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Studies on PD excretion in camels, llamas and yaks
Italian researchers Mura and co-workers were the first to examine the purine metabolites in urine and plasma of camels (Camelus dromedaries) in comparison to zebu cattle, in a qualitative approach. They noted that xanthine and hypoxanthine were present in urine and plasma at a higher concentration than uric acid [74], while allantoin was still the main component. Camels lacked xanthine oxidase in the liver and also had a lower level of purine degradation enzymes than zebu cattle, and the authors suggested that this was in part the animal’s N-economy strategy so that exogenous purines could be reused[75,76].Quantitative aspects of PD excretion in camel were examined in greater details by Guerouali et al. [56] under the Joint FAO/IAEA Division’s research programme. Urinary PD contained allantoin, xanthine plus hypoxanthine, and uric acid (in order of magnitude). Xanthine oxidase was detected in liver and intestine, but absence from the blood. Total PD excretion was linearly correlated with DOMI (the slope was 11 mmol PD/kg DOMI). When purine bases were infused into the duodenum, the recovery of the infused purines as PD in the urine averaged 0.52. This recovery factor was different from cattle and sheep. The fasting excretion was 0.240 mmol/W0.75/d. Based on the fact that exogenous purines are available for utilization (or salvage) by the animal, it is expected that the response curve of PD to intestinal absorption of purines should be curvilinear as in the case of sheep. There were no sufficient data points in the work to define this equation.
Bakker et al. [77] measured the PD excretion in llamas (Lama glama and L. guanicoe). Urinary PD contained allantoin, uric acid and xanthine plus hypoxanthine (in order the magnitude), but during fasting the proportion of xanthine plus hypoxanthine were higher than uric acid. Fasting excretion averaged 0.177 mmol/W0.75/d. The PD excretion was 12-18 mmol/kg DOMI, similar to sheep. It was also observed that llamas were unique in maintaining a high concentration of uric acid in the plasma by actively re-absorbing uric acid, but not allantoin, from the kidney tubules.
Long et al. [78] reported a preliminary study on yaks (Bos grunniens) in China. Urinary PD only contained allantoin and uric acid. Fasting excretion averaged 0.220 mmol/W0.75/d. When the animals were fed with different levels of feed, PD excretion increased and correlated with the DOMI. The slope was 13 mmol/kg DOMI.
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the paper by Bakker et al.
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