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Effect of Low Energy, High Fiber Diets on Divergent Residual Feed Intake Lines in Swine
Residual feed intake (RFI), a measure of feed efficiency, is the difference between an individual’s observed and expected feed intake based upon growth and maintenance requirements. Barrows and gilts from generation 8 (G8, n=168) and 9 (G9, n=166) of the Iowa State RFI swine lines, which were selected for high (HRFI) and low RFI (LRFI) under a standard corn-soybean diet, were utilized to evaluate their performance on a low energy, high fiber diet (LEHF) compared to a traditional corn-soybean diet that was high energy, low fiber (HELF), in two replicates. Littermate gilts and barrows from the two lines were split between the two diets and grown out from ~40 to 118 kg in 12 pens with a single-space electronic feeder (FIRE©) to record individual feed intake. Body weight was recorded every two weeks and ultrasound scans for backfat depth (BF) and loin muscle area (LMA) were taken at off-test. Average daily feed intake (ADFI), average daily gain (ADG), gain to feed ratio (G:F), BF and LMA for the test period 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 BF (G8: P<0.01, G9: P<0.1), and greater G:F (P<0.05) and LMA (G8: P<0.01, G9: P=0.45). The effect of the LEHF diet differed between generations and lines. Compared to the HELF diet, pigs on the LEHF diet had similar ADFI in G8 (P=0.37) but greater ADFI in G9 (P<0.01), lower ADG, BF, and G:F (P<0.03), and greater LMA in G8 (P<0.01) but lower LMA in G9 (P<0.01). Within line, the LEHF diet resulted in lower ADG (P<0.01), lower G:F (P<0.01 except G8 HRFI: P=0.13), and BF (P<0.0001 except G9 HRFI: P<0.1). Under the LEHF diet, compared to the HRFI line, the LRFI line had similar ADG (P>0.05), lower ADFI (G8: P=0.14, G9: P=0.03) and BF (G8: P<0.1, G9: P<0.01), and greater LMA (G8: P<0.05, G9: P<0.1). For G:F, the LRFI line had significantly greater feed efficiency than the HRFI line in G9 (P<0.01) but only marginally in G8 (P=0.06). In conclusion, response to selection for feed efficiency under standard corn-soybean diets may not result in similar increases in feed efficiency under a LEHF diet although selected pigs are still expected to be at least as efficient as non-efficient pigs. Funding provided by AFRI-NIFA grant #2011-68004-30336.
Keywords: RFI, feed efficiency, swine