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Studies of two lines of pigs to understand feed efficiency

Given today’s high feed costs and environmental considerations, there is a considerable emphasis placed on the improvement of feed efficiency in pigs (i.e., the gain to feed ratio) to propose optimized and sustainable pork production systems. A divergent selection experiment for Residual Feed Intake (RFI), an indicator of feed efficiency, was undertaken at INRA as a relevant animal model to better understand the genetic, physiological and behavioral bases of variation in productive efficiency of pigs.

Increased energy metabolism in muscle and liver

Growing pigs selected for a high RFI (i.e., the less efficient animals) were fatter, they had more intramuscular lipids, but less glycogen in muscle leading to a better technological meat quality. Activities of glycolytic and oxidative enzymes in skeletal muscle were greater in high RFI pigs, suggesting a greater use of carbohydrates and lipids in cells of the less efficient pigs. This enhancement of muscle energy metabolism in high RFI pigs was associated with an increased activity of AMPK (AMP-activated protein kinase), a sensor of the cellular energy deficit acting as a master switch to stimulate glucose and fatty acid oxidation. In the liver, an increased capacity to oxidize fatty acids and to synthetize glucose from lactate (neoglucogenesis) was also observed in pigs selected for a high RFI. The current findings suggest an accelerated cycling of nutrients between organs in high RFI pigs, which may lead to energy losses within cells, and in fine, impair the feed efficiency of these pigs. A feed restriction strategy has been also applied to the high RFI pigs to decipher between the direct effects of genetic divergence and indirect responses associated with differences in voluntary feed intake and behavior between RFI lines. The metabolic responses in the liver had a genetic basis, while, in skeletal muscle, they were more strictly related to differences in feed intake.

Novel metabolic parameters for efficient animals

Increased energy metabolic activities in cells were associated with a lower feed efficiency in growing pigs. The involvement of the AMPK pathway in the regulation of energy metabolism and its relation with feed efficiency and technological meat quality have been confirmed in response to contrasted environmental conditions such as low ambient temperature. Other studies are conducted to decipher its role in response to differences in feed energy sources. The hierarchy and interaction among cellular traits acting on these metabolic pathways will be also determined using cell cultures.

For further information

These studies have been supported by a grant from the French National Agency for Research (ANR; PigFeed project). Two theses were defended in 2013 (Justine Faure and Thierry Le Naou), and several publications and communications in scientific meetings have been produced, including:

Le Naou T., N. Le Floc’h, I. Louveau, H. Gilbert, F. Gondret. 2012. Metabolic changes and tissue responses to selection on residual feed intake in growing pigs. J. Anim. Sci. 90: 4771-4780. (DOI)

Faure J., L. Lefaucheur, N. Bonhomme, P. Ecolan, K. Meteau, S. Metayer Coustard, M. Kouba, H. Gilbert, B. Lebret. 2013. Consequences of divergent selection for residual feed intake in pigs on muscle energy metabolism and meat quality. Meat Sci. 93: 37-45. (DOI)

Louveau I., A. Vincent, F. Gondret, H. Gilbert, L. Lefaucheur. 2013. Divergent selection on residual feed intake influences gene and protein expressions in pig muscle. In: Book of abstract of the 64th annual meeting of the EAAP, p. 590. Wageningen Academic Publishers. [link]

Contact

Louis Lefaucheur, team physiology and metabolisms of growth (louis.lefaucheur[at]rennes.inra.fr)