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. 2023 Apr 17;9(4):1656–1665. doi: 10.1002/vms3.1139

Effect of dietary dexamethasone on the morphologic and morphometric adaptations in the lymphoid organs and mortality rate in broilers

Rafiqul Islam 1, Nasrin Sultana 1,✉, Ziaul Haque 1, Mohammad Rafiqul Islam 1
PMCID: PMC10357247  PMID: 37067539

Abstract

Background

Thymus, bursa of Fabricius and spleen are the major lymphoid organs of avian species that plays a crucial role in their immunity. Though glucocorticoids are reportedly used as growth promoters, they also suppress the immune system.

Objectives

The objective of this study was to investigate the morphologic and morphometric adaptations in the lymphoid organs as well as the mortality rate in broilers in response to long‐term treatment with dexamethasone (DEX).

Methods

A total of 80 one‐day‐old broiler chicks (Cobb 500) were randomly divided into four homogenous groups (control – C and treatment groups – T1, T2, and T3). The treatment groups received DEX at the rate of 3, 5, and 7 mg/kg commercial feed. Samples, i.e. thymus, bursa of Fabricius, and spleen, were collected on 7, 14, 21, and 28 days of the experiment. Relative weight of the organs was calculated on each sampling day. The tissues were then processed and stained with haematoxylin and eosin stain for morphological and morphometric study.

Results

The relative weight of lymphoid organs was found substantially (p < 0.05) less in the DEX‐treated groups. Significant (p < 0.05) reduction in lobular size and the cortical‐medullary ratio was observed in the thymus of the DEX‐treated broilers. Follicular atrophy and massive depletion of lymphocytes were evident in the bursa of Fabricius. The mortality rate was also increased which was largely dependent on the dose and duration of DEX treatment.

Conclusions

The study results indicate that DEX treatment can alter the morphology and morphometry of lymphoid organs which might result in severe immunosuppression and increased mortality rate in broilers.

Keywords: broiler, bursa of Fabricius, dexamethasone, spleen, thymus

Glucocorticoids are reportedly used as growth promoters that also suppress the immune system. In this context, the goal of this study was to investigate the morphologic and morphometric adaptations in the lymphoid organs as well as the mortality rate in broilers in response to long‐term treatment with dexamethasone (DEX). The study results indicate that DEX treatment can alter the morphology and morphometry of lymphoid organs which might result in severe immunosuppression and increased mortality rate in broilers.

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1. INTRODUCTION

Global consumption of animal meat and demand for animal‐derived protein is rising which is primarily driven by population growth and increasing income. This trend is most likely to continue in future as the meat consumption has increased by 58% over the last two decades and reached 360 million tonnes in 2018 (Whitnall and Pitts, 2019). Due to the potential health risks of red meat (Wolk, 2017), the trend of meat consumption is shifting towards poultry meat. As a result, the poultry population has become 23 billion as per the FAO database in 2016 with an annual growth rate of around 7.4% in the East and South‐East Asian region (Mottet & Tempio, 2017). Growing demand and low‐cost availability to consumers are the pivotal reasons behind the phenomenal expansion of this agricultural subsector. Broiler weight is increased by about 60 times from hatching to slaughter and gains five times more weight than the laying chicken within the same rearing period (Havenstein et al., 2003; Zhao et al., 2004). Increasing the growth rate of meat‐purpose chickens like broilers by genetic selection and modification has always been the primary concern for the breeders (Hartcher & Lum, 2020). In addition to this, various growth‐promoting agents (GPs) are also used to maximise the genetic potentiality to promote feed efficiency and growth rate (Dhama et al., 2014; Mostafa et al., 2016).

The potential role of GPs in improving intestinal ecology to maximise dietary energy utilisation and growth performance has motivated researchers to discover a wide range of GPs as feed additives (Dhama et al., 2014). Antibiotics, steroids, prebiotics, probiotics, psychobiotic, synbiotics, oligosaccharides, essential oils, herbal extracts etc. are reportedly supplied with the diet to enhance feed efficiency and growth of broilers. Steroids boost muscle growth and lipid metabolisation resulting in the augmentation of growth rate (Liu and Wu, 2019). Steroids have been popularly used in different countries as GPs to increase the growth rate of livestock, particularly cattle. According to previous study reports, steroids are used indiscriminately in large animals for fattening purposes in Bangladesh (Islam et al., 2013; Kamal et al., 2019).

Glucocorticoids (GCs) are steroid hormones (available as both natural and synthetic derivatives), the action of which is mediated by intracellular glucocorticoid receptors (GRs) and thus control different functions in the body like metabolism, development, and reproduction. GCs are also used in treating inflammatory and autoimmune diseases (Kadmiel & Cidlowski, 2013). An increased level of GC modifies the metabolic pathways in the body to fulfil the altered energy demands. Prolonged GC therapy at higher doses upregulates the catabolic gene expression that leads to various side effects like fat deposition, weight gain, etc. (Schoneveld et al., 2004). Synthetic GCs are drugs that are almost similar to the natural ones but differ in their potency and metabolic clearance. Prednisolone, dexamethasone (DEX), and budesonide are the widely prescribed GCs. DEX, unlike natural GCs, is not inactivated by 11b‐HSD2, which intensifies its local availability (Kadmiel & Cidlowski, 2013). As of now, stress is regarded as one of the biggest risk factors for poultry production in the poultry industry as stress leads to varying degrees of immune suppression. Stress‐induced immune suppression happens through two major routes: the hypothalamic‐pituitary‐adrenal (HPA) axis and the autonomic nervous system (Srivastava & Kumar, 2015). Stress enhances the secretion of GCs and catecholamines that have a detrimental impact on the functionality of the immune system including suppressed NK cell activities, lymphocyte count, production of antibodies as well as the reactivation of latent viral infections and thus resulting in immune suppression (Srivastava & Kumar, 2015; Marketon & Glaser, 2008). Due to the close proximity of DEX to the endogenous corticosteroids, it has the potential to produce homologous effects like increased corticosterone levels and activates stress‐related signalling pathways (Calefi et al., 2016). Dietary DEX has been used in many previous studies to induce stress for studying the effects in poultry in response to stress (Osho & Adeola, 2020).

Bursa of Fabricius, thymus and spleen are the major lymphoid organs of avian species that play a crucial role in developing and maintaining their immunity. However, factors causing immune deficiency or immunosuppression are one of the leading issues that negatively affect the poultry industry. In a previous study, it was shown that stressors increase the blood levels of heterophils while decreasing the blood levels of lymphocytes (Post et al., 2003). Elevated levels of GCs cause immunosuppression by blocking antibody production from B cells, T cell production, and by suppressing phagocytic activities (Engler & Stefanski, 2003). Furthermore, DEX therapy caused granulocytophilia and decreased mononuclear cells in humans, lymphopaenia and neutrophilia in rats, neutrophilia and eosinopaenia linked to lymphopaenia in cattle, and neutrophilia and lymphopaenia in pigs (Aengwanich, 2007). Depletion of blood lymphocytes and reduction of the relative weight of immune organs were previously reported in broiler in response to DEX therapy (Aengwanich, 2007; Vicuña et al., 2015). DEX can trigger apoptosis in both thymocytes and spleen cells, which is compatible with the consequences of stress on the body (Ayroldi et al., 2007). Prolonged DEX treatment can result in glomerular and tubular atrophy, depletion of the leydig cell population in the testes as well as the alteration in liver morphology in the broiler (Islam et al., 2021; Sultana et al., 2021; Sultana et al., 2020a). In addition to this, negatively affected growth performance, increased weight of liver, and decreased relative weight of immune organs were also reported in broiler in response to corticosterone therapy (Mehaisen et al., 2017).

However, proper attention has not been given yet to the immune status of broiler in respect of using steroids as GP in broiler production. Therefore, the research was set to provide a comprehensive picture of the potential effects of dietary DEX on the morphologic and morphometric adaptations of the lymphoid organs (thymus, bursa of Fabricius and spleen) of broiler.

2. MATERIALS AND METHODS

2.1. Experimental design

The study was performed on 80 healthy one‐day‐old ‘Cobb 500’ broiler chicks of either sex to study the macroscopic and microscopic structure of the lymphoid tissues (thymus, bursa of Fabricius and spleen). The chicks were housed in an acclimatised room, with the provision of sufficient artificial light and ventilation. Four homogenous groups (n = 20) were then formed by randomly selecting the chicks and allocating them to different groups (one control and three DEX treatment groups – T1, T2, and T3). The broilers were maintained on a commercial broiler diet. The DEX treatment groups received dietary dexamethasone (Decason®, Opsonin Limited, Bangladesh) at a concentration of 3 mg/kg in group T1, 5 mg/kg in group T2, and 7 mg/kg in group T3 with their diet (Aengwanich, 2007; Li et al., 2009; Osho & Adeola, 2020). Each group was reared in separate pens with a constant supply of feed and drinking water ad libitum. Mortality records were kept as they occurred to calculate the mortality rate (%) [Mortality rate (%) = (Total death of birds in a group/Total no of birds present at that time in that particular group) × 100]

2.2. Collection of sample

To study the effect of dietary DEX on the lymphoid organs (thymus, bursa of Fabricius, and spleen), five broilers from each group were sacrificed by cervical subluxation method on day 7 (D7), day 14 (D14), day 21 (D21), and day 28 (D28) of the experiment. Individual body weights were also recorded on each sampling day before sacrificing the broilers. The thymus was collected following dissection of the ventral neck whereas the spleen and bursa of Fabricius were collected after opening the abdomen.

2.3. Macroscopic study

As part of the macroscopic study, the colour and weight of the lymphoid organs were recorded. The colour of the organs was visually investigated. The weight was measured in gram using an FGH Series high precision balance (AND Company Limited, Korea). The relative weights of the lymphoid organs were calculated using the following formula: (organ weight/body weight) × 100. Required photographs were then captured by using a digital camera (Canon EOS 1200D, Japan) for a better illustration of the macroscopic attributes of lymphoid organs.

2.4. Microscopic study

For the histological study, the samples were fixed in 10% neutral buffered formalin for 72 h. Then the samples were processed and stained (haematoxylin and eosin; H&E) following standard procedure (Sultana et al., 2020b). The stained tissue sections were then investigated under a light microscope (Leica DMR; Leica Microsystems, Wetzlar, Germany) at 100× magnification. For morphometric measurements, the length and width of the thymic lobe and bursal follicle, cortical and medullary areas of the thymus were measured using ImageJ Free Hand Tool software. The scale of measurement was set as micrometre (μm). The cortical‐medullary ratio was calculated by the following formula: the area of the cortex/the area of the medulla. Thus, a total of five sections were evaluated for each group. Necessary photomicrographs were captured by a photomicroscope (Model: CX41U‐LH50HG, Olympus Corporation, Tokyo, Japan) at 100× magnification for a better presentation of the histological findings.

2.5. Statistical analyses

All the obtained data from this study were analysed by the SPSS software version 22 (IBM SPSS Statistics 22). The normality distribution of the data set was tested using Shapiro–Wilk test. Comparison among the groups was done using one‐way analysis of variance (ANOVA) with post hoc Duncan's multiple range test. Probability (p) values less than 0.05 were considered significant and p values less than 0.01 were considered highly significant. All data were presented as mean ± standard error of the mean (SEM).

3. RESULTS

3.1. Effects of dexamethasone on thymic morphology and morphometry

Macroscopically, the thymus showed marked atrophy (Figure 1‐A1). The relative weight of the thymus was found significantly (p < 0.05) less in the DEX‐treated groups when compared to group C. On D7, no significant difference in the relative weight was seen between group C and T1, though it was decreased significantly (p < 0.05) in groups T2 and T3 when compared to group C. However, from D14, the difference between group C and DEX‐treated groups was highly significant (p < 0.01). The only significant difference between the DEX‐treated groups was found between groups T1 and T2 on D14 (Figure 2).

FIGURE 1.

FIGURE 1

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Representative images of lymphoid organs of broiler (A1 – thymus, A2 – spleen, and A3 – bursa of Fabricius) of different experimental groups: C: represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively, after collection of sample on D28.

FIGURE 2.

FIGURE 2

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Effect of dietary DEX on the relative weight of thymus of broiler of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Columns with different alphabetic superscripts are significantly different from each other (p < 0.05).

Microscopically, the lobes of the thymus were covered with a connective tissue capsule which gave rise to the thin interlobular septa subdividing the lobes into lobules. Each lobule exhibited a distinct inner medulla surrounded by an outer cortical region. The thymic cortex was densely packed with lymphocytes which gave this region a characteristics dark bluish appearance. On the other hand, the medulla mainly consisted of epithelial reticular cells which gave this region its characteristic light bluish pink appearance. No alteration in the histomorphology of the thymus was seen in the DEX‐treated groups (Figure 3). However, significant histomorphometric alterations were evident in the DEX‐treated groups compared to group C (Figure 4).

FIGURE 3.

FIGURE 3

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Representative photomicrographs of broiler thymus of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively on D28 (haematoxylin‐eosin stained). Cx – cortex; M – medulla. Magnification – 100×.

FIGURE 4.

FIGURE 4

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Length (a) and width (b) of the thymic lobules in different groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively, of broilers on different days of the experiment. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Stacked bars with different alphabetic superscripts are significantly different from each other (p < 0.05).

On D7, there was no significant (p > 0.05) difference in the length and width of the thymic lobule among the experimental groups. However, lobular length and width were found significantly (p < 0.05) less in the DEX‐treated groups on D14, D21, and D28 of the experiment. The cortical‐medullary ratio was also decreased significantly in the DEX‐treated groups on different days of the experiment. The highest cortical‐medullary ratio was found in the control group whereas the lowest value was found in the treated groups (Table 1). Though the DEX‐treated groups showed a dose‐dependent decrease in the morphometric parameters, the differences were not significant (p > 0.05).

TABLE 1.

Cortical‐medullary ratio in the thymus of broiler on different days of the experiment.

Days of the experiment
Experimental groups D7 D14 D21 D28
C 0.69 ± 0.05a 0.97 ± 0.09a 1.22 ± 0.12a 1.56 ± 0.21a
T1 0.48 ± 0.02b 0.76 ± 0.06b 1.03 ± 0.10b 1.23 ± 0.13b
T2 0.47 ± 0.04b 0.71 ± 0.07b 0.96 ± 0.06b 1.13 ± 0.11b
T3 0.41 ± 0.03b 0.73 ± 0.05b 0.92 ± 0.07b 1.08 ± 0.08b
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C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Values with different alphabetic superscripts in the same age groups are significantly different.

3.2. Effects of dexamethasone on morphology and morphometry of bursa of Fabricius

Macroscopically, the bursa of Fabricius was composed of numerous mucosal folds where the mid‐region was thicker than the base or apical region (Figure 1‐A2). Morphologically, there was no noticeable difference between the control and DEX‐treated groups. However, significant morphometric alterations were seen in the DEX‐treated groups. The relative weight of the bursa of Fabricius was substantially (p < 0.05) less in the DEX‐treated groups. There were also significant (p < 0.05) differences among the treated groups. The maximum relative weight was found in group C whereas the minimum weight was found in group T3 on different days of the experiment (Figure 5).

FIGURE 5.

FIGURE 5

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Effect of dietary DEX on the relative weight of the bursa of Fabricius of broiler of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Columns with different alphabetic superscripts are significantly different from each other (p < 0.05).

Microscopically, each fold consisted of numerous lymphatic follicles. The follicles were distinctly separated by connective tissue fibres. In group C, each follicle was composed of a light central zone (medulla), a dark peripheral zone (cortex) and a corticomedullary junction. The peripheral cortical zone was closely packed with dark blue lymphocytes whereas the pale stained medulla contained numerous epithelial reticular cells and few lymphocytes. On the other hand, there was substantial follicular lymphocytic depletion, especially in the middle and apical regions of the bursal folds in the DEX‐treated groups. The lymphocytic depletion was ameliorated with the increase in DEX dose. In the T2 group, vacuolation in the medullary region was noticed due to the excessive loss of lymphocytes. In the T3 group, the medullary region of the lymphatic follicles was vacuolated and the normal histoarchitecture of the lymphatic follicles was completely lost (Figure 6).

FIGURE 6.

FIGURE 6

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Representative photomicrographs of the broiler bursa of Fabricius of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively on D28 (haematoxylin‐eosin stained). CM – corticomedullary junction, Cx – cortex; M – medulla. Magnification – 100×.

The histomorphometric study also revealed marked alterations in the length and width of lymphatic follicles indicating follicular atrophy. Both the length and width decreased significantly (p < 0.05) in the DEX‐treated groups. However, there was no significant (p > 0.05) difference between the DEX‐treated groups (Figure 7).

FIGURE 7.

FIGURE 7

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Length (a) and width (b) of the bursal follicles in different groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively, of broilers on different days of the experiment. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Stacked bars with different alphabetic superscripts are significantly different from each other (p < 0.05).

3.3. Effects of dexamethasone on splenic morphology and morphometry

There was no noticeable morphologic alteration in the spleen in the control and DEX‐treated groups. The spleen appeared small and rounded with brownish‐red colour. However, marked alterations were found in the gross morphometric study. The relative weight of the spleen in the DEX‐treated groups was significantly (p < 0.05) less compared to group C. There were also substantial differences among the treated groups. The maximum relative weight of the spleen was found in group C whereas the minimum weight was found in group T3 on days 7, 14, 21, and 28 of the experiment (Figure 8).

FIGURE 8.

FIGURE 8

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Effect of dietary DEX on the relative weight of the spleen of broiler of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively. Data were analysed using one‐way ANOVA followed by post hoc Duncan's multiple range test. Columns with different alphabetic superscripts are significantly different from each other (p < 0.05).

Microscopically, the spleen was covered with a thick capsule with a small number of trabeculae. The splenic parenchyma was composed of red pulps containing red blood cells and white pulps containing mostly lymphocytes. No noticeable alteration was seen in the DEX‐treated groups compared to group C (Figure 9).

FIGURE 9.

FIGURE 9

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Representative photomicrographs of broiler spleen of different experimental groups: C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively on D28 (haematoxylin‐eosin stained). Cp – capsule, Rp – red pulp, Wp – white pulp. Magnification – 100×.

3.4. Mortality rate

The mortality rate (%) of broilers in different groups is shown in Table 2. The mortality rate was nil in the control group throughout the experiment. After a 100% survival rate for the first 3 weeks, the T1 group showed a higher mortality rate in the fourth week. In the T2 and T3 groups, the mortality rate rose gradually with the course of DEX treatment duration. The lowest and the highest incidence of mortality were found in the C and T3 groups, respectively.

TABLE 2.

Mortality rate (%) of broilers in different experimental groups.

Week Mortality rate (%)
C T1 T2 T3
1st 0 0 6.67 13.33
2nd 0 0 9.09 10
3rd 0 0 0 0
4th 0 33.33 25 33.33
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C represents the control group and T1, T2, and T3 represent the treatment groups treated with dexamethasone at the rate of 3, 5, and 7 mg/kg, respectively.

4. DISCUSSION

The poultry sector is currently undergoing a highly productive period with high market demand. Improving resistance to diseases in chicken is essential for ensuring market supply including the industry's continuous expansion. Stress‐stimulated suppression of the immune system is one of the major causes of diseases in poultry (Carvalho et al., 2018; Lv et al., 2018). Research on the regulation mechanism of immune suppression in poultry has both theoretical and production value. GC is a type of steroid hormone, which can modulate immune function. GCs can exert varying effects on the lymphoid organs like lymphocytic depletion, and atrophy of the lymphoid organs (Vicuna et al., 2015; Li et al., 2017). The effect of GC is dependent on the dose, route and period of administration, the genetic makeup of the broiler, etc. (Higgins et al., 2002; Carvalho et al., 2018). In the current study, we investigated the time and dose‐dependent effect of dietary DEX on the morphology and morphometry of the thymus, bursa of Fabricius and spleen of broiler chicken.

4.1. Effects of dexamethasone on thymic morphology and morphometry

The thymus is one of the primary lymphoid organs which can also act as a secondary lymphoid organ and is capable of playing a significant role in building up immunity in broiler chicken (Treesh et al., 2014). However, stress or different immunosuppressive drugs like DEX can affect its functionality through morphologic and morphometric alterations (Li et al., 2017; Sultana et al., 2020b). In the current study, DEX treatment substantially reduced the relative weight of the thymus. Such reduction in relative weight was also observed in the previous studies (Yang et al., 2015; Mehaisen et al., 2017; Carvalho et al., 2018). However, the histomorphological study of the thymus of both control and DEX‐treated groups revealed the normal histoarchitecture described in earlier studies (Akter et al., 2006; Treesh et al., 2014). On the other hand, the histomorphometric study revealed significantly reduced length and width of the thymic lobule in the DEX‐treated broilers. We also detected a significantly reduced cortical‐medullary ratio in the DEX‐treated groups. In a previous study, a similar reduction of corticomedullary ratio of the thymus in response to DEX treatment was reported (Carvalho et al., 2018). A similar finding was reported in another study where apoptosis of cortical lymphocytes of the thymus along with thymic atrophy in the DEX‐treated rabbits was found (Cannizzo et al., 2010). These findings might justify the reduction in the relative weight of the thymus in the current study.

4.2. Effects of dexamethasone on morphology and morphometry of bursa of Fabricius

In the present study, the relative weight of bursa in the control group was found between 0.22% and 0.29%. This is in line with a previous study where a relative weight of 0.21%–0.29% was reported (Carvalho et al., 2018). The relative weight of bursa decreased significantly in the DEX‐treated broilers which is in agreement with earlier study reports (Vicuna et al., 2015; Yang et al., 2015; Mehaisen et al., 2017; Carvalho et al., 2018). We also detected marked depletion of the number of lymphocytes in the bursa of Fabricius treated with DEX compared to the control group. Apoptosis, or programmed cell death, is considered to be the cause of lymphocytic depletion (Higgins et al., 2002). Bursal lymphocytes in chickens have larger amounts of GC receptors compared to the thymus, making the bursa more vulnerable to the GC effects (Schaumburg & Crone, 1971). However, the exact mechanism of GC‐induced programmed cell death is still unknown. DEX treatment significantly reduces the population of proliferating lymphocytes of the bursa of Fabricius (Higgins et al., 2002, Mehaisen et al., 2017). Though we did not investigate the expression pattern of GC receptors in the bursa of Fabricius in the current study, it is likely that activation of the GC receptors by DEX might control the reduction of relative weight and lymphocytic depletion. In the histomorphometric study, the length and width of bursal follicles were found significantly less in the DEX‐treated groups which indicate poor development of bursa in response to DEX treatment. This finding is in line with previous reports where follicular atrophy was reported in response to DEX therapy (Carvalho et al., 2018).

4.3. Effects of dexamethasone on splenic morphology and morphometry

The spleen is a secondary lymphoid organ of the body that plays a vital role in the development of local immunity and regulation of immune response (Li et al., 2017). Hence, the integrity of splenic histoarchitecture is crucial. In our study, we found significantly less relative weight of spleen in the DEX‐treated broiler which is in line with the prior research (Vicuna et al., 2015; Yang et al., 2015). However, no histomorphological alteration in the spleen was noticed in the DEX‐treated groups which is similar to the previous study (Sultana et al., 2020b). Notwithstanding, Sultana et al. (2020b) reported delayed development and decreased length and width of splenic pulps in response to treatment with DEX at a higher dose (7 mg/kg). DEX treatment also reduces the macrophage population in the spleen (Calefi et al., 2016). Li et al. (2017) reported significantly reduced spleen index, splenic lymphocytic proliferation, and increased percentage of splenic cell apoptosis in response to DEX therapy. These might be the underlying cause of decreased relative weight in the DEX‐treated broilers.

4.4. Mortality rate

DEX affects the feed intake, weight gain, immunity and the overall health status of broilers (Lv et al., 2018). In the current study, we detected a higher mortality rate in the DEX‐treated groups, in keeping with the compromised immune status of the treated broilers. It is noteworthy that the higher dose group showed more susceptibility which indicates the dose‐dependent effect of DEX treatment. In the previous studies, an increased rate of mortality in the DEX‐treated broilers was reported (Vicuna et al., 2015; Lv et al., 2018). DEX treatment affects the health of the broiler by increasing the metabolic burden, oxidative stress, and suppressing the immune system (Lv et al., 2018; Mehaisen et al., 2017). In the T1 group, mortality cases were found only in the fourth week which indicates the time‐dependent effect of DEX treatment.

Broilers are very susceptible to different stresses that create disasters for the farmers by reducing their productivity and increasing diseases and mortality rates (Lv et al., 2018). So, a better understanding of stress‐induced immune suppression is needed to combat pathogenic infection as well as to reduce the mortality rate. Stress‐induced immune suppression is mostly regulated by the neuroendocrine pathways where endogenous corticosteroids play a key role. As dexamethasone is a synthetic analogue of endogenous corticosteroids, the current findings can be implemented at the farming level to manage stress for optimum health and productivity of broilers (Calefi et al., 2016).

Lymphocytes are considered one of the key immunocytes, and hence their proliferation, differentiation, and maturation are critical for an immunological response. The excessive apoptosis of lymphocytes may lead to compromised immunity with a higher risk of infection. In our current study, we found marked atrophy of the lymphoid organs in response to DEX treatment. Though no distinguishable histomorphological alteration was noticed in the case of the thymus and spleen, the histomorphometry of these organs was significantly affected by DEX treatment. The bursal follicles also showed excessive depletion of lymphocytes. All these alterations may lead to severe immunosuppression in broiler chickens. The increased mortality rate in the DEX‐treated broilers also supports these findings. However, further study is required to detect the effects of DEX on lymphocyte proliferation, cell apoptosis and plasma cell distribution in the lymphoid organs.

AUTHOR CONTRIBUTIONS

Rafiqul Islam: formal analysis; investigation; methodology; project administration; writing – original draft. Nasrin Sultana: conceptualisation; funding acquisition; supervision; validation; writing – review & editing. Ziaul Haque: resources; software; supervision; writing – review & editing. Mohammad Rafiqul Islam: resources; supervision; validation; writing – review & editing.

CONFLICT OF INTEREST STATEMENT

All authors declare no conflict of interest for this article.

ETHICS STATEMENT

The study was conducted following the institutional ethical standards and authorisation [Authorisation No.: AWEEC/BAU/2020(3)] was taken from the ‘Animal welfare and Experimentation Ethics Committee’, Bangladesh Agricultural University (BAU), Mymensingh 2202, Bangladesh.

PEER REVIEW

The peer review history for this article is available at https://publons.com/publon/10.1002/vms3.1139.

ACKNOWLEDGEMENTS

We acknowledge the support from the Department of Anatomy and Histology, Faculty of Veterinary Science (FVS), BAU, Bangladesh for providing the laboratory facilities. We are also thankful to the Bangladesh Agricultural University Research System (BAURES) for granting the research fund (Grant number: 2020/57/BAU).

Islam, R. , Sultana, N. , Haque, Z. , & Rafiqul Islam, M. (2023). Effect of dietary dexamethasone on the morphologic and morphometric adaptations in the lymphoid organs and mortality rate in broilers. Veterinary Medicine and Science, 9, 1656–1665. 10.1002/vms3.1139

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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