Animal Breeding, Selection and Reproduction
Breeding systems
- Inbreeding and line breeding use close relatives; outbreeding covers outcrossing, crossbreeding and grading (upgrading).
- Crossbreeding exploits heterosis for milk yield and early maturity; grading replaces local genes gradually over generations.
Selection methods
- Mass selection on the animal's own performance; family selection on relatives; progeny testing when heritability is low.
- Response to selection R = h² × S. Fat % (h² about 0.5–0.6) moves quickly; milk yield (h² about 0.25) and fertility traits move slowly.
Reproduction numbers
- Oestrus cycle: cattle 21 days (18–24), buffalo 21 days; heat about 12–18 hours.
- Gestation: cattle 280–285 days, buffalo 305–310 days, sheep ~148, goat ~150, pig ~114.
- Service period 60–90 days; dry period about 60 days.
Worked example
A cow is bred 90 days after calving and carries the calf 282 days. Calving interval = 90 + 282 = 372 days, roughly 12.2 months. To reach a 12-month interval the service period must fall to about 83 days, since interval = service period + gestation. The reasoning, not the arithmetic alone, earns the marks.
Traps
Grading is not crossbreeding; buffalo gestation is longer than cattle gestation and is a common wrong option; low-heritability traits need progeny testing rather than mass selection; buffalo show silent heat, so AI depends on careful detection.