Genetic improvement of small ruminant local breeds with nucleus and inbreeding control : a simulation study

In small ruminant local breeds of Southern Europe genetic selection is often constrained by small population sizes, poor animal identification, inadequate animal performance and pedigree recording, and organizational shortcomings. Under these conditions nucleus breeding schemes can offer practical and cost effective solutions. The paper investigated genetic gain in stochastically simulated dairy small ruminant nuclei of 100, 200 and 400 females, supporting commercial populations from 500 to 5000 females. In the nucleus, a young sire selection scheme was used, with optimum contribution selection on a dairy trait, at an annual inbreeding rate of 0.3%, corresponding to a generation inbreeding rate of 0.001. Sires, both selected and not-select as sires of sires, after 1 year of use in the nucleus were utilized in the commercial population for one, or alternatively, 2 years. Annual genetic gain ranged from a minimum of 0.073 SD with 100 females nucleus supporting a commercial population of 500 females, to a maximum of 0.138 SD with a 400 females nucleus supporting a commercial population of 5000 females. Negligible differences in genetic gain were observed between nuclei and corresponding commercial populations. When sires were used for only 1 year in the commercial population, we observed 7.7 years of genetic lag with the nucleus, that increased to 8.2 years when sires were used for 2 years. Results showed that there are opportunities for selection even in populations of a few hundreds of females. Considering a specific breeds, or a specific farming area, a cost benefit analysis should be carried out to orientate the choice of nucleus size and strategy of use of sires.