Selection and Breeding
Selection and breeding questions test whether you can choose an animal on records rather than looks, and whether you know how a chosen sire's genes reach the herd.
Selection on records
- Individual performance: 305-day milk yield, lactation length, fat and SNF per cent, age at first calving (target 24–30 months for crossbreds), calving interval (12–13 months), udder shape, teat placement, temperament.
- Pedigree: dam's and sire's records; useful for young animals with no record yet.
- Progeny testing: the most reliable test of a bull; a sire is judged by his daughters' yields. Slow and costly, so it is done by AI organisations and cooperatives.
- Selection index or BLUP: combines several traits with economic weights so that one trait is not chased at the cost of another.
Breeding systems
- Crossbreeding introduces exotic genes for yield; grading up raises the exotic share each generation; inbreeding increases uniformity but also inbreeding depression (fertility and vigour fall); outcrossing brings in unrelated blood.
- Avoid mating close relatives, keep a record for every service, and replace bulls periodically.
Artificial insemination
- Detect standing heat: restlessness, mucus, swollen vulva, standing to be mounted.
- Inseminate 12–18 hours after the onset of standing heat (AM–PM rule: heat in the morning, inseminate in the evening, and vice versa).
- Thaw frozen semen at 35–37 °C for 30–40 seconds, never above 40 °C; handle the straw by the cotton plug; deposit in the body of the uterus with a clean, lubricated gun.
Worked example
A cow is first seen standing at 6 a.m. and still standing at 10 a.m. Reasoning: onset is about 6 a.m., so the fertile window is 12–18 hours later, that is 6 p.m. to midnight. The inseminator should come in the evening of the same day; if she is off heat by then, inseminate early next morning and record the date, expecting calving about 280 days later.
Traps
- Selecting on coat colour or size alone.
- Using a single high daily yield instead of a 305-day record.
- Thawing semen in boiling or very hot water.
- Inseminating at the first sign of heat, or repeating blindly without checking for heat.
- Ignoring age at first calving, which drives lifetime profit.