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Science & technology
科技版块
Sheep farming
绵羊养殖
Turning the worms
改变蠕虫
Gut bacteria may help fight nematode infestations in sheep
肠道细菌可以帮助绵羊抵御线虫的侵袭
Sheep farmers in Australia and New Zealand have a problem.
澳大利亚和新西兰的牧羊人有一个问题。
Their charges are susceptible to intestinal nematode worms which cause them to waste away and can, in severe cases, kill them.
他们的羊群容易受到肠道线虫的影响，这些蠕虫会使它们日渐消瘦，在严重的情况下，会令它们死亡。
Over the years, the worms have evolved resistance to drugs once used to attack them.
多年来，这些蠕虫已经对曾经攻击它们的药物产生了抗药性。
But a second approach is to breed countermeasures into the sheep themselves.
但第二种方法是在绵羊体内培育对策。
This can be done by counting the number of worm eggs in animals’ droppings and selecting as sires and dams those that have the fewest, on the assumption that these are the sheep with the least worm-friendly guts, and that this property will show up in their offspring as well.
这可以通过计算动物粪便中的虫卵数量，并选择那些虫卵最少的作为公羊和母羊培育后代，假设这些羊的肠道对虫子最不友好，这种特性也会在它们的后代中表现出来。
That works.
这很管用。
But how, has been obscure.
但如何做到这一点还是个未知数。
A study just published in Animal Microbiome, by Erwin Paz of the University of Western Australia and his colleagues, throws light on the matter.
西澳大利亚大学的Erwin Paz和他的同事刚刚在《动物微生物组》上发表的一项研究揭示了这一问题。
It suggests that what is being bred for is a propensity to develop a worm-hostile gut microbiome.
这表明，繁殖的目的是为了培养一种对蠕虫不利的肠道微生物群。
Gut microbial health, once a fringe medical interest, is now mainstream for human beings, as bugs in the alimentary canal are linked with conditions ranging from obesity to arthritis.
肠道微生物健康曾经是医学界中的冷门领域，但如今已成为人类医学研究的主流方向，因为消化道中的细菌与肥胖、关节炎等一系列疾病有关。
But what is true of people is true of other animals, too.
对人类来说是这样的，对其他动物也是这样。
And, in the case of sheep, Dr Paz and his collaborators seem to have hit the jackpot.
在绵羊的例子中，Paz博士和他的合作者似乎大获成功。
Dr Paz knew from past work that sheep with severe worm infestations tend to have abnormal bacterial populations in their faeces.
Paz博士从过去的工作中了解到，患有严重蠕虫感染的绵羊的粪便中往往细菌种群不正常。
This led him to wonder whether the bugs in the guts of resistant sheep were somehow hampering the worms’ activities.
这让他很好奇，抗蠕虫绵羊肠道中的细菌是否以某种方式阻碍了蠕虫的活动。
He and his team therefore looked at a flock of 200 sheep at a farm in Western Australia and selected ten that had particularly high loads of worm eggs in their faeces (1,940 per gram, on average) and ten that had low loads (410 per gram).
因此，他和他的团队研究了西澳大利亚一个农场的200只绵羊，选择了10只粪便中虫卵含量特别高的羊(平均每克含1940只蠕虫)和10只虫卵含量低的(每克含410只蠕虫)。
These unfortunate sacrificial beasts were then slaughtered and their entrails examine -- not for auguries of the future but for their microbial populations.
这些不幸的绵羊随后被屠宰，并检查了它们的内脏——不是为了预示未来，而是为了检查它们体内的微生物种群。
As they had hoped to, the researchers did indeed find systematic differences between the microbiomes of the two groups.
正如他们所希望的那样，研究人员确实发现了两组微生物群之间的系统性差异。
These differences were particularly notable in the small intestine, where the worms live, with resistant sheep having richer and more diverse bacterial populations in this part of the gut than vulnerable animals did.
这些差异在蠕虫生活的小肠中尤为明显，与易受感染的动物相比，抗蠕虫绵羊在肠道的这一部分拥有更丰富和更多样化的细菌种群。
In particular, the team noticed that populations of bacteria which ferment carbohydrates such as cellulose and turn them into short-chain fatty acids were especially abundant in the resistant animals.
特别是，研究小组注意到，在抗蠕虫绵羊体内，可将其转化为短链脂肪酸的发酵纤维素等碳水化合物细菌种群尤其丰富。
It is, of course, possible, that the worms are affecting the sheep’s microbiomes, rather than the other way around.
当然，有可能是蠕虫影响了绵羊体内的生物群，而不是体内生物群影响了蠕虫。
But Dr Paz thinks this is unlikely, because all of the sheep looked at had at least some worms.
但Paz博士认为这不太可能，因为所有被观察的绵羊都或多或少有一些蠕虫。
Rather, he suspects, genetically resistant sheep are providing an intestinal environment conducive to bacteria which either produce compounds that repel the worms or consume resources which the worms depend upon.
相反，他怀疑，具有基因抗性的绵羊正在提供一个有利于细菌的肠道环境，这些细菌要么产生驱除蠕虫的化合物，要么消耗蠕虫所依赖的资源。
If that is correct, it opens up a third approach to worm control, which is to employ probiotics to shape the gut microbiomes of flocks directly, rather than relying on selective breeding to do it at one remove.
如果这个猜想正确的，它开辟了第三种控制蠕虫的方法，即使用益生菌直接塑造羊群的肠道微生物群，而不是依赖于选择性繁殖一次完成。
