عنوان مقاله [English]
Introduction: Fat inclusion in the diet presents positive features such as essential fatty acids and vitamin supply, slowing the passage rate, and lubricating the feed milling equipment. The price of conventional added fat sources has been increasing in the last few years; therefore, there is a growing interest in the use of alternative energy sources in poultry feeding. In this context, coproducts derived from the soybean oil refinement process represent an economic alternative and permit giving added value to residual products. Soybean lecithin, which is extracted from the soybean oil degumming process, is mainly composed of polar lipids (>60%), especially of phospholipids, but also contains an important amount of neutral lipids (30–40%), as triacylglycerols and free fatty acids. Soy lecithin may also act as a source of polyunsaturated fatty acids, which are important precursors of eicosanoids for human health benefits and neonatal growth. The inclusion of lecithin in the diet could improve lipid digestibility, liver function, and performance. Therefore, the present study was designed to evaluate the effect of fat source and soybean lecithin on performance, egg quality, nutrient digestibility, and blood parameters in laying hens.
Materials and methods: A total of 144 Nick Chick laying hens were randomly divided into six treatments, six replicates, and four hens per replicate as a 2×3 factorial experiment in a completely randomized design. The experimental treatments included: 1) 3% soybean oil, 2) 3% soybean oil + 0.1% lecithin, 3) 3% tallow, 4) 3% tallow + 0.1% lecithin, 5) a mixture of soybean oil + tallow in equal proportions, and 6) a mixture of soybean oil + tallow in equal proportions + 0.1% lecithin. Lecithin contains 7480 kcal/kg metabolizable energy and is added to experimental diets at one kg/ton as per company recommendation. Productive performance and egg quality traits were recorded from 37 to 44 weeks of age. Egg production and egg weight were recorded daily and feed intake was recorded weekly. This information was used to calculate the feed conversion ratio. Egg quality was measured in four eggs which were individually weighed and the external and internal quality (shape index, yolk index, yolk weight, yolk color, Haugh unit, shell weight, and shell thickness) was determined. At the end of the experiment (44 weeks of age) celite was added to experimental diets as an insoluble marker. Apparent metabolizable energy, dry matter, fat and crude protein digestibility were measured. Liver enzymes’ activity (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase concentrations) and blood parameters (triglyceride, cholesterol, HDL, and LDL) were measured at the end of the experiment.
Results and discussion: Feed intake (P<0.01), egg production, and egg mass improved by a mixture of soybean oil + tallow (P<0.05) in the entire experiment. The effects of the source of oil on the productive performance of laying hens are contradictory and depend on the oil source and fatty acid compositions of oil/lipids, strain, and age of hens. Inclusion of lecithin in the diet increased feed intake and yolk color (P<0.01) but decreased Haugh unit (P<0.05). The reasons for the discrepancies among researchers concerning the effects of dietary lecithin on poultry production are not known but might depend on the type of bird used, as well as on the characteristics of the diet, including the level, source, and fatty acid profile of the lipid source used. The information available on the effects of lecithin on yolk pigmentation is scarce. The unsaturated fatty acid profile of lecithin is more favorable for xanthophyll absorption and utilization than that of the more saturated fatty acid profile of animal fat. Lecithin facilitates the absorption and transfer of fats, so it can cause the absorption of pigment substances as fat-soluble compounds. Yolk color increased and eggshell thickness was decreased (P<0.05) by a mixture of soybean oil + tallow. Apparent metabolizable energy, dry matter, fat, and protein digestibility were not affected by fat source, lecithin inclusion, or fat source × lecithin interaction. Moreover, the data indicated that the addition of soy oil decreased the cholesterol in the plasma (P<0.05). Aspartate aminotransferase (P<0.01), lactate dehydrogenase (P<0.05), triglyceride (P<0.01), cholesterol, and LDL (P<0.05) concentrations of the plasma decreased by lecithin inclusion in the diet. Lecithin is one of the natural elements that have dispersing properties. Lecithin is capable of reducing LDL cholesterol. It also promotes HDL cholesterol synthesis. In addition, it is used to help reduce cholesterol and triglycerides and protect the liver in the prevention of kidney stone formation. The lecithin modifies the cholesterol homeostasis in the liver, increasing the HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase) and alpha 7 hydroxylase cholesterol activities. The LDL concentration and size are also significantly reduced and the bile acid pool and bile lipid secretion are increased.
Conclusions: In general, soybean lecithin can be added, in combination with soybean oil and tallow as an energy source in laying hens' diet to improve performance.