02480naa a2200241 a 450000100080000000500110000800800410001910000130006024500530007326000090012652018760013565000160201165000210202765000100204865000250205865000140208365300270209765300140212470000170213870000150215570000190217077300490218915310912022-04-13       2002    bl uuuu     u00u1 u    #d1 aSIMM, G.  aResponses to selection for lean growth in sheep.  c2002  aThis paper reports the selection responses achieved, and related results, folIowing 9 years of index selection for lean growth in Suffolk sheep. The breeding goal of the index used comprised carcass lean weight and carcass fat weight at a constant age, with relative economic values of + 3 and -1 per kg. The selection criteria were live weight (LWT), ultrasonic fat depth (UFD) and ultrasonic muscle depth (UMD) adjusted to a constant age of 150 days. By year 9,  responses in LWT, UFD and UMD in both sexes, as judged by the divergence between selection and control line  performance, amounted to 4.88 kg, -1.1 mm and 2.8 mm respectively; these responses are between 7 and 15% of the overaIl means of the traits concerned. Although selection was originalIy on index scores based on phenotypic records, the retrospective analyses reported here used the mixed model applications of residual maximum likelihood to estimate parameters and best linear unbiased prediction to predict breeding values. The statistical model comprised fixed effects plus random effects accounting for direct additive, maternal additive and temporary environmental variation. Estimated genetic trendl; obtained by regressing estimated breeding values on year of birth were similar to annual responses estimated by comparing selection and control line means. Estimates of direct  heritabí/íties were 0.054,0.177,0.286, 0.561 and 0.410 for birth weight (BWT), weaning weight (WWT), LWT, UFD and UMD respectively. Corresponding estimates of maternal heritabilities were 0.287, 0.205, 0.160, 0.083  and 0.164. Phenotypic correlations between alI pairs of traits were positive and usualIy moderately high. There were Ilow negative direct additive correlations between BWT and WWT, and between BWT and LWT, but higher positive maternal additive correlations between alI other pairs of weight traits.  aCrescimento  aGenética Animal  aOvino  aParâmetro Genético  aSeleção  aMelhoramento genético  aUltra-som1 aLEWIS, R. M.1 aGRUNDY, B.1 aDINGWAL, W. S.  tAnimal Sciencegv. 74, pt 1, p. 39-50, 2002.