare indicator in L. catta, they do highlight the myriad of behavioural and environmental factors in addition to stress that modify cortisol excretion in this species in captivity. The present results emphasise the challenges associated with using cortisol to monitor well-being and highlight that caution must be exercised when planning experiments to measure welfare and assess subjective feelings in order that confounding variables be minimised.
| Date of Award | Dec 2006 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Northern Ireland Department of Employment and Learning |
| Supervisor | Robert Elwood (Supervisor) |