Dietary polyunsaturated fatty acids modulate responses of pigs to Mycoplasma hyopneumoniae infection.

Polyunsaturated fatty acids (PUFA) are immunomodulators, but few studies have examined how these dietary components influence infectious respiratory disease. Groups of nine pigs were fed casein and corn starch-based diets containing 10.5 g/100 g corn oil (CO), linseed oil (LO), menhaden oil (MO), linseed + corn oil (LC, 1:1) and menhaden + corn oil (MC, 1:1). As a methodological control, one group of pigs (n = 15) was fed a commercial ration (control diet; C). Pigs inoculated intratracheally with Mycoplasma hyopneumoniae after 4 wk of consuming the diets were killed 3 wk later. Gross lung lesions in MO-fed pigs were less (P < 0.05) than those in LC- and MC-fed pigs. Pigs fed MO had less peribronchial inflammation (P < 0.05) than all other groups. Gross lung lesions correlated negatively with basal in vitro alveolar macrophage tumor necrosis factor (TNF) production in pigs fed diets that contained negligible levels of (n-3) PUFA (C and CO). Basal macrophage TNF production did not correlate with lung lesion scores for diets containing more (n-3) PUFA than C or CO (LO, MO, LC and MC). For pigs fed the LO, MO, LC and MC diets, mean gross lung lesions increased as the mean ratio of (n-3):(n-6) PUFA in alveolar macrophage lipids decreased. Serum levels of alpha1 acid glycoprotein (AGP) were less (P < 0.05) in pigs fed MO, and there was a rise in mean lung lesions scores for each PUFA-fed group as mean AGP levels increased. These results indicate that dietary PUFA can affect disease pathogenesis and that the (n-3):(n-6) PUFA ratio may modulate the host response.