The effect of using different culling regimens on genetic response with two-trait, two-stage selection in a nucleus broiler stock

Stochastic simulation was used to study the effect on genetic response and inbreeding of various two-stage two-trait culling strategies. Four differen t parameter sets were considered for the two traits, BW and egg number. Sel ection of replacement animals was based on animal model best linear unbiase d prediction (BLUP) to obtain estimated breeding values (EBV) at the second stage. Culling at Stage 1 was based on either animal model BLUP or phenoty pes, and information from culled animals was either available or not availa ble for calculation of second stage EBV. Besides founder individuals, six d iscrete generations were considered. Culling based on BLUP of two traits at Stage 1 produced higher response than culling on phenotypic evaluations. I t was found that culling based on phenotypic evaluation and not carrying in formation to the second stage reduce rates of response by 9 to 17% and prod uced inbreeding higher than or close to that of BLUP selection. This study clearly shows that a double penalty of less response and higher inbreeding is generally paid for not using all information. Optimum selection schemes will depend on relative costs and benefits of collecting and processing the extra information required for full BLUP selection schemes.