Topic 5 of 7 · Form 6
Animal breeding and reproduction
Mashona, Tuli and Nkone cattle are hardy, tick-tolerant and fertile under harsh conditions; crossbreeding them with exotic breeds combines hardiness with productivity.
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Reproductive physiology
- Oestrous cycle in cattle: about 21 days; signs of heat (mounting, restlessness, mucus discharge). Gestation: cattle about 283 days, goats about 150 days, pigs about 114 days.
- Hormones: FSH, LH, oestrogen, progesterone, oxytocin.
Breeding methods
- Natural mating and artificial insemination (AI) – AI spreads superior genetics, reduces disease and the cost of keeping bulls.
- Embryo transfer and oestrus synchronisation.
Breeding systems
- Inbreeding (concentrates traits but risks depression), line breeding, outbreeding, crossbreeding (heterosis), and grading up.
- Selection: by individual performance (performance testing), by relatives (progeny testing), and by breed standards.
- Heritability: the proportion of variation in a trait due to genes. High heritability traits (e.g. carcass traits) respond well to selection; low heritability traits (e.g. fertility) respond more to management.
Indigenous breeds
Mashona, Tuli and Nkone cattle are hardy, tick-tolerant and fertile under harsh conditions; crossbreeding them with exotic breeds combines hardiness with productivity.
Reproductive management
Calving interval (target about 12 months), calving rate, record keeping, bull fertility testing and good nutrition (body condition score).
Worked example: 80 cows are bred and 64 calves are weaned. Find the weaning percentage.
64 ÷ 80 × 100 = 80%
Exam tip: Use heritability to justify whether to improve a trait through breeding or management.
Check yourself
- What is the length of the oestrous cycle in cattle?
- Give two advantages of artificial insemination.
- Why might a farmer cross Mashona cows with a Brahman bull?
Show answers
- About 21 days.
- Any two: spreads superior genes widely, no bull needed, reduces disease spread, cheaper, records easier.
- To combine the hardiness and fertility of the Mashona with the size and growth of the Brahman (heterosis).
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