Cow diet and digestion

Cows and other ruminants have amazing adaptations that allow them to gain nutrients from plants. DairyNZ experts explain how the process works.

Questions for discussion:

• What are the two types of digestion that cows use to extract nutrients from food?

• Carbohydrate types are compared to LEGO brick structures. Why is this analogy used?

• How does a cow deal with a hard-to-digest plant diet?

• What is the role of the reticulum?

Transcript

Dr Elena Minnée

A balanced diet for the cow – you know, cows, like humans, require similar things. They require energy in the form of carbohydrates, and they require protein and various minerals and vitamins that are present in the pasture. So the dairy cow needs an adequate supply of protein to maintain a good milk production. But on the flip side, you also need a ready supply of carbohydrate in order for the animal to use that protein. So essentially, she needs energy to be converting that protein into product. She needs an amount of fibre, which comes in the form of the structural carbohydrate that holds the plants together, and this sort of stimulates her digestion.

Ben Fisher

They can survive on just grass, but if you want to get the best out of your animals, having those different feeds provides them with better quality throughout the season, because obviously different species do better through the different seasons.

Holly Flay

To throw out some rough calculations, around about 18 kilos of dry matter would do a cow who is producing milk and might be in the early stages of pregnancy. She might be in her peak of her lactations. 18 kilos of dry matter actually works out to something like 100 kilos of pasture, fresh weight. So it’s quite a huge amount that they’re actually eating in a day.

Dr Elena Minnée

The cows are amazing, amazing species, turning something that a human could never eat into something really, really nutritious and allows them to produce a lot of milk and grow babies.

Kieran McCahon

Why can’t we, as humans, eat pasture, yet cows can? It comes down to the carbohydrates within the pasture itself and also the role of lignin in the plant.

Dr Elena Minnée

The cell wall of plants is made up of cellulose, hemicellulose and lignin. So essentially, we call them carbohydrates, but lignin is really the glue that kind of sticks the cellulose and hemicellulose together, and lignin is very indigestible, but the cow digestive system’s so unique and it’s just an amazing system.

Holly Flay

The first three components of the cow’s stomach is the rumen, the reticulum and the omasum. And that’s largely your microbial fermentation. There’s a whole lot of bacteria in there that are helping to digest that food and break it down and get out what they need from it and absorb it. As a cow swallows their food, it’ll go from the rumen into the reticulum, and that reticulum acts as a filter, and so the particles that are small enough will carry on through the digestive system, whereas the particles that are still a bit big and need more digesting or a bit more chewing can be regurgitated for chewing their cud.

So once it has gone through the reticulum and the particles have been small enough to pass through, it heads into the omasum. The omasum is largely for water absorption. And then from there, it carries on through to the abomasum. The abomasum is often referred to as the true stomach of a cow. It’s the most similar to what our stomachs are like – to non-ruminants’ stomachs. And that’s where they have the chemical digestion occurring. They again have more nutrients being absorbed. Then it follows through to their small intestines and through the large intestines. From there, anything that hasn’t been digested through the system will get excreted as faeces or poo.

As you can imagine, if they’re eating 100 kilos of pasture a day, it’s got to go somewhere. So cows poo about 60 kilos each day and litres of urine – of wees – every day. But on top of that, they also produce about 20 litres of milk.

Acknowledgements Dr Elena Minnée Ben Fisher Holly Flay Kieran McCahon DairyNZ

Acknowledgement

This resource has been produced with the support of DairyNZ.