The present study was designed to evaluate the possible effect of dietary oregano etheric oils as non-specific immunostimulating agents in growth-retarded, low-weight growing-finishing pigs. Forty-nine growth-retarded (> 10% under average weight in a group) growing-finishing pigs of the same age were assigned to two groups and treated as follows: Group 1 (n = 25): the animals weighed 58.2 +/- 2.4 kg and were fed until slaughter ad libitum with a commercial fattening diet supplemented with 3000 ppm commercial oregano feed additive (Oregpig Pecs, Hungary). Oregpig is dried leaf and flower of Origanum vulgare, enriched with 500 g/kg cold-pressed essential oils of the leaf and flower of Origanum vulgare. Analysis of Oregpig: 60 g carvacrol and 55 g thymol/kilogram. Group 2 (n = 24): the animals weighed 57.9 +/- 2.6 kg and were fed until slaughter with the same diet without Oregpig supplementation. Oregpig-receiving pigs showed a significantly (P < 0.05) better average daily gain and feed conversion rate than the non-treated animals (Oregpig group 788.1 +/- 31.3 g, control animals 709.3 +/- 42.2 g; 2.96, vs. 3.08, respectively). Mortality was significantly (P < 0.001) higher in the non-treated animals (Oregpig group, 1 animal = 4%; control, 8 animals = 33.3%). The proportion of CD4, CD8, MHC class II antigen, and non-T/non-B cells in peripheral blood lymphocytes was significantly higher in the Oregpig-receiving pigs than in the control animals. The proportion of CD4+ CD8+ double-positive T lymphocytes in peripheral blood and mesenteric lymph nodes was higher in the Oregpig-receiving pigs than in the control animals.
Implication: Dietary oregano improves growth in growth-retarded growing-finishing pigs and has non-specific immunostimulatory effects on porcine immune cells.