44 MUSCLE FATTY ACID COMPOSITION AND LIPOGENIC GENE EXPRESSION IN ADULT BOVINE CLONES AND CONTROL CATTLE

Abstract

Previous evaluation of milk and meat from clone cattle compared with AI control cows indicated that these products were in the normal range of data, but slight differences were observed in their fatty acid (FA) composition and muscle Δ⁹-desaturase indexes (Heyman et al. 2007 Animal 1, 936-972). It was therefore hypothesized that epigenic modifications induced by the nuclear transfer technology may affect the expression of the 2 genes [stearoyl-coenzyme A desaturase (SCD)-1, SCD5] responsible for Δ⁹-desaturation in bovines. The aim of the present experiment was to analyze the differences between clones and controls on FA composition and on SCD1 and SCD5 gene expression of the semitendinosus (ST) muscle. Biopsies of ST were taken from 5 clones from 2 different Holstein genotypes and 5 Holstein AI controls at 26 months of age. Each sample was immediately split into 3 aliquots, frozen in liquid nitrogen, and stored at -80°C until analysis. Fatty acid composition was analyzed by gas chromatography after lipid extraction and methylation according to Bas et al. (2005 Meat Sci. 71, 317-326). Total RNA was isolated from 300 mg of muscle tissue and abundance of SCD1 and SCD5 genes transcripts was determined by RT-PCRas described by Bernard et al. (2005 J. Dairy Sci. 88, 1478-1489) and Lengi and Corl (2007 Lipids 42, 499-508). Results are expressed as percentage of total FA for the FA composition and mRNA abundance of SCD1 and SCD5 determined as relative to the abundance of cyclophilin A mRNA. Statistical analyses were performed using the GLM procedure of SAS (SAS Institute, Cary, NC). Single degree of freedom orthogonal contrasts were used to compare effects of cloning (AI controls v. clones) as well as effects of clone genotypes (genotype 1 v. genotype 2). The C14:0, C14:1 cis-9, C16:0, C16:1 cis-9, and C18:0 proportions in ST were not different between clones and controls. However, clones tended to have a lower proportion of C18:1 n - 9 (-3.1% of total FA; P < 0.07) and higher proportions of C18:2 n - 6 (+1.2% of total FA; P < 0.01), C18:3 n - 3 (+0.7% of total FA; P < 0.05) and n - 3 polyunsaturated FA (+1.17% of total FA; P < 0.05) than controls. Ratios of C14 and C16 Δ⁹-desaturation in ST were not different between clones and controls but a lower C18 Δ⁹-desaturation ratio for the clones compared with controls was observed (0.76 v. 0.79; P < 0.05). The mRNA abundance of SCD1 was lower in clone compared with control cows (3.8 v. 8.5; P < 0.05), which could be explained by the higher proportion of n - 3 polyunsaturated FA observed in clones because of the negative effects of these polyunsaturated FA on SCD gene expression. The only difference observed between genotypes was for the C18:0 proportion in muscle (P < 0.05). In conclusion, in our set of animals, cloning decreased the ST muscle gene expression of SCD1 but not of SCD5, which is related to a slight decrease in C18 Δ⁹-desaturation ratio.