Principles of Livestock Production · Agriculture

Breeds and breeding

A breed is a group of animals of the same species with common features. Tanzanian cattle include indigenous Zebu (Tanzania Shorthorn Zebu, Boran), improved breeds such as Friesian, Ayrshire and Jersey (dairy), and crosses between them. Common breeds of other livestock include Saanen and Toggenburg (dairy goats), Landrace and Large White (pigs), and Rhode Island Red and Leghorn (chickens).

Purpose	Cattle breeds
Beef	Boran, Zebu, Hereford
Dairy	Friesian, Ayrshire, Jersey
Dual purpose	Sahiwal, crosses

Breeding improves animals. In selection, the best animals become parents. Inbreeding (mating of relatives) concentrates good and bad features; outbreeding (unrelated animals) gives vigour; crossbreeding mixes two breeds to combine the high yield of exotic breeds with the toughness of indigenous ones; artificial insemination (AI) uses semen from the best bulls and avoids the need to keep a bull.

Genetic improvement by selection

R = response in the next generation, h² = heritability (the fraction of variation that is inherited), S = selection differential (how much better the parents are than the herd average).

Worked exampleSelection response

The herd average is 8 litres of milk per day. Selected cows average 12 litres. Heritability is 0.3. How much better will the daughters be?

Selection differential.
Response.

Answer: The daughters are expected to give about 9.2 litres (8 + 1.2).

Reproduction and breeding records

Animal	Gestation	Heat cycle	Offspring
Cattle	283 days	21 days	1 (calf)
Goat	150 days	21 days	1–3 kids
Sheep	147 days	17 days	1–2 lambs
Pig	114 days	21 days	8–12 piglets
Chicken	21 days to hatch	—	about 10–15 chicks per clutch

The time from mating to birth differs among animals.

Try itSelection response

Choose the heritability and how much better the selected parents are.

Check yourself Friesian cattle are kept mainly for

Check yourself Artificial insemination uses

Check yourself The gestation period of a pig is about

Key terms

Breed: A group of animals with common features.
Selection: Choosing the best animals as parents.
Crossbreeding: Mating animals of different breeds.
Heritability: The fraction of variation caused by genes.

Summary

Breeds are chosen for beef, milk or dual purpose.
Breeding methods: selection, inbreeding, outbreeding, crossbreeding and AI.
R = h² × S.
Know the gestation periods of farm animals.