Effect of Low Energy, High Fiber Diets on Divergent Residual Feed Intake Lines in Swine

Barrows and gilts from generation 8 (G8, n=168) and 9 (G9, n=166) of the Iowa State residual feed intake (RFI) swine lines, which were selected for high (HRFI) and low RFI (LRFI) under a standard high energy, low fiber diet (HELF), were evaluated for performance on a low energy, high fiber diet (LEHF). Littermate gilts and barrows from the lines were split between diets into 12 pens and grown out from ~40 to 118 kg with individual feed intake recording. Average daily feed intake (ADFI), average daily gain (ADG), gain to feed ratio (G:F), off-test ultrasound backfat (BF) and loin muscle area (LMA) were evaluated. Consistent with previous studies under the HELF diet, compared to the HRFI line, the LRFI line had similar ADG (P>0.05), lower ADFI (G8: P<0.01, G9: P<0.1), and greater G:F (P<0.05). Compared to the HELF diet, the LEHF diet resulted in similar ADFI in G8 (P=0.37) but greater ADFI in G9 (P<0.01), and lower ADG and G:F (P<0.03). Within line, the LEHF diet resulted in lower ADG (P<0.01) and G:F (P<0.01 except G8 HRFI: P=0.13). Under the LEHF diet, compared to the HRFI line, the LRFI line had lower ADFI (G8: P=0.14, G9: P=0.03), and similar ADG and G:F (P>0.05). In conclusion, response to selection for feed efficiency under HELF diets may not result in similar increases in feed efficiency under a LEHF diet, although selected pigs are expected to be at least as efficient as non-selected pigs. Funding provided by AFRI-NIFA grant #2011-68004-30336.