Broadening breeding objectives for maternal and terminal sheep

Economic values have been calculated and selection indexes defined for maternal and terminal traits for sheep in New Zealand. Using trait-by-trait bio-economic models, economic weights (EW), in $ per lamb born per genetic standard deviation in the trait for maternal and terminal sire performance traits respectively, have been calculated. The EW after accounting for the genetic standard deviation for the traits in the base maternal index were; $1.49 for weaning weight direct, $0.93 for weaning weight maternal, $2.86 for carcase weight, −$1.54 for ewe mature weight, $0.14 for lamb fleece weight, $0.23 for one-year-old replacement fleece weight, $0.77 for ewe fleece weight, and $2.80 for number of lambs born. For those traits not in the base maternal index, EWs ranged from $0 to $0.66 for lean and fat yield traits, $0.53 to $1.12 for one-year-old dam reproductive performance traits, $2.34 to $2.58 for lamb survival traits, −$1.11 to −$0.94 for faecal egg count traits, −$0.38 to $0.09 for resilience traits, −$0.40 to −$0.27 for dag score traits, and −$0.91 to −$0.35 for facial eczema traits. The EW for twinning rate was $1.45. For traits in the base terminal index trait EWs were $1.07 for weaning weight direct, $2.14 for carcase weight, $0.21 for shoulder lean yield, $0.52 for leg lean yield, $0.50 for loin lean yield, −$3.74 for fat yield, and $1.83 for lamb survival direct. For traits not in the base terminal index, faecal egg count EWs ranged from −$0.79 to −$0.69, and the EW for lamb dag score was −$0.11. The inclusion of a wide range of traits in indexes for terminal and maternal sires spanning production, lambing, maternal, and health traits increases the scope by which breeders and commercial farmers alike can assess the suitability of selection candidates for target end use of the progeny. Although the genetic variation in merit of additional traits when compared to those in the base indexes does not have such a large impact as growth and reproduction (maternal) and yield (terminal), their inclusion represents an opportunity for farmers to further optimise animal performance and to define a market difference for the genotype they are developing with their breeding programme.