Production and characteristics of wool from the hogget progeny of sheep intensively screened for fleece weight

A high fleece weight Romney ewe flock was established by selecting the top 0.6% on greasy weight (GFW) from 32,000 hoggets (average selection differential 40%). These ewes were mated in 1985 and 1986 by Romney rams with high positive deviations for GFW (selection differentials 48% in 1985 and 57% in 1986). Relative to random progeny, the high fleece weight progeny born in 1985 and 1986 had 0.66 kg (28%) and 0.36 kg (12%) higher mean GFWs, respectively. Estimates of realised heritability were 0.45 and 0.22 for the 1985 and 1986 born hoggets, respectively. Two sires used in 1985 had progeny distributions for GFW consistent with their having 1 copy of a single gene for GFW with an additive effect of approximately 1 kg. The single gene hypothesis is being examined by further progeny testing. From birth to hogget shearing the high fleece weight hoggets had a significantly higher live weight than the control hoggets. Fleeces from the high fleece weight and control hoggets did not differ in yield or brightness. The high fleece weight hoggets had greater staple length, tibre diameter and staple strength with lower bulk and greater yellowness. Estimates of the heritability of live weight, fleece weight and wool characteristics agreed with published estimates, as did estimated genetic correlations between GFW and other characteristics. The heritability of brightness was low.