Abstract:
The widespread use of artificial insemination in the pig industry has provided breeders access to genetic material from superior boars from around the world. Selection of parent stock is based on estimated breeding values (EBVs) which are regularly computed in all countries performing genetic evaluations. Application of EBV s, are restricted to the country of estimation for animals part of the genetic evaluation. In dairy cattle, conversion equations, and more recently Multiple Across Country Estimation (MACE), have successfully been applied for comparison of breeding values across countries. The purpose of this study was firstly to investigate estimation of conversion equations for South African, Canadian and USA breeding values of boars based on number born alive (NBA), 21 day litter weight (21DLWT), average daily gain (ADG), feed conversion ratio (FCR) and back fat thickness (BF) for Duroc, Landrace and Large White pigs. The analyses were based on data provided by the South African Stud Book Association. The correlations estimated for these traits highlighted several data restrictions such as differences in measurement of traits between the countries. Insufficient data further resulted in non-significant (P >0.05) correlations and accurate conversion equations could not be developed. The second phase of the study focused on the value of foreign sires in the South African pig industry by comparing the on-farm performances of progeny for average daily gain (ADG), feed conversion ratio (FCR) and back fat thickness (BF) form progeny sired by USA and Canadian born sires to the performance of progeny from local sires and to progeny with paternal USA grandsires (F1-US sires). The progeny analysed included Duroc, Landrace and Large White pigs. Sex differences were highly significant (P <0.0001) for all traits as males outperformed females. Farm differences were highly significant (P <0.0001) for all traits except Duroc BF (P <0.05). Due to large differences seen in progeny performances on farms in similar climatic regions, farm differences were expected to be due to management rather than environmental influences. The effect of country was significant (P <0.05) in all the models. However, although the USA-sired progeny performed better overall, the effect of country, as measured by a stepwise R2, was the smallest across all models except BF in the Landrace, with farm, sex and year-season contributing larger portions of the variation seen in the on-farm progeny performances. These results indicates limited superiority of imported semen with most of the variation attributed to differences in farm as explained by management.
