Sex and age effects on genetic parameters for wool production and qualities.
Heritabilities and genetic correlations were estimated for New Zealand Romney sheep from within the selected and control lines of a 25-year selection experiment for greasy hogget fleece weight and yearling body weight. Average repeatability of clean fleece weight in 1- to 5 year-old ewes was 0.56, 25% higher than the average heritability of 0.44. The average genetic correlation among measurements at different ages was 0.89. Sexual dichotomy in the relative predictive power of hogget records was most apparent for greasy and clean fleece weights but was evident to some degree for bulk and brightness as well, due mainly to lower heritabilities in male compared with female hoggets. Average coheritability of greasy hogget with adult clean fleece weight was 25% lower for male (0.26) than for female (0.35) hoggets, in this case because of a lower genetic correlation (0.69 vs. 0.81) and lower heritability (0.33 vs. 0.43). A repeatability model seemed an adequate approximation for the estimation of breeding merit for most wool quality traits studied, but not for lifetime wool production.