Impact of the relative emphasis on growth and litter size in a maternal index for selecting sheep

Selection responses in sheep were predicted for a maternal index with different emphases on litter size and lamb growth to assess the need for correct economic values. Ratios of economic values for litter size relative to growth from 2 to 200 were tested. Genetic change per generation in market weight of lambs (1.75 to 0.03 kg) was sensitive, but genetic change per generation in number of lambs born (0.11 to 0.17) was practically independent of the economic values applied in the index.