Digesting the science of Ruminants
It’s not just us humans that take advantage of fermentation to enhance food. This biochemical process also happens in the stomachs of a group of animals called ruminants, including cows. Joining Georgia Mills to spill the guts on the science of cow digestion was Chris Creevey from the Institute for Global Food Security at Queen’s University Belfast. But why are microbes important to cows?
Chris - Mammals in general are not very well equipped to digest the carbohydrates that are found in plant cell walls so ruminants like cows and sheep and goats and giraffes have evolved a multi chambered stomach; the first chamber which is the largest and contains a highly diverse microbial community whose sole job is to digest and break down those carbohydrates into more easily absorbed forms for the host.
Georgia - Right. So the cows have such a poor poor choice of diet, I suppose. If they didn't have this community of microbes inside them, they just wouldn't be able to digest the grass.
Chris - That's exactly it. In reality, the cows are not really living off the grass as much as they are living off the microbes themselves. The activity of the microbes and even down to the cell walls of microbes themselves are quite important as a protein source for the cows.
Georgia - Right. So they're eating the grass to feed the microbes and then the microbes are feeding them.
Chris - Yeah you can look at it that way.
Georgia - Interesting. And what about when the microbes are breaking down all this grass? What what kind of things does that produce?
Chris - In general, it produces a lot of nutrients which are very important to the cow. But there are also... this community is quite diverse: there's bacteria, archaea, fungi. And some of these are not very important to the core fermentative process that's ongoing, some of them are kind of like hanging on on the side and being a bit opportunistic. One of those is the archaea, which are utilizing free hydrogen in the in the room and as part of their metabolism are producing methane as a byproduct.
Georgia - Right. And what is methane and why is this a problem?
Chris - For us, one of the issues about methane is that it's a potent greenhouse gas, It's about 24 times more potent than than carbon dioxide as a greenhouse gas. So when you add up the large numbers of animals that are around the world in agriculture, it adds up to a significant number of potentially greenhouse causing emissions. Up to about 7 or 8 percent of global emissions on average.
Georgia - Right. And I have to say you dispelled me of a notion I had before when we were talking before the show. I always thought cows farted out methane.
Chris - Yeah. This is one which a lot of people have. Because the rumen in is the very first chamber in the digestive system, the methane is burped out. The vast majority of it. So yes, no they don't fart that much methane.
Georgia - Either way, charming. Is there anything we can do about this?
Chris - So there's a lot of research ongoing, looking at different ways of reducing methane and also to increase the efficiency of these animals in general, because the methane production itself represents a loss of energy to the cow. So if you can decrease the methane then you can increase the amount of energy getting into the animal.
These are taking different forms: some of them are additives; some additives into feed such as the algae is a very interesting potential for reducing methane; other ways which may work and which are being investigated are looking at breeding animals, because you may be a to breed them to produce less methane; or maybe even you can inoculate them and give them a vaccine to produce their own antibodies to specifically reduce the archaea in the rumen. So there’s a lot of very interesting research.
Georgia - Could we get some cows to burp our oxygen instead of methane?
Chris - Well that would be quite a feat. The rumen in is a very anaerobic environment, there is no oxygen really in there at all. And the organisms that live there are highly sensitive to it, so any oxygen that is in there can actually stop the whole fermentative process from occurring at all. So perhaps not oxygen.
Georgia - Well never mind. And given that they're so important, what happens when, say, a farmer gives antibiotics to an animal? Could this potentially wipe out this community and mean they’re unable to digest grass?
Chris - In general the antibiotics tend to be quite specific to certain groups of organisms so they don't tend to wipe everything out. Antibiotics have been used traditionally in the past as an additive in feed simply just to increase the growth rate of the animals. That's primarily in feedlot situations. But that practice has been banned here in the EU since the early 2000s and it's being gotten rid of in other jurisdictions around the world - and this is quite important because what we don't want is a situation where we increase the incidence of things like antimicrobial resistance genes, and microbiomes that are associated with with our food chain.
Georgia - Right. So if we pump antibiotics into cows, then antibiotic resistance can sort of grow in them. And then, I guess, we eat the cows?
Chris - Yeah it's complex because, you know, antibiotics are natural compounds produced by microbes and they're found a lot in these communities and these microbiomes. And as such you always find antimicrobial resistance genes as well because it's kind of like a warfare between the two groups.
I guess it's always there, but if we add in antimicrobials to the system what we can do is increase the prevalence of the anti-microbial genes in the community, and we can risk that community becoming a reservoir for antimicrobial resistance genes to be transferred in down the food chain and and even possibly into human pathogens, so we really have to be quite careful about how we use them.