Document Type : Research Articles
Authors
Department of Animal Science, College of Agriculture, University of Birjand, Birjand, Iran
Abstract
Introduction: Pelleting is the most common thermal process in the poultry feed industry. Pelleting aims to compact smaller feed particles into larger ones to increase economic benefits through increased feed intake and consequently improved growth performance, safety, and health of broiler chickens. Heat, moisture, and mechanical pressure during pelleting induce chemical and physical changes that may affect feed components, bird growth, and health, from a nutritional point of view, the partial denaturation of proteins during pelleting improves their digestibility and allows easier access to proteases (Dozier, 2001). Gelatinization is the irreversible loss of the crystalline form of starch granules, which makes the surface of the starch molecule accessible to reagents, solvents and enzymes, which can then break down its glycosidic bonds and increase the digestibility of the starch (Moritz et al., 2005). Therefore, this study aimed to evaluate the effects of feed processing conditions in conditioners on pellet quality and growth performance, immune response, and blood indices of broilers.
Materials and Methods: A total of 480 one-day-old Ross 308 broiler chicks were used in a completely randomized design. Treatments were arranged in a 2×4 factorial arrangement with four temperature levels (70, 76, 82, and 88 °C) and two conditioning time levels (45 and 65 seconds). The pellet durability index (PDI) was calculated to determine pellet quality. The diets were fed for 42 days in diets with three periods of starter (1-10 days), grower (11-24 days), and finisher (25-42 days). Growth performance involving body weight gain, and feed intake, were measured at the end of each experimental period and the feed conversion ratio was also calculated at the same. At the end of the experimental period, two birds of each replicate were slaughtered and blood samples were collected from two birds of each replicate. After centrifuging the blood at 2500 rpm, the plasma was stored at -20°C until biochemical indices until analyzing. The plasma protein, cholesterol, triglyceride, LDLD, and HDL, and the enzyme activity of AST and ALT were determined by the autoanalyzer spectrophotometry. At the end of the experimental period, two birds from each replicate were slaughtered, and carcass weight and other internal organs were measured. Additionally, jejunal tissue samples were also collected for morphological analysis and preserved in formalin.
Results and Discussion: The results of this study showed that conditioning time and temperature did not have a significant effect on pellet quality and strength. However, performance indices were affected by the experimental treatments (P<0.05). Pellets produced at the highest temperature had the lowest daily weight gain and higher feed conversion ratio throughout the growth, finisher, and overall rearing periods as compared to the diets pelleted at 76oc and 65 second (P<0.001). The highest carcass efficiency (72.62) and breast relative weight (25.66) and the blood concentration of total protein (6.44) and albumin (3.7) was observed in broilers consuming diets pelleted at 82°C and 65 seconds (P<0.001) as compared to other treatments. The treatments affected the concentrations of glucose, total protein, albumin, cholesterol, triglycerides, HDL, LDL, and aspartate aminotransferase enzyme (P<0.001). The concentration of blood glucose was higher in broiler fed with diets pelleted at 70oc and 45 or 65 seconds as compared other treatments. The concentration of blood cholesterol, triglyceride and HDL was higher in broiler fed with diets pelleted at 70oc and 65 seconds as compared other treatments. Increasing the conditioning temperature reduced the concentrations of glucose, cholesterol, triglycerides, and LDL and increased the concentration of AST enzyme (P<0.001). Intestinal morphological indices such as villus height, villus height to crypt depth ratio, and absorptive surface area were also affected by the experimental treatments (P<0.05). Broilers consuming pellets processed at 76°C and 65 seconds had the highest villus length, villus height to crypt depth ratio, and villus surface area compared to other treatments (P<0.05). The broilers fed diets pelleted at 88oc had the lowest performance indices and higher blood lipid (P<0.05).
Conclusion: The findings of the present study showed that a temperature of 76°C and time of 65 seconds improved the growth performance, and intestinal histological indices of broilers, and a temperature of 82°C and time of 65 seconds improved carcass efficiency. The diets pelleted at temperature of 88°C reduced growth performance and histological and biochemical indices of blood. Therefore, for higher growth performance and improving histological indices of the digestive tract of broilers, a temperature of 76°C and time of 65 seconds is recommended, and to improve biochemical indices of blood and carcass efficiency, a temperature of 82°C and a time of 45/65 seconds is recommended for pelleting feed for broilers.
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