Why cows do most of the chewing in the evening

Dear Daktari, I keep a few animals as my retirement project. I was a long distant truck driver and spent a better part of my life on the road. I am concerned about this chewing that my mature animals do in the evening. Please explain why they do it. [Juma Mwakazi, Taita Taveta]

Thank you Mwakazi for the good question. That chewing is called rumination and happens when the animal is resting. Domestic ruminant animals include cattle, sheep and goats. Wild ones include antelopes, buffaloes, deer among others. They have a special digestive system and you will characteristically see them chewing curd. This enables them to get more nutrients from fibrous feeds unlike any other group of herbivores (animals that feed on plants). Ruminants have a digestive system that ferments feeds. The fermentation is aided by millions of microbes that live in this unique digestive systems that is composed of four stomachs. The microbes include bacteria, fungi and protozoa. Monogastrics (animals with one stomach) like pigs and poultry do not have this advantage.

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Ruminants will grab and swallow whole feeds during grazing. This way less time is wasted on chewing. Cattle will for example use their tongue to sweep and swallow lots of food. It is this behaviour that will enable them swallow nails, metals and even wood blocks that later cause diseases. The dental formula of ruminants is designed to enable maximum feed intake with lots of salivary glads to wet the feeds and enable smooth swallowing.

Why so they chew cud?

Cows will on average spend two thirds of their time grazing, one third chewing cud and the other third idling. Initial feeding is done in a hurry. When chewing the cud, ruminants regurgitate - force back the food into the mouth for further chewing before being swallowed again into the rumen for fermentation. During fermentation the micro-organisms aid in breaking down the fibre which would have gone to waste into nutrients.

Young ruminants are not "Ruminants"

It should be noted that this ruminant digestive system does not come in a ready to use form. It develops, and this is nature's way of protecting the young ones from developing digestive disorders when consuming milk. Young ruminants come with a mechanism that directs milk to the omasum and then to abomasum. By-passing the reticulum and rumen. If this milk was to go into the reticulum or rumen it would ferment and cause digestive system diseases. Slowly as the calf matures it acquires the ruminal micro-organisms from the environment and subsequently develops its capacity to later digest fibre. Ruminants provide animal protein in their meat and milk. They optimally utilise feeds or low "value"- fibres to produce milk, meat and leather. Others by-products include manure. In arid lands ruminants offer nutrition to pastoralists who might not be able to engage in any other agricultural activity. Where crop agriculture is carried out alongside ruminant production, the ruminants eat the crop by-products to produce milk and manure that fertilises soils. Interestingly, this unique digestive system is currently being blamed for the global warming phenomenon due to the methane production. The silver lining in this has been the emphasis on proper nutrition of ruminants to reduce global warming.

[Dr Othieno is a veterinary surgeon and the head of communications at the Food and Agriculture Organisation of the United Nations (FAO) Kenya. The views expressed here are not necessarily those of FAO]