Genetics-nutrition interactions influencing wool spinning fineness in Australian crossbred sheep

Our objective in this study was to investigate the interactions between sire genetics, supplement and gender on spinning fineness (SF) in crossbred sheep either grazing or supplemented with dietary protein. Correlations between SF and other wool traits were also investigated. We utilized 5 sires (Texel, Coopworth, White Suffolk, East-Friesian and Dorset) and mated them with 500 Merino ewes at a ratio of 1:100 in individual paddocks. Five hundred of the F1 progeny were raised on rye grass until weaning at 12 weeks of age. Forty of the weaners with initial BW range of 23–31kg (average of 27 ± 3.2 kg) were subjected to a supplementary feeding trial that lasted for 6 weeks. They were randomly assigned to 4 treatment groups in a 5 × 2 × 2 × 2 factorial experimental design representing 5 sire breeds, 2 supplementary feeds (canola and lupins), 2 feeding levels (1 and 2% BW) and 2 sexes (ewes and wethers). SF of the wool was commercially measured at the Australian Wool Testing Authority. The data were statistically analyzed in SAS using MIXED models procedures with sire fitted as a random effect, while sire breed, supplement, level of supplementation and gender and their interactions were fitted as fixed effects. We found highly significant interactions between sire breed × level of feeding (P < 0.0043) and sire breed × gender (P < 0.019) on SF that ranged from 22.7 ± 0.16 microns in White Suffolk-sired progeny to 25.1 ± 0.21 in East-Friesian crosses. Coopworth-sired sheep supplemented with either canola or lupins at 1%BW recorded the highest spinning fineness. There were significant correlations between SF and wool fiber diameter (0.93), CV of fiber diameter (−0.40), wool curvature (−0.12) and wool yield (0.10). We concluded that the significant interactions between sire genetics and nutrition would impact on choices sheep farmers make in selecting sires and supplementary feeding levels to achieve desirable spinning fineness in their crossbreds. The correlations between spinning fineness and other wool traits should be taken into account when designing breeding programme