Economic values for ewe prolificacy and lamb survival in New Zealand sheep

Economic values of changes in ewe prolificacy (EP) and two lamb survival traits were quantified for situations where each trait is changed by either quantitative genetic selection or the introduction of major genes for prolificacy. The economic value of EP was shown to be highly variable ($11.55 to $24.26 for lambs born per ewe lambing) across farm types. The economic values of the Booroola and Inverdale genes which affect EP also varied substantially from farm to farm. Values ranged from $5.24 to $16.23 per ewe lambing for a single allele of the Booroola gene and from $4.69 to $12.53 for a single allele of the Inverdale gene. The additional value of a second allele of the Booroola gene was relatively small or negative (-$0.76 to $2.29). The key factors influencing variability in economic values for EP were shown to be: 1, the current average level of flock prolificacy; 2, the relative survival rates of lambs born in alternative Litter sizes and 3; slaughter of lambs at fixed age versus fixed weight. The economic values for survival until 24 hours post-partum per lamb born and for survival from 24 hours post-partum until weaning per lamb alive at 24 hours were moderately variable across farm types ($0.22 to $0.28 and $0.31 to $0.36 respectively for an improvement of 1%). (C) 1999 Elsevier Science BN. All rights reserved.