Some of you will know that cows are my favourite animals so you can imagine how delighted I was to see a headline a few years ago in the Telegraph…
“McDonald’s launches study into flatulent cows used in its burgers”
This seems to include several of my favourite scientific themes; namely cows, the scientific method, food and burping (eructation). What joy! This research is a response to concerns over the environmental impact of beef production, particularly the methane released by cows. Methane is a greenhouse gas and much more potent than carbon dioxide.
Cows have a complicated digestive system because they are ruminants and rely on a huge population of micro-organisms in their stomach to do most of their digestion for them. Living on grass is difficult because it is mostly cellulose and hard to digest. Their stomach has four chambers: reticulum, rumen, omasum and abomasum. The rumen is a fermentation vat where bacteria can respire anaerobically whilst breaking down the cellulose in the cell walls of the grass.
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To help break down the grass, cows ‘chew the cud’, which means they regurgitate undigested grass back into their mouths to give it a re-chew. If you watch them when they are not actively feeding, their jaws are nearly always moving as they grind down the cell structure one mouthful at a time. This gives the microbes in their rumen something to work with and the cellulose is further broken down into simple sugars called monosaccharides and disaccharides. These are less complicated than they sound; the first is a single sugar like glucose and the second is a double sugar like sucrose (fructose and glucose combined). These can be used for respiration by the cow’s cells and the microbial cells.
The fermentation process in the rumen also produces a lot of gas, mostly methane and carbon dioxide, which the cows are constantly releasing through their mouth and nose. It can be as much as 50 litres of gas per hour.
The fourth chamber (abomasum) is similar to our own stomach and excretes an enzyme that digests any bacteria that reach it: not a very generous thank you for the effort they have put in to the digestive process! They are a good additional source of nutrition, mostly as a supply of amino acids for protein production.
Other products of the digestive process are absorbed in their very long small intestines. Farmed cattle are usually also fed grain, which has a higher proportion of digestible starch than does grass. This increases milk production in cows and increases the growth rate in beef cattle. It also alters the types of fat produced by the cattle. Slow growing, grass-fed cattle have a greater proportion of omega-3 polyunsaturated fats (ones that are pretty good for you!)
McDonald’s buys beef from over 16,000 British and Irish farms so they are an important part of the rural economy. Agriculture accounts for about 7% of the UK’s greenhouse gas emissions. It is thought that gas from cattle makes up about 5% of that total. It might be possible to change the composition of the gases produced by altering the diet the cattle are fed. I found this very encouraging article from October 2016 suggesting that adding dried seaweed to cattle feed will reduce the methane production by up to 70%. It may also be that selective breeding (or genetic modification) could produce strains of cattle that use their food more efficiently, resulting in less methane being released. Perhaps the most obvious way we could help would be to either stop eating beef or to regard it as a very special treat and only eat it occasionally. That is going to be a tricky case to argue I suspect!
Questions…
- What mineral do we get from drinking milk and why is it important?
- Which vital component of our diet is often supplied by eating lean meat?
- Methane is a hydrocarbon. What does the word hydrocarbon mean?
- What products are released when methane is burned in plenty of air?
- Describe a chemical test for one of those products.
- Cows are mammals like you and me. Suggest a physical characteristic all mammals share?
- Apart from cellulose cell walls, what other feature might you find in a plant cell but never in an animal cell?
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