This post follows on from talking about the rumen and other three stomachs of the cow. We'll just chew the cud on fermentation a little bit more...
Stay with it 'cos it can get a little complicated (though I'm simplifying things where I can). Cast your mind back to rumen fermentation and the microbiome... the most important bugs by far are the bacteria, at least in terms of their ability to digest plant material. As said, they produce volatile fatty acids (VFAs), which as their name suggests, are acidic. Because of this, the rumen normally operates at a slightly acidic environment: pH 5.5-6.5. It's very important the pH doesn't dip below 5.5 (more acidic) because if it does you get a different population of bacteria taking over which, instead of VFAs, produce lactic acid, which is a much stronger acid. This doesn’t do the cow (or her guts) a lot of good at all. It is called “acidosis”.
It can be a bit of a challenge to avoid acidosis when feeding cows, especially wherever cereals are fed (high yielding dairy herds, and finishing beef cattle for example). Basically, cereals contain a lot of starch which can make the bugs go a little crazy, producing a lot of volatile fatty acid, dropping the pH dangerously low. The altered pH changes the microbiome and the rumen stops working like it should. If I can make an analogy here to the wider World, if the rumen pH drops below 5.5 it’s a little bit like how global warming might potentially change everything if the temperature rises another couple of degrees and our whole ecosystem might get a lot messed up.
Thankfully, the cow has lots of mechanisms for dealing with acidity, to maintain a safe and steady pH. One way the rumen is buffered is through the cow's saliva and “chewing the cud”. You'll see in the video, it's incredibly soporific watching cows chew their cud. She will spend around eight hours a day ruminating (cudding), during which she regurgitates a bolus of her rumen contents once every minute or so, chews it a bit more whilst mixing it with saliva which is alkaline (contains sodium bicarbonate), before re-swallowing it. During this process, a cow produces around 100 litres of saliva per day which contains around 3.5 kg of bicarb. That's a pretty amazing fact! (pub quiz anyone?)
Then, another buffering method (actually the most important) is that the cow very efficiently absorbs the VFAs from the rumen into her bloodstream (to be processed in her liver), whilst simultaneously actively pumping yet more bicarbonate back into the rumen. As long as she can absorb those VFAs at a similar rate to which they are being produced, all’s good.
And then there is a very important third way in which the rumen pH is kept stable. If you remember your chemistry, you’ll know that acid is really just lots of excess hydrogen ions (H⁺). These are very reactive and is why acid burns and corrodes. Cast your mind back to the previous blog and you might remember "archaea" included in the list of the different types of rumen bugs. These little fellas are a very primitive life form. We apparently all evolved from them - those little single celled organisms which crawled out of the primordial volcanic pools and salty sea waters. The ones that came 3.5 billion years ago, before algae and bacteria and fungi and lichens and coral and microscopic sea creatures and seaweeds and plants and insects and reptiles and animals and us. Something that's very special about archaea is that they don't need much, and they survive in brutal environments where there's no oxygen, and even where there is acid. In fact they like acid! That's because, they mop up those pesky hydrogen ions, combine them with CO₂ (carbon dioxide), and make methane plus water. They have another name as "methanogens", a fancy term for methane-producing organisms.
Archaea are responsible for farts too. Apart from rumens and our own guts, they live in lots of other inhospitable places: Archaea are a major part of Earth’s life. They produce methane in soil, in the sea bed, in rubbish dumps, in sewerage farms, in marshland and even in glaciers.
So that's kind of where I wanted to get to in this post: to explain where the methane comes from. It’s not the cows themselves, it’s the archaea inside their rumens, and cows just belch it out, nice and politely, with barely a squeak or a rumble when a bit of it accumulates as a gassy bubble. Methane production is a very healthy part of their digestion. If we stop them producing methane, we'll knacker up rumen stability and make them unhealthy as well as reducing their ability to harness nutrients out of forages that lesser animals can't reach. I’ll be returning to cows and methane for sure at another time 'cos it’s important when understanding cows and their place in the World.
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