If you have cattle, sheep or goats on your lifestyle block then you have some ruminant animals on your hands. Ruminant animals have a unique way of digesting their feed which is quite different to how monogastric (single-stomached) animals do. When we talk about feeding our ruminants, we need to consider the needs of the billions and billions of microorganisms that live in their rumen who are really doing the bulk of the digestion for that animal. If we keep the microorganisms in the rumen of the ruminant animal happy, then in turn we will have a happier and healthier ruminant animal so it’s important we take them into consideration when feeding our ruminants.

Ruminant animals have evolved to get nutritive value out of very high fibre feeds that monogastric animals such as pigs and humans cannot. Most people know the fact that cows have four stomachs which is sort of true, really, it’s four different stomach chambers with each chamber having its own unique functionalities important to digestion. A majority of the digestion of feed that takes place is by the billions of microorganisms that live in the rumen, this is known as foregut fermentation. Ruminant animals also ‘chew the cud’. This means that they bring back up feed they have previously eaten and re-chew it to further breakdown it down and increase the surface area available for the microorganism to access the feed while in the rumen. This amazing and complex digestive system allows the production of high-quality proteins such as milk and meat from high-fibre feeds that most of the animal world cannot utilise. Members of the ruminant family include cows, sheep, goats, deer, elk, buffalo, giraffes, and camels.

Now let’s take a look at each stomach chamber to see what they are up in:

Rumen

The largest and most important stomach compartment. The rumen is where the feeds that are consumed are fermented by microorganisms. It is a huge compartment that can be up to 200 litres in size in a mature cow. Absorption of nutrients also occurs here. The rumen wall is covered in finger-like projections called villi which increase the surface area to aid in the absorption of nutrients.

Reticulum

Important for feed particle size sorting and rumination (bringing feed back into the mouth for re-chewing)

Omasum

Water and electrolytes are absorbed here.

Abomasum

The ‘true’ stomach, with a lower pH, compared to the rumen. This stomach compartment actually acts very similarly to a monogastric stomach like a human.

Ruminants share a symbiotic relationship with the microorganisms that reside in their rumen, which means they both get something good out of the relationship. The ruminant animal is the host animal, it gives the microorganism an environment to live in that suits its needs – it’s warm, dark, moist, anaerobic (free of oxygen) and the ruminant works hard to try and maintain a pH around 6 which is what the microorganisms like. There is a constant supply of food for them coming in from the host ruminant animal too. But what does the host ruminant get out of the relationship? Well in return the microorganisms digest the feed the ruminant consumes using enzymes that can break down the cell wall components of high fibre feed such as cellulose and hemicellulose and they turn them into an energy form that is absorbable by the host animal. The microorganisms also provide the host animal with a protein source by incorporating amino acids and non-protein-nitrogen into their own body protein and when they are eventually washed through to lower parts of the digestive tract the microorganisms themselves can be broken down and absorbed by the host animal in the abomasum – so maybe it's not all good for the microorganisms in the end!

When feeding the ruminant, you are really feeding the billions of microorganisms that reside in the rumen and when they are functioning well and have everything they need to thrive and grow the rumen will be functioning optimally which means that feed will get processed more efficiently and the ruminant will be healthier and more productive. When the conditions are not optimal for the microorganisms they will not be functioning optimally, and the host ruminant animal’s dry matter intake may fall which can cause a drop in production and health issues. The microorganisms are a wee bit fussy too and they take time to adjust to new diets. This is why when we are introducing new feeds, we need to do it slowly and transition on to them – especially if the feed we are introducing is high in sugar or starch and the rumen takes longer to adapt to these feeds.

Carbohydrates are the main source of energy for rumen microorganisms and consequently are also indirectly the main source of energy for the host ruminant animal. Rumen microorganisms utilise carbohydrates and produce volatile fatty acids which are then absorbed by the ruminant animal as a form of energy. Fibre is one of the three types of carbohydrates - along with sugar and starch. Fibre is classed as a ‘structural’ carbohydrate and is fermented in the rumen by microorganisms more slowly than sugar or starch. Fibre is found in abundance in forages in the form of hemicellulose and cellulose in plant cell walls and exists within plants to give rigidity and structure. Not all fibre is created equal and some fibre fractions are more slowly fermentable in the rumen than others, with hemicellulose being the more rapidly fermentable fibre fraction compared to cellulose.

Feeding adequate amounts of fibre in a ruminant diet is important for meeting nutritional requirements as well as promoting overall rumen health. Adequate ‘effective’ fibre in the diet is important for stimulating the act of rumination (chewing the cud). Rumination promotes the flow of saliva, which contains bicarbonate that helps to buffer the rumen and lift the pH. When there is not enough ‘effective’ fibre in the diet, the need to chew the feed to break down the particle size decreases as does the amount of saliva flowing into the rumen. This reduces the buffering capacity of the rumen and can cause acidosis. Some feeds may be high in fibre but low in ‘effective’ fibre due to the processing of the feed. Palm Kernel Expeller is a good example of this; it is high in fibre but has been ground up to fine particle size so it does not stimulate chewing activity.

As a rough rule of thumb, fibre can be deemed ‘effective’ if the chop length is longer than about 4cm for cattle. There must always be some effective fibre in the diet that will stimulate chewing activity to keep our ruminants healthy.

Fibre is an important dietary component for ruminants, however too much can also be a problem, particularly for high-producing animals such as lactating ruminants. More mature, very bulky forage (such as hay) can have a very high fibre level and when consumed in large quantities can limit dry matter intake due to the increased rumen retention time associated with its digestion. In a nutshell, the microorganisms take so long to process the tough fibre in very mature forage that it must stay in the rumen longer, and while it is in their fermenting away the host animal will feel full and eat less.

It's all about balance when it comes to any animal’s diet, and we must pander to those all-important microorganisms when we are thinking about feeding our ruminants. Hopefully, I have given you a bit of insight into how these amazing animals digest their feed and in a future article, I hope to give you some more practical tips and tricks to best look after your very special ruminant animals.