Influence of sire breed, protein supplementation and gender on wool spinning fineness in first-cross Merino lambs

Our objectives were to evaluate the effects of sire breed, type of protein supplement, level of supplementation and sex on wool spinning fineness (SF), its correlations with other wool characteristics and prediction accuracy in F1 Merino crossbred lambs. Texel, Coopworth, White Suffolk, East Friesian and Dorset rams were mated with 500 purebred Merino dams at a ratio of 1:100 in separate paddocks within a single management system. The F1 progeny were raised on ryegrass pasture until weaning, before forty lambs were randomly allocated to treatments in a 5 x 2 x 2 x 2 factorial experimental design representing 5 sire breeds, 2 supplementary feeds (canola or lupins), 2 levels of supplementation (1% or 2% of liveweight) and sex (wethers or ewes). Lambs were supplemented for six weeks after an initial three weeks of adjustment, wool sampled at the commencement and conclusion of the feeding trial and analyzed for SF, mean fibre diameter (FD), coefficient of variation (CV), standard deviation, comfort factor (CF), fibre curvature (CURV), and clean fleece yield. Data were analyzed using mixed linear model procedures with sire fitted as a random effect, and sire breed, sex, supplementary feed type, level of supplementation and their second-order interactions as fixed effects. Sire breed (P<0.001), sex (P<0.004), sire breed x level of supplementation (P<0.004), and sire breed x sex (P<0.019) interactions significantly influenced SF. SF ranged from 22.7 ± 0.2µm in White Suffolk-sired lambs to 25.1 ± 0.2µm in East Friesian crossbred lambs. Ewes had higher SF than wethers. There were significant (P<0.001) correlations between SF and FD (0.93), CV (0.40), CF (-0.94) and CURV (-0.12). Its strong relationship with other wool quality traits enabled accurate predictions explaining up to about 93% of the observed variation. The interactions between sire breed genetics and nutrition will have an impact on the choices that dual-purpose sheep producers make when selecting sire breeds and protein supplementary feed levels to achieve optimal wool spinning fineness at the farmgate level. This will facilitate selective breeding programs being able to better account for SF and its interactions with other wool characteristics.