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What do all these feed stuffs have in common? They can all be digested by rumen microbes and turned into milk!

If you could sum up a cow in five words, it would be “a fermentation vat on legs”. That is, their rumen is a large, heated vat that stirs together carbohydrates, water and bacteria to produce gas and acids. A cow uses these acids (called volatile fatty acids or VFAs) to live, grow and make milk.

Rumen anatomy

The structure of the rumen is a pretty neat bit of biology. In the picture below, you can see how the contents separate into different layers. Each layer has its own special population of bacteria. Lighter feeds, like hay, are forced upwards into the drier, less dense fibre mat in the top of the rumen. As they are soaked, fermented and mixed, feeds become smaller and heavier and sink to the liquid zone. Once broken down into small enough particles, feed can then move out of the rumen for further digestion in the gastrointestinal tract.

A quote from the useful resource From Feed To Milk: Understanding Rumen Function:

“Ruminants are excellent recyclers. They consume fibrous feeds and waste by-products that are not suitable for consumption by single-stomached animals and convert them into nutritious feeds like meat and milk.”

And this is true  – at a recent talk to high school students, we discussed which feeds could be fed to cows. The bacteria within the rumen can use almost any carbohydrate as fuel: grass, silage, waste from wineries and breweries, even chocolate and lollies. But with an important qualifier: everything in moderation, and the diet must be balanced for energy, protein and fibre. Cardboard and newspaper might provide fibre, but they contain very little of anything else!

The importance of fibre

Fibre is a vital part of a cow’s diet as it helps stimulate rumination. Cows are born to ruminate – that is, they regurgitate some of the fibre mat and chew it when at rest. Rumination is important as it:

  • Helps break down the feed for microbes and enhances digestion
  • Provides saliva – which is filled with bicarbonate– to buffer the VFAs in the rumen and keep the rumen environment healthy

Rumination bouts last 30 seconds to 2 hours, with up to 20 bouts per day. Cows ruminate when at rest and generally at night. Cows spend 2.4-8.5 hours a day eating and 2.5-10.5 hours ruminating.

This figure shows the grazing and ruminating pattern of cows. Cows will chew 12-30 thousand times a day while eating, and 20-40 thousand times during rumination. That’s a lot of chewing!

Fibre sources

When considering a cow’s diet, the Rumen8 Feed Companion is a useful reference to compare the merits of different feeds. For example, you might choose PKE over mill run if you needed a supplement with higher levels of fibre and choose mill run over almond hulls if you needed to increase the diet’s protein.

Fibre (NDF % DM) Energy (MJ/kg DM) Crude protein (% DM)
Mill run 34 (6% effective) 11 17
Almond hulls (whole) 35 (90% effective) 9 5
Palm Kernel Extract (PKE) 69 (34% effective) 11 17