نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Introduction Sulfur-containing amino acids, including methionine and cystine, are functional amino acids that affect protein structure, and metabolism (Zhang et al., 2024). Methionine irreversibly converts into cystine through the trans-sulfuration pathway. Therefore, the requirements for methionine alone and methionine + cystine (Met+Cys) are considered together, known as total sulfur-containing amino acids (Castro et al., 2019). Commercial poultry feed is usually supplemented with solid DL-methionine with 99% purity or liquid methionine hydroxy analogue (MHA) with 88% active ingredient content (Bateman et al., 2005). Birds can utilize methionine isomers and analogs for protein synthesis (Sahebi-Ala et al., 2021). The form of amino acids used in animal tissues is the L isomer, and the D isomer has no biological activity. However, in the case of methionine, birds can utilize both isomers (Kalbande et al., 2009). Before being used by animals, DL-methionine must be converted to L-methionine in the liver or kidney through a two-step reaction (Teng et al., 2023). Considering the role and importance of methionine in laying hens, this experiment aimed to compare two sources of DL-methionine with liquid MHA and investigate the effect of the level of digestible Met+Cys in the diet on the production performance indices, egg chemical composition and blood serum metabolites.
Materials and Methods A total of 324 Shaver White laying hens was used as a 2×3 factorial arrangement in a randomized complete block design with 6 treatments, 6 replicates and 9 birds each, in the age of 34-46 wk. The treatments included three levels of digestible Met+Cys, namely 0.555% (25% less than recommendation), 0.742% (equal to the recommendation) and 0.929% (25% more than the recommendation) in diet from two sources of MHA (equivalent to 88% of methionine) and DL-methionine. All birds had free access to drinking water and feed during the experiment. The lighting program was performed as 16 h of lighting and 8 h of blackout. The experimental period included the first two wk (32-34 wk old) for the period of adaptation to the place and conditions of the experiment, where the birds were fed with the same ration and in the age period of 34 to 46 wk, the birds were fed with experimental diets and record taking was done in this period. The supplements required for this experiment including DL-Methionine (white crystalline powder with 99% methionine content and 58.1% crude protein) and MHA (liquid with 88% methionine content) and the equivalent of zero crude protein) were prepared from Evonik Degussa and Adiseo France, respectively. Experimental corn-soybean meal diets were formulated with UFFDA software based on recommendations for Shaver White laying hen management guide (2020). During the experiment, the amount of egg production in each replicate was recorded on a daily basis (number and weight) and the average egg laying percentage and mass production of eggs (g/hen/d) were calculated during the experiment. Average egg weight was calculated by dividing the total weight of eggs by the number of eggs per day in each replicate. The feed conversion ratio in each replicate was calculated by dividing the feed consumed by the egg mass. To check body weight changes, the birds of each experimental unit were weighed in groups at the beginning and end of the experiment. To determine the chemical composition of eggs, white and yolk were separated and after weighing, they were placed in an oven at a temperature of 75 ○C for 72 h. Then the percentage of dry matter (DM) of white, yolk and whole egg (without shell) was calculated. For the measurement of crude protein and fat, yolk and white DM were used. Crude protein percentage of yolk and egg white was measured using Kjeldahl method and fat percentage of yolk was also measured using Soxhlet method and diethyl ether solvent. The percentage of crude protein and fat of white, yolk and whole egg (without shell) was calculated and reported according to their dry matter (AOAC, 2019). At the end of the experiment sera samples were obtained from one bird in each replicate and the level of blood metabolites including cholesterol, triglycerides, low density lipoproteins (LDL), high density lipoproteins (HDL), albumin, total protein, creatinine and uric acid were measured by using Pars Azmoon biochemical kits and auto analyzer (Model, BT3000).
Results The birds fed with diets containing two levels of digestible Met+Cys equaled or exceeded the recommendation had higher eggs production compared to the lower than recommended level (P < 0.05), and with the increase in the digestible Met+Cys level, the daily egg mass, the egg weight and feed intake were increased and the feed conversion ratio was decreased. The levels of triglyceride and creatinine in the blood serum in lower or equaled Met+Cys levels were higher than the recommended level and blood albumin in high Met+Cys level was less than the recommended level. Diet digestible Met+Cys level did not have any significant effect on changes in body weight, and measured blood serum metabolites. The effect of methionine source and the interaction effect of level with methionine source were not significant on any of the studied indicators. The results of this study showed that a higher than recommended level of methionine in the diet can increase the size of eggs and egg mass and improves the feed conversion ratio, and also MHA without reducing yield can be a suitable substitute for DL-methionine in the diet of laying hens.
Conclusion The results of this experiment showed that the concentration of methionine+cystine in the diet of Shaver White laying hens 25% higher than the recommended level for the strain, increases the egg size and egg mass and improves the feed conversion ratio. Also, no significant difference was observed between two sources of methionine (DL-methionine and liquid methionine hydroxy analogue) on production performance, chemical composition of eggs and blood metabolites of laying hens. Therefore, the use of methionine hydroxy analogue, taking into account the methionine content of 88%, can be a suitable substitute for DL-methionine in the diet of laying hens without negatively affecting the productive performance indices and the chemical composition of the eggs.
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