J. Anim Sci., doi: 10.2527/jas.2007-0396
©Copyright, 2007, The American Society of Animal Science
Selection response and genetic parameters for residual feed intake in Yorkshire swine
W. Cai 1,
D. S. Casey 2,
J. C. M. Dekkers 1*
1 Department of Animal Science, Iowa State University, Ames 50011
2 Pig Improvement Company, Hendersonville, TN 37075
* To whom correspondence should be addressed. E-mail: jdekkers{at}iastate.edu.
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Abstract |
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Residual Feed Intake (RFI) is a measure of feed efficiency defined as the difference between observed feed intake and that predicted from average requirements for growth and maintenance. The objective of this study was to evaluate response in a selection experiment consisting of a line selected for low RFI and a random control line and to estimate genetic parameters for RFI and related production and carcass traits. Starting with random allocation of purebred Yorkshire littermates, in each generation, electronically measured average daily feed intake (ADFI), average daily gain (ADG), and ultrasound backfat (BF) were evaluated during a ~40 to ~115 kg test period on ~90 boars from first parity and ~90 gilts from second parity sows of the low RFI line. Following evaluation of first parity boars, ~12 boars and ~70 gilts from the select line were selected to produce ~50 litters for the next generation. About 30 control line litters were produced by random selection and mating. Selection was on EBV for RFI from an animal model analysis of ADFI, with on-test group and sex (fixed), pen within group and litter (random), and covariates for interactions of on- and off-test weight, on-test age, ADG, and BF with generations. RFI explained 34% of phenotypic variation in ADFI. After 4 generations of selection, estimates of heritability for RFI, ADFI, ADG, FE (=ADG/ADFI), and ultrasound-predicted BF, loin muscle area (LMA), and intramuscular fat (IMF) were 0.29, 0.51, 0.42, 0.17, 0.68, 0.57, and 0.28, respectively; predicted responses based on average EBV in the low RFI line were -114, -202, and -39 g/d for RFI (=0.9 phenotypic SD), ADFI (0.9 SD), and ADG (0.4 SD), 1.56 % for FE (0.5 SD), -0.37 mm for BF (0.1 SD), 0.35 cm2 for LMA (0.1 SD), and -0.10 % for IMF (0.3 SD). Direct phenotypic comparison of the low RFI and control lines based on 92 low RFI and 76 control gilts from the 2nd parity of generation 4 showed that selection had significantly decreased RFI by 96 g/d (P=0.002) and ADFI by 165 g/d (P<0.0001). The low RFI line also had 33 g/d lower ADG (P=0.022), 1.36 % greater FE (P=0.09), and 1.99 mm less BF (P=0.013). There was not a significant difference in LMA and other carcass traits, including subjective marbling score, despite a large observed difference in ultrasound-predicted IMF (-1.05% with P<0.0001). In conclusion, RFI is a heritable trait and selection for low RFI has significantly decreased the feed required for a given rate of growth and backfat.
Key Words:
feed efficiency, pigs, residual feed intake, selection
