2010-Bunter_et_al - Selection to reduce residual feed...

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K. L. Bunter, W. Cai, D. J. Johnston and J. C. M. Dekkers juvenile insulin-like growth factor-I concentration Selection to reduce residual feed intake in pigs produces a correlated response in doi: 10.2527/jas.2009-2445 originally published online February 12, 2010 2010, 88:1973-1981. J ANIM SCI http://jas.fass.org/content/88/6/1973 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on June 14, 2011 jas.fass.org Downloaded from
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ABSTRACT: Data from a selection experiment for residual feed intake (RFI) were used to estimate genetic correlations between measures of efficiency and perfor- mance traits with juvenile IGF-I, and to demonstrate direct and correlated responses to selection. The herita- bility of IGF-I was 0.28 ± 0.06 and genetic correlations of IGF-I with feed intake (0.26 ± 0.17), backfat (0.52 ± 0.11), and feed conversion ratio (0.78 ± 0.14) were moderate to large. The estimated and realized genetic correlations between RFI and IGF-I were 0.63 ± 0.15 and 0.84. In contrast, genetic correlations between IGF- I and lifetime or test period growth did not differ ( P > 0.05) significantly from zero (0.06 ± 0.14 and −0.19 ± 0.14). Selection for decreased RFI produced a direct response in RFI, as expected, and was accompanied by downward correlated responses in ADFI, juvenile IGF- I, backfat, and growth traits, listed in order of decreas- ing relative magnitude, and an increased loin muscle area. The correlated response in IGF-I to selection on RFI demonstrates that this physiological measure is ge- netically associated with efficiency, and is thus useful as an early information source to estimate genetic merit for efficiency before performance testing. Decreased ju- venile IGF-I is associated with leaner, more efficient animals. Key words: genetic parameter, heritability, insulin-like growth factor I, selection line, swine ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:1973–1981 doi:10.2527/jas.2009-2445 INTRODUCTION Residual feed intake ( RFI ) is a measure of produc- tion efficiency in growing animals. Residual feed intake is defined as the amount by which actual feed intake differs from expected intake, given the predicted re- quirements for maintenance and production output of an animal. The definition of production output typi- cally includes growth (cattle) and composition traits (pigs), but it can also include other forms of output, such as egg or milk production, in other species. Dif- ferent trait definitions of RFI can obviously result in different outcomes under selection. Within the range of possible definitions for RFI, and with all other factors held constant, differences between individuals in their RFI are thought to be related to variability in factors other than growth and body com- position (or production output), such as feeding be- havior, nutrient digestion, maintenance requirements or activity, and energy homeostasis or partitioning. The current lack of understanding about the biological con- sequences of selection on RFI was part of the motiva-
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