Ruminant digestion
Ruminants are mammals with specialised digestive systems that use fermentation processes to gain nutrients from plant material. Cattle, sheep, deer, goats and camels are all ruminants. They are also called herbivorous or secondary producers in food chains and have adaptations to allow them to thrive on a plant-only diet.
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?
Ruminant digestion
There are two main types of carbohydrates found in plants – non-structural carbohydrates made of sugars and starch. Soluble sugars, such as glucose and fructose, are primarily found in plant leaves and are easily digested by microbes and the cow. Starch has a different bond structure than soluble sugars and is found in grains, leaves, plant stems and bulbs. Rumen enzymes are needed to break the bond between the glucose units within a starch molecule and so are slower to digest.
The amazing 3D cow
The animated 3D cow allows you to see inside a cow and view from different angles using your mouse or finger – find out more about cows amazing digestive system, milk production, heart and liver.
View The Amazing Cow interactive
Have a look at DairyNZ’s FeedRight resources for a more in-depth look at ruminant digestion.
Structural carbohydrates made of cellulose and hemicellulose are sugar subunits found in plant cell walls and provide structural support to the plant. The microbes in the rumen produce cellulase – an enzyme required to break the complex bonds between the glucose units held in these molecules .
Cows are an amazing species, turning something that a human could never eat into something that is really, really nutritious and allows them to produce a lot of milk and grow babies.
Dr Elena Minnée
Each part of the digestive system from the mouth to the intestine has a part to play in the breakdown of plant material. The adaptation that sets ruminants apart from other animals is their complex multi-chambered stomach comprising the rumen, omasum, reticulum and abomasum.
Ruminant digestion
Cows are ruminants. They have especially adapted digestive systems that allow them to only eat plants.
Rumen fermentation
Carbohydrates are the main energy source for cows and make up a large portion of plant dry matter. The bacteria in the rumen break down larger carbohydrate molecules found in plant cells into simple sugars in a process called fermentation. The microbes use some of these sugars to grow and multiply, and the rest are used by the cow. Fermentation also produces gases, heat and volatile fatty acids. The gases produced are carbon dioxide (CO2) and methane (CH4) which are belched out by the cow. These gases are greenhouse gases, and research is targeted at finding solutions to reduce these greenhouse gas emissions.
Methane emissions – cow burps, not farts
It’s a misunderstanding that methane emissions come from the back end of cows. Fortunately, they are burped out, which means we can target the start of the digestive system to find ways to reduce emissions. The DairyNZ experts in this video are researching how forages like plantain may help reduce the amount of methane in cow burps.
Question for discussion:
What causes cows to produce methane?
Impacts of feed sources
Dairy cows are fed on pasture and supplement feed to ensure maximum yield of milk solids. The New Zealand dairy industry pasture-based system has multiple environmental impacts. Nitrogen leaching into soils and groundwater and a reduction of methane gas production are two of the main areas of ongoing research. Mitigation of these impacts has been the focus for DairyNZ and many other research organisations over decades.
Urine is a metabolic byproduct. It contains 95% water and 2.5% urea (CH4N2O), and the remaining 2.5% is a mixture of salts, hormones, enzymes and minerals. Urine plays an important role in the cycling of nitrogen in pastoral systems.
Dung and urine
One project involves research into the herb plantain. Compared to other forages, plantain is lower in nitrogen and has a high water content. It is also known to have diuretic properties – it increases the amount of urine excreted. It’s been shown that cows grazing pasture that contains 30% plantain urinate more frequently. This dilutes the nitrogen in urine patches, which has a direct effect in reducing nitrogen leaching. Researchers are also investigating plantain’s impact on methane production, and the research is showing positive results in reducing methane produced by ruminant digestion.
It is very early days, but the trends that we’re observing, it looks like there is a reduction in methane emissions per unit of feed eaten when cows are fed plantain, and this is really exciting.
Dr Elena Minnée
Nature of science
Research to find solutions to wicked problems we face is essential. Often, research starts off with an idea or existing science understanding or from mātauranga knowledge. The process of science will explore whether the thinking/theories have any merit. The challenge is scaling up the implementation of any findings.
Related activity and related content
The sudent activity Explore a cow’s digestive system is an interactive approach to identifying the main parts of a ruminant digestive system.
Find out more about soil, farming and science.
The Farm management practices article describes ways to minimise nutrient leaching.
Find out more about DairyNZ’s plantain research.
Explore the impact of farming on the nitrogen cycle.
The article Dairy farming – key terms will support learning in this area.
Dairy farming and climate change – a context for learning offers further resources, including a labelling activity for students.
Explore a range of resources in our Ruminants Pinterest collection.
Acknowledgement
This resource has been produced with the support of DairyNZ.
DairyNZ
DairyNZ is the industry organisation that represents all New Zealand dairy farmers. DairyNZ supports farmers through investing in research, resource development, extension and advocacy to ensure sustainable dairy farming and food production.
