Genetic parameters for measures of residual feed intake and growth traits in seven generations of Duroc pigs
Introduction
The cost of feeding animals is a major determinant of profitability in almost any animal production system and thus any effort at improving the efficiency of feed use will help to reduce feed cost. This has long been recognized by the swine industries, where feed cost accounts for about two third of total production expenses. Selection programmes that emphasize efficiency rather than growth rate on ad libitum feeding have led to a reduction of daily feed intake, which may be detrimental in the long term (Web, 1989, Smith et al., 1991). Selection against that portion of feed intake not required for growth rate, i.e. residual feed intake (RFI), may provide an alternative measure (Hoque et al., 2006).
Feed efficiency is difficult to measure for individual pigs and results in high labor and equipment costs. Direct selection for improving feed efficiency has not always been effective because efficiency of feed use is not a directly measurable trait. It is usually computed as the ratio of feed intake to product, and direct selection on feed efficiency ratio may not be the best way to improve this component trait because of complex additive and multiplicative relations (Luiting, 1990). It may even result in undesired correlated selection responses because of the ratio aspect (i.e., feed over gain). Therefore, feed efficiency in swine may be improved indirectly by selection for growth rate and against backfat (Cleveland et al., 1983).
RFI is estimated by the difference between actual and predicted feed intake for an animal. The predicted feed intake is the amount of feed the animal is expected to consume on the basis of its maintenance and production. Variation in RFI may reflect differences in the efficiency with which animals digest and utilize energy for maintenance and production. Therefore, selection against RFI might improve efficiency of energy utilization without reducing appetite required for production of product (Mrode and Kennedy, 1993). Inclusion of this trait in a breeding programme depends on its heritability and its relationships with other traits of interest. The objective of this study was to estimate genetic parameters for and genetic relationships between measures of RFI and growth traits, and to examine the genetic trends of these traits in Duroc pigs over seven generations of selection based on average daily gain (ADG), loin eye area (LEA), backfat thickness (BF), and intramuscular fat (IMF).
Section snippets
Animals at performance test
Duroc pigs used in this study were of a line that had been selected for ADG, LEA, BF, and IMF through seven generations at the Miyagi Prefecture Animal Industry Experiment Station, Japan during 1995–2001. A total of 1642 (380 boars, 868 gilts, and 394 barrows) pigs were tested, which were the progeny produced from 125 sires and 356 dams. For estimating the variance components, a pedigree file was constructed and the total number of animals, including testing animals, was 1780 pigs in the
Results
Mean values, heritabilities, and genetic and phenotypic correlations among FI and growth traits are summarized in Table 1. The mean values for these traits are consistent with other reports (Mrode and Kennedy, 1993, Suzuki et al., 2005) in the same breed. For growth traits, heritability estimates for ADG and LEA were moderate, whereas the corresponding estimate for BF was high (0.72). Appetite, as measured by FI, was moderately heritable (0.49). Common environmental effects on these traits were
Discussion
Estimated heritabilities for ADG in the present study were close to the estimate (0.43) reported by Mrode and Kennedy (1993) in Duroc, Yorkshire and Landrace breeds, and to the literature average (0.45) reported by Hutchens and Hintz (1981). However, Bereskin (1986) reported a considerably lower heritability (0.10) for ADG of group fed Duroc and Yorkshire gilts. The reasons for differences in estimates of heritability might be due to feeding method (Jungst et al., 1981). Higher values of
Conclusion
Results of this study indicate that residual feed intake was moderately heritable, and should respond to selection. Genetic correlations indicate that it should be possible to select for reduced residual feed intake without adversely affecting average daily gain. Daily feed intake and backfat would also decrease, and eye muscle area would increase. The amount of change in backfat or eye muscle area would depend on which measure of residual feed intake one uses.
Acknowledgement
This work was supported by Grants-in-Aid for Scientific Research (No. 18.06220) from the Japan Society for the Promotion of Science.
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