Animal Breeding II – SS1 Livestock Farming Lesson Note (First Term)

A system of mating is the way a farmer pairs male and female animals according to how closely they are related.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Name the three main systems of mating in livestock.
2. Describe inbreeding, linebreeding and crossbreeding with examples.
3. State the advantages and disadvantages of each system.
4. Explain inbreeding depression and hybrid vigour (heterosis).
5. Say which system suits a small-scale farmer in Nigeria and why.

What are the systems of mating?

There are three main systems of mating in livestock: inbreeding, linebreeding and crossbreeding.

• Inbreeding: mating animals that are very closely related.
• Linebreeding: mating animals that are more distantly related but share a good ancestor.
• Crossbreeding: mating animals of different breeds.

• The farmer chooses a system according to the aim of the farm.
• This lesson follows the last one on selection, natural mating and artificial insemination (AI).

What are the key terms in animal breeding?

Key terms are the words a student must know before comparing the systems of mating.

• Breed: a group of animals of the same species with shared features, such as the Muturu cattle breed.
• Pure breed: animals of one breed mated only with their own breed.
• Crossbred: an animal whose parents belong to different breeds.
• Trait: a feature of an animal, such as skin colour, growth rate or milk yield.
• Inbreeding depression: the loss of size, health and fertility caused by mating close relatives.
• Hybrid vigour (heterosis): the extra strength and growth shown by crossbred offspring.

What is inbreeding?

Inbreeding is the mating of animals that are very closely related.

• Examples: a father mated to his daughter, or a brother mated to his sister.
• Purpose: a farmer uses it to make a particular trait “stick” in a family.
• Illustration: if a family of pigs has a skin colour that buyers like, inbreeding keeps that colour pure.

What are the advantages of inbreeding?

• Uniformity: the animals become alike and the breed stays “pure”.
• Removal of faults: bad traits in a family show up, so the farmer can remove those animals from breeding.

What are the disadvantages of inbreeding?

• Inbreeding depression: this is the biggest problem. The young often become small, weak or unable to reproduce.
• Disease: weaknesses and diseases become more common in the family.

What are the signs of inbreeding depression?

• Small size: offspring are smaller than their parents.
• Slow growth: animals take longer to reach market weight.
• Low fertility: fewer young are born, or animals cannot breed.
• Weakness: more young animals fall ill or die.
• Deformities: some young are born with defects.

What is linebreeding?

Linebreeding is a milder form of inbreeding in which the animals mated are more distantly related.

• Examples: mating cousins, or a grandfather to a granddaughter.
• Purpose: it keeps the “good blood” of a famous ancestor, such as an outstanding bull, in the herd.
• Safety: it carries less risk of weakness than close inbreeding.

What are the advantages of linebreeding?

• Keeps quality: it maintains the good qualities of a chosen ancestor.
• Lower risk: it is safer than close inbreeding.

What are the disadvantages of linebreeding?

• Delayed weakness: if done without care, it can cause the same problems as inbreeding over a long time.

What is crossbreeding?

Crossbreeding is the mating of two animals from different breeds.

• Use in Nigeria: it is a common practice.
• Example: a local Muturu bull (tough and tolerant of local diseases) mated to a foreign Holstein cow (high milk yield).
• Aim: the young should carry useful traits from both parents.

What are the advantages of crossbreeding?

• Hybrid vigour (heterosis): the young are often better than their parents. They grow faster, are stronger and produce more.
• Combined traits: it joins the toughness of a local breed to the high production of a foreign breed.

What are the disadvantages of crossbreeding?

• Loss of pure breed: the farmer may lose the pure local breed over time.
• Higher cost: crossbred animals often need better feed and medicine than local ones.

How do the three systems compare?

The table below sets inbreeding, linebreeding and crossbreeding side by side.

How can a farmer avoid inbreeding depression?

A farmer avoids inbreeding depression by keeping control of which animals mate.

1. Keep records of the parents of every animal.
2. Do not mate parents with their young or brothers with sisters.
3. Change the breeding male after some time, or buy one from another farm.
4. Use artificial insemination with semen from an unrelated male.
5. Remove weak or deformed animals from breeding.

Which system should a farmer choose?

A small-scale farmer in Nigeria usually gains most from crossbreeding.

• Crossbreeding: the animals grow faster and bring in more money.
• Inbreeding: research farms may use it to produce pure breeding stock to sell to others.
• Backyard farm: avoid mating close relatives, or the animals will become small and sickly.

Evaluation

1. Name the three main systems of mating.
2. A farmer keeps one male goat for many years and his goats get smaller each year. Explain why. (Hint: think about inbreeding.)
3. What is hybrid vigour?
4. State one advantage and one disadvantage of crossbreeding.
5. Give two signs of inbreeding depression.

Assignment

Visit a nearby farm or ask a local cattle herder if the animals include “crosses” (mixed breeds) and why the farmer likes them. Write the answer in three sentences.