Ruminants
Senior 2 · Agriculture
Ruminants
Lesson 1 of 5
20 min
Let's begin
Walk past a zero-grazing shed in the afternoon and you will often see the cows lying down, jaws moving steadily, even though there is no grass in front of them. They are not eating. They are chewing the cud: bringing swallowed grass back up to chew it a second time.
Animals that do this are called ruminants. In Rwanda the three farmed ruminants are cattle, goats and sheep. Cattle matter deeply here: they give milk, meat, manure and hides, they are an important cultural gift, and since 2006 the Girinka programme ("One Cow per Poor Family") has given cows to poor households. To rear ruminants well, you first need to know how their bodies work and which breed suits which farm.
A ruminant is a plant-eating (herbivorous) mammal with a stomach divided into four compartments, in which microbes break down the tough fibre of plants before the animal digests it. Chewing swallowed food a second time is called rumination, or chewing the cud. Mammals such as pigs, rabbits and humans have a simple, single stomach and are called monogastric.
Plant fibre is mostly cellulose. Mammals cannot make the enzyme cellulase, so on their own they cannot digest it. Ruminants carry billions of bacteria, protozoa and fungi in the rumen that do the job for them.
| Compartment | What happens there |
|---|---|
| Rumen | The largest part. A warm, wet fermentation vat without oxygen, where microbes ferment cellulose into volatile fatty acids that the animal absorbs for energy. |
| Reticulum | Works with the rumen. Forms swallowed food into balls of cud that are sent back to the mouth. Heavy objects such as nails collect here. |
| Omasum | Has many folds (leaves). Squeezes water out of the food and absorbs it with some fatty acids. |
| Abomasum | The "true stomach". Produces acid and enzymes, like a human stomach, and digests the food and the microbes that come with it. |
Ruminants also have no upper front teeth (incisors). A hard dental pad takes their place, and the lower incisors press grass against it.
A cow eats Napier grass. Follow it through:
So the correct order is: mouth → rumen → reticulum → (back to mouth) → omasum → abomasum → small intestine.
| Species | Adult male | Adult female | Young |
|---|---|---|---|
| Cattle | bull (a castrated male is a steer or ox) | cow (a young female that has not calved is a heifer) | calf |
| Goat | buck (billy) | doe (nanny) | kid |
| Sheep | ram | ewe | lamb |
A breed is a group of animals of the same species that share characteristics (colour, size, horn shape, production) and pass them on to their offspring. Breeds found in Rwanda fall into three groups:
| Breed | Type | Main characteristics |
|---|---|---|
| Ankole (including the Inyambo) | Local, dual-purpose | A Sanga breed of East and Central Africa. Usually red-brown, with very long, wide horns. Hardy: tolerates heat, long walks, poor grass and some diseases. Gives only a few litres of milk a day. |
| Friesian (Holstein Friesian) | Exotic, dairy | Black and white (sometimes red and white) patches. The highest milk yield of any breed. A large animal; a mature Holstein cow commonly weighs 680–770 kg. Needs plenty of good feed and water, and suffers badly from tick-borne disease. |
| Jersey | Exotic, dairy | Small, light brown to fawn. Less milk than a Friesian, but the milk is rich in butterfat. Copes with heat better than a Friesian and eats less. |
| Crossbreds (e.g. Ankole × Friesian, Ankole × Jersey) | Dairy or dual-purpose | More milk than the Ankole, more hardy than a pure exotic. Common on smallholder zero-grazing farms. |
Dairy type versus beef type. A dairy cow has a wedge-shaped body when seen from the side, a large, well-attached udder, prominent milk veins under the belly and a lean frame. A beef animal has a deep, rectangular ("blocky") body, thick muscles and short legs.
| Breed | Species | Main use and characteristics |
|---|---|---|
| Local (small East African) goat | Goat | Meat. Small, hardy, many colours, breeds well on poor feed. |
| Boer | Goat | Meat. From South Africa; white body with a red-brown head; grows fast. Boer bucks are crossed with local does to raise growth rate. |
| Saanen, Toggenburg, Alpine | Goat | Milk. From the Alps of Europe; Saanen goats are white. |
| Local hair sheep | Sheep | Meat. Hardy, short hair rather than wool. |
| Dorper | Sheep | Meat. From South Africa; usually a black head and white body; grows fast. |
| Merino | Sheep | Fine wool; suited to cool climates. |
Tip
Memory hook: the order of the stomach spells "Real Rwandan Oxen Ate": Rumen, Reticulum, Omasum, Abomasum. Only the last one, the Abomasum, is the "true" stomach.
Exam technique: when asked to "state characteristics of a breed", give features you could see or measure: colour, size, horns, milk yield, hardiness. "It is a good cow" earns no marks.
Explain why a goat can live on grass and leaves but a pig cannot.
Solution: A goat is a ruminant. Microbes in its rumen ferment cellulose, which the goat itself cannot digest. A pig is monogastric: it has a single stomach without a large microbial fermentation chamber, so it needs feeds such as grain and kitchen waste that are easier to digest.
Name the compartment of a cow's stomach that (a) is the "true stomach", (b) is the largest, (c) absorbs water from the food.
Solution: (a) abomasum; (b) rumen; (c) omasum.
A calf is born to a Friesian bull and an Ankole cow. What is this calf called, and what advantages might it have?
Solution: It is a crossbred (cross). It is likely to give more milk than a pure Ankole and to be hardier (more tolerant of heat, poor feed and ticks) than a pure Friesian.
Give the name of: (a) a young female cow that has not yet calved; (b) a male sheep; (c) a young goat.
Solution: (a) heifer; (b) ram; (c) kid.
A farmer sees a cow with a wedge-shaped body, a large udder and prominent milk veins. Is it a dairy or a beef type? Give one reason.
Solution: Dairy type. The large udder and milk veins show a body built for milk production, not for meat.
Summary
Sources and credits
The Rwandan examples, worked examples and practice questions are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
