Palm oil protects α-linolenic acid from rumen biohydrogenation and muscle oxidation in cashmere goat kids

BACKGROUND: In ruminants, dietary C18:3n-3 can be lost through biohydrogenation in the rumen; and C18:3n-3 that by-passes the rumen still can be lost through oxidation in muscle, theoretically reducing the deposition of C18:3n-3, the substrate for synthesis of poly-unsaturated fatty acids (n-3 LCPUFA) in muscle. In vitro studies have shown that rumen hydrogenation of C18:3n-3 is reduced by supplementation with palm oil (rich in cis-9 C18:1). In addition, in hepatocytes, studies with neonatal rats have shown that cis-9 C18:1 inhibits the oxidation of C18:3n-3. It therefore seems likely that palm oil could reduce both rumen biohydrogenation of C18:3n-3 and muscle oxidation of C18:3n-3. The present experiment tested whether the addition of palm oil to a linseed oil supplement for goat kids would prevent the losses of C18:3n-3 and thus improve the FA composition in two muscles, Longissimus dorsi and Biceps femoris. To investigate the processes involved, we studied the rumen bacterial communities and measured the mRNA expression of genes related to lipid metabolism in Longissimus dorsi. Sixty 4-month-old castrated male Albas white cashmere kids were randomly allocated among three dietary treatments. All three diets contained the same ingredients in the same proportions, but differed in their fat additives: palm oil (PMO), linseed oil (LSO) or mixed oil (MIX; 2 parts linseed oil plus 1 part palm oil on a weight basis). RESULTS: Compared with the LSO diet, the MIX diet decreased the relative abuandance of Pseudobutyrivibrio, a bacterial species that is positively related to the proportional loss rate of dietary C18:3n-3 and that has been reported to generate the ATP required for biohydrogenation (reflecting a decrease in the abundance of rumen bacteria that hydrogenate C18:3n-3 in MIX kids). In muscle, the MIX diet increased concentrations of C18:3n-3, C20:5n-3, C22:6n-3, and n-3 LCPUFA, and thus decreased the n-6/n-3 ratio; decreased the mRNA expression of CPT1β (a gene associated with fatty acid oxidation) and increased the mRNA expression of FADS1 and FADS2 (genes associated with n-3 LCPUFA synthesis), compared with the LSO diet. Interestingly, compared to Longissimus dorsi, Biceps femoris had greater concentrations of PUFA, greater ratios of unsaturated fatty acids/saturated fatty acids (U/S), and poly-unsaturated fatty acids/saturated fatty acids (P/S), but a lesser concentration of saturated fatty acids (SFA). CONCLUSIONS: In cashmere goat kids, a combination of linseed and palm oils in the diet increases the muscle concentration of n-3 LCPUFA, apparently by decreasing the relative abundance of rumen bacteria that are positively related to the proportional loss rate of dietary C18:3n-3, by inhibiting mRNA expression of genes related to C18:3n-3 oxidation in muscle, and by up-regulating mRNA expression of genes related to n-3 LCPUFA synthesis in muscle, especially in Longissimus dorsi.