So, we all know that cows don’t digest their food the same way we do, right?
It’s crucial for dairy farming and should have been a focus a long time ago but with the widespread use of collars and other tech which shows cows’ ruminating times, it’s finally in the spotlight where it belongs.
Cows, along with other ruminants such as sheep, goats, deer and even giraffes and camels, have four stomachs.
Note that list doesn’t include horses – talk to a horse owner and you’ll start to understand the many problems of feeding horses because they eat basically the same stuff as cows but are not ruminants.
A cow’s four stomachs, in the order in which the grass (but not milk – more on that later) passes through them are the rumen, the reticulum, the omasum and finally the abomasum.
It’s the first one, the rumen, which is the most important one to understand but even scientists are still getting to grips with it. They can’t reproduce all that it does yet in the lab.
However, some of its secrets may one day help farmers lower greenhouse gas emissions and nitrogen losses as well as making more milk from less feed.
But we should start at the beginning. Cattle eat grass by wrapping their tongues around the stuff and tearing it from the plant and pulling it into their mouths. They chew it first with the lower jaw incisors and then with their back molars.
This chewing stimulates saliva production. The saliva contains enzymes that start breaking down the fats and starches in the feed and helps keep the pH level of the rumen and reticulum at a nice and healthy neutral. Cows can swallow up to 100 litres a day of saliva depending on how much time they spend chewing (one of the reasons why they need lots of water to drink).
The pH of the rumen is vital because there are things living in there. Lots of things. If the rumen is too acidic these things die which is not good.
The things can be divided into four main groups but about half of them are bacteria and different rumen bacteria do different things. Some break down carbohydrates to simple sugars, others ferment the sugars into fatty acids, carbon dioxide and yep, methane.
Then there are those that break down proteins and a group that change the unsaturated fatty acids to saturated fatty acids so they can be absorbed in the small intestine later.
The bacteria use the feed the cows are eating to make more of themselves. So if the cow is not eating, no rumen bacteria. And rumen bacteria don’t just happen overnight. It takes weeks to increase their numbers.
But the rumen bacteria die when they are washed into the last two stomachs where the higher pH kills them and they are absorbed into the cow as protein.
So, the cow is not only feeding itself, it’s feeding the rumen bacteria, which then feeds the cow.
The other three groups of things living in the rumen are protozoa, fungi and bacteriophages which also help to break down what the cow is eating. They’re all anaerobic – they don’t need oxygen to live.
And they are all constantly mixed up by the rumen which is contracting up to three times a minute. Plus, the cow regurgitates it all for further chewing to break down the grass into smaller pieces – what you see when the cows are lazing about but their jaws are moving from side to side. This is what the smart collars and ear tags are measuring as rumination time.
Some of the rumen organisms love foods high in carbs, others are keen on protein, and they are particular about which types of carbs and proteins. They’re incredibly fussy. So even changing your cow’s diet from grass to silage, which is still grass, will mean there may not be enough rumen organisms to convert it to stuff the cow can utilise.
This is why “transitional feeding” are the buzz words for dairy nutritionists and consultants.
Changing the cow’s diet by adding grain or feeding them brassicas will need an increase of some rumen microbes and a decrease in others which can take weeks. If you don’t do it slowly enough, it won’t go well.
Even changes in spring pasture can cause problems. Spring’s fluctuating temperatures change the protein/carbohydrate composition of the grass, meaning the rumen bacteria population don’t know what to expect from the cow’s next mouthful.
And then when it starts raining after an autumn dry – they’ll be yelling out “What happened here!”
Which is why feeding grain works so well. While the composition of grass is ever changing, grain stays mostly the same so there can be a steady population of grain-loving rumen organisms doing their thing.
But didn’t cows evolve eating grass? Why does the changing nature of grass affect them so much?
Because back when they roamed the savannahs, they could take their pick of what they wanted. Today we fence them into paddocks.
So, after the rumen, the partly broken-down feed passes into the much smaller reticulum which is also pH neutral and has lots of microbes. You may hear the name of this stomach when your vet tells you your cow has “hardware disease”. It’s the stomach that collects anything the cow has eaten which it shouldn’t have – nails and pieces of wire.
Next is the omasum which is lined with large folds of tissue that resemble the pages of a book. These folds absorb water and nutrients. Finally is the abomasum, which is the stomach most like our own. It has an acidic pH and digestive enzymes which break down the last of the feed and the microbes from the rumen. It is the abomasum which is the only fully developed stomach when a calf is born because it is the one which digests milk.
If you only feed a calf milk, the other three stomachs won’t develop because they are not being used and there will be no rumen microbes which is why it’s so important to get calves eating hay, grass and grain in their first few weeks.
What is known as “weaning shock” has nothing to do with no longer feeding milk. It’s because there are not enough rumen microbes to break down the grass the calf is now eating and depending upon to stay alive.
Because milk goes straight into the abomasum, never, ever, ever put drench in your calf milk to drench your calves.
Parasite drenches are made to be slowly absorbed in the rumen. By putting it in the milk, it goes straight into the abomasum speeding up absorption causing toxicity and most likely causing death.
Remember four stomachs are good and you need to look after them all.
