Genetic basis of feed efficiency in the growing pig – PIC_FEED
Improving feed efficiency in pig production has two main consequences: (i) increasing competitiveness of pig industry by reducing the cost of pork production – in a context of dramatic rise of the cost of feedstuffs – and (ii) decreasing environmental impact of pig farms, in particular that concerning phosphorus and nitrogen excretion. The measure of feed intake for individual pigs is, however, difficult and costly. Until now, the genetic improvement of feed efficiency has mainly been achieved through selection for higher average daily weight gain and lower lipid content of the weight gain. However, variations of the two latter traits explain only 50 % of the variation of feed intake in pig. Thus, it is tempting to improve “feed efficiency per se”, i.e. at constant growth rate and body composition.
Residual feed intake (RFI) is a measure for assessing feed efficiency: it estimates the difference between actual feed intake and feed intake predicted from production and maintenance requirements. This trait is moderately heritable in livestock species, including pigs. It shows phenotypic and genetic correlations with major production traits. Relationships with reproduction traits were essentially explored in mice and poultry, showing low to moderate unfavorable correlations. Furthermore, lower RFI is suspected to reduce fitness and to increase susceptibility to stress factors. The main biological sources of genetic variation of RFI have been investigated in poultry and beef cattle, but mostly remain unknown in pigs.
The PIG_FEED project is based on two experimental pig lines divergently selected for RFI and aims to provide 1) a better understanding of the genetic basis of feed efficiency and its genetic relationships with traits of interest in pig production, 2) a better understanding of the physiological consequences of selection for RFI in the growing pig. Through the PIG_FEED project, we will be able to evaluate the impact of selection on sustainable goals for pig breeding, such as reduced environmental impacts, reduced food inputs, reduced drug distribution, increased tolerance to hot environments. The lines result from a five-generation divergent selection experiment, from a common Large White population. Previous genetic studies on pig RFI have mainly targeted breeds, whereas responses to selection in “high” and “low” lines selected from the same base population should essentially reflect consequences of selection.
Previous studies of RFI+ and RFI- lines have validated a significant divergence for the selection criterion. Correlative responses in meat quality, carcass composition and energy expenditure measurements were obtained. The PIG_FEED project is composed of four tasks.
In the first task, we propose to analyze the divergent lines to measure correlative responses on production traits, reproduction traits, feeding patterns and activity related traits. These phenotypes will be analyzed under different feeding levels and consequences in terms of excretion levels and biological regulations will be inferred.
In the second task, we propose to find associations between RFI and particular marker haplotypes, taking advantage of a pig SNP chip of 60K and the biological samples collected on founder animals and across all generations of selection. Moreover, a QTL detection design based on a backcross with females from the RFI experiment should permit to refine the haplotypes first detected. Strategies to take benefit of genomic associations with RFI in commercial populations should be proposed.
In the third task, consequences of selection for RFI will be examined, using three series of transcriptomic and proteomic analysis, for the following aspects: muscle metabolism and adipose tissue metabolism during growth, muscle metabolism at slaughter and consequences on meat quality, and immune response. These data will be explored to identify physiological pathways affected by selection on RFI.
In the fourth task , responses to stress challenges will be explored in the two RFI lines, with an immune challenge, a digestive and a nutrient challenges and a challenge to heat exposition. When required, the direction of nutrient use from growth to other physiological functions might be less efficient in RFI– than in RFI+ pigs. The results obtained in the PIG_FEED project should give us novel ideas for proposing breeding strategies for various selection objectives.
Madame Hélène Gilbert (Organisme de recherche)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Help of the ANR 367,549 euros
Beginning and duration of the scientific project: - 36 Months