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# Samantha, Josh's sister, runs commercial cattle just south of Josh's place.

Samantha, Josh's sister, runs commercial cattle just south of Josh's place. Samantha wants to improve the probability of conception (PC) in her yearling heifers, but conception is an all-or-none threshold trait for which Samantha can achieve little selection intensity. The bulls that Samantha buys have EPDs for scrotal circumference (SC), a trait known to be related to heifer conception rate. Samantha is contemplating two strategies: (1) practicing phenotypic selection for probability of conception by retaining only those heifers that conceive in their first season, and (2) selecting bulls for scrotal EPD. The following genetic parameters have been estimated for these traits:

h2???????? = 0.10 h2???????? = 0.50 ????P???????? = 0.46 ????P???????? = 2.0 cm

???? = 0.25 BV????????,BV????????

Assume:

Samantha breeds all her heifers and keeps 40% for replacements.

Typical heifer conception rate is 70%

The bulls that Samantha buys represent the equivalent of the top 5% of her herd for SC Accuracy values for SC EPDs average 0.90

Lm =Lf =5years

1. a) Calculate selection response in probability of heifer conception using strategy 1.
2. b) Calculate annual selection response in probability of heifer conception using strategy 2.
3. c) Which strategy works better? Why?

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