A cow spends 8 hours a day chewing her cud. Just lying there, chillin'
Cudding is an essential part of digesting her food. First, a bolus of food is regurgitated from the rumen, then it is chewed between 60-70 times whilst it is simultaneously mixed in with lots of gloopy saliva, and then it is re-swallowed to re-enter the rumen. This is repeated around every minute or so. Mostly, cows will be lying down whilst they do this, but they can chew the cud whilst standing up too.
The reason for doing it is two-fold. Firstly, the chewing helps grind up her fibrous diet into smaller pieces, which are more easily digested by the rumen bacteria and other microbes. Secondly, the saliva contains lots of bicarbonate which helps to buffer the acids produced during rumen fermentation, in order to maintain an optimal rumen pH; about 5.5-6.5, just on the acidic side of neutral.
Grazing cows spend a similar amount of time eating as they do cudding - around 8-9 hours per day. They have no front teeth on their upper jaw, but in their place is a hard leathery pad (the dental pad). Their bottom jaw does have front teeth, and these are sharp, cutting the grass against the dental pad. Different to goats and sheep, which have very mobile lips to help manipulate forage into their mouths, a cow relies on her tongue to grasp mouthfuls of grass. This means cows prefer longer grass swards than sheep.
Cows fed indoors can eat all they need in much shorter time - around 4-5 hours per day. Their feed is pre-cut, so it is just a matter of standing in one place (at the feed barrier) and almost hoovering up the feed presented to her. Although, if you watch closely, you'll often notice her making a little bowl in her food with her muzzle and gently nudging the edges so that the tasty bits of corn and other cereals fall to the bottom, and can be eaten first. This is called "sorting" and cows are expert at it.
Compared to the diets fed to indoor cows, grass is quite a wet feed - around 80% water. So after 40 minutes or so of grazing, our grazing cow will feel quite full up. Each 40-minute meal might consist of around 10 kg of grass. She will then lie down - typically for around an hour, much of which she'll spend chewing her cud - after which she will be ready for another bit of grazing. This is how cows like to live: graze - lie - cud - repeat. All in all, our grazing cow will spend around 8-9 hours eating, 8-9 hours lying down and the rest socialising, being milked (if she is a milking cow), having a drink, or walking about. Typical of most prey animals, she will spend very little time asleep, always on the alert for potential predators. Cows do sleep though, but only for around half an hour a day and taken in little naps. By the end of a busy day, and over the course of around 10 meals spread evenly throughout the day and night, a grazing cow will typically eat around 100kg of grass (20 kg dry matter).
There are some differences, then, to how our indoors cow spends her time. She will still eat for around 40 minutes before feeling full, but because the feed is not so wet, and because she also doesn't need to move around whilst eating, she will have eaten far more (excluding the water) than a grazing cow in a similar amount of time. This is a bit more risky from a rumen health perspective, because larger meals tend to create more acidic conditions. Over the course of the entire day and night, the indoors cow will eat for slightly less time (around 5 hours) but will have consumed more (around 24 kg dry matter), and will have had fewer meals (around 6-7 instead of 10-12). She will still spend the same amount of time chewing her cud (8-9 hours). If you do the maths, you'll notice that cows indoors have a little bit more time on their hands because they spend less time eating. In fact this allows her to lie down a little longer - which is a good thing for housed cows, as too much time stood on hard concrete floors is not good for their feet.
It takes some skill getting the housing just right for cows kept indoors. It is a very big part of my work as a farm vet to help dairy farmers design their buildings and management well enough for housed cows, so that they can behave as closely as possible to how they are designed to (i.e. the grazing cow). This means that cows should be able to eat little and often: achieved by providing lots of feed space; no competition at the feed barrier and fresh, tasty feed always easily in reach. They should have comfy beds which have plenty of grip, so that they are happy to get up and down as often as possible, ideally lying down for 10-12 hours in a 24 hour period, but in eight or more bouts. They should be able to socialise without conflict, and always get to where they want to be, which means they will happily do the little-and-often eating, mixed in with little-and-often lying down, which gives the best contentment as well as health. A side benefit for the farmer is more milk.
In essence, cows spend the vast majority of their time standing and eating or lying down chewing their cud. As herd animals, they are often all doing the same thing in synchrony with each other, although larger groups are more likely to be out of synch somewhat. At any one time, it is possible to observe and assess herd behaviour: if at least 85% of the herd are either standing and eating or lying down, that is good. Of those lying down, at least 85% should be chewing their cud, and, if you watch a while, each cud bolus should involve around 60-70 chews before it is re-swallowed. These basics of cow behaviour are fascinating. If you have cows of your own, go and take a look! If you don't have your own cows, bad luck, but next time you notice a herd when out for a walk, spend a little time tuning into their World and see what you can notice.
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