The Impact of Measuring Adult Fleece Traits With Genomic Selection on Economic Gain in Merino Selection Indexes

Stochastic simulation of a Merino sheep breeding program showed that measurement of adult fleece weight and fibre diameter, the two key adult production traits in Merino sheep, increased economic gain compared to measuring yearling expressions of the traits alone. Comparing three different selection indexes, gain increased in fleece weight by up to $1.10 per ewe per year over 10 years of selection, depending on the importance of the trait in the selection index. For fibre diameter the increase in gain was lower, to a maximum of $0.70 per ewe per year, because genetic correlations between yearling and adult performance are higher for fibre diameter. There was little benefit in multiple adult measurements of these traits, and since the Australian sheep industry's evaluation system already accommodates one adult measurement, most of the gains possible can be realised by breeders. Genomic selection of young rams resulted in further increases in gain when combined with adult measurements, particularly for fleece weight.