The Many Uses of Cow Dung: A Natural and Renewable Resource
A Useful and Abundant Material
Cow dung, manure, or feces is indigestible plant material released on to the ground from the intestine of a cow. Feces is generally not a favourite topic of conversation, whether it comes from an animal or a human. Cow dung is worth discussing, though. It's a useful material and helps us in a variety of ways. It's also a plentiful and renewable resource. It's a shame when it's wasted.
Cow manure has a soft texture and tends to be deposited in a circular shape, which gives dung patches their alternate names of cow pies and cow pats. The manure is used as a rich fertilizer, an efficient fuel and biogas producer, a useful building material, a raw material for paper making, an insect repellent, and a disinfectant. Cow dung "chips" are used in throwing contests and cow pie bingo is played as a game. The manure also plays an essential role in the lives of various animals, plants, and microbes, including dung beetles and the Pilobolus fungus.
Fuel and Biogas From Cow Manure
Dried cow dung is an excellent fuel. In some cultures dung from domestic cows or buffalo is routinely collected and dried for fuel, sometimes after being mixed with straw. Pieces of dung are lit to provide heat and a flame for cooking. Dried dung has lost its objectionable odour.
Even in North America people are making use of the energy stored in cow dung, although this is usually done indirectly by making a biogas from the dung. A biogas is a mixture of gases produced by the anaerobic digestion of organic matter by bacteria. An "anaerobic" process occurs in the absence of oxygen. The organic matter that is digested can be animal dung, sewage, plant material, or food waste.
A Biogas Digester
Production and Uses of a Biogas
The general process for making an anaerobic digester for cow dung starts with placing dung and water in an airtight container. The container must be kept warm and left undisturbed so that bacteria can do their work. The gas that is produced is withdrawn through a tube and stored.
Once a biogas has formed, it can be reacted with oxygen to produce energy. The gas can be used to cook food, heat water in a boiler, and replace conventional fuel in motor vehicles. In addition, the energy in a biogas can be used to produce electricity.
Biogas produced from cow dung generally consists of methane, carbon dioxide, and other components, such as hydrogen sulphide. Since there is so much methane in the gas, it's important that it doesn't escape into the environment. Methane is a major greenhouse gas and contributes to global warming.
Using Cow Dung as a Building Material
A mud and cow dung paste is often applied to the floors of rural homes in India and may be applied to the walls as well. The mixture reportedly forms a waterproof layer that helps to insulate the house from heat entry or loss and doesn't smell unpleasant. A relatively new process is to make building bricks from cow dung mixed with straw dust. The bricks are much lighter than conventional ones.
It's been suggested that the manure residue from biogas production could be used instead of sawdust to make fibreboard. The manure, which contains fibres, would be sterilized and then mixed with resin to make the board. Fibreboard has many uses. It's used to manufacture furniture and floors in homes, for example.
The high fibre content of cow dung also enables people to make paper from the dung. The dung is washed to extract the fibres, which can then be pressed into paper on a screen. Some people make cow dung paper as a hobby. The paper can also be bought commercially.
Dung as an Insect Repellent and a Disinfectant
The smoke from burning cow dung has been found to repel insects, including mosquitoes, leading to the use of cow dung as a pesticide in some areas. Strange as it may sound, in some cultures cow dung is applied to walls and floors as a disinfectant as well as an insulator. There may be some value in this seemingly bizarre practice, as the FAO quote shown below suggests. Unsterilized cow dung may contain microbes that can infect humans, though, so it's not a good idea to spread dung over a wound.
Cow dung and cow urine possess complex degrading substances and may possess antibacterial properties.— FAO (Food and Agriculture Organization of the United Nations)
Cow Manure as a Fertilizer
Removing cow dung from fields is important because the dried pats reduce the grazing area. In addition, the cow pats give off methane, which acts as a greenhouse gas in the atmosphere. Water runoff can carry some of the dung into rivers and other bodies of water, polluting them with excess nutrients.
Many people are aware that cow manure can make a good fertilizer and are reminded of this every time they pass a fertilized and odoriferous field. Cow manure is rich in minerals, especially nitrogen, phosphorus, and potassium. It can support the growth of beneficial microorganisms when it's mixed with soil. Manure can also improve the texture of the soil and help it to maintain moisture. Often, however, manure is too rich in certain chemicals and needs to be diluted or left to sit in the soil for a while before crops are planted.
Playing Cow Pie Bingo
Cow Pie Games
Cow Chip Throwing
Yes, cow pies really are used as a source of entertainment! A cow chip throwing contest is much like it sounds. People throw dried cow pats as far as they can. The person who throws their "chip" the farthest wins. Cow chip throwing is popular at some fairs.
Cow Pie Bingo
In cow pie bingo, chalk squares are drawn on an area of grass, which is cordoned off from its surroundings. Each square is identified with a number or letter. People pay for a square. One or more cows are then led on to the grass. As the cows wander and graze, the spectators wait for a cow pie to be released (which gives a new meaning to the term "spectator sport"). When a cow pie lands on a person's square, that person is the winner.
Cow Chip Throwing at a Sweetcorn Festival
Humans aren't the only ones to make use of cow dung. As their name suggests, the manure is very important in the life of dung beetles. The dung of any herbivorous mammal will do for their purposes.
Most dung beetles belong to the insect family called the Scarabaeidae. They live on every continent except Antarctica. Some of them have a brightly coloured, metallic appearance and are attractive insects.
Dung beetles are classified as rollers, tunnellers, or dwellers.
- Rollers take a small piece of dung from a cow pat and shape it into a ball. They roll the ball away and bury it in the ground. The beetles use the ball as food or as a place to lay eggs.
- Tunnellers dig a tunnel through the cow pat and into the soil underneath it, where they lay eggs. The dung that enters the tunnel is their food source.
- Dwellers live inside the cow pat in a shallow pit. Here they feed and lay eggs.
The beetles often play an important role in their environment. They aerate and fertilize the soil and remove cow pats from its surface. This clears the land and prevents dung from being washed away by rain to contaminant waterways. The nutrient-rich dung also provides good food for earthworms.
Beetles Competing for Dung on the Serengeti Plains
Dung beetles were known as scarabs by Ancient Egyptians. They considered the beetle known today as Scarabaeus sacer to be a sacred animal. Its habit of repeatedly rolling a ball away from dung reminded them of Khepri, a sun god. He was believed to roll the sun across the sky every day in a similar fashion.
Dung Beetles for Farmers
Pilobolus: An Enterprising Fungus
Pilobolus is a fungus that grows on herbivorous dung, including the dung of cows. Like other fungi, Pilobolus can't make its own food and must absorb nutrients from its surroundings. It does this by secreting digestive enzymes into manure and then absorbing the products of the digestion. Pilobolus, other fungi, some bacteria, and some animals are decay organisms. They slowly break down and remove cow pats.
Fungal Life Cycle
Pilobolus is famous for its method of distributing its spores. Cows eat the spores as they're grazing on grass. The spores have a tough coat and pass through the cow's digestive tract unharmed. They leave the digestive tract in the cow's feces. The spores then germinate, producing the fungal body, or mycelium, in the cow pat.
The mycelium eventually produces new spores. At this point a problem arises. Cows avoid eating their own dung, so how are the fungal spores going to get into another cow's digestive tract to complete their life cycle? The solution is to "shoot" the spores beyond the cow pat and onto the surrounding grass.
The Dung Cannon
The spores of Pilobolus are located in a sac called a sporangium. This is borne at the top of a stalk projecting beyond the surface of the cow pat. Below the stalk's tip is a light-sensitive area that detects sunlight and causes the stalk to bend towards the light. The tip of the stalk becomes swollen with liquid and eventually bursts, shooting the sporangium into the air and beyond the "zone of repugnance" around a cow pat. The sporangium can move as fast as 35 feet a second, reach a height of 6 feet, and travel as far as 8 feet away. Pilobolus is also known as the hat-throwing fungus and the dung cannon because of its interesting behaviour.
Pilobolus Spore Production and Release (Sped Up)
Safety Precautions for Handling Dung
If you want to experiment with cow dung, remember that the raw material may contain pathogens (microorganisms that can cause disease). Gloves should be worn or hands should be washed thoroughly after handling dung of any kind. If you're tempted to make your own mini anaerobic digester, as some people do, make sure that you follow the assembly instructions carefully. The pressure of a gas in a confined space such as a digester can be very dangerous. In addition, the methane in a biogas is flammable. With these precautions in mind, though, cow dung can be a wonderful resource.
Information about cow dung building bricks from Inhabitat
Biogas from cow dung information from the World Economic Forum
Cow dung as a bioresource from Bioresources and Bioprocessing and the Springer publishing company
Facts about dung beetles from the San Diego Zoo
Dung fungi facts (including information about Pilobilus) from the University of Sydney
How dung beetles use poo from The Conversation
© 2014 Linda Crampton