Ruminants
Senior 2 · Agriculture
Ruminants
Lesson 3 of 5
22 min
Let's begin
Feed is usually the biggest cost on a livestock farm, and poor feeding is the most common reason why Rwandan dairy cows give less milk than they could. A Friesian cross that could produce 10 litres a day may give only 3 litres if it is fed dry, old grass and too little water.
Every litre of milk and every kilogram of meat is built from what the animal eats. In this lesson you will learn the main types of feed, how ruminants are fed in Rwanda, and how to calculate how much feed an animal needs.
| Class | Description | Examples in Rwanda |
|---|---|---|
| Roughages | Bulky feeds high in fibre. The basis of every ruminant diet. | Napier (elephant) grass, Brachiaria, Rhodes grass (Chloris gayana), maize stover, bean haulms, banana leaves and pseudostems, sweet potato vines, hay, silage |
| Legume fodder | Leaves of leguminous plants and trees; rich in protein. | Calliandra, Leucaena, Desmodium, lablab |
| Concentrates | Low in fibre, rich in energy or protein. Given in small amounts, mainly to milking cows and young stock. | maize bran, rice bran, cotton seed cake, sunflower cake, soybean meal, commercial dairy meal |
| Minerals and vitamins | Needed in small amounts for bones, milk and fertility. | salt licks, mineral blocks, mineral powder mixed into feed |
| Water | The cheapest and most often neglected nutrient. Milk is mostly water. | clean water available all day; a milking cow may drink well over 50 litres a day |
Napier grass (Cenchrus purpureus, also called elephant grass) is the most important fodder for smallholder dairy farmers in East Africa. It is planted from stem cuttings and, for feeding, is cut every one to three months. If it is left to grow too long, it becomes stemmy and harder to digest, so it should be cut young and chopped before feeding.
All fresh feed contains water. Dry matter (DM) is what is left when the water is removed; it contains all the nutrients. A useful rule of thumb is that a cow eats about 3% of its body weight in dry matter each day.
Worked example
A cow weighs 400 kg. Fresh Napier grass is about 20% dry matter. How much fresh Napier does she need per day?
That is a lot of grass to cut and carry, which shows why a zero-grazing farmer needs a good fodder plot.
From June to September there is often no rain, and fresh fodder runs short. Farmers conserve feed when grass is plentiful:
Worked example
The 400 kg cow above needs 12 kg DM a day through a 90-day dry season. How much hay (85% DM) must be stored?
A newborn calf, kid or lamb must drink colostrum, the thick first milk, within the first few hours of life. Colostrum carries antibodies that protect the young animal from disease until its own immune system develops. A common guide is to give a calf milk equal to about 10% of its body weight each day, and to offer good hay and a little concentrate from the second week so the rumen develops.
Tip
Memory hook: "Roughage fills, concentrate fuels." Roughage is the bulk every ruminant needs to keep its rumen working; concentrates top up energy and protein for high producers.
Exam technique: in feed calculations always convert to dry matter first, then divide by the DM fraction to get the fresh weight. Write the units on every line.
Classify each feed as roughage, concentrate or legume fodder: (a) maize bran; (b) Napier grass; (c) Calliandra leaves; (d) cotton seed cake.
Solution: (a) concentrate; (b) roughage; (c) legume fodder; (d) concentrate (protein-rich).
A 350 kg cow is fed fresh grass that is 15% dry matter. Using the 3% rule, how much fresh grass does she need each day?
Solution: DM needed = 0.03 × 350 = 10.5 kg. Fresh grass = 10.5 ÷ 0.15 = 70 kg.
Explain why silage must be sealed airtight.
Solution: Without oxygen, lactic acid bacteria ferment sugars into acids that preserve the fodder. If air gets in, moulds and other spoilage organisms grow and the silage rots.
A newborn calf weighs 35 kg. Using the 10% guide, how much milk should it receive per day?
Solution: 10% × 35 kg = 3.5 kg, so about 3.5 litres per day, split into two or more feeds.
Give two advantages of zero-grazing for a farmer with half a hectare near Huye.
Solution: It uses little land, since fodder is grown intensively and carried in; all manure is collected for the crops; animals meet fewer ticks and sick animals, so less disease; feeding can be controlled, which raises milk yield.
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.
