Due to the small nature of our premises, our two Anglo-Nubian goats (Fudge and Olaf by name) happily chew a cud made up of delicious hay. Its always lovely to see them crashed out and comfy, jaws circularly rotating as if chewing gum while they contemplate the world. The question I want to answer in this article is this: just what are those goats up to? There are a number of animals that chew the cud (sheep, cows and reindeer to… name but a few) but why do they do this strange act?
The problem for the herbivore eaters is that plants are pretty tough critters, evolutionarily responding to their constant destruction by beefing up their structure. They produce a molecule known as cellulose, a tough polymer that refuses to be broken down, and incorporate it into their structure. This cellulose grinds down the teeth of those who try to consume and make sure the plant can’t be digested. This way, the animal won’t eat them as there’s little point. Job done.
Only evolution has a crafty way of combating the adaptations of others. The herbivorous diners developed large molars to grind away at leaves whilst some developed a new type of digestive system. Ruminants are animals with a special type of ‘stomach’ known as the rumen. In here, bacteria and microorganisms sit, not to infect and cause illness but to work in a symbiotic relationship with their animal friend.
This relationship is mutualistic, when both organisms gain something from it, different to parasitism as the organism that dines will be the sole one to benefit. The bacteria gain a source of food and protection from the elements, taking their share of the food that the ruminant consumes. So what does the goat, sheep or cow gain? Well, those microbes have designed enzymes to break down cellulose, biological molecules that allow such reactions to occur efficiently. The cellulose that could not be destroyed is now digested, just as if the herbivore could do it itself. However, there is one problem.
Once cellulose is broken down, it must be digested further and unfortunately this process occurs in the mouth. Having already passed this part of the digestive system, it means that the herbivore has no means of obtaining the nutrients…or does it? Cleverly, the ruminants have developed muscles that pull the food back up into the mouth! If you watch carefully while a ruminant chews, you may even notice a pause and sudden movement up the neck when the food is brought up! The animal will then grind away with its teeth, the mouth digesting the products of the broken down cellulose, in its casual, carefree way. Repeating the swallow and regurgitate process, the food will eventually pass on to the next part of the gut and finish its passage through the animal.
So next time you see livestock chewing happily, spare a thought for the animals who have to grind up their own regurgitated gut contents!