Ebook Relationship between diet, body condition, behaviour, and faecal glucocorticoid concentrations in African elephants
Wild animals are dependent on seasonal changes in the quality and availability of food. The area in which they range plays a vital role in determining the quality of food found and thereby the body condition of the animal during the year (Poole 1989). Changes in body condition might have an influence on the behaviour of an animal, possibly by physiologically effects e.g. changes in circulating glucocorticoid concentrations. In rats for example it has been shown that a reduction in dietary energy causes an elevated level of urinary corticosterone (May, 1986). It has also been demonstrated that a reduction in body weight due to limited access to water and food causes elevated glucocorticoid levels in female elephants(Foley et al. 2001).
Generally speaking, an elevation of glucocorticoid levels is caused by release of corticotrophin-releasing hormone (CRH) from the hypothalamus. The CRH triggers the anterior pituitary to release adrenocorticotropic hormone (ACTH). ACTH, in turn, stimulates the adrenal gland to secrete glucocorticoids such as cortisol (Fieß, 1999). A possible explanation for the rise in circulating glucocorticoid concentrations might be that a diet low in energy represents a form of physiological stress (Foley et al., 2001). However, to properly understand the link between changes in circulating glucocorticoid concentrations and qualitative and quantitative changes in food intake, it is necessary to know more about the circumstances which trigger reduced feeding / dietary intake.
In the wild, male African elephants live either alone or in all-male groups, so called bachelor herds, having left their natal families at the onset of puberty at around the age of 12 -15 years. From that time on, they live in a highly dynamic world where sexual state, behaviour, rank and associations change a lot over time (Ganswindt et al., 2005a), and may be reflected in changes in body condition during the year. One of the factors thought to influence body condition of male African elephants is competitive reproductive behaviour during their sexually active period (Poole, 1987, 1989, Ganswindt et al., 2005a), the so called “musth” state. It is thought that musth is a strategy that bulls “use” to increase reproductive activity or success. Musth is detectable by behavioural, physiological and physical changes, e.g. a higher probability of aggressive behaviour. During musth, bulls walk longer distances, and therefore feed less, to associate with female herds. This might have an influence on their body condition.
It is suggested that captive elephants are, on average, in better body condition then free ranging elephants, due to a higher quality and more constant availability of food than in the wild (Poole 1989, Ganswindt et al., 2005b); this might cause the early onset and prolonged periods of musth sometimes seen in captive bulls which can show signs of musth as early as 9-13 years of age, whereas male elephants in the wild rarely come into musth before 25 years of age (Poole, 1987).
Wild bulls have to cope with a higher fluctuation in food resources and might therefore start musth at an older age (Ganswindt et al., 2005b). During musth, elephant bulls show a fall in glucocorticoid concentrations as well as a rise in androgens. This is probably due to a decreased corticosteroid binding globulin capacity. The reduced binding of glucocorticoids has a negative feedback on the adrenocorticotropic hormone release (Ganswindt et al., 2005a). These alterations in circulating hormones might in turn affect an elephant bulls’ behaviour (Poole, 1989).
To date, little is known about the relationship between food availability, glucocorticoid levels and body condition in African elephants. Similarly, little is known about changes in feeding habits associated with reproductive state and the underlying physiological mechanisms. More knowledge about the relationship between food availability, body condition, reproductive behaviour, and activation of the hypothalamic-pituitary-adrenal (HPA) axis would therefore be useful. In this context, a feeding experiment was designed to determine the effects of high- and low-energy diets on circulating glucocorticoid concentrations under controlled conditions.
As mentioned above, a decrease in an elephant’s body condition might cause a rise in glucocorticoid release as a result of stress due to the lack of food. The glucocorticoids would then bind to circulating globulins in the bloodstream. The globulins also bind androgens, present during musth (and the cause of the typical behavioural changes (Ganswindt et al., 2005a). It is therefore possible that a decreased body condition causing an elevated level of circulating glucocorticoids would block androgens from binding to the circulating globulins and therefore have a negative feedback effect. Furthermore, reducing the amount and quality of food might negatively affect body condition of the bulls and thereby shorten the duration of musth. Reduced circulating androgens might then influence the bulls’ behaviour, causing the animal to be more handle able and therefore provide a saver environment for animal trainers to work in. Studies of body condition are therefore also necessary to understand interactions between the HPA- and HPG-axes.
Because wild elephants are difficult to approach, it would be very useful to have a validated body condition scoring system that can be performed at distance. The second aim of this study was thus to examine new methods for body condition scoring by testing them on elephants that were known to change in body condition. A number of methods are available for scoring body condition. One is the visual body condition score described by Poole (1989), and another is the recently established body condition scoring system described by Wemmer et al. (2006). Poole’s body condition score is frequently used for African elephants, but gives only a rough indication of the animals’ body condition, whereas Wemmer’s method gives a more accurate measurement, but was originally developed for Asian elephants. To be able to use the more accurate method of Wemmer, his scoring system was adapted in such a way that it could be used for African elephants.
In addition, Wemmer’s adapted visual body condition scoring system was used to validate new methods which could be used to indirectly measure elephants’ body condition. These methods included a visual technique based on computer assisted analysis of digital photographs, and a physiologic technique using the urinary urea nitrogen (UN):creatinine (C)-ratio. This physiological indicator was chosen because it has been shown that the urinary UN decreases in red foxes subjected to dietary restriction; the body recycles nitrogen rather than excreting it into the urine (Newman et al., 2002). It was hoped to validate one of these techniques for future use to detect changes in body condition in both wild and captive animals.
In short, different diets were fed in this experiment to study the influence of food intake on body condition, glucocorticoid concentrations and behaviour of African elephants. Different methods for detecting body condition would be examined.
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