Part A: 14 marks
You are wishing to breed sheep for increased fleece weight. Fleece weight is measured annually, beginning at 12 months of age. Heritability for fleece weight is 31%, repeatability is 50% and genetic standard deviation is 0.4 kg.
The ewe flock is 1000 ewes, which can lamb first as hoggets (1 year of age), and have a total of 5 litters. Assume no losses of ewes between first and last litter. Lambing percentage is 125% and the mating ratio is 1:100. Rams are kept for 2 seasons, and must be at least 2 years old before they have progeny.
The following selection strategies are being considered:
i. 1 record on each individual
ii. 3 records on each individual
iii. 3 records on the males, one record on the females
iv. 1 record on the individual for males, randomly selecting females
v. 4 records on the dams of the individuals (note that rTI in this case is half the value for rTI for multiple own records)
vi. 5 progeny records on the males, randomly selecting the females. Progeny testing would be conducted outside the nucleus flock.
vii. 50 progeny records on the males, randomly selecting the females. Progeny testing would be conducted outside the nucleus flock.
Each record for fleece weight costs $4.
1. Draw a timetable for measurement, selection and offspring birth for each selection strategy.
2. For each possible selection strategy, calculate the rate of genetic gain for fleece weight.
3. What is the annual cost of measurement in each scenario?
4. Assuming you supply rams to be used over 20,000 commercial ewes, and that fleece is worth $20/kg, what selection strategy provides the best return on investment for the industry?
5. Imagine a series of genetic markers for fleece weight were discovered, that allow 100% accuracy for prediction of genetic merit on a sample collected from an individual at birth. What would be the possible rate of genetic gain if this technology was used instead of the strategy you identified in question 4? What is the maximum amount it would be worth paying for this test?
Part B: 6 marks
You are breeding bulls for short gestation length for use over late-calving dairy cows. Gestation length is 21% heritable and 34% repeatable.
You have the following bulls available for selection:
Fury’s gestation length was 276 days.
Patter’s gestation length was not recorded, but his 27 calves had a mean gestation length of 276 days.
Boomer’s sire’s gestation length was 276 days, but Boomer’s gestation length was not recorded.
Snatcher is Fury’s son, and Snatcher also had a 276-day gestation.
The population mean for gestation length is 282 days.
1. Calculate the breeding value for gestation length for each of Fury, Patter, Boomer and Snatcher.
2. A cow produces $8.50 worth of milk per day. New Zealand dairy herds are dried off on a fixed date, regardless of calving date, so for every day earlier the cow calves, she produces an extra $8.50 worth of milk. A lactating cow eats approximately $3 worth of feed per day more than a non-lactating cow. A dairy farmer expected 40 cows to conceive to each bull she puts out in her herd.
How much extra could she pay for Boomer compared with an average bull (with a breeding value of 0)?
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