Effect of lower-energy, higher-fiber diets on pigs divergently selected for residual feed intake when fed higher-energy, lower-fiber diets

Authors: MAUCH, EMILY - Iowa State University; YOUNG, JENNIFER - North Dakota State University; SERAO, NICHOLAS - Iowa Association Of Municipal Utilities; HSU, LI - University Of Washington; PATIENCE, JOHN - Iowa State University; Kerr, Brian; WEBER, TOM - Kalmbach Feeds; GABLER, NICHOLAS - Iowa State University; DEKKERS, JACK - Iowa State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2018
Publication Date: 4/11/2018
Citation: Mauch, E.D., Young, J.M., Serao, N.V.L., Hsu, W.L., Patience, J.F., Kerr, B.J., Weber, T.E., Gabler, N.K., Dekkers, J.C.M. 2018. Effect of lower-energy, higher-fiber diets on pigs divergently selected for residual feed intake when fed higher-energy, lower-fiber diets. Journal of Animal Science. 96:1221-1236. https://doi.org/10.1093/jas/sky065.
DOI: https://doi.org/10.1093/jas/sky065

Interpretive Summary: Feed costs account for over half of total production costs in swine production, which has resulted in increased interest in more economical feedstuffs and trying to improve the genetic capacity for improved feed efficiency. One approach to mitigate high feed costs has been to substitute lower energy and higher fiber feedstuffs in place of corn and soybean meal, this however, may reduce pig growth and feed efficiency. Another approach used to reduce feed costs is genetic selection for more feed efficient pigs. The aim of the research herein was to assess the effect of lower-quality feedstuffs, particularly those lower in energy and higher in fiber, on pigs that have been divergently selected for improved feed efficiency when fed a standard high-energy diet. The results of this study show that feeding low-energy, high-fiber diets to pigs resulted in decreased pig performance regardless of genetic selection, but the reduction was less than typically noted between these two lines of pigs when fed a higher-energy, low-fiber diet. Research results described in this report suggest that for swine producers to capitalize on the genetic gain made by breeding companies in terms of feed efficiency, it appears a similar diet fed during genetic selection should be fed to pigs to observe these differences. On the other hand, breeding companies may want to alter the diet fed during selection to a diet more similar to that fed in commercial production in order to maximize the genetic gain achieved at the production level.

Technical Abstract: Residual feed intake (RFI) is the amount by which the observed and predicted feed intakes differ, given growth and maintenance requirements of an individual animal. In purebred Yorkshire pigs, divergent selection for increased (Low RFI) and decreased (High RFI) feed efficiency was carried out over 10 generations (G) while feeding a corn and soybean-meal based diet. Utilizing these divergent RFI lines, the impact of lower-quality feedstuffs on performance and growth, diet digestibility, and genetic parameter estimates and response to selection were assessed. In G8 to 10, barrows and gilts (n = 649) of the Low and High RFI lines were fed 2 diets that were formulated to represent a commercial, standard higher-energy, lower-fiber diet (HELF) and a diet incorporating co-products that was lower in energy and higher in fiber (LEHF). The diets differed by 14% in ME and by 175% in NDF. In general, the LEHF diet reduced performance of both RFI lines. When fed the HELF diet, the Low RFI pigs had lower ADFI and energy intake, ADG, and backfat depth (BF); similar loin muscle area (LMA); and increased feed efficiency (i.e. increased G:F and lower RFI) compared to the High RFI line. These patterns of line differences by trait were still present under the LEHF diet but differences were reduced compared to the HELF diet. Apparent total tract digestibility (ATTD) of the HELF and LEHF diets was assessed in 116 barrows and gilts from G8 of both RFI lines. When fed the HELF diet, ATTD of DM, GE, N, and NDF were similar between RFI lines (P > 0.27), but when fed the LEHF diet, the Low RFI pigs had greater digestibility of these components compared to the High RFI line (P < 0.04). To measure response to selection for RFI and estimate genetic parameters between diets, observations from all 10 generations were utilized (HELF, n = 2,310; LEHF, n = 317). Heritability estimates of performance traits ranged from 0.21 to 0.63 and genetic correlations of traits between diets were high and positive, ranging from 0.87 (RFI) to 0.99 (BF and LMA). By G10, RFI in the Low RFI line was 3.86 and 1.50 genetic SD lower than in the High RFI line when fed the HELF and LEHF diets, respectively. Taken together, the results of this study demonstrate that responses to selection for feed efficiency when fed a HELF diet are not fully realized when pigs are fed an extremely LEHF diet. Thus, feeding diets that differ from those used for selection may not maximize genetic potential for feed efficiency.