3 Things Every Grazier Must Know About Fibre To Unlock Animal Performance

The ability to process fibrous plant material is a defining characteristic of ruminants who recycle leaves and stems into rich manure that feeds the soil.

However, each year, around the same time, our grasses form so much fibre that even the cows have a hard time processing it. This dietary blockade can have huge implications on the health of our livestock and the profitability of our grazing enterprises.

We can see the grass turning brown and becoming stalky, but what is actually happening to it?

     1.Fibre Content Increases With Age

Grass in northern Australia undergoes a life cycle, starting growth in spring/summer with leaf development. As autumn/winter approaches, it matures, increasing stem and seed production. With maturity, fibre accumulates, which simply refers to the plant cell wall structure.

To simplify a plant cell, which includes the wall and its contents, I thought we could imagine a coconut. Coconut water is the cell contents, which contains all the essential nutrients such as protein and sugar. A diet of mainly coconut water would be the equivalent of cows grazing immature grass in spring, with too much protein and not enough fibre, which is why they scour. 

Now, picture we have coconut water and also the white flesh. The flesh is our cell wall once it’s thickened up that balances out the rich cell contents or coconut water. Translated to the paddock this would be the optimal maturity to graze the plant in, with enough fibre to slow up digestion and allow the animal to absorb nutrients. 

Lastly, let's combine the water, flesh, and husk to complete the entire coconut. This is now an accurate representation of a plant cell that has fully matured and “hayed off” in winter.                

The coconut husk represents the fibrous cell wall in our grasses, which has built up in a woody-like substance called lignin to protect itself from pests and pathogens during dormancy. This defense mechanism serves a purpose for the plant, however, it drastically reduces the nutritional value from a livestock perspective.

     2. What Your Dominant Pasture Species Is

Another huge determinant of how much fibre builds up in your pastures is the species you have. Grasses can be grouped into 2 main categories: C4 warm season grasses, such as Rhodes, Buffel, and Bluegrass, or C3 cool season grasses like Phalaris and ryegrass. 

C4 grasses are adapted to hot climates, where they efficiently use monsoonal rain to generate large amounts of biomass. Conversely, C3 species are adapted to cold environments, and whilst they're not as productive as warm seasons, they're far more nutritious per kg of dry matter.

A simple way to understand this is that, the further you move away from the equator, the lower the yield in grass but the higher the quality, but the closer you get to the equator the lower the quality but the higher the yield. The tradeoff in having high-yielding C4 grasses means they develop copious amounts of fibre (Figure 1) that dilutes valuable nutrients. 

So by knowing the dominant species in your pasture, the better understanding you’ll have of its fibre, content, nutritional value, and whether you’re heading into winter with a paddock of cardboard or a nutritious stockpile.   

      3. How It Can Restrict Animal Performance 

The role of fibre in a cow's diet is to ensure sufficient rumination time, without reducing the animal's voluntary intake. 

It’s important to understand the beast is simply a harvesting mechanism and it’s actually millions of microbes within the rumen which digest forage. So given these bacteria and fungi are doing most of the work we must pay attention to their needs.

They need sufficient protein to maintain a healthy population, and they don't want too much fibre, because it’s hard to process.

I’ll put up a graph from an old MLA publication that shows the change in cell structure in tropical grasses as they mature.    

In their juvenile phase, the grass is about 35% Fibre, and 65% contents. Towards the end of maturity, this inverses to 60% fibre and 40% contents. Protein drops from 33% to 7% and Lignin increases to 7%. 

These undesirable conditions that we encounter in winter lead to an inefficient digestive system. Fibre keeps piling in however there aren’t enough microbes to process it, so the cow becomes constipated and nutrient-deficient. 

We can’t do much about plants becoming more fibrous as they mature, but we can change the environment of the cow's stomach to build up an army of microbes that will help efficiently break it down.