Genotype-environment interactions and genetic parameters in New Zealand Romney sheep : a thesis submitted for the degree of Doctor of Philosophy at Massey University, New Zealand

Performance records of 1,113 New Zealand Romney ewe hoggets from two subflocks maintained on control (CSR) and intensive (HSR) stocking rates were analysed. The data represented the progeny of 34 sires and were collected between 1967 and 1974 inclusive which covered four consecutive two-year sire periods. The traits investigated were hogget live-weight (HLW), greasy fleece weight (GFW), clean wool weight per unit area (WA), clean scoured yield (Y), staple length (SL), mean fibre diameter (MFD), standard deviation of the fibre diameter (SFD), quality number (QN), crimps per centimeter (CPC), total crimp number (TCN), character (CHG), tippiness (TG), handle (HG), lustre (LG), greasy colour (GCG), scoured colour (SCG), discoloured area (DAG), cotting (CG), cotted area (CAG) and soundness (SG). Stocking rate had significant effect on all the traits excepting MFD, SFD, TCN and HC. HSR depressed the traits investigated excepting Y, SFP, QN, CPC, HG, GCG, SCG, CG and CAG. Year effects except in DAG were an important source of variation. The influence of birth-rank except on HLW, SFD, CHG and HG was small. Stocking rate x year interactions except in CPC, TCN, CHG, TG, HG, GCG and CAG were important. Sire x stocking rate interactions were significant in HLW, MFD, SFD, TCN and GCG only, whereas sire x year interactions were significant in HLW, GFW, HG and SCG. Sire x stocking rate and sire x year interactions were included in different ways in some formulae for calculation of heritability estimates. These estimates were calculated from paternal half-sib analyses in CSR, HSR and combined data. The various estimates for the different traits were in the following ranges:- HLW 0.21 - 0.72, GFW 0.38 - 0.61, WA 0.31 - 0.49, Y 0.19 - 0.53, SL 0.54 - 0.63, MFD 0.34 - 0.87, SFD 0.35 - 0.66, QN 0.46 - 0.72, CPC 0.48 - 0.88, TCN 0.65 - 1.09, CHG 0.24 - 0.34, TG 0.13 - 0.27, HG 0.23 - 0.66, LG 0.32 - 0.42, GCG 0.22 - 0.44, SCG 0.10 - 0.39, DAG 0.04 - 0.21, CG 0.12 - 0.67, CAG 0.13 - 0.53, SG 0.00 - 0.22. No significant differences between the estimates in the two stocking rates except in CG and SG were observed. The relevance of these comparisons is discussed in terms of sire x stocking rate and sire x year interactions. Intra-trait genetic correlations between the two stocking rates were close to unity except in HLW (P<0.05); Y, SFD, GCG, SCG (0.05<P