The Effect of Duration of Performance Test on Genetic Gain in Pigs

The problem of making the best use of a limited number of performance-testing places in the genetic improvement of pigs is examined. A model is given which balances the duration of testing and its effect on the accuracy of breeding value determination, against throughput and its effect on selection intensity. The model is a phenotypic one with easily estimated parameters in lieu of the more exact genetic one whose parameters are difficult to estimate. It is illustrated with data taken from the Queensland performance-testing station which evaluates boars on an index combining feed conversion ratio, growth rate and back fat. Full performance records from 26 to 90 kg liveweight are subdivided into four consecutive parts of equal weight interval. A range of feasible one and two stage selection schemes based on performance in one or more of these parts are compared. Relative to the present full testing scheme, the best single stage selection, that based on performance in the last two parts (3 + 4), is 14% more efficient. The best two stage selection scheme, also a 3 + 4 part test with a 50% culling at the end of part 3, is 19 0/, more efficient. Highest efficiencies are achieved by imposing a preliminary culling on growth rate before entry to the testing facility; e.g. selection of the best 25 % on part 3 growth rate followed by part 4 index selection within the test facility is 36% more efficient than the present full test. The limitations of the model and some practical problems of part testing schemes are discussed.