The co-administration effects of florfenicol and lasalocid on performance, biochemical and pathological parameters of muscle, heart, liver, kidney and sciatic nerve in broiler chickens.

The study aimed to examine the effect of simultaneous application of florfenicol and lasalocid on the performance and vital organ function of chickens. For this, 300 chicks were divided into four groups. Group one to three received florfenicol, lasalocid and lasalocid plus florfenicol, respectively. Group four as the control group received a basic diet without lasalocid or florfenicol. Lasalocid was used from 7 to 35 days old, continuously. Florfenicol was used at 21 days old for 5 days. The growth indices were measured at the end of each week. The chickens were euthanized at the ages of 28 and 35 days old after collecting blood samples with and without anticoagulants. The liver, heart, muscle, kidney and sciatic nerve were collected in formalin 10% for histopathological examination. The blood and serum samples were used to determine clinical pathologic and hematologic indices. The ratio of internal organs to body weight and ratio of the right ventricle to the total ventricles (RV/TV) of the heart was measured. Results showed, the use of lasalocid decreased feed conversion rate and triglyceride, and increased total protein. Simultaneous administration of lasalocid and florfenicol affected histopathology of the liver and heart and significantly increased creatine phosphokinase, uric acid and the ratio of RV/TV of heart. The eosinophil percentage in the chickens who received florfenicol plus lasalocid was significantly higher than chickens who received florfenicol alone (p < 0.05). In conclusion, it seems that simultaneous administration of the florfenicol and lasalocid induces side-effects especially on cardiac function and it is not recommended.

INTRODUCTION

A wide range of antimicrobials are used in poultry production all over the world (Landers et al., 2012; Sahoo et al., 2010) The antimicrobials are natural or synthesized compounds that can destroy microbial pathogens or inhibit their growth. Antimicrobials are one of the essential components in poultry production to treat and control bacterial infections. The mutual relationships between bacteria, antimicrobial agents, the host and the simultaneous administration are determinant factors in designing logical plans of antibiotic therapy (Landoni & Albarellos, 2015). Florfenicol influences most Gram‐negative bacteria such as Escherichia coli and Salmonella spp. By inhibiting protein synthesis, it can inhibit peptidyl transferases enzyme (Ismail & El‐Kattan, 2009; Shen et al., 2003). Florfenicol belongs to a wide spectrum of antibiotics with a structure that is similar to chloramphenicol; however, unlike chloramphenicol it does not cause aplastic anaemia for lack of O‐nitro group (Ben et al., 2019). Florfenicol is similar to chloramphenicol in terms of activity and range of effect, and it is more active in some infections compared to chloramphenicol. Since hydroxyl group is replaced with fluorine molecule, bacteria have lower resistance to florfenicol than chloramphenicol (Giguère et al., 2013). Wide and relatively more intensive pharmaceutical activity and higher sensitivity of bacteria to florfenicol, and lack of resultantaplastic anaemia have made florfenicol a popular choice in the treatment of infectious diseases in poultry (Giguère et al., 2013; Wang et al., 2013).

Lasalocid is one of the ionophore coccidiostats used to control coccidiostats in chicken and turkey. The compound is also featured with selective antimicrobial activity against Gram‐positive bacteria (Anadón & Martínez‐Larrañaga, 2014; Rychen et al., 2017). Compared to other ionophore drugs, lasalocid has higher safety and is more compatible with other additives and drugs (Novilla, 2018). Despite the fact that ionophores and tiamulin cannot be used simultaneously, lasalocid can be used with tiamulin (Giguère et al., 2013; Perelman et al., 1986). In general, the high safety and its compatibility with other drugs make it a common choice as a coccidiostat in the poultry industry (Noack et al., 2019). It is reported that the simultaneous use of chloramphenicol and lasalocid causes muscular lesions and, in some cases, causes paralysis and ataxia in chickens without negative effect on feed consumption (Perelman et al., 1986). Tacking account of the similar structure of florfenicol and chloramphenicol, the present study is an attempt to examine simultaneous use of florfenicol and lasalocid in broilers. Lasalocid is a coccidiostat compound that can be used in diet from the early days of feeding until five days before slaughtering (Sundar et al., 2017). Infections such as colibacillosis can occur during the growing period, and depending on an antibiogram, florfenicol might be prescribed. Since there has been no report on drug interaction for these drugs, the present study is an attempt to examine simultaneous administration of lasalocid and florfenicol.

MATERIALS AND METHODS

Study design

In total, 300 1‐day broiler chicks were allocated to four groups with three replications. Each replicates contained 25 chicks and they were reared under same nutritional and management condition from 1‐day‐old to 42‐days old. The chickens had access to water and food freely (ad libitum) and a continuous light program was used throughout the experiment. The experiment group A received solution of florfenicol 10% (1 cc/L for 5 days from 21–26 days old), group B received lasalocid 15% (800 g/Tfrom the age of 7 days until five days before euthanization at 42 days of age), group C received florfenicol and lasalocid (with the mentioned time, dose and duration as group A and B) and group D received no lasalocid or florfenicol as control group. The food diet of all the groups was balanced according to Ross instruction (Table 1). All chickens received infectious bronchitis, Newcastle disease and Gumboro disease vaccines based on the conventional vaccination program in the local state. Data of body weight gain (WG), feed consumption (FC) and feed conversion ratio (FCR) were recorded and analyzed weekly and cumulatively.

TABLE 1

The diet ingredients and nutrients value

Ingredients	Starter diet (1–3 weeks)	Finisher diet (4–6 weeks)
Corn	57.00	57.50
Soybean meal	37.00	34.00
Vegetable oil	2.50	4.00
Salt (Sodium chloride)	0.30	0.30
Dicalcium phosphate	1.30	1.70
Shell	1.00	1.50
Methionine	0.25	0.30
Lysine	0.15	0.20
Commercial premix*	0.50	0.50
Total	100	100

Sampling

At the end of the fourth week (28 days old) blood samples were collected from half of the chickens and then they were euthanized. The other half were kept alive until 35 days of age to check the growth indices. The euthanized chickens were dissected and the heart, liver, intestine and bursa of Fabricius were weighed. To conduct histopathology examinations, the heart, liver, kidney, skeletal muscle (leg trapezius muscle) and sciatic nerve samples were collected in formalin (10%). The blood sample was collected with and without anticoagulant for haematology and clinical pathology examination, respectively.

Haematology

Haematology examinations were performed on blood samples containing anticoagulants and covered haematocrit percentage, white and red blood cell count (WBC & RBC), neutrophil, lymphocyte, monocyte, eosinophil and basophile percentage. In addition, mean cell volume (MCV), mean cell haemoglobin (MCH) and mean concentration of haemoglobin cell (MCHC) were measured.

Clinical pathology

Clinical pathology examinations were conducted on serum samples to measure uric acid, total cholesterol (CHL), triglyceride (TG), sodium (Na), potassium (K), creatine phosphokinase (CPK), alanine aminotransferase (ALT), aspartate aminotransferase (AST), total protein (TP), high‐density lipoprotein (HDL) and high‐density lipoprotein (LDL). To measure the parameters, an autoanalyzer (Technicon RA‐1000; 83014H102S1‐8N11, USA) was used. The commercial kits for examine the tests were prepared from Pars Azmon Co. (Iran). The total weight of the heart, liver, kidneys, intestines and bursa of Fabricius was measured. In addition, the ratio of each body organ to the body weight was also measured. The weight of the right/total ventricles of the heart was measured.

Histopathology

The tissue samples were fixed in neutral 10% formalin solution, embedded in paraffin and cut into 4 μm thick sections. After deparaffinization, the sections were stained with haematoxylin‐eosin (H & E) (Bancroft, 1996).

The tissue sections were examined qualitatively and quantitatively. The qualitative description was limited to highlighting lesions on each tissue section and the qualitative description consisted of the extent and severity of lesions from 0 (no lesion) to +3 (severe lesion).

Statistical analysis

The collected data including weekly and accumulative FC, WG, FCR, haematological indices, clinical‐pathological indices and histopathology results were analyzed by SIGMA STATE (v.2.0) software program. To examine the mean difference between the groups, a one‐way ANOVA method was used. The extent of significant differences was measured using Tukey's test with a confidence level of 0.5.

RESULTS

Growth indices

Feed consumption

Weekly and cumulative FC in different groups showed that the cumulative FC in chickens who received lasalocid was significantly higher than that the chickens who received florfenicol at the end of the fifth week (p < 0.05). Among other groups, no significant difference in FC was found during the experiment (Table 2).

TABLE 2

Growth indices in different treatment groups

Groups	Control	Florfenicol + Lasalocid	Lasalocid	Florfenicol
Index
One day old weight	46.00 ± 2.35a	45.33 ± 2.45a	46.33 ± 2.15 a	46.00 ± 2.98 a
Cumulative FC in third week (g/chicken)	795.83 ± 8.07 a	788.17 ± 12.59 a	805.15 ± 12.52 a	787.07 ± 9.04 a
Cumulative WG in third week (g/chicken)	650.00 ± 3.15 a	692.15 ± 9.73 b	709.25 ± 9.39 b	641.31 ± 4.58 a
Cumulative FCR in third week	1.22 ± 0.01 a	1.13 ± 0.02 b	1.10 ± 0.02 b	1.21 ± 0.02 a
FC in fourth week (g/chicken)	698.03 ± 11.94 a	717.57 ± 12.50 a	739.13 ± 18.54 a	692.53 ± 17.35 a
WG in fourth week (g/chicken)	406.67 ± 7.61 a	444.17 ± 8.76 b	481.76 ± 10.51 c	400.18 ± 7.54 a
FCR in fourth week	1.71 ± 0.01 a	1.69 ± 0.03 ab	1.503 ± 0.03 b	1.72 ± 0.09 a
FC in fifth week (g/chicken)	876.76 ± 12.23 a	894.71 ± 13.56 a	915.99 ± 9.20 a	874.01 ± 7.30 a
WG in fifth week (g/chicken)	457.50 ± 7.79 a	492.50 ± 8.91 b	529.17 ± 7.63 c	462.50 ± 6.18 a
FCR in fifth week	1.91 ± 0.37 a	1.82 ± 0.02 ab	1.78 ± 0.02 b	1.98 ± 0.07 a
Cumulative FC in fifth week (g/chicken)	2370.83 ± 25.16 ab	2399.88 ± 20.80 ab	2459.15 ± 23.70 b	2353.35 ± 23.95 a
Cumulative WG in fifth week (g/chicken)	1514.17 ± 12.01 c	1629.61 ± 7.16 b	1720.83 ± 17.18 a	1509.50 ± 5.20 c
Cumulative FCR in fifth week	1.52 ± 0.04 a	1.47 ± 0.01 b	1.42 ± 0.01 b	1.55 ± 0.01 a

The different superscript in each row represents significant differences between treatments (p < 0.05).

Data represented as mean ± SEM

Weight gain

Weekly and accumulative WG in different groups indicated a significant difference between lasalocid fed chickens and other groups (p < 0.05). WG in the end of third week showed no significant difference between lasalocid fed chickens and chickens who received lasalocid plus florfenicol. However, in the fourth and fifth week of growing, weekly and cumulative WG in chickens who received lasalocid was significantly higher than chickens who received lasalocid plus florfenicol (p < 0.05) (Table 2).

Feed conversion ratio

For FCR, there was no significant difference between lasalocid fed chickens and other chickens in another group until the end of the third week. In the fourth and fifth week of growing, the FCR in lasalocid fed chickens was significantly lower than chickens in another group (p < 0.05). Moreover, cumulative FCR at the end of the fifth week in chickens who received lasalocid was significantly lower than control and chickens who received florfenicol (Table 2).

As the results showed, haematocrit, WBC and RBC count, neutrophil, lymphocyte, monocyte, basophil percentage, hemoglobin, MCV, MCH and MCHC were not significantly different between the chickens in all groups. Only eosinophil percentage in the chickens who received florfenicol plus lasalocid was significantly higher than chickens who received florfenicol alone (p < 0.05) (Table 3).

TABLE 3

The hematological indices in different treatment groups

Groups	Control	Florfenicol + Lasalocid	Lasalocid	Florfenicol
Index
PCV (%)	33.67 ± 1.76 a	33.11 ± 1.77 a	35.00 ± 2.55 a	32.44 ± 1.89 a
RBC (106 /mm3)	3.68 ± 0.10 a	3.62 ± 0.16 a	3.86 ± 0.88 a	3.57 ± 0.25 a
WBC (106 /mm3)	2.66 ± 0.09 a	2.53 ± 0.10 a	2.78 ± 0.12 a	21133 ± 765 a
Neutrophils (%)	34.11 ± 2.00 a	37.56 ± 2.43 a	36.67 ± 3.27 a	40.55 ± 2.20 a
Lymphocytes (%)	60.56 ± 2.64 a	54.88 ± 2.62 a	59.89 ± 2.79 a	56.00 ± 2.35 a
Monocytes (%)	2.89 ± 0.39 a	3.33 ± 0.48 a	2.44 ± 0.38 a	2.44 ± 0.16 a
Eosinophils (%)	1.90 ± 0.60 ab	3.10 ± 0.85 b	1.00 ± 0.27 ab	0.80 ± 0.39 a
Basophils (%)	0.33 ± 0.23 a	0.67 ± 0.28 a	0.00 ± 0.00 a	0.22 ± 0.17 a
Hb (g/dl)	11.19 ± 0.72 a	11.33 ± 0.59 a	11.63 ± 0.80 a	10.81 ± 0.16 a
MCV (fl)	91.23 ± 0.35 a	91.44 ± 0.25 a	90.87 ± 0.21 a	90.93 ± 0.28 a
MCH (pg)	30.49 ± 0.09 a	30.46 ± 0.08 a	30.29 ± 0.09 a	30.31 ± 0.09 a
MCHC (%)	33.39 ± 0.01 a	33.31 ± 0.01 a	33.30 ± 0.09 a	33.39 ± 0.09 a

The different superscript in each row represents significant differences between treatments (p < 0.05).

Data represented as mean ± SEM

The AST, ALT, total CHL, K and HDL values were not significantly different between chickens in different groups. The uric acid value was significantly higher in chickens who get florfenicol plus lasalocid in comparison with control chickens (p < 0.05). CPK level was significantly higher in chickens who received florfenicol plus lasalocid than control chickens (p < 0.05). In addition, the Na level in chickens who used florfenicol plus lasalocid was significantly higher than the other chickens (p < 0.05). The TP was significantly higher in chickens fed lasalocid in comparison with control chickens (p < 0.05). Conversely, TG level was significantly lower in chickens fed lasalocid compared with control chickens (p < 0.05) (Table 4).

TABLE 4

The clinical pathologic parameters in different groups

Groups	Control	Florfenicol + Lasalocid	Lasalocid	Florfenicol
Index
Uric acid (mg/dl)	2.54 ± 0.26b	5.17 ± 0.60 a	3.33 ± 0.34 ab	3.96 ± 0.61 ab
CPK (U/L)	40.33 ± 7.25 b	82.00 ± 15.34 a	56.73 ± 11.97 ab	60.33 ± 14.00 ab
Aspartate transferase (AST) (U/L)	227.66 ± 13.6 a	274.67 ± 10.6 a	222.21 ± 10.8 a	232.65 ± 0.1a
Alanine aminotransferase (ALT) (U/L)	4.11 ± 0.31 a	5.00 ± 0.41 a	4.78 ± 0.61 a	4.89 ± 0.90 a
Cholesterol (CLH) (mg/dl)	116.17 ± 6.24 a	127.22 ± 8.49 a	118.22 ± 8.89 a	116.00 ± 4.10 a
Sodium (Na) (mg/dl)	152.53 ± 2.31 a	167.78 ± 2.13 b	155.89 ± 2.21 a	156.44 ± 2.19 a
Potassium (K) (mg/dl)	3.63 ± 0.08 a	4.44 ± 0.32 a	4.00 ± 0.46 a	4.08 ± 0.20 a
Total protein (TP) (g/dl)	3.00 ± 0.12 a	3.43 ± 0.11 ab	3.92 ± 0.16 b	3.39 ± 0.27 ab
High‐density lipoprotein cholesterol (HDL) (mg/dl)	62.70 ± 16.47 a	69.89 ± 11.43 a	73.33 ± 14.32 a	76.67 ± 21.24 a
Triglyceride (TG) (mg/dl)	72.33 ± 10.68 a	53.56 ± 4.71 ab	44.78 ± 2.83 b	75.67 ± 10.04 ab

The different superscript in each row represents significant differences between treatments (p < 0.05).

Data represented as mean ± SEM

Qualitative histopathologic examination

Heart

No heart lesions were observed in control chickens and chickens that received florfenicol or lasalocid, but focal necrosis and rupture of myofibrils were observed in heart of chickens that received lasalocid plus florfenicol (Figures 1 and 2).

FIGURE 1

Myofibril rupture in heart, in chickens received florfenicol and lasalocid simultaneously (H&E, X400)

FIGURE 2

Necrosis of myofibrils and infiltration of inflammatory cells in heart, in chickens received florfenicol and lasalocid simultaneously (H&E, X400)

Liver

No liver lesion was observed in the control chickens. Mild hyperaemia and inflammation in the arteries of the central vein, portal vein and liver sinusoids was seen in chickens that received florfenicol and lasalocid, simultaneously. In these chickens, foci of necrosis, increased connective tissue in the portal infiltration of mononuclear inflammatory cells with the presence of fibroblasts and collagen filaments were observed in some areas of necrosis, which may be due to acute inflammation (Figure 3).

FIGURE 3

Necrosis, fibrosis and infiltration of inflammatory cells in portal area of liver (H&E, X400)

Kidney

Only mild hyperaemia of renal arteries and renal tubular capillaries was observed in the kidney of control chickens and chickens that received florfenicol or lasalocid. Atrophy of the renal tubules, dilatation of the urethra and increased connective tissue between renal tubules were seen in chickens get florfenicol plus lasalocid (Figure 4).

FIGURE 4

Dilation of collecting tubules and fibrosis of around tissues in kidney (H&E, X400)

Skeletal muscles

Rupture of skeletal myofibrils was observed in chickens that received florfenicol and lasalocid, simultaneously. In these areas, transverse lines were lost, nuclei disappeared and the cytoplasm of myofibrils became eosinophilic, which may indicate muscle cell degeneration. No pathological lesion was observed in other groups.

Sciatic nerve

No lesions were observed in the histopathological sections of sciatic nerve in all groups.

Quantitative histopathologic examination

Depending on the severity and extent of the injuries, a grade from zero to 3 was assigned to each pathological section. The results are shown in Table 1. Analysis of quantitative data showed that heart lesions in chickens that received florfenicol plus lasalocid were significantly higher than other chickens (p < 0.05). In addition, liver lesions in chickens that received florfenicol plus lasalocid were significantly higher than the control chickens and chickens who received lasalocid (p < 0.05). The microscopic lesions in kidney, skeletal muscle and sciatic nerve were not statistically different between groups (Table 5).

TABLE 5

The quantitative histopathological results in different treatment groups

Groups	Control	Florfenicol + Lasalocid	Lasalocid	Florfenicol
Index
Heart	0.10 ± 0.09 a	1.40 ± 0.75 b	0.10 ± 0.08 a	0.15 ± 0.13 a
Liver	0.40 ± 0.25 a	2.40 ± 0.24 b	0.80 ± 0.20 a	1.40 ± 0.40 ab
Kidney	0.40 ± 0.25 a	1.00 ± 0.36 a	1.00 ± 0.36 a	0.60 ± 0.25 a
Skeletal muscle	0.20 ± 0.00 a	1.40 ± 0.40 a	0.80 ± 0.20 a	0.80 ± 0.34 a
Sciatic nerve	0.00 ± 0.00 a	0.00 ± 0.00 a	0.00 ± 0.00 a	0.00 ± 0.00 a

The different superscript in each row represents significant differences between treatments (Pp < 0.05).

Data represented as mean ± SEM

Organ weight ratio

The ratio of heart, liver, intestine and bursa of Fabricius weight to body weight was not statistically different in all groups. The ratio of right ventricle weight to total heart ventricles in florfenicol plus lasalocid‐receiving chickens was significantly higher than control chickens (p < 0.05) (Table 6).

TABLE 6

The organ to body weight ratio in different treatment groups

Groups	Control	Florfenicol + Lasalocid	Lasalocid	Florfenicol
Index
Heart/ BW	0.65 ± 0.06 a	0.73 ± 0.02 a	0.71 ± 0.03 a	0.78 ± 0.04 a
RV/ TV of Heart	16.12 ± 2.44 a	26.06 ± 2.61 b	22.58 ± 1.12 ab	22.54 ± 1.23 ab
Liver/ BW	2.54 ± 0.11 a	2.99 ± 0.25 a	2.49 ± 0.18 a	2.74 ± 0.58 a
Intestine/ BW	5.27 ± 0.14 a	4.55 ± 0.24 a	4.42 ± 0.10 a	4.57 ± 0.78 a
Bursa/ BW	0.11 ± 0.02 a	0.16 ± 0.08 a	0.16 ± 0.05 a	0.12 ± 0.02 a

Note: Data represented as mean ± SEM The different superscript in each row represents significant differences between treatments (p < 0.05).

Data represented as mean ± SEM

DISCUSSION

Several studies have been conducted on the simultaneous administration of coccidiostat drugs and antibiotics (Kim et al., 2018). However, there has been no study on the simultaneous use of florfenicol and lasalocid. There are some reports related to lasalocid effect on growth indices. Bains (1980) reported a significant decrease in growth after using 126 ppm lasalocid (Bains, 1980). Mc Dougald and Mequision reported that the administration of lasalocid in poultry diet can increase FC (McDougald & McQuistion, 1980). Here, the increase in FC in chickens fed lasalocid was not significant and FCR and WG were significantly higher than control chickens. Also, it was found that co‐administration of these two compounds can reduce FC and WG and ultimately increase the FCR. These differences were significant only in WG in comparison with chickens who were fed lasalocid.

Evaluation of haematological parameters revealed that only the eosinophil percentage in the chickens receiving florfenicol plus lasalocid was significantly higher than the chickens who get florfenicol. However, there is no significant difference between the other haematological parameters. For function of eosinophil in hypersensitivity reactions, it seems that the increase in the percentage of eosinophils following the co‐administration of these two compounds is due to the induction of allergic reactions. However, based on the available information, there are no similar findings in the interaction of the two drug combinations and the occurrence of hypersensitivity reactions.

In a recent study, one of the other criteria for evaluating the effects of florfenicol and lasalocid combination was the study of liver and kidney histopathological feature and enzymatic activity of the liver and kidney as two target organs in the metabolism and excretion of most drugs, including florfenicol and lasalocid. Comparison of uric acid (as an enzymatic indicator of renal activity), sodium and potassium shows that although co‐administration of these two compounds may exert a greater metabolic load on kidney, but the higher metabolic load did not lead to failure in renal function. This finding is confirmed by renal histopathological results that showed that the renal histological injuries in different groups are not significantly different.

Regarding liver function evaluation, although the combined use of lasalocid and florfenicol may induce pathological lesions in the liver, the severity and extent of the lesions are not sufficient to alter the serum biochemical profile or size of the liver. Since the study was designed based on the report of interaction between lasalocid and chloramphenicol and in that report, the interaction occurred in the form of the appearance of a myopathy; so in the present study, the CPK activity was measured to evaluating myopathy. Elevated serum level of this enzyme may indicate the presence of a myopathy (Broz & Frigg, 1987; Perelman et al., 1986). Comparison of serum levels of this enzyme in different groups show that CPK is significantly higher in the chickens receiving florfenicol plus lasalocid than control chickens. Comparison of pathological injuries in skeletal muscles shows the effect of co‐administration of these two drugs on heart tissue.

In the design of the recent study, in addition to myopathy, the histopathology of the sciatic nerve was examined for possible neuropathy. The results showed that co‐administration of florfenicol and lasalocid did not lead to neuropathic lesions. According to the novelty of this research, there is no information for or against it. However, in the previous study on the interaction of lasalocid with chloramphenicol, Perelman et al. (1986) investigated the pathological and biochemical effects of the concomitant use of lasalocid and chloramphenicol and the results showed that the simultaneous administration of these two drugs causes symptoms such as leg weakness, abnormal gait, physical weakness and severe weight loss. Furthermore, the histopathological lesions of the nerves were observed that including demyelination of certain areas of the spinal cord and sciatic nerve, as well as atrophy of muscle fibres. Biochemical experiments in that study showed that serum acetylcholinesterase, GOT, LDH, calcium and magnesium levels were not significantly different from control chickens (Perelman et al., 1986). In another study by Kart et al. (2009), the neurotoxic effects of phenyl saligenin phosphate (PSP) and lasalocid in chickens were studied by evaluating motor nerve conduction velocity (MNCV), clinical ataxia and esterase activity. The results showed that the activity of esterase enzyme in chickens who received lasalocid plus PSP was significantly lower than control chickens and chickens that received lasalocid. The onset of ataxia in chickens who received these two drugs appeared early and intensified compared with control chickens. As a result, PSP and lasalocid can cause significant reductions in MNCV and cause ataxia. Therefore, it seems that neuropathic organophosphates can be exacerbated by lasalocid ionophore polyether (Kart & Bilgili, 2009). Also, Broz and Frigg (1986) studied the concurrence of lasalocid and long‐term use of chloramphenicol in broilers. The results showed that the use of these two drugs reduces FC and increases FCR. Symptoms of toxicity including ataxia, leg weakness and paralysis were observed. Biochemical experiments in infected birds showed an increase in GOT and CPK, which confirmed leg weakness and paralysis due to myofibril degeneration (Broz & Frigg, 1987). In our study, although no similar clinical symptoms were observed, elevated CPK and cardiac myopathy may indicate the effect of concomitant use of lasalocid and florfenicol on cardiac tissue and heart function.

The overall results of this study indicate that co‐administration of lasalocid and florfenicol may have adverse effects on cardiac structure and heart function, which requires further investigation using more accurate tests such as echocardiography and electron microscopy to prove this finding. As a general result, it is recommended not to use co‐administration of lasalocid and florfenicol in poultry production as much as possible.

ETHICAL STATEMENT

The study was undertaken with approval from the Islamic Azad University, Shahrekord Branch ethics committee for care and use of animal for research.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

AUTHOR CONTRIBUTIONS

MGA designed the study and co‐worked in laboratory examinations; MKD wrote the manuscript and co‐worked in laboratory examinations; AN prepared the pathological sections and evaluated the pathological findings, HS reared the chickens, sampling, and achieved the laboratory experiments, AAD analyzed the data, edited the manuscript and co‐worked in laboratory examinations and AM edited the final version of manuscript.

PEER REVIEW

The peer review history for this article is available at https://publons.com/publon/10.1002/vms3.626