Effects of dietary trace element supplementation on performance of laying hens and mineral content of egg yolk

 

 

M.N. Aghdashi; A. Nobakht^#; Y. Mehmannavaz

Department of Animal Science, Maragheh Branch, Islamic Azad University, Maragheh, Iran

 

 

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ABSTRACT

In this experiment, 320 laying hens of Hy-Line W-36 strain were used in a 2 x 2 x 2 factorial design (eight treatments and eight birds in each pen). The treatments were 0 and 400 mg/kg iron salt, 0 and 450 mg/kg iodide, and 0 and 0.1 mg/kg vitamin B12. There were five replicates of each treatment combination and the birds were from 26 to 39 weeks old. The interaction of iron salt and iodide, the use of 450 mg/kg iodide and 0 levels of iron salt increased the iodide content of yolks. In the treatments with 400 mg/kg of iron salt combined with iodide and with 400 mg/kg of iron salt with 0 levels of iodine salt this caused a sharp decrease in the iodide content of the yolk. In the interaction of treatments containing iron salt and vitamin B12, the lowest amount of cobalt and the highest level of Iodide were observed at the 0 levels of both supplements, whereas the combined use of iron salt and vitamin B12 increased the level of cobalt and decreased the yolk iodine content. In the three-way effects between these salts, yolk iron and cobalt content increased, and the highest amount of Iodine was observed in the third treatment (without vitamin B12 and iron). Overall the use of iron salt, iodine, and vitamin B₁₂ could improve the performance of hens and the composition of egg yolk.

Keywords: cobalt, ferrous sulfate, iodine, vitamin B₁₂, yolk

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Introduction

Numerous studies have shown that trace elements affect the performance of livestock significantly, including that of birds. Nevertheless, the nutrition of birds, in particular laying hens, can vary, depending on factors such as type of the bird, genetic variation, location, time of year, stage of growth and production. Elements such as iron, iodide and vitamin B₁₂ are vital to the overall health of birds. Minerals and vitamins that are good antioxidants can improve the internal and external quality of the eggs considerably (El-Hack et al., 2018).

Iron (Fe) is important to the performance of laying hens and the optimal dose has been demonstrated to be 75 to 80 ppm per kg of poultry feed (Liao et al., 2017). The biochemical processes involved include electron transport, peroxidase and catalase activities, oxygen transport and storage (haemoglobin and myoglobin), porphyrin metabolism, collagen synthesis, lymphocyte and granulocyte function, and neurotransmitter anabolism and catabolism (Abd El-Hack et al., 2020; Hamidi et al., 2021). According to the NRC (1994), 80 ppm of iron per kg of feed per day was recommended for the optimal performance of Hy-Line W-36.

Iodine is an essential microelement for humans and animals, and is required for the synthesis of triiodothyronine, thyroxine, and tyrosine (iodinated amino acid). Iodine deficiency reduces the production of thyroid hormones, causing morphological and functional changes of the thyroid gland and thus reducing the secretion of thyroxin (Pearce, 2017; Gaurav et al., 2021).

Naber and Squires (1993) showed that vitamin B12 supplementation could increase the B12 content of the egg. Increasing the dietary concentration of vitamin B12 from 0.5 to 16 Mg/kg for 28 to 70 week old commercial white Leghorn chickens improved vitamin B₁₂ level of the yolk by eleven-fold.

The mineral composition of egg can be enriched through manipulating the diet (Abd El-Hack et al., 2020; Macit et al., 2021; Rattanawut et al., 2021). According to recent studies, there is a dearth of information about the main effects of iron, iodine and vitamin B₁₂ on functional characteristics of laying hens. Therefore, this study was designed i) to investigate the possibility of enhancing the yolk quality with the administration of potassium iodide, vitamin B₁₂, and ferrous sulfate, ii) to improve the iodine, cobalt, and iron contents of eggs through dietary augmentation, and iii) to determine the effects of these nutrients on egg quality and poultry production. The experiment was implemented by providing supplemental iron salts, iodine and vitamin B₁₂ to Hy-Line layers.

 

Materials and Methods

The protocol (no. 1361-IAU. 11.17.2019) was approved by the Experimental Animal Ethics Committee of Maragheh Islamic Azad University. The experiment was conducted at Aghlary Farm Centre, Khoy, West Azerbaijan Province, between 18 November 2019 and 17 January 2020.

Three hundred and twenty Hy-Line W-36 hens were used in a 13-week study. They were 26 to 39 weeks old and weighed from 1.48 to 1.52 kg. Treatments were arranged in a 2 x 2 x 2 factorial design. There were five replicates with eight birds in each replicate. Two adjacent cages (cage dimension 40 χ 20 χ 25 cm) containing four hens were considered an experimental unit. The hens received 16 hours/day of artificial lighting, with ventilation maintaining the building at a natural ambient temperature. Feed and water were provided ad libitum throughout the experiment. After an adaptation period of 10 days, the number of eggs produced, egg weight, and the amount of feed consumed were recorded daily. Feed conversion ratio (FCR) was calculated from average daily feed intake and the average egg mass produced per day (MP). The percentage of days on which a hen produced an egg (PP) was also calculated. After 13 weeks, 20 eggs were randomly selected from each treatment and were analysed for their cobalt and iron contents (Research Department of Chromatography, Iranian Academic Centre for Education, Culture and Research (ACECR), Urmia, West Azerbaijan, Iran).

A basal corn-soybean meal basal diet was formulated according to the National Research Council (1994) for laying poultry (Table 1). Experimental diets were obtained by supplementing the basal diet with synthetic 0 and 400 mg/kg of iron (Fe), 0 and 450 mg/kg of iodine (I), and 0 and 0.1 mg/kg of vitamin B₁₂.

To analyse the mineral content of the yolk, 2.5 g of the yolk sample was weighed and placed inside the crucible. The crucible was then placed a kiln and heated to a temperature of 550 °C. After the whole ash was prepared, the crucibles were allowed to cool, and then a solution of nitric acid was used to dissolve the ash at 75 °C. The content of each crucible was transferred to a 25 cc balloon using a funnel, and the vessel was rinsed several times with distilled water, which was also added to the balloon. Measurements of cobalt and iron were done in the Research Department of Chromatography, Iranian Academic Centre for Education, Culture and Research (ACECR) at Urmia, Iran. Standards containing 1000 ppm iron and cobalt were prepared. The atomic absorption rate of the samples was recorded using atomic absorption apparatus (Analyst 800, PerkinElmer, Inc., Waltham, Massachusetts, USA). The amounts of cobalt and iron in each sample were calculated with a calibration curve and expressed per 100 g of the sample.

After 13 weeks, 20 eggs were randomly selected from each treatment and the iodine content of the egg yolk was measured by kinetic spectrophotometry (Haap et al., 2017; Todorov et al., 2018; Tufarelli et al., 2021). Iodine was also measured in the Research Department of Chromatography, ACECR.

The data were analysed using the PROC GLM procedure of SAS 9.4 software (SAS Institute Inc., Cary, North Carolina, USA). When the variance was unequal across treatments, the data were log-transformed before they were analysed (Milani et al., 2013). Means were compared with Tukey's multiple range test at α = 0.05.

 

Results and Discussion

Mean concentrations of iron, cobalt and iodide in the egg yolk are shown in Table 2. The three-factor interaction was significant for iron and iodide, The main effects of vitamin B12 and iodide were significant for the cobalt content of the egg yolks, which was increased when supplemental B₁₂ or iodide was provided. The significance of these interaction effects required that the interacting treatments should be considered simultaneously in interpreting the results. The highest levels of iron in the yolk were found when i)iodide was supplemented without iron and B12, ii) iron was supplemented without iodide and B12, and iii) the diet was augmented with iron, iodide and B12. Conversely, the lowest levels of iron in the yolk were found when i) no supplemental nutrients were provided, and ii) supplemental iron was provided with iodide or B12. The Iodine content of the egg yolk was highest when the diet was supplemented with iodide and without additional iodide or B12 and lowest when the diet was unsupplemented. The remaining treatments produced responses that were intermediate between these extremes.

The effects of the various supplements on the performance of laying hens are shown in Table 3. Mean egg weight and feed intake were not affected by the dietary supplements (P >0.05). The PP, MP, and FCR were all affected by the three-factor interaction among the treatments (P <0.05) with the observed differences in MP and FCR probably being attributable to the treatment effects on PP. The PP was highest from hens that were supplemented with iron, iodide and vitamin B12 and lowest for hens that were provided only supplemental iodide. The remaining treatments produced intermediate responses that were not significantly different from either extreme value. As with PP, hens that received all three dietary supplements had the highest MP and hens that received supplemental iodide produced the lowest MP. All of the remaining treatments produced values similar to the extreme values, with the exception that the supplementation with iron alone resulted in higher MP than supplementation with iodide alone.

At 28 - 36 weeks old, there were no significant differences in feed intake. Saki et al. (2019) and Jarosz et al. (2021) observed that feed intake decreased significantly with iron supplementation in broiler diets, which is not consistent with the results of the present study. In this study, however, there was no significant effect of iron on feed intake. Supplementing poultry diets with Iodine had no significant effect on eggs and egg mass (Damaziak et al., 2018; Sarlak et al., 2020).

Because of improved production traits, it seems that the microelement requirements recommended by NRC for laying poultry need to be revised. Thus, to meet the fundamental requirements of minerals and vitamins in industrial poultries, it is necessary to conduct some studies. Egg yolk has good potential for enrichment with diets supplemented with various minerals and vitamins. It is possible to increase the vitamin content of eggs significantly through fortifying the laying hen diet with synthetic vitamins, and table eggs can be changed to a rich source of microelements (Bagheri et al., 2019; Kang et al., 2020; Sun et al., 2021).

Cobalt is not considered an essential mineral for hens, even though it may amount to 4% of the composition of the molecule of vitamin B₁₂. Therefore, in this study, cobalt was investigated as an indicator of B12. Table 2 shows that when the diet of laying hens is supplemented with B12, the level of cobalt increases significantly. However, adding vitamin B₁₂ to the diet did not affect (P >0.05) cobalt concentration in the liver and yolk (Souza et al., 2020).

Iron is one of the components of materials found in bodies and is involved in many reactions, in metabolism, and in energy transformation (Xie et al., 2019). Sarlak et al. (2021) stated that the iron contents of yolk, albumen, and shell rose gradually with increasing concentrations of iron. Damaziak et al. (2018) found that the dietary addition of 10 mg iodine/kg caused a beneficial effect on the laying performance of hens in egg production, egg weight, and feed conversion efficiency. Sarlak et al. (2020) demonstrated that supplementation of diets with 2 or 4 mg iodine/kg increased the iodine content of eggs without adverse effects on hen performance and egg quality traits. Janist et al. (2019) noted that vitamin B₁₂ did not affect the production performance and egg quality.

Furthermore, iron and iodide were increased in the egg yolk when the levels of these microelements in diets were elevated. When iron and iodideare added to salt and in the presence of oxygen, the iodine moiety of the double-fortified salt is likely to be unstable owing to evaporation and catalytic oxidation of the negatively charged iodide ion to iodine (Sattarzadeh & Zlotkin, 1999). According to the present result, iron in the diet and the iodine content of the egg were negatively correlated, indicating the antagonistic effect of iron on iodine. According to Table 3, to enrich eggs with iron, special attention should be paid to the level of iodine in the diet or the iodide should be prevented from being evaporated, since reducing the iodine content of eggs lowers their nutritional value.

 

Conclusions

Generally, the use of iron, iodine, and vitamin B12 salt supplements increased the performance of chickens, the egg content, including iron, iodine, and cobalt, and improved some of the economic characteristics of chickens. This study showed that to enrich eggs yolk with iron, special care should be paid to iodine levels in the poultry diets. However, owing to the increasing accumulation of iron and iodine in the eggs, further studies are necessary to evaluate the safety of egg fortification with iron and iodine.

Authors' Contributions

MNA collected the data for this study, YM conducted the statistical analyses, MNA and AN developed the original hypotheses and designed the experiments, All authors have read and approved the finalized manuscript

Conflict of Interest Declaration

The authors declare that they have no known competing financial interests or personal relationship that could have appeared to influence the work reported in this paper.

 

Acknowledgements

The article was extracted from the PhD. thesis prepared by Mir Nima Aghdashi, under the guidance of Prof. Ali Nobakht.

 

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Submitted 8 July 2021
Accepted 12 August 2021
Published 8 November 2021

 

 

# Corresponding author: anobakht20@yahoo.com