MULTISTAGE SELECTION IN A CLOSED DAM LINE OF PIGS

The objective of this study was to optimize multi-stage selection in closed dam lines of pig breeding programmes. A stochastic simulation model was used to study the effects of time of selection on the accuracy of selection for production and reproduction traits, response to selection and rate of inbreeding. Traits were assumed to be affected by many unlinked loci, each of small additive effect. First stage selection of boars was before the performance test. The proportion of boars selected in the first stage (p1) was varied between 100 and 25%. From p1 = 100% to p1 = 50%, the reduction in overall response was on average 3.5%, while from p1 = 50% to p1 = 25% the reduction was an additional 6%. The optimum of p1 depends on the costs for testing and on the size of the nucleus population relative to the total breeding pyramid. With a relatively large nucleus breeding herd, a low proportion of boars tested can be justified. Breeding schemes with sequential culling of sows (weaned sows competing with replacement gilts) were compared to schemes without sequential culling (no genetic culling after weaning). Sequential culling gave on average 2β3% extra response. © 1990.