Selection Strategies for Breeding Objectives in Growing Pigs

Abstract

Breeding objectives (BO) have been extended recently for sire lines in Australia to include average daily gain (ADG), backfat, post-weaning survival (PWS), loin weight and belly weight and some consideration of feed cost as either feed conversion ratio (FCR) or daily feed intake (DFI). This study evaluated six selection strategies for two BO that included either FCR or DFI using genetic parameters previously estimated for Australian populations. Response was expressed for one round of selection and a selection intensity of one which is similar to the annual genetic gain that can be achieved in practice. The predicted response in the BO with FCR varied from $3.61 to $4.59 per pig and from $3.48 to $4.00 for the BO with DFI. The lower response in the BO with DFI was partly due to unfavourable genetic association of DFI with ADG. Although PWS was the most important trait in the BO relative to the genetic variation, response in PWS was less than 0.0009 (or 0.09%) due to limited information available for selection candidates. No genetic associations between PWS and other traits were modelled because this information is currently lacking and response in PWS will depend on its genetic associations with other traits. Adding FCR records to the selection index increased response in the BO by 3.6% only because FCR has multiple favourable genetic associations with other traits. In contrast, selection response in DFI was achieved only when juvenile IGF1 and/or DFI were recorded. Therefore, considering feed costs in the BO with DFI is most effective if DFI is also recorded.