Increasing accuracy in estimation of economic values for resistance to gastrointestinal helminths in meat sheep

The impact of utilising different indices and numbers of index traits in estimation of economic values (EVs) for resistance to gastrointestinal (GI) helminths were investigated. Seven indices based on yearling weight (YW), litter size (LS) and ewe live weight (ELW) were evaluated under a scheme that considered individual records (Scheme 1) and one that utilised extra information from individual's relatives (Scheme 2). Under an objective where index response in YW was maximum (R(IYW) = max) economic values were US$ 0.00, 0.41, 0.35 and 1.58 in scheme 1 and -0.07, 0.25, -1.10 and -0.02 in scheme 2 for indexes 1, 2, 3 and 4 respectively. In the determining the effect of the number of index traits on the estimates of EVs, calculations were done for five breeding objectives. Eight scenarios (indices) under each objective that differed in the number of traits considered were evaluated. In all scenarios, EVs under R(IYW) = max were positive and were US$ 0.00, 0.79, 2.68, 2.66, 2.66, 2.62, 2.44 and 2.62 for scenarios 1-8 respectively. Generally, economic value estimates varied across breeding schemes and objectives.