Maximizing genetic response in crossbreds using both purebred and crossbred information

Abstract

A combined crossbred and purebred selection (CCPS) method, i.e. using crossbred and purebred information, was proposed to achieve genetic response in crossbred animals. Selection index theory was applied to establish a CCPS index. The CCPS was compared with pure-line selection (PLS) and crossbred selection (CS) methods. The genetic correlation between purebred and crossbred performance (r_pc) and crossbred heritability (h_c²) are crucial factors in the comparison. The CCPS is always better than PLS or CS when a fixed number of purebred progeny is tested. With a fixed total number of purebred and crossbred tested progeny, CCPS is only worse than PLS for very high values of rpc (>0·8). Superiority of CCPS over PLS increases and over CS decreases with decreasing r_pc. The larger h_c²is, relative to purebred heritability (h_c²the more response CS and CCPS will achieve. The robustness of CCPS against inappropriate assumptions on r_pcand h_c²values was investigated. The expected response is always an overestimate, and the actual response is smaller than the optimal response when r_pcis assumed one but the true r_pcis smaller. The difference between actual and optimal response increases as r_pcdecreases but it is small for large r_pcvalues (e.g. 0·7). The expected response is smaller than the actual response when r_pcis large and h_c²> h_p²Finally, the actual response to CCPS is larger than the optimal response to PLS for positive values for r_pc. The main conclusions are: (1) CCPS method is optimal for obtaining genetic response in crossbreds; and (2) CCPS with inappropriate assumptions on r_pcand h_c²values (e.g. recognizing crossbreds as purebreds) achieves more genetic response than PLS for common values of r_pcand crossbred heritability.