عنوان مقاله [English]
Introduction Wheat is an important cereal due to high starch, available energy and protein contents and is used in poultry diets. Thermal processing is one of the common ways to increase the digestibility of feed, nutritional value of protein through denaturing the anti-nutritional compounds.
Materials and Methods This project was conducted in two experiments at the Poultry Research Center of Ferdowsi University of Mashhad.
First experiment: This trial was designed to determine the apparent metabolizable energy and the digestibility of crude protein and dry matter in four heat treated wheat with and without enzyme supplementation. One hundred twenty mixed sex day-old broiler chicks were fed standard starter (0-10d) and grower (11-15d) diets, 96 of them were divided into 48 groups of two each and randomly assigned to 48 metabolic cages on day 15. Eight diets in which the sole source of energy and protein was wheat, were prepared and each was randomly fed to six replicates of two chicks each from 15-21d. At 18th day of age, 12 hours of starvation were imposed on all chicks; then trays were placed under each cage and feeds were supplied to all cages for 72 hours when the 2nd 12 hours of starvation was imposed and the collection of excreta continued until the end of the second starvation period. The amount of feed consumed by chicks in each cage in three days was determined by the differences of feed supplied and remained. Excreta collected from each cage was placed in a room air flow for 48 hours and then placed in an oven at 60°C for 72 hours to dry completely.
Second experiment: in this trial, 576 birds (11d) were divided into two groups, (male and female) from which six males and six females were randomly assigned to one of the 48 pens. To prepare 8 experimental diets, only one grower diet (11-24days) containing 70.11% wheat was formulated based on Ross 308 nutrients recommendation and an untreated and three heat treated wheat with and without enzyme supplementation (Rovabio) were replaced to prepare the 8 diets. The experiment was conducted in a completely randomized design with factorial (2×4) arrangement with 6 replicates of 12 birds each. Diets were randomly assigned to 48 pens in a way that each diet fed 6 replicate birds. On the final day of the trial (24d), one male bird from each replicate group was weighed and slaughtered. The carcass, breast, thighs, back, wings and neck, as well as the weight of internal organs including the heart, spleen, proventriculus, gizzard, liver, pancreas, bursa fabrisius, abdominal fat, duodenum, jejunum and ileum were measured. Duodenum, jejunum and ileum length were also measured. To evaluate the effect of different untreated and heat treated wheat at different temperatures with and without enzyme supplementation on the microbial condition of the digestive contents of the ileum digesta on 24d, about 3 grams of the contents of the ileum region from each slaughtered chicken transferred to the sterile tube containing 9 ml of buffer phosphate and placed in an ice flask and transferred to laboratory.
Results and Discussion Thermal treatment significantly improved the apparent metabolizable energy, digestibility of crude protein and dry matter of wheat, so that the highest apparent metabolizable energy and dry matter of wheat was obtained when wheat was processed at 85°C. Whereas the highest digestibility of crude protein in wheat was obtained at 70°C thermal processing. The effect of enzyme on apparent metabolizable energy, apparent digestibility of crude protein and dry matter of wheat was not significant. The results of this study showed that thermal processing of wheat has a significant effect on feed consumption, daily gain, body weight gain and feed conversion ratio. Whereas the feed conversion ratio in chicks fed with diet containing wheat processed at 70°C was similar to those fed other diets contained heat treated wheat and was significantly better than those fed control diet. Dietary enzyme supplementation had a significant effect on body weight, daily gain and conversion coefficient, so that the daily gain of chicks fed diet containing enzyme was increased by 4.5% and the conversion factor was improved by 4.2% compared to those fednon-enzyme diet. Thermal treatment of wheat significantly affect relative percentage of thigh weight and relative weight of broiler chickens at 24 day age, so that the highest relative percentage weight of thigh and breast was in chicks fed diet contained wheat processed at a temperature of 70°C. On the other hand, thermal treatment of wheat significantly affect the relative percentage of abdominal fat, which increased compared to untreated wheat. Also, the present study showed that processed wheat did not have a significant effect on the percentage of carcass weight, back, wings and neck, liver, pancreas, heart, spleen and bursa. Also, the interaction effect of thermal processing of wheat and enzyme supplementation on the relative weight of carcass, its parts and internal organs was not significant. The supplementation of enzyme had only a significant effect on ileum weight. Thermal processing of wheat at different temperatures had a significant effect on the height and width of villi in jejunum, but did not have a significant effect on the depth of the crypt and villi height to crypt depth. The lactobacillus population in the ileum region has not been affected by the heat treatment of wheat and a negative response to Salmonella infection was observed in all chickens. On the other hand, the use of enzyme supplementation did not have a significant effect on villi height and depth of crypt and villi height to crypt depth. The interaction effect of heat treated wheat and enzyme supplementation was not significant for neither of the measurements.
Conclusion The results of this experiment showed that although thermal processing of wheat at 85°C increased the apparent metabolizable energy by 5.32% and dry matter digestibility by 5.61%. In addition, the inclusion of heat treated wheat in diet led to an increase in height and width of jejunal villi and improvement of feed intake weight gain and feed conversation ratio in broiler chickens.