عنوان مقاله [English]
Introduction The digestion and absorption of dietary fats involve processing of insoluble triglycerides in water, which is done by bile activity to emulsify the fats and then to hydrolyze them by lipase. Lipid digestion is not optimal, especially in young birds and it is improved with increasing age; this is due to the low capacity of the digestive system in the secretion of lipase and bile acids, so that the lipase function in one-day-old chickens is one percent of its activity in 21 days of age. Emulsifiers can distribute fat droplets in the emulsion, which is required for the digestion and absorption of fats. Lysophospholipids increase the ability of the emulsion of the fat in the diet and facilitate the development of the chylomicron and, as a result, it increases the digestive capacity and absorption of lipids, such as essential fatty acids and lipid soluble vitamins in the small intestine. The purpose of this study was to estimate the added value of lysophospholipid supplement in corn-soybean diets and its added effect on metabolizable energy (ME) of different types of fat during the growth period of broiler chicks.
Materials and methods Three hundred and fifty day-old male Ross 308 broiler chicks were obtained from a commercial hatchery unit. First, the whole chicks were kept in the pan for up to 14 days of age and fed with standard starter (1-10 days) and grower (11-14 days) diets. At 15 d of age, 288 chicks were divided into 144 two-part groups, then they were transferred randomly to metabolic cages and fed with experimental diets. The trial was conducted in a completely randomized design with factorial arrangement of two lysophospholipid (0 and 250 g/ton) levels, three fat sources (soybean oil, tallow and their mix) and four levels of fat (0, 3, 6 and 9 % replaced in diet) with 6 replicates of 2 male birds each. Twelve experimental diets were prepared by replacing and mixing four levels of soy oil, tallow and/or their mixture (50:50) in the basal diet. Then, each diet was divided into two equal parts; one part was mixed with 0.25 g/kg of supplemental lysophospholipid and the other one was kept intact to make 24 diets.
Results and Discussion According to the different ratio of saturated fatty acids to unsaturated fatty acids (SFA: UFA) between tallow (33:60) and soybean oil (16:84), it is known that saturated fatty acids are less digestible in animal fats compared with fatty acids of vegetable oils. Addition of supplemental lysophospholipid did not have any significant effects on dietary ME, digestibility of dry matter (DM) and crude fat (CF). The interaction effect of the replacement level and the sources of fat was significant for the ME of diet, in which the basal diet with 9 percent soybean oil replacement had the highest ME compared to the other levels and the other fat sources. Two and three way interactions were not significant for ME and digestibility of dietary DM and CF. No significant effect of lysophospholipids on the digestibility of dietary nutrients using 1 and 1.5 g/kg of diet. The effects of lysophospholipids on the digestibility of nutrients depend on factors such as the difference in the base diet, especially in ingredient, the composition and ratio of fat in the diet and the emulsifier (lysophospholipid), which can lead to different responses. Soybean oil had the most ME among the sources of fat. The ME of soybean oil, tallow and their mixture was determined using replacement method to be 8367, 6134 and 6547 kcal/kg, respectively. Studies have shown that the degree of saturation, the amount of free fatty acids, and the position of fatty acids on the glycerol basis affect utilization of fat by the bird. Possibly, the effect of lipophospholipids on the digestibility of crude fat from diets containing tallow can complete the function of bile salts. In normal conditions, there is little effect on high amounts of saturated fatty acids. The lysophospholipid supplementation improved the ME of various sources of fat about 596.4 kcal/kg. The estimated added value (matrix) of lysophospholipid supplement for ME in each kilogram of soybean oil, tallow and their mixture, were 157, 43 and 211 kcal/kg, respectively.
Conclusion The results of this study showed that the lysophospholipid supplementation increased the ME of supplemental fats but had no significant effect on the ME, digestibility of DM and CF in diet.