كليدواژه :
انرژي , پيه گاوي , جوجه گوشتي , روغن كلزا , عملكرد
چكيده لاتين :
Introduction The terms of fat and oil refer to triglycerides of several profiles of fatty acids. Fatty acids that are not bound to other organic components as glycerol are the so-called free fatty acids. Lipids constitute the main energetic source for animals and they have the highest caloric value among all the nutrients. Linoleic acid is the only fatty acid whose dietetic requirement has been demonstrated. Besides supplying energy, the addition of fat to animal diets improves the absorption of fat-soluble vitamins, increases diet palatability, and the efficiency of utilization of the consumed energy. Furthermore, it reduces the rate of food passage through the gastrointestinal tract, which allows a better absorption of all nutrients present in the diet. The energetic value of oils and fats depend on the following: the length of the carbonic chain, the number of double bonds, the presence or absence of ester bonds (triglycerides or free fatty acids), the specific arrangements of the saturated and unsaturated fatty acids on the glycerol backbone, the composition of the free fatty acid, the composition of the diet, the quantity and the type of the triglycerides supplemented in the diet, the intestinal flora, the sex and the age of the birds.
Dietary energy is one of the major effective nutrient, representing high percent of total cost of the diets for broilers. Diet energy has important effects on the regulation of the amount feed intake and performance in broilers. Fats are the main sources of energy in broiler diets. Different research showed that the advantages of fats especially in low energy diets.
Materials and Methods This experiment was conducted as a (2*2*2) factorial arrangement including 2 fat sources (tallow fat and canola oil), 2 levels of fat (3% and 6%), and two levels of diet metabolizable energy (2900 and 3100 Kcal.Kg) with 432 Ross-308 broilers in 8 treatments, 4 replicates and 12 chicks in each replicate in two experiment period (grower from 11 to 24 days and finisher from 25 to 42 days) in a completely randomized design. Chicks were fed from 1 to 10 days with a common starter diet that recommended by Ross company. During experiment periods all birds had free access to water and feed. Measuring of weight gain and feed intake were done at the end of experimental periods and feed conversion ratio was calculating by dividing the amount of feed intake to the amount of weight gain. Carcass traits were measured at the end experiment period by killing 2 birds from each replicate. Blood sampling was done at the end of experimental period.
Results and Discussion At the end of experimental period, using canola oil in contrast to beef tallow reduced the amount of daily feed intake, whereas improved the feed conversion ratio, final weight and production index (P <0.05). Fat level had no significant effects on performance of broilers (P >0.05). Diet with 3100 Kcal.Kg ME caused the amount of weight gain and production index increase and feed conversion improve (P <0.05). Interaction between fat sources and amounts and energy levels, 6% beef tallow increased the feed conversion ratio (P <0.05). In interaction between fat source and energy level, diet with canola oil and 3100 had the best feed conversion ratio (P <0.05). No significant effects had been seen fat level with diet energy level (P >0.05). Interaction between fat sources, fat level and energy level, using 3% and 6% of canola oil increased the amounts of daily feed intake, daily weight gain and final weight and feed conversion ratio improved (P <0.05). Fat sources, fat and energy levels had not significantly affect the carcass traits of broiler (P >0.05). Diet with beef tallow increased the amount of HDL in blood (P <0.05). Diet with 3100 Kcal/Kg ME reduced the amounts of cholesterol, HDL and LDL in broiler blood (P <0.05). In interaction effect between fat sources and fat levels, using 6% beef tallow increased the amount of HDL in blood (P <0.05). In interaction between fat sources and diet energy level, diet with beef tallow and 2900 Kcal/Kg ME increased the amounts of cholesterol and HDL in blood (P <0.05). In interaction between fat levels and diet energy levels, using 6% canola oil with 3100 Kcal/Kg ME reduced the values of cholesterol, HDL and LDL in blood of broilers (P <0.05). In interaction between fat sources, fat levels and energy levels, using 6% canola oil with 3100 Kcal/Kg reduced the amounts of cholesterol, HDL and LDL in broilers blood (P <0.05). Diet with 3100 Kcal/Kg ME significantly reduced the blood level of Cholesterol, HDL and LDL (P <0.05). Reducing of broiler performance by using higher level of tallow fat may be have different reasons such as the composition and saturation of fatty acids, the amount of essential fatty acids and their digestibility. In poultry the digestibility of saturated fats in contrast with unsaturated fats is low. As the large amount of energy can be supply by fats, in this condition usually the energy deficiency is the main problem. As the energy have important role in other nutrients metabolism, o, in this condition the broiler performance reduced. As the metabolism rate of broilers is high, for this process, broilers need more levels of diet energy. For these reasons there showed the best performance by diet with high level of ME. As the performance of broiler with high levels of ME was better, so the considerable of nutrients especially fats consumed in this field, so the remove amount of nutrient that should be consume in formation of blood lipid be low and for this reason the blood levels of Cholesterol, HDL and LDL were reduced.
Conclusion The overall results showed that in broilers, using diet with 3100 Kcal/Kg metabolizable energy and canola oil up to 6% have positive results in broilers, but using more than 3% tallow have negative effect on broiler performance.
