Duration of feeding linseed diet influences expression of inflammation-related genes and growth performance of growing-finishing barrows

The aim of the study was to investigate the effects of dietary linseed (rich in n-3 PUFA) on expression of inflammation-related genes and on growth performance of growing-finishing barrows. Two isoenergetic and isonitrogenous diets were formulated, one as the basal diet and the other containing 10% linseed. Twenty-four Landrace x Yorkshire barrows weighing 35 [+ or -] 3.7 kg were randomly assigned to 1 of 4 treatment groups, with 6 pigs per group. During the entire experimental period of 90 d, these 4 groups of pigs were first fed the basal diet and then fed the linseed diet for 0, 30, 60, and 90 d before slaughter, respectively. Pig growth; messenger RNA (mRNA) expression of peroxisome proliferator-activated receptor-[gamma] (PPAR[gamma]), IL-1[beta]30, IL-6, and tumor necrosis factor-[alpha] (TNF-[alpha]); and plasma concentrations of the 3 proinflammatory cytokines were measured and analyzed. Average daily feed intake did not differ among treatment groups (P > 0.05), but ADG (P < 0.05) and G:F (P < 0.01) responded quadratically to the duration of linseed diet feeding, and pigs in the 60-d treatment group had the greatest ADG and G:F. The mRNA expression of PPAR[gamma] in loin muscle and spleen increased linearly (P < 0.01) with the duration of linseed diet feeding, whereas its expression in adipose tissue was not affected (P = 0.095). Tumor necrosis factor-[alpha] and IL-6 mRNA expression in muscle, adipose, and spleen, as well as serum concentration of TNF-[alpha], decreased linearly (P < 0.01) with the duration of linseed diet feeding. Peroxisome proliferator-activated receptor-[gamma] mRNA abundance was negatively correlated with IL-1[beta], IL-6, and TNF-[alpha] mRNA abundance both in muscle ([R.sup.2] = 0.63, P < 0.001) and in spleen ([R.sup.2] = 0.69, P < 0.001), and PPAR[gamma] mRNA expression in spleen ([R.sup.2] = 0.59, P < 0.01) and muscle ([R.sup.2] = 0.52, P < 0.05) was negatively correlated with serum TNF-[alpha] concentration. There were also significant quadratic relations between ADG and expression of PPAR[gamma] (P < 0.05) and splenic TNF-[alpha] (P < 0.05). These data suggest that intake of n-3 PUFA from the linseed diet led to significant decreases in the expression of proinflammatory cytokine genes, which may stimulate growth in growing-finishing barrows, at least in part, through a PPAR[gamma]-dependent mechanism. Key words: growth, linseed, n-3 polyunsaturated fatty acid, peroxisome proliferator-activated receptor-[gamma], pig, proinflammatory cytokine