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Merino yearling records from 1988 to 1992 birth years in ultrafine wool selection and random control flocks at Tara Hills High Country Station, New Zealand were analysed for live weight, fleece weight and wool characteristics. Estimates of heritability, genetic and phenotypic correlations among traits using REML methods are presented. Heritabilities (h 2 ) of birth, weaning, autumn, spring and summer live weights and greasy and clean fleece weights were estimated as being 0·35were found to be high among the live weights but low to moderate among fleece weight and wool characteristics. Heritability estimates of fibre diameter, fibre diameter variation and staple length were found to be higher in New Zealand fine wool Merinos than most of those reported in the literature. The results indicate that selection for reduced fibre diameter will have little effect on other major production traits such as live weight and fleece weight.

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This investigation examined an alternative option to selection within breed for improving wool bulk by crossbreeding traditional long-wooled sheep with introduced Texels. A flock of bulky high-fleece-weight sheep was established by crossbreeding high-fleece-weight-selected (HF) Romney ewes with bulky-wooled Texel rams. A local Romney control flock (LC) was formed at the same time. These two flocks were grazed together at the Gore Research Station. The HF flock established earlier and its random control (RC) flock were both located at another site (Woodlands Research Station), and were also included in the comparison through common RC-LC sire linkages. The Texel x Romney (TR) flock had significantly (P < 0.01) higher liveweights and fleece weights than its LC. The TR flock was 7 and 5% heavier than the HF flock for birth and weaning weight, and significantly (P < 0.01) heavier for spring liveweight and 16-month liveweight at 11 and 9% respectively. Wool return per head predicted for the TR flock was 10% higher than for HF Romney at 12-month-old shearing. Fleece characteristics, namely bulk (+27%) and brightness (+3%) were significantly (P < 0.01) improved for TR compared with HF Romney, whereas yield and A94072 yellowness were similar in both flocks. The effects of sex, birth/rearing ranks, and age of dams were more pronounced for liveweight than for fleece weight. Phenotypic correlations were significantly positive for spring liveweight with 16-month (2 tooth) liveweight (P < 0.001), for hogget greasy fleece with 16-month greasy fleece weight (P < 0.001), for all liveweights with all fleece weights (P < 0.05), and for yield with brightness (P < 0.01). The study highlighted that crossbreeding HF Romney (and/or screened) ewes with bulky Texel sires can improve wool bulk without substantially losing fleece weight.

The reproducibility and bias associated with the measurement of mean fibre diameter of fleece samples was evaluated for five methods of measurement. The instruments used were the airflow (AF), sonic fineness tester (SFT), liquid scintillation spectrometer (LSS), fibre fineness distribution analyser (FFDA), and projection microscope (PM). Duplicate fleece samples from 48 sheep within each of the Merino, Corriedale, Perendale, Romney, and Coopworth breeds were measured using each method. Overall mean diameters for these breeds were 23.0, 30.1, 37.0, 38.0, and 38.3 Itm, respectively. The variability of diameter measurement (betweenduplicate, within-sample variance) was 0.06,0.09, 0.48,0.64, and 0.96 Itm 2 for AF, SFT, LSS, FFDA, and PM methods, respectively. The deviation of each method from the mean of all five methods was examined. AF and SFT methods agreed closely and FFDA gave results similar to those of AF and SFT. These three methods gave lower readings than LSS and PM, with the negative bias becoming more pronounced as diameter increased. Relative to PM, LSS gave lower readings at fine diameters and higher readings at coarse diameters.