By Rogers, G. W., Journal of Dairy Science, 1991
Description
Milk yield (MY), somatic cell count (SCC), udder depth (UD), teat placement (TP) and foot angle (FA) were evaluated in an index (sire index with 50 daughters) to improve an aggregate genotype, which included MY, mastitis, milking labour and laminitis. Parameters and economic values were taken from the literature if available. Sensitivity analyses were conducted for various parameters. Correlations between the index and aggregate genotype, responses in the aggregate genotype, and standardized index coeff. (b-values) were calculated for full and reduced indices (MY always included). Selection on MY, SCC, UD, TP and FA would improve efficiency of response by 2-3% over selection on MY alone. Most improvement in efficiency over selection on MY alone came from adding SCC and/or UD. Undesirable responses in mastitis were reduced when SCC, UD and/or TP were added to the index. Standardized index coeff. for MY were 3 to 4 times the sum of the standardized coeff. for SCC, UD, TP and FA when all were included in the index. Index coeff. were always negative for SCC, and positive for UD, TP and FA
Milk yield (MY), somatic cell count (SCC), udder depth (UD), teat placement (TP) and foot angle (FA) were evaluated in an index (sire index with 50 daughters) to improve an aggregate genotype, which included MY, mastitis, milking labour and laminitis. Parameters and economic values were taken from the literature if available. Sensitivity analyses were conducted for various parameters. Correlations between the index and aggregate genotype, responses in the aggregate genotype, and standardized index coeff. (b-values) were calculated for full and reduced indices (MY always included). Selection on MY, SCC, UD, TP and FA would improve efficiency of response by 2-3% over selection on MY alone. Most improvement in efficiency over selection on MY alone came from adding SCC and/or UD. Undesirable responses in mastitis were reduced when SCC, UD and/or TP were added to the index. Standardized index coeff. for MY were 3 to 4 times the sum of the standardized coeff. for SCC, UD, TP and FA when all were included in the index. Index coeff. were always negative for SCC, and positive for UD, TP and FA
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