Maximizing genetic response in crossbreds using both purebred and crossbred information
AbstractA 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 (rpc) and crossbred heritability (hc2) 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 rpc. The larger hc2 is, relative to purebred heritability (hc2 the more response CS and CCPS will achieve. The robustness of CCPS against inappropriate assumptions on rpc and hc2 values was investigated. The expected response is always an overestimate, and the actual response is smaller than the optimal response when rpc is assumed one but the true rpc is smaller. The difference between actual and optimal response increases as rpc decreases but it is small for large rpc values (e.g. <3% for rpc >0·7). The expected response is smaller than the actual response when rpc is large and hc2> hp2 Finally, the actual response to CCPS is larger than the optimal response to PLS for positive values for rpc. The main conclusions are: (1) CCPS method is optimal for obtaining genetic response in crossbreds; and (2) CCPS with inappropriate assumptions on rpc and hc2 values (e.g. recognizing crossbreds as purebreds) achieves more genetic response than PLS for common values of rpc and crossbred heritability.