Multi-trait selection indexes for sustainable UK hill sheep production

Three selection indexes for the UK hill sheep sector are derived to suit th e extremes of hill production systems. These are: (i) intensive, where all surplus lambs not required for breeding are finished for slaughter, (ii) ex tensive, where all surplus 'store' lambs are sold to other farmers for fini shing, and (iii) semi-intensive, which is intermediate between the two extr emes, i.e. farms finish some lambs for slaughter and sell others as store l ambs. Parameters for 12 breeding goal and index traits were estimated using a total of 3962 lamb records and 5944 ewe lambing records from Scottish Bl ackface sheep on two Scottish Agricultural College experimental hill farms. The breeding goal comprised carcass, maternal and survival traits. The eva luation of these indexes showed that improvements in maternal traits are po ssible, along with more modest improvements in carcass quality traits. Resp onses to selection are expected to be lower for the extensive farm in gener al, compared with the intensive farm. Evaluations of alternative indexes sh ow that an index using measurements of fat and muscle on ewes rather than o n lambs may be more cost-effective to implement in practice, compared with the original index, although this change results in a higher (i.e. undesira ble) gain in mature size. Sensitivity analyses showed that in general, the indexes are robust to changes in economic values and to changes in heritabi lity estimates.