圈养大熊猫碘营养的初步调查。

Chengdu Research Base of Giant Panda Breeding, 610081, Chengdu, China; Sichuan Key Laboratory of Conservation Biology for Endangered Wildlife, 610081, Chengdu, China; Sichuan Academy of Giant Panda, 610081, Chengdu, China.

Key Laboratory of Trace Element Nutrition of National Health Commission of the People's Republic of China, Department of Trace Element Nutrition, National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention, 100050, Beijing, China.

J Trace Elem Med Biol. 2021 Sep;67:126780. doi: 10.1016/j.jtemb.2021.126780. Epub 2021 May 18.

BACKGROUND/OBJECTIVE: The giant panda belongs to the family Ursidae and, as a species of bear, still retains the simple digestive system of a Carnivoran. However, under the pressure of a specific habitat they had to adapt to a plant mono-diet consisting of bamboo with different species and growth stages around the year. A plant-based diet has relatively low iodine content with risk of iodine deficiency. Furthermore, bamboo contains cyanogenic glycosides releasing cyanide whose detoxification metabolite the thiocyanate acts as antagonist against iodine uptake and storage in the thyroid. To date very little is known about the iodine nutritional status of the giant panda, thus this study was conducted to receive the first information about the iodine nutrition of captive giant panda.

SUBJECTS/METHODS: Here we investigated the iodine content of bamboo with different plant parts/vegetation stage and species and further compounds of the captive giant panda diet. Next, the urinary iodine (UI) and urinary thiocyanate (UT) levels of infant, sub-adult, adult and geriatric captive giant pandas was measured during the periods when the pandas consume both bamboo leaves- and culm (bamboo leaf-culm stage). Afterwards, the UI of 19 adult giant pandas was measured again for the different iodine intake during bamboo shoot stage. Finally, in this study part also the fecal iodine concentration was analyzed for calculation of total iodine excretion in relation to the iodine intake.

RESULTS

Bamboo leaves had the highest iodine content (453 μg/kg dry matter (DM)), followed by the shoots (84 μg/kg DM, p <  0.05), while bamboo culm had the lowest value (12 μg/kg DM, p <  0.05). During bamboo leaf-culm stage, giant pandas of different age groups had different UI and UT levels (p <  0.05). Furthermore, UI and UT were positively correlated among sub-adult, adult and geriatric giant pandas (p <  0.05). In adult giant pandas during bamboo shoot stage, the iodine excretion in feces was not different from that in urine while their total iodine excretion was less than their iodine intake (p <  0.05). Moreover, during bamboo shoot stage, the UI level of adult giant pandas was much lower than noted during bamboo leaf-culm stage (p <  0.05).

CONCLUSIONS

Our results indicate that UI of captive giant pandas was related to their age as well as to the vegetation stage/part of bamboo they consumed reflecting a different periodic iodine supply. Thiocyanate and fecal excretion should be emphasized when considering the iodine nutrition of giant pandas.

背景/目的：大熊猫属于熊科，作为一种熊，仍然保留着肉食动物简单的消化系统。然而，在特定栖息地的压力下，它们不得不适应由全年不同种类和生长阶段的竹子组成的植物单食。植物性饮食的碘含量相对较低，有碘缺乏的风险。此外，竹子含有释放氰化物的氰苷，其解毒代谢产物硫氰酸盐作为碘在甲状腺摄取和储存的拮抗剂。迄今为止，关于大熊猫的碘营养状况知之甚少，因此进行了这项研究，以首次了解圈养大熊猫的碘营养状况。

对象/方法：本研究调查了不同植物部位/生长阶段和种类的竹子以及圈养大熊猫饮食中其他化合物的碘含量。接下来，测量了处于食用竹叶-竹秆阶段的幼体、亚成体、成年和老年圈养大熊猫的尿碘（UI）和尿硫氰酸盐（UT）水平。之后，在竹笋阶段不同碘摄入量期间，再次测量了 19 只成年大熊猫的 UI。最后，在这项研究中，还分析了粪便中的碘浓度，以计算与碘摄入量相关的总碘排泄量。

结果

竹叶的碘含量最高（干物质 453μg/kg，DM），其次是竹笋（84μg/kg DM，p<0.05），而竹秆的碘含量最低（12μg/kg DM，p<0.05）。在竹叶-竹秆阶段，不同年龄组的大熊猫 UI 和 UT 水平不同（p<0.05）。此外，亚成体、成年和老年大熊猫的 UI 和 UT 呈正相关（p<0.05）。在竹笋阶段的成年大熊猫中，粪便中的碘排泄与尿液中的碘排泄没有差异，而其总碘排泄量小于其碘摄入量（p<0.05）。此外，在竹笋阶段，成年大熊猫的 UI 水平远低于竹叶-竹秆阶段（p<0.05）。