Hudyma V. Biochemical parameters of tissues and eggs of laying hens fed by diets with different particle size of limestone and different levels of vitamin D3.

Purpose of this work was to determine the optimal particle size of limestone in the diet of laying hens for the improving of the egg production; and to find out the impact of different amounts of dietary vitamin D3 on the metabolism in laying hens. Metabolic and productive effects of adding into the diet of laying hens limestone with different particle size (less than 1 mm, 1-2 mm, 2-3 mm) and different amounts of cholecalciferol (1250, 2500, 3750, 5000, 10000 IU/kg DM) have been investigated. Methods: biochemical, immunological, morphometric, and statistical. Scientific novelty: For the first time shown the corrective effect of particle size of limestone in hen diet on lipid metabolism. For the first time proved stimulating effect of high content of vitamin D3 in the diet on laying hens non-specific resistance. Theoretical and practical results: Increasing limestone particles size led to increased concentrations of glucose, triacylglycerols, cholesterol, calcium, and 25-OH vitamin D3 and decreased concentration of magnesium in hens' blood. Size of limestone particle did not affects the concentration of blood phosphorus. On average during the experiment, egg weight of hens treated with limestone fractions of 1-2 and 2-3 mm were to 3.09 and 6.69 %, and the eggshell weight to 5.16 and 3.49% higher than in chickens fed diet with limestone smaller than 1 mm. The strength of eggs shell in hens fed by diet with limestone particle size of 2-3 mm was 6.02% higher, compared to the eggs of hens that fed limestone particle size up to 1 mm. Rising of vitamin D3 content in the diet increased the concentration of 25-OH D3 in the serum. Increasing the amount of vitamin D3 more than 3750 IU/kg of diet increases the red blood cells count and hemoglobin concentration. At the same time, pseudo-eosinophil and monocyte counts grew and lymphocyte count down, whereas blood phagocytic and bactericidal activities were amplified. Feeding vitamin D3 in an amount greater than 3750 IU/kg of diet did not affect the egg-laying qualities, egg weight, composition and strength of the shell. The results of feeding laying hens with fractionated limestone were tested and implemented at poultry farms. Area of application - industrial poultry.