Answer Happy

Slim Maverick, Ace's brother, runs commercial cattle just south of Ace's place. Slim wants to improve the probability of conception (PC) in his year- ling heifers. But conception is an all-or-none threshold trait for which Slim can achieve little selection intensity. The bulls that Slim buys have EPDS for scrotal circumference (SC), a trait known to be related to heifer conception rate. Slim 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 ge- netic parameters have been estimated for these traits: hpc = .10 hc=.5 PPC = 46 PSC = 2.0 cm BVSC BV PC Assume: Slim breeds all his heifers and keeps 40% for replacements. Typical heifer conception rate is 70%. = .25 The bulls that Slim buys represent the equivalent of the top 5% of his herd for scrotal circumference. Accuracy values for scrotal circumference EPDs average .9. Lm = L = 5 years a. Calculate annual selection response in probability of heifer conception us- ing strategy 1. b. Calculate annual selection response in probability of heifer conception us- ing strategy 2. c. Which strategy works better? Why?