evaluation of performance and humeral immune system (antibody titer against gambaro vaccine, cerloplasmin concentration and hetrophyl to lymphocyte ratio) in broiler chickens fed different levels of probiotic

the effects of different dietary levels of soybean oil (2, 4 and 6%) and probiotic primalac (0, 0.1 and 0.15 %) were investigated on performance and immune system of broiler chickens from day one to day 42 of age. for this purpose, five hundred and forty day-old male broiler chicks (cobb) in 9 groups of 60 each were used. the birds of each group were divided into 6 pens of 10 birds. the experimental treatments were analyzed in a 3×3 factorial experiment with a completely randomized design all the birds received a same starter diet until day 7 of age but fed the grower (from day 7 to 21 of age) and finisher (from day 22 to day 42 of age) diets afterwards. the results of the recent experiment showed that soybean oil or probiotic supplementation improved the feed consumption, body weight gain and feed conversion ratio (p< 0.01) of broilers during whole the experimental period. moreover a significant interaction was observed between the probiotic and soybean oil for feed conversion ratio (p< 0.05). probiotic or soybean oil supplementation increased the feed consumption during 24 hours post-vaccination and antibody titer against gamboro vaccine and decreased the plasma cerloplasmin and hetrophil to lymphocyte ratio (p< 0.01). furthermore a significant interaction was observed between the soybean oil and probiotic supplementation for post vaccination feed consumption and produced antibody titer (p< 0.05). none of the treatments affected the proportional weight of bursa fabrciuos but probiotic supplementation increased the proportional weight of spleen at day 42 of age. it was concluded that dietary supplementation of 4% soybean oil with 0.1% of probiotic has the best effect on performance of broiler chickens but higher levels of soybean oil (6%) with either of 0.1 or 0.15% of  probiotic is needed for the best immune response (lower blood cerloplasmin concentration and heterophil to lymphocyte ratio).