Document Type : Research Paper
Authors
1 Animal Science Research Department, Isfahan Agricultural and Natural Resources Research and Education Center, AREEO, Isfahan, Iran
2 Animal Science Department, Faculty of Agriculture, University of ShahreKord, Chaharmahal and Bakhtiari, Iran
3 Animal Science Department, Faculty of Agriculture, University of Birjand. Birjand, Iran
4 Faculty of Veterinary Medicine, Shiraz University, Shiraz, Iran
Abstract
Objective: Occasionaly, significant quantities of imported soybean seeds are stored for long periods in customs warehouses at the country's ports. The soybean meal produced from these stored seeds is often darker in appearance compared to other soybean meals. The use of such stored soybean meal may potentially have adverse effects on the health and productive performance of birds. Therefore, the aim of this study was to evaluate the effects of replacing various levels of stored soybean meal with imported soybean meal on the productive performance and egg quality of laying hens.
Materials and Methods: This experiment was conducted over a period of 12 weeks using 375 commercial laying hens (White Shaver strain) at 34 weeks of age, arranged in a completely randomized design with 5 treatments and 5 replicates of 15 birds per each. The treatments consisted of replacing 0%, 25%, 50%, 75%, and 100% of imported soybean meal with stored soybean meal in the diet. At the beginning of the experiment, chemical compositipon of soybean meals samples were analysed. During the experimental period, the following parameters were measured: average daily feed intake, egg production percentage, average egg weight, and feed conversion ratio. To assess egg quality traits, six eggs were collected from each replicate every four weeks and transported to the laboratory. The following parameters were measured: egg shape index, yolk index, Haugh unit, and percentages of shell, yolk, and albumen. Additionally, the absolute weights of eggs, yolks, albumen, and shells were recorded, along with egg length and width, yolk height and diameter, and albumen height. Lipid peroxidation of egg yolk as malondialdehyde content was determined.
Results and Discussion: Laboratory results indicated that the crude protein content of stored soybean meal (44.6%) was 3.5% higher than that of regular soybean meal (41.1%), which could be attributed to differences in the source, harvest stage, type, processing method, and storage conditions. The ether extract percentage of regular soybean meal was 0.93%, whereas stored soybean meal exhibited a higher level of ether extract (1.36%), likely due to differences in oil extraction methods and systems. The urease activity in stored soybean meal was reported as 0.1, compared to 1.7 in regular soybean meal. Based on the lower urease index of the stored soybean meal, it can be concluded that the processing temperature was optimal. Therefore, the hypothesis that Maillard reactions caused the darker color of the stored soybean meal can be rejected. The experimental results showed that replacing various levels of stored soybean meal with imported soybean meal did not have a significant effect on average feed intake, egg production percentage, egg mass, egg weight, or feed conversion ratio (P > 0.05). Throughout the experimental period, the Haugh unit, shell strength, shell thickness, yolk color, yolk index, and the weight percentages of albumen, yolk, and shell were not significantly affected by the treatments (P > 0.05). However, replacing soybean meal with 100% stored soybean meal resulted in an increase in malondialdehyde concentration in the egg yolk (P < 0.05). Using stored soybean meal in commercial laying hen diets up to 75% of the imported soybean meal level did not have a negative impact on productive performance or egg quality characteristics.
Conclusion: In general, when soybean meal derived from long-stored soybean seeds is introduced to the market, its chemical properties—particularly crude protein content and unavailable protein—should be evaluated to determine its suitability as a replacement for regular soybean meal in diets.
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