Effects of Dietary Organic Chromium Supplementation on Laying Performance, Egg Quality, Immune and Blood Biochemical Parameters of Laying Hens in the Late Phase of Production

Introduction: Although minerals include a small part of the total cost of poultry feed, they perform special functions in the body. Given that today's birds are primarily raised under stressful conditions (including high production demands, environmental stress, heat, and exposure to various other stress factors), their nutrient metabolism, including the absorption of minerals, has changed. This has led to decreased feed consumption, reduced mineral absorption, and consequently, increased excretion of minerals. Minerals that serve as cofactors for many enzymes are crucial; thus, to support proper functioning and enhance the immune system's response, higher amounts of these nutrients are required in diets. Chromium (Cr) is a critical micronutrient for humans and animals. It contributes to physiological and nutritional efficiency. Chromium increases glucose glycogenesis, promotes glucose transport, and increases protein synthesis. Chromium is important in protein digestion and reduction of lipid peroxidation and increased growth production. Chromium deficiency is associated with reduced growth rate, and glucose, and protein metabolism. Under environmental, nutritional, and hormonal stress, the benefits of chromium supplementation clearly demonstrated. Considering that with the increase in age and egg size, the egg quality decreases, and also the function of the immune system decreases at the late phase of egg production. Therefore, supplementation of layer hen diets with some nutrients at the end of the production period can improve the egg quality and potentiate the humoral immune response. Thus, the subject of the current study was to investigate the effects of dietary supplementation of chromium-methionine on egg laying performance, egg quality traits at different storage times and temperatures, humoral immune response, and some blood biochemical parameters of laying hens at late–phase of the egg production cycle.Materials and Methods: A total of 120 Leghorn laying hens (Hy-line W36, 73 weeks- old) were assigned in a completely randomized design with 6 dietary treatments, 5 replicates and 4 laying hens in each replicate for 6 weeks. The experimental treatments were 6 levels of chromium-methionine supplementation (0, 400, 800, 1200, 1600, and 2000 μg/kg of diet) of corn-soybean meal-based diet. The hens were housed in a 60 × 60 × 40 cm cage. All hens were housed in an environmentally controlled house with temperature maintained at approximately 25ºC. The house had controlled ventilation and lighting (16L: 8D). All hens were supplied with feed and water ad libitum. The hen-day egg production, egg weight, egg mass, feed intake, and feed conversion ratio were recorded daily. The feed conversion ratio was expressed in kilograms of feed consumed per kilogram of the egg mass. The effects of organic chromium supplementation of laying hens on egg quality traits were evaluated every 2 weeks at 75, 77, and 79 weeks of age. The egg shape index was calculated by dividing egg length to egg width. At the end of the experiment, to measure certain blood parameters, one bird from each replicate was selected, and blood was drawn from the wing vein. After preparing the serum, the concentrations of triglycerides, cholesterol, total protein, albumin, globulin, uric acid, alanine transaminase, aspartate transaminase, glucose, and malondialdehyde were measured using Pars Azmoon kits according to the manufacturer's instructions.Results and Discussion: Supplementing the diet with chromium-methionine had a significant effect on laying performance (including feed intake, feed conversion ratio, and egg production) and egg quality traits (such as eggshell weight, yolk color, yolk weight, albumen height, and Haugh unit). The results showed that birds fed 2000 µg/kg chromium-methionine had the lowest feed intake and the best feed conversion ratio and egg production percentage were observed with the addition of 1600 and 2000 g/kg organic chromium. By suppressing stress factors, chromium can increase the ovulation rate and increase the percentage of egg production. Addition of organic chromium except 2000 μg/kg improved albumen height and Haugh unit compared to the control group. The interaction effect between egg storage time and storage temperature on the yolk height and yolk percentage, albumen and yolk pH were significant. Carotenoids are responsible for the color of the yolk and they are a part of the fat-soluble compounds, so any factor that can improve the digestion and absorption of fats will probably lead to an increase in the color of the egg yolk. Haugh unit is a measure to determine the quality of egg white, which determines the quality of the egg. The higher HU means better egg quality (fresher, higher quality eggs have thicker whites). Blood serum cholesterol of chickens fed with 800 µg/kg of chromium-methionine decreased compared to the control group. The lowest serum concentration of malondialdehyde was observed using 1600 and 2000 µg/kg organic chromium. Addition of 1600 µg/kg of chromium-methionine increased total immunoglobulin production against sheep red blood cells. The effects of dietary chromium supplementation on improving immune responses can be attributed to its antioxidant activity. By enhancing antioxidant activity, chromium reduces the production of corticosterone, a potent suppressor of immune system function. This reduction in corticosterone levels prevents the decrease in lymphocyte production and proliferation, ultimately supporting the continued production of antibodies.Conclusion: In total, dietary supplementation of 1600 μg/kg chromium-methionine can improve egg laying performance including feed conversion ratio, egg production, and egg mass, as well as egg quality traits such as egg shell weight and albumen height of laying hens at the late-phase of laying cycle. Supplementation of layer diets with 1600 μg/kg organic chromium improved the humoral immune response at the late-phase of egg production cycle by increasing the production of total immunoglobulin against sheep red blood cells.