نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Introduction: Mineral supplements are an important component of the diet of laying hens to improve biochemical processes, embryonic development, and bone structure (Leeson, 2005). Micronutrients are involved in the structure of numerous proteins and hormones as intermediates in metabolism (Tom Dieck et al., 2003). In current commercial practice, micronutrients are added to the diet in inorganic form at levels much higher than those recommended by the National Research Council (NRC) (Leeson, 2005; Bao et al., 2007).Research shows that the addition of micronutrients of organic origin increases the bioavailability of the elements and improves performance due to their insoluble nature and organic complexation (Mézes et al., 2012). Consequently, formulating laying hen diets with trace elements from organic sources due to their higher bioavailability is considered a strategy to reduce the excretion of minerals in the animal’s feces. However, these sources are significantly more expensive, making them difficult to access for general use and increasing the cost of the feed. Trace minerals in hydroxychloride form possess several advantages resulting from their unique crystalline structure, such as increased stability and reduced reactivity in feed formulations (Hawthorne & Sokolova, 2002).
Materials and Methods: This experiment was conducted with 240 laying hens of the Hy-Line strain (W-36) from 40 to 50 weeks of age for 10 weeks in a completely randomized design with 8 groups in 5 replications and 6 birds per experimental unit. The experimental groups included: Group 1- negative control (without zinc supplementation), groups 2, 3 and 4, respectively, included the negative control diet with 80, 120 and 160 mg/kg zinc sulfate with a purity of 34%, and groups 5, 6 and 7, respectively, included the negative control diet with 50, 75 and 100 mg/kg zinc hydroxychloride with the chemical formula Cl2.H20 (Zn5 (OH8) with a purity of 55%, and group 8 included the negative control diet with 124 mg/kg zinc-methionine complex with a purity of 22%. The chickens were allocated to 40 metal cages (6 birds per cage) in a completely random manner within the weight range of 1590 ± 25 g. The composition of the basal diet was adjusted based on the guidelines for the (W-36) strain and the age of 40 to 50 weeks according to Table 1. The temperature range of the house was 24 ± 2 °C and the lighting schedule was set to 16 hours of light and 8 hours of darkness throughout the day according to the recommendations of the breeding guideline .Throughout the experimental period, egg mass production, laying rate, percentage of defective eggs, and survival rate were recorded and calculated for each replicate. Serum concentrations of zinc, copper, and manganese were determined using an atomic absorption spectrophotometer according to the method described by Dozier et al. (2003). To determine the bioavailability (retention) of zinc, copper and manganese, one bird from each replicate was randomly selected and slaughtered at the end of the experiment. Tissue samples, including breast muscle, liver, and tibia, were collected for mineral analysis. The results were analyzed in a completely randomized design. For this purpose, the GLM procedure of SAS software version 9.4 (2015) was employed, and Duncan's test at a significant level of 0.05 was used to compare the means.
Results and Discussion: The results presented in Table 2 indicate that zinc accumulation in the pectoral muscle increased linearly with increasing dietary zinc supplementation levels. These changes were influenced by both the bioavailability and the dietary levels of the zinc sources used. Similarly, the storage of zinc in the tibia is strongly affected by the levels and type of its source. Therefore, the zinc storage index in the tibia is a better criterion for measuring its bioavailability. An inverse relationship was observed between dietary zinc concentration and copper accumulation in the pectoral muscle. Specifically, supplementation with 160 mg/kg zinc sulfate and 100 mg/kg zinc hydroxychloride resulted in a significant reduction (P < 0.05) in copper deposition in muscle tissue. The results of this study agree with the findings that state the level of zinc in the pectoral and tibia muscles depends on the type of source and its levels in the diet, so with increasing it in the diet, its storage in the tissue increases. This increase in the organic form is due to the specific absorption mechanism of the element chelated with the organic peptide (Afshar Bakeshlo et al., 2024; Hu et al., 2022). The results of Table 3 show that the survival rate in the flock was not affected by the source and level of zinc in the diet (P> 0.05). Egg mass was not significantly affected by dietary treatments (Table 3). However, a numerically lower laying rate was observed in the negative control group, which may reflect a compensatory physiological response to zinc deficiency. Also, the increase in egg mass, due to the biological limitations of the bird, is more affected by the amount of energy and protein in the diet than by the zinc element. In confirmation of these findings, it has been reported that different sources and levels of zinc, copper and manganese do not affect the production rate and egg weight in laying hens (Chen et al., 2022; Domel et al., 2024).
Conclusion: The use of mineral sources with higher bioavailability and longer tissue retention represents an effective strategy for enhancing the nutritional quality of animal products. Increasing the amount of zinc with conventional inorganic forms, such as zinc sulfate, can reduce copper absorption and lead to negative biological consequences. On the other hand, the use of an organic source, despite retention, is associated with increased production costs and difficulty in supply. Therefore, it is recommended to use a level of 75 mg/kg of zinc hydroxychloride to improve the zinc storage index in eggs, while also enhancing the biological response of the hens.
کلیدواژهها English
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