Free-ranging African elephants Loxodonta africana use their front feet frequently during the process of foraging and this could be the reason for the high prevalence of physical injuries to these parts of the body.
Although the occurrence of severe lameness caused by foot lesions in adult elephants has already been investigated and the clinical and pathological findings have been reported, the effect of foot injuries on glucocorticoid levels as a potential physiological stress response has not been examined.
Given the practical difficulties involved in monitoring unpredictable events in free-ranging animals, like the occurrence of foot injuries in elephants, it is not surprising that information regarding the endocrine correlates of physical injury is still limited for elephants.
In our study we investigated the effects of foot injuries on concentrations of faecal glucocorticoid metabolites (GCM), body condition score (BCS) and reproductive behaviour in two GPS/radio-collared elephant bulls in the Kruger National Park, South Africa.
We monitored the bulls aged 40+ (Bull 1) and 30+ (Bull 2) 2-3 times per week for 13 months starting in June 2007 and frequently collected faecal samples for non-invasive hormone monitoring. Faecal samples were lyophilised, extracted and assayed with an enzyme immunoassay which detects GCM with a 3a-hydroxy-11-oxo-structure.
Both bulls acquired foot injuries (right front), which caused temporary lameness, but the effect of injury on GCM concentration differed between bulls (P , 0.001).
In Bull 1 the injury lasted6250 days and was associated with an up to four-fold increase in GCM concentrations (P,0.001) and his BCS reduced from ’good’ to ’very thin’ by the end of the injury period.
In Bull 2 the injury lasted 65 days and was associated with a smaller increase in GCM concentrations (P ¼ 0.03) together with a reduced loss in condition when compared to Bull 1.
Following recovery, the condition of both bulls improved progressively and faecal GCM returned to baseline concentrations.
Collectively, the data clearly underlined the value of non-invasive hormone measurements as a tool to provide information on the level of stress experienced by elephants. Thus, monitoring GCM levels could help improve the assessment of an elephant’s state of health.