Breeding objectives and selection indices for New Zealand pig improvement

The breeding goal or objective for within‐breed genetic improvement of pigs is defined here as increasing $ net income/kg carcass. The important animal traits which contributed to genetic differences in this objective are defined as feed conversion ratio (FCR), carcass grading profile (FAT), average daily gain (ADG), and carcass weight (CW). These traits were assigned values (conventionally called economic values) according to their potential contribution to variability in the objective (H). The four traits were combined non‐linearly as follows: The potential variability available was indicated by σ H which, from current New Zealand data, had a value of $0.041/kg carcass (=$2.47 per pig). Four linear selection indices were used as predictors of H, and they consisted of combinations of easily obtainable measurements. The most accurate selection index considered was a combination of measurements of FCR, three separate fat depths, and ADG, and had correlation with H of 0.665. Using this index the range of potential variability measurable in breeding stock was $9.84 per pig. The simplest combination used as an index (i.e., FAT and ADG) had a correlation with H of 0.569. In the objective FCR was expected to contribute 61.4% of the change in $/kg carcass, FAT being next important (30.6%). Using representative pig population parameters, annual genetic progress in boar breeding herds (and the herds which they supply with boars) could be about $0.020/kg carcass or $1.23 per pig.