چكيده انگليسي :
The present study aimed to investigate the effects of different levels of organic selenium in diets with varying ratios of omega-6 to omega-3 fatty acids on various parameters in broiler chickens. These parameters included performance, relative organ weights, white blood cell count, humoral immune responses, microbial population, intestinal histomorphology, and meat quality. The study used a factorial (4x2) experiment based on a completely randomized design with 8 treatments, 6 replications, and 25 birds per replication, resulting in a total of 1200 broiler chickens. The experimental factors included different levels of omega-6 to omega-3 fatty acids (high and low) and different levels of organic selenium (900, 600, 300, and 1200 µg/kg) in the diets. At the end of the experiment, two birds from each replication were randomly selected, and tissue and blood samples were collected for analysis. The findings of the study showed that in the starter and grower periods, the use of 600 µg/kg of organic selenium in diets containing soybean oil and 900 µg/kg in diets containing fish oil significantly increased feed intake and average daily weight gain (p<0.01). Furthermore, the main effects analysis revealed that the use of at least 600 µg/kg of organic selenium significantly decreased the feed conversion ratio in both omega-6 to omega-3 fatty acid ratios during the growth, finishing, and overall periods (p<0.01). The use of fish oil significantly reduced the relative weight of abdominal fat (p<0.05), decreased the heterophil-to-lymphocyte ratio (p<0.05), increased the total antibody titer and IgG concentration in the primary immune response to SRBC (p<0.05), and increased the total antibody titer and IgM concentration in the secondary immune response to SRBC (p<0.01). The use of at least 600 µg/kg of organic selenium resulted in a significant increase in the relative weight of the bursa of Fabricius (p<0.01). Additionally, higher levels of organic selenium significantly reduced the heterophil-to-lymphocyte ratio (p=0.07) and led to the highest titer of total antibody and IgM concentration in the secondary immune response to SRBC when using at least 900 µg/kg of organic selenium (p<0.01). Although different ratios of omega-6 to omega-3 fatty acids did not have any effect on the histology of the digestive system, diets with 900 and 1200 µg/kg of organic selenium significantly increased the length of the jejunum and apparent absorption area (p<0.01). Under the influence of fish oil and increasing levels of organic selenium, the population of Escherichia coli decreased (p<0.01, p<0.05), while the population of Lactobacillus increased (p<0.05, p=0.09). In diets based on soybean oil, the use of a minimum of 600 µg/kg of organic selenium resulted in improvements in the total antioxidant capacity of blood, water-holding capacity, and a decrease in the cooking loss percentage of thigh muscle, whereas these indices improved in diets based on fish oil when supplemented with 900 µg/kg of organic selenium (p<0.01). The use of fish oil led to a significant reduction in the concentrations of total cholesterol, triglycerides, and LDL, as well as the enzyme activities of AST and ALT (p<0.01). Furthermore, diets with 900 and 1200 µg/kg of organic selenium resulted in the lowest plasma concentrations of cholesterol, LDL, and MDA, the lowest ALT enzyme activity, the highest total antioxidant capacity of blood, and selenium concentration (p<0.01). In soybean oil-based diets, the use of a minimum of 600 µg/kg of organic selenium improved the total antioxidant capacity, water-holding capacity, and decreased the percentage of muscle loss in thigh muscles, while these indices improved in diets based on fish oil when supplemented with 900 µg/kg of organic selenium .