In captivity, cheetahs (Acinonyx jubatus) are known to suffer from several chronic diseases that do not occur in their wild-living counterparts. These include lymphoplasmacytic gastritis, glomerulosclerosis, renal amyloidosis, veno-occlusive disease of the liver, adrenal hyperplasia and several ill-defined neurological disorders. Many factors have been proposed as possibly being the cause of this phenomenon – factors such as stress, lack of exercise, low genetic variability and the provision of unnatural diets in captive facilities – but to date convincing pathophysiological explanations for these diseases have been lacking or unsatisfactory. Doctor Adrian Tordiffe investigated this problem using a systems biology approach – in other words, he attempted to understand as many of the components of the cheeatah’s metabolic system as possible. He did this by using untargeted metabolomic analysis of serum and urine from captive and free-ranging cheetahs, thereby generating new physiological data for this species in the hope of developing a better understanding of their metabolism.

Before the actual quantification of serum or urine metabolites, he created a new, more objective, method of approximating the body condition in cheetahs by developing a body mass index value, similar in concept to the same index used in humans. Unsurprisingly the body mass indices obtained in the study population showed significant differences between males and females, but importantly, all the animals fell within a healthy body mass index range. The impact of body condition on various serum and urine metabolites could thus be objectively assessed. He also evaluated the use of either urine creatinine concentrations or urine specific gravity values for the correction of spot urine samples obtained from the cheetahs. Creatinine is used in other species (including humans) to correct for differences in urine concentration between different study subjects because of differing levels of hydration. However in cheetahs, Adrian as able to show that there are other factors which affect creatinine concentration and therefore this method is unreliable in this species. He, instead, found that measuring the specific gravity of the urine in each sample provided a better indication of urine dilution. Urine specific gravity was therefore used to correct urine metabolite concentrations in this study.