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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2008-1345v1 87/14_suppl/E64    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Herd, R. M. Articles by Arthur, P. F. Search for Related Content PubMed PubMed Citation Articles by Herd, R. M. Articles by Arthur, P. F.

Physiological basis for residual feed intake¹

R. M. Herd^*,2 and P. F. Arthur

^* New South Wales Department of Primary Industries, Beef Industry Centre, Armidale, New South Wales 2351 Australia; and Elizabeth Macarthur Agricultural Research Institute, Camden, New South Wales 2570 Australia

² Corresponding author: robert.herd{at}dpi.nsw.gov.au

Residual feed intake (RFI) is a measure of feed efficiency that is independent of level of production, such as size and growth rate in beef cattle, and thus is a useful new trait for studying the physiological mechanisms underlying variation in feed efficiency. Five major physiological processes are likely to contribute to variation in RFI, these being processes associated with intake of feed, digestion of feed, metabolism (anabolism and catabolism associated with and including variation in body composition), physical activity, and thermoregulation. Studies on Angus steers following divergent selection for RFI estimated that heat production from metabolic processes, body composition, and physical activity explained 73% of the variation in RFI. The proportions of variation in RFI that these processes explain are protein turnover, tissue metabolism and stress (37%); digestibility (10%); heat increment and fermentation (9%); physical activity (9%); body composition (5%); and feeding patterns (2%). Other studies in cattle and studies in poultry similarly found these processes to be important in explaining RFI. The physiological mechanisms identified so far are based on very few studies, some of which have small sample sizes. The genomic basis to variation in these physiological processes remains to be determined. Early studies have shown many hundred genes to be associated with differences in RFI, perhaps in hindsight not surprising given the diversity of physiological processes involved. Further research is required to better understand the mechanisms responsible for the variation in RFI in target populations and to marry the physiological information with molecular genetics information that will become the basis for commercial tests for genetically superior animals.

Key Words: body composition • efficiency • feed intake • net feed intake • residual feed intake • selection