Effect on Rendement Napole genotype on metabolic markers in Ossabaw pigs fed different levels of fat

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The Rendement Napole (RN−) gene mutation was discovered in the mid‐1980s as a mutation in the Hampshire breed that results in a significant increase (approximately 70%) in the skeletal muscle glycogen content (Le Roy, Naveau, Elsen, & Sellie, 1990; Monin & Sellier, 1985). The gene has two segregating alleles RN− and rn+ that results in three genetic groups: homozygous wild‐type (WT; rn+/rn+), RN− carrier (RN−/rn+, CAR) and homozygous mutants (RN−/RN−). RN− is a dominant mutation because of the lack of difference in glycogen content between the RN− carrier (RN−/rn+) and homozygous mutants (RN−/RN−; Estrade, Vignon, Rock, & Monin, 1993). RN− mutation results in higher muscle glycolytic potential, high lean meat percentage and meat with a much lower ultimate pH because of post‐mortem glycogenolysis (Estrade et al., 1993; Le Roy et al., 2000). The RN− was later traced to a single missense mutation (Arg200 → Gln, R225Q) in the protein kinase AMP‐activated γ3 gene, PRKAG3, which encodes the γ3 isoform of AMP‐activated protein kinase (AMPK; Milan et al., 2000). RN− carriers also have high oxidative capacity, which results in increased citrate synthase and β‐hydroxy‐acyl‐coenzyme A dehydrogenase (Lebret et al., 1999) activity. As a result of high oxidative capacity, Hemann et al. (2000) reported that RN−/rn+ pigs had reduced backfat thickness compared with rn+/rn+ pigs. This suggests that alteration in substrate utilization from the DNA mutation could be a major determinant of pig body composition.
Ossabaw pigs are miniature pigs that exhibit a thrifty genotype which allows them to store a large amount of fat during periods of abundant availability of feed resources (Le et al., 2007). Consequently, Ossabaw pigs fed a high‐fat diet easily deposit large amounts of fat resulting in obesity (Dyson, Alloosh, Vuchetich, Mokelke, & Sturek, 2006; Lee et al., 2009). Because fat deposition is energetically more expensive than muscle deposition, the Ossabaw pig background represents a good genetic environment for determining the effect of constitutively active AMPK gene on efficiency of fat deposition. Therefore, the objective of this study was to determine the effect of RN gene mutation on growth performance, back fat and the expression of selected gene markers of lipid metabolism in cross‐bred Ossabaw pigs.
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