Differences in feed efficiency during the nursery phase of pigs divergently selected for residual feed intake during grow-finish phase

Abstract Text: Feed is the largest variable cost in swine production. Since 2001, purebred Yorkshire pigs at Iowa State University have been divergently selected for Residual Feed Intake (RFI) during the grow-finish phase, with one line selected for increased feed efficiency (Low RFI line) and the other line selected for decreased feed efficiency (High RFI line). The performance of the RFI lines during the grow-finish phase has been extensively investigated, but little is known about these selection lines during the nursery phase. Therefore, the objective of the study was to evaluate the effects of selection for RFI in the grow-finish phase on feed efficiency during the nursery growth phase. Piglets from generation 10 of the RFI lines were evaluated for differences in average daily feed intake (ADFI), average daily gain (ADG), and feed conversion rate (FCR) during the nursery phase. Weaning-age piglets (27±3 days) were group penned by litter (Low RFI: n=26; High RFI: n=16), with 9.5±2.4 and 9.0±2.6 piglets per pen for Low and High RFI, respectively, and pen feed intake was recorded for approximately 39 days. Weights were collected on all piglets (n=394) at the beginning and end of the test period. ADFI, ADG and FCR were calculated on a pen basis. Statistical analyses were run in SAS using a mixed procedure with a fixed effect of line and weighted by number of piglets per pen. Results showed that Low RFI litters consumed less feed (P<0.0001) and gained less weight on average (P=0.02) than High RFI litters during the nursery period. Low RFI litters also had a lower FCR than the High RFI litters (P<0.001). The average ADFI was 0.54 and 0.67 kg/day for the Low RFI and High RFI lines, respectively. Average ADG estimates were 0.39 kg/day for the Low RFI line and 0.43 kg/day for the High RFI line. The Low RFI litters had an average FCR of 1.39 (kg feed/kg gain) compared to 1.58 for the High RFI line. In conclusion, piglets selected for increased feed efficiency based on RFI during the grow-finish phase also consumed less feed and had increased feed efficiency during the nursery phase. However, similar to the grow-finish phase, growth rate was also slightly lower for the low RFI line in the nursery phase. A second replicate to validate these findings is currently underway. Funding provided by AFRI-NIFA grant #2011-68004-30336.

Keywords: Feed Intake, Nursery Piglets, RFI