RELATIVE MERIT OF SIB VERSUS OWN PERFORMANCE IN SELECTION FOR LEAN MEAT PRODUCTION IN SWINE

The relative selection efficiency (RSE) of direct selection for a trait of basic interest and indirect selection on an alternate trait was examined with consideration given to several population sizes, selection intensities and genetic parameters. Slaughter of litter samples resulting in a reduction of the population available for selection was associated with the direct but not the indirect selection procedure. Values of RSE increased with increasing values of the genetic correlation, but for any given value of the genetic correlation, RSE was inversely related to the heritability of the basic trait. Population size was important only for herds comprising fewer than 10 breeding females.Using predicted percent yield of lean cuts, (A), as the trait for direct selection with [Formula: see text] of 0.2, 0.3 and 0.4 and the live back fat probe, (B), as the trait for indirect selection, with [Formula: see text] and assuming a genetic correlaton between A and B of 0.6, it was demonstrated that, respectively 38, 19 and 9% faster genetic gains in the basic trait accrued from indirect as compared with direct selection. It is suggested that the inherent reduction in population size, coupled with other practical aspects associated with carcass testing, might make the indirect selection method preferable even when RSE is less than unity.