Effect of prophylactic vitamin C administration on the efficiency of florfenicol or sulfadiazine-trimethoprim antimicrobial therapy in chickens with staphylococcal arthritis

Septic arthritis (SA) in chickens shows improper response to antibacterial therapy. This study evaluates the effect of prophylactic vitamin C administration on the efficiency of sulfadiazine-trimethoprim (SDT) or florfenicol (FF) in broilers with experimental SA. Broilers (210) were randomly allocated into 7 equal groups: (I) negative control (NC) (normal birds); (II) positive control (PC) arthritic birds by injection of Staphylococcus aureus in tibiotarsal joint at the age of 35 days; (III) vehicle control (injected with sterile medium); (IV) arthritic FF-treated (20 mg/kg/day); (V) arthritic vitamin C + FF-treated (as above + vitamin C at 15 g/100L of D.W. from day 25 of age); (VI) arthritic SDT-treated (35 mg/kg/day); (VII) arthritic vitamin C + SDT-treated. Antibacterial therapy started at day 39 of age and lasted for 5 days. Samplings were performed at the age of 44 and 54 days. A long lasting SA with severe fibrinoheterophilic synovitis and reduced body weights developed in PC broilers as compared to NC group (p < 0.05). Oxidative stress was present at sampling 1. Arthritis was not reflected in IL-6 levels of synovial fluid of PC group. None of the antibacterials resulted in completely successful treatment. Vitamin C did not appreciably improve lameness and arthritis scores, although it decreased lipid peroxidation and improved weights of FF treated-arthritic birds. For SDT-treated birds, vitamin C only ameliorated histopathological changes. In conclusion, except for improving body weight in FF-treated birds, prophylactic administration of vitamin C is not associated with improvements in clinical outcome of antimicrobial therapy of broilers with SA, although it ameliorates oxidative stress and some histopathological changes.


Introduction
Septic arthritis (SA) with resultant lameness in broiler chickens compromises the birds' welfare and imposes economic loss to poultry industry due to reduced birds' performance and increased mortality and carcass condemnation in slaughterhouses. Among bacterial causes of SA, Staphylococcus aureus is considered as a major culprit which is also important from public health view (Marcon et al. 2019).
The bacteria are associated with chondronecrosis with osteomyelitis in chickens that most commonly affects proximal end of the femur and tibiotarsus in birds around 35 days of age (McNamee and Smyth 2000).
Different predisposing factors are involved in the development of the disease which include stress, immunosuppression, vascular disorders, and nutritional deficiencies (Wijesurendra et al. 2017).
Unfortunately, when established, the disease shows improper response to antibacterial therapy, due to the fact that the bacteria remain in sites which are usually inaccessible to antibiotics and even some immune components of the host (Wideman Jr 2016). Hiding from immune system and antibacterial agents may result in recurrence of the disease even after antimicrobial therapy. In 2016, Mosleh and colleagues evaluated the therapeutic efficiency of four different antibacterials including sulfadiazine-trimethoprim (SDT), florfenicol (FF), oxytetracycline, and enrofloxacin in the treatment of experimentally induced staphylococcal arthritis in broilers. They found that none of the antibiotics results in completely successful therapy of affected birds although they suggested SDT as the preferred agent with regard to most of the assayed criteria.
Vitamin C or ascorbic acid, as a well-known antioxidant, is routinely administered to stressed broilers such as those under heat stress since under stressful conditions, the need of bird is not met by internal synthesis of this vitamin (Khan et al. 2012;Abidin and Khatoon 2013).
This vitamin is also famous for its role in bone and cartilage development and health (Aghajanian et al. 2015). It has been clearly demonstrated that vitamin C supplementation during rearing period improves bone mineralization and resistance in broilers (Franchini et al. 1994).
Immunomodulatory (both cell-mediated and antibodymediated pathways) and anti-inflammatory properties of vitamin C (Shojadoost et al. 2021) are also reported in poultry. Interestingly, vitamin C has shown inhibitory effects on in vitro growth of S. aureus by affecting metabolic pathways of the bacteria (Kallio et al. 2012;Golonka et al. 2017). The synergistic effects of vitamin C with antibacterials are another intriguing property of this vitamin that has been reported against Pseudomonas aeruginosa and Helicobacter pylori (Cursino et al. 2005;Kaboli et al. 2009).
These previously reported properties of vitamin C as well as its common use in poultry farms encouraged us to evaluate the plausible effect of prophylactic administration of this vitamin on the efficiency of two different antibacterials (SDT or FF) in a challenge study on chickens with experimental staphylococcal arthritis. Clinical and histopathological features of the disease, serum antioxidant status, and synovial fluid concentration of IL-6 in infected birds were evaluated.

Bacteria isolation, identification, and antibacterial sensitivity test
The S. aureus bacteria that were used to challenge birds were isolated from bumble foot lesions of poultry in a local farm. In biochemical tests, the bacteria were beta hemolytic, catalase, and coagulase positive. The genus and species of the bacterium were confirmed by polymerase chain reaction (PCR) to amplify a species-specific region of the DNA coding for rRNA. Moreover, PCR method was used for to determine resistance to methicillin (primer sequences are shown in Table 1). To further characterize the bacteria, multilocus sequence typing (MLST) was performed by primers specific to seven housekeeping genes as described by Enright et al. (2000).
Kirby-Bauer disk diffusion susceptibility test on Mueller-Hinton agar was performed based on Clinical and Laboratory Standards Institute (CLSI) guidelines. All disks were prepared by Padtan Teb Co., Tehran, Iran.

Study design
Two hundred and ten Ross 308 broiler chickens from both sexes were reared at the same condition as instructed in the manual. The birds had access to commercial feed and tap water during the experiment ad libitum. All birds were randomly allocated into 7 equal groups with 30 birds each and treated as summarized in Table 2.
Induction of arthritis was performed at the age of 35 days. After weighing the birds, 1 ml of a suspension of S. aureus bacteria containing 1.4*10 8 CFU in TSB medium was injected in right tibiotarsal joint as described previously by Mosleh et al. (2016). The proper bacterial concentration for injection was determined in a pilot study. Florfenicol (Fluorfen® 10%, Rooyan Darou, Semnan, Iran) was administered at 20 mg/kg/day in drinking water. Vitamin C (vitamin C 50%, Rooyan Darou, Semnan, Iran) at the dosage of 15 g/100 l of drinking water (equivalent with 11.25 mg/kg body weight of vitamin C) as the routine dosage of vitamin C for chickens in stressful conditions was administered from day 25 of age and continued to the end of the experiment. The dosage of SDT (Kimiaprim 48®, sulfadiazine 400 mg/ ml + trimethoprim 80 mg/ml, Kimiafam Pharmaceutical Co., Tehran, Iran) was 35 mg/kg in drinking water.
All dosages were as manufacturers' recommendations. Administration of both antibacterials was started at the age of 39 (4 days after induction of arthritis when birds showed fulminant clinical signs of arthritis) and lasted for 5 consecutive days. Two samplings were performed, first at the age of 44 (10 birds of each group) and the second at the age of 54 (the remained birds), respectively. Birds were weighed and monitored for clinical signs. Lameness in birds was scored as indicated in Table 3. Severity of arthritis in the right tibiotarsal joint was also scored (Bremell et al. 1992) by macroscopic inspection with a score of 0 to 3 (0, normal; 1, mild swelling and/or erythema; 2, moderate swelling and erythema; and 3, marked swelling and occasional ankylosis). Blood samples were collected from wing vein of birds from each group for determination of oxidative stress parameters. Then, birds were euthanized by decapitation and samples from synovial fluid of right tibiotarsal joint were collected for determination of IL-6 level. Moreover, the joint was fixed in 10% neutral buffered formalin for histopathological evaluation.

Determination of serum malondialdehyde concentration and total antioxidant capacity
Blood samples were coagulated at room temperature and sera were harvested after centrifugation at 3000 rpm for 10 min. Harvested sera were kept at − 40 °C until use.
Serum malondialdehyde (MDA) concentration and total antioxidant capacity (TAC) were determined by using kits prepared by Zell bio, Germany, based on colorimetric assays as described by manufacturer. The product codes were ZB-MDA-96A/48A and ZB-TAC-96A/48A, respectively.

Determination of IL-6 concentration in synovial fluid
A sandwich ELISA kit intended for quantitative measurement of IL-6 in chicken's biological fluids (product code: E0004Ch) was used for determination of IL-6 in synovial fluid samples. The kit was prepared by Bioassay Technology Laboratory, China, with intra-assay and inter-assay CVs of < 8% and < 10%, respectively. The protocol was performed as described by the manufacturer.

Histopathological evaluation
After fixation, nitric acid decalcification method was used. After 48 h in 10% nitric acid solution, demineralization was checked, and if the specimen was not decalcified, the process continued for an extra 12-24 h. Then, samples were trimmed and routinely processed, embedded in paraffin, and 5 µm sections from paraffin blocks were taken and stained with hematoxylin and eosin for light microscopic (Olympus, Japan) examination. Histopathological changes were evaluated blindly by an expert veterinary pathologist with specialty in avian species histopathology. The changes were considered as mild, moderate, and severe based on the overall degree of different lesions including fibrin deposition, hyperemia, edema, inflammatory cells infiltration, degeneration, and necrosis.

Statistical analysis
All data were presented as mean ± SD for all groups. Statistical analysis was performed by one-way ANOVA followed by Tukey's multiple comparison test with p < 0.05 as the level of significant difference. Data analysis and generation of graphs were performed by Graph Pad Prism 6 software. -- Difficulty in moving and a tendency to sit 4 Severe lameness 5 Debilitated and kept sitting position (unable to stand)

Body weight and clinical outcome parameters
Before induction of SA, birds of different groups had statistically the same body weights (p > 0.05) (data not shown). However, in both sampling time points (day 44 and 54 of age), birds in PC group had significantly lower body weight as compared to NC birds (p < 0.0001 in both cases) while VC birds showed statistically the same weight in comparison with NC group (p > 0.05). Interestingly, administration of SDT was associated with a significant increase in body weight of birds at both samplings as compared to PC birds (p < 0.05 for both comparisons); however, FF treatment had no significant effect on this parameter at first sampling while decreased the body weight of birds in sampling 2 as compared to PC group (p < 0.01). Although prophylactic vitamin C administration was not associated with a significant change in body weights of birds that received antibiotics at first sampling, birds that received vitamin C and FF showed significantly higher body weight as compared to FF group in sampling 2 (p < 0.01). The values for SDT and VitC + SDT groups remained statistically the same at the second sampling ( Fig. 1). Induction of staphylococcal arthritis resulted in severe lameness in birds of PC group at both samplings. Lameness scores were statistically similar among PC birds and birds in groups that received antibiotics with or without prophylactic vitamin C administration in sampling 1 (p > 0.05). In sampling two, birds in VitC + SDT group showed significantly lower lameness score as compared to PC group (p < 0.01), while prophylactic administration of vitamin C slightly decreased lameness scores as compared to birds that only received antimicrobial therapy (Fig. 2).
As shown in Fig. 3, birds in all groups with staphylococcal arthritis showed moderate to marked swellings at tibiotarsal joint with a statistically similar arthritis severity scores among these groups in sampling one (p > 0.05). In sampling 2, mild to moderate swelling was still present in these birds. Administration of antibiotics with or without prophylactic administration of vitamin C was not associated with a significant decrease in this parameter as compared to PC group. Interestingly, birds that were treated with SDT or VitC + SDT had significantly lower scores as compared to birds that received FF as the single agent (p < 0.0001 and p < 0.01, respectively). Vitamin C administration with antibiotics did not change this parameter as compared to birds that were only treated with antibiotics (p > 0.05).

Fig. 1
Body weight (mean ± SD) of birds in different groups at two sampling time points (day 44 and 54 of age, respectively). Columns with at least one common superscript letter have no significant difference (p > 0.05). NC negative control (no specific treatment), PC positive control with S. aureus-induced arthritis, VC vehicle control, FF birds with arthritis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim

Serum oxidative stress parameters
Induction of arthritis was associated with a significant increase in serum MDA concentration of birds in PC group as compared to NC birds in sampling 1 (p < 0.01). Prophylactic administration of vitamin C resulted in a significant decrease in serum MDA in birds of VitC + FF group as compared to birds that were treated only with FF (p < 0.01); however, birds in VitC + SDT group showed statistically the same level of serum MDA in comparison with SDT birds (p > 0.05). In second sampling, serum MDA concentration of PC birds showed no significant difference with NC or VC groups, while birds in FF and VitC + FF groups had lower serum MDA concentrations as compared to PC group (p < 0.05 and p < 0.01, respectively). Prophylactic administration of vitamin C was associated with a significant decrease in this parameter in FF-treated groups when compared with birds that only FF birds with arthritis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim Fig. 3 Arthritis severity scores (mean ± SD) of birds in different groups at two sampling time points (day 44 and 54 of age, respectively). Columns with at least one common superscript letter have no significant difference (p > 0.05). NC negative control (no specific treatment), PC positive control with S. aureus-induced arthritis, VC vehicle control, FF birds with arthritis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim received antimicrobial therapy (p < 0.01) in sampling 1 (Fig. 4).
As shown in Fig. 5, PC birds had significantly increased TAC as compared to NC or VC groups in sampling 1 (p < 0.001 and p < 0.01, respectively), while this parameter was statistically the same among abovementioned groups in second sampling (p > 0.05). Moreover, no significant difference was observed among vitamin C plus antibiotictreated groups with those that only received antibiotic in both samplings.

Synovial fluid level of IL-6
In both samplings, birds in PC group showed statistically the same level of IL-6 in synovial fluid as compared to NC or VC birds (P > 0.05). In sampling 1, birds in SDT and VitC + FF groups showed significantly higher levels of IL-6 as compared to NC group (p < 0.01 for both cases). In both samplings, all treated groups had statistically the same level of synovial fluid as compared to PC birds (p > 0.05); moreover, administration of vitamin C did not result in a significant Fig. 4 Serum malondialdehyde (MDA) concentration (mean ± SD) of birds in different groups at two sampling time points (day 44 and 54 of age, respectively). Columns with at least one common superscript letter have no significant difference (p > 0.05). NC negative control (no specific treatment), PC positive control with S. aureus-induced arthritis, VC vehicle control, FF birds with arthritis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim

Fig. 5
Serum total antioxidant capacity (TAC) (mean ± SD) of birds in different groups at two sampling time points (day 44 and 54 of age, respectively). Columns with at least one common superscript letter have no significant difference (p > 0.05). NC negative control (no specific treatment), PC positive control with S. aureus-induced arthritis, VC vehicle control, FF birds with arthritis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim change in this parameter in both antibiotic-treated groups when compared to birds that were treated with antibiotic as the single agent (Fig. 6).

Histopathological findings
Normal histological features of tibiotarsal joint including articular cartilage, joint capsule, and synovial membrane were observed in birds of NC and VC groups at both samplings while the histopathological lesions were severe in PC birds as follows. Degeneration and necrosis were vastly seen in synovial membrane cells accompanied by hyperemia, edema, infiltration of inflammatory cells mostly heterophils, and deposition of fibrin as severe fibrinoheterophilic synovitis (Fig. 7). Erosions were observed on the surface of articular cartilage in some samples.
The articular capsule was thickened with edema and fibrinoheterophilic exudate containing bacterial colonies.
At first sampling, birds of FF group showed moderate degree of degeneration and necrosis in synovial cells accompanied by edema, fibrin deposition, and infiltration of heterophils and mononuclear inflammatory cells (Fig. 8). The changes were also moderate in VitC + FF group. Edema and infiltration of heterophils and mononuclear cells were mostly seen in perivascular regions. In second sampling, birds of FF group showed only mild changes with infiltration of few Fig. 6 Synovial fluid concentration of interleukine-6 (IL-6) (mean ± SD) of birds in different groups at two sampling time points (day 44 and 54 of age, respectively). Columns with at least one common superscript letter have no significant difference (p > 0.05). NC negative control (no specific treatment), PC positive control with S. aureus-induced arthritis, VC vehicle control, FF birds with arthri-tis that treated with florfenicol, VitC + FF birds with arthritis that received prophylactic vitamin C with florfenicol, SDT birds with arthritis that treated with sulfadiazine/trimethoprim, and VitC + SDT birds with arthritis that received prophylactic vitamin C with sulfadiazine/trimethoprim Fig. 7 Severe degree of fibrinoheterophilic arthritis associated with intra lesional bacterial colony in a tibiotarsal joint of positive control group heterophils and mononuclear inflammatory cells in perivascular regions. Similar degree of changes was present in birds of VitC + FF group at this sampling time point.
In SDT group at first sampling, moderate fibrinoheterophilic synovitis with degeneration and necrosis of synovial membrane cells, hyperemia, edema, fibrin deposition, and infiltration of heterophils was observed (Fig. 9). These changes were also present in second sampling but at a moderate degree. Moderate hyperemia, edema, and fibrin deposition were present at both samplings. The histopathological changes that were observed in birds of VitC + SDT group were almost the same as SDT group at first sampling, but in sampling 2, fibrin deposition was absent and the degree of inflammation including edema, hyperemia, and heterophils infiltration were milder in these birds (Fig. 10) as compared to SDT group.

Discussion
In this challenge study, we evaluated the possible effects of prophylactic vitamin C administration on the efficiency of two common antibacterials in broilers with a multi drug and methicillin-resistant S. aureus-induced SA.
Staphylococci are ubiquitous bacteria in the poultry farm environment which can cause opportunistic infections in poultry. S. aureus, as the most pathogenic Staphylococcus species, results in clinical symptoms often seen in bones, joints, and tendon sheaths with usually a chronic nature (Szafraniec et al. 2020).
As it was expected, we observed that the induction of arthritis is associated with a negative effect on birds' weight of PC group at both samplings that can be described by the arthritis-associated pain and discomfort that limits the birds' Fig. 8 Moderate degree of degeneration and necrosis in synovial cells accompanied by edema, fibrin deposition, and infiltration of heterophils and mononuclear inflammatory cells especially around vessels are seen in FF group Fig. 9 Moderate fibrinoheterophilic synovitis including degeneration and necrosis of synovial membrane cells, hyperemia, edema, fibrin deposition, and infiltration of heterophils are seen in SDT group tendency to move. Although less severe, the arthritis was still present in sampling 2 (20th day after induction) with severe lameness that shows the long-term nature of the disease. The histopathological findings also confirmed the presence of inflammatory reactions accompanied by degeneration and necrosis in synovial membrane cells and damage to articular cartilage at sampling 2. Moreover, intra lesional bacterial colonies were present that reflect the inability of immune system for clearing the persistent infection. In fact, it has been demonstrated that the damage associated with SA is not only due to the bacterial invasion, but also the immense response by immune system that result in a sustained inflammation with destructive consequences in joints (Corrado et al. 2016).
Birds in SDT and VitC + SDT groups showed higher body weights as compared to PC group which was more prominent in sampling 2. This finding may be related to lower scores for lameness and arthritis severity, especially for VitC + SDT group that showed significantly lower lameness score as compared to PC birds, which can result in increased ability of birds to reach food. Notably, administration of FF was associated with body weights statistically lower than PC group at sampling 2 (10 days after the last treatment). This finding was consistent with a study by Hassanin et al. (2014) on broilers that were challenged with E. coli and received FF for 5 consecutive days; the authors reported a decreasing effect of FF administration on body weight at 7 and 14 days after stopping treatment.
In the present study, administration of vitamin C significantly increased body weights of birds in VitC + FF group in comparison with FF group in sampling 2. This increasing effect on body weight was not associated with reduced arthritis severity or lameness scores. Njoku (1986) reported a positive effect of dietary vitamin C supplementation on body weight of broilers in tropical environment without affecting their feed intake. Consistently, in a study by Gouda et al. (2020), vitamin C positively affected growth performance of broilers under heat stress by improving hormonal and health status parameters of birds. Therefore, the increase in body weight of VitC + FF group does not seem to be the result of improved moving ability of birds for reaching food and may be related to better hormonal parameters of these birds due to vitamin C administration, although this needs to be confirmed in future studies.
When established, SA is not easily treated with antibacterials, which can be related to the characteristics of infection site as well as the possibility of multi drug resistance of the pathogen. In sampling 2, we observed that arthritic birds that were treated with SDT had significantly lower arthritis severity score as compared to those that received FF. In a closely related study on the comparative efficiency of different antibiotics (including FF and SDT) in broilers with staphylococcal SA, Mosleh et al. (2016) reported that SDT generally has better therapeutic outcome than other antibacterials.
In the present study, although milder histopathological changes were observed in birds of VitC + SDT group as compared to SDT birds in sampling 2, prophylactic administration of vitamin C did not significantly improve the effect of both antibacterials on arthritis severity or lameness. In contrast to our results, Mal et al. (2012), reported that administration of vitamin C with gentamicin enhances the reducing effect of this antibiotic on inflammatory response in mice with staphylococcal arthritis. The discrepancy may be related to the antibacterial type and/or animal species.
It has been demonstrated that neutrophils are the major recruited immune cells to the joint during the immune response against S. aureus SA and production of reactive oxygen species (ROS) is one of the major mechanisms that neutrophils use to kill bacterial pathogens (Boff et al. 2018).

Fig. 10
Mild heterophilic synovitis including degeneration of synovial membrane cells, hyperemia, edema, and infiltration of a few heterophils and mononuclear inflammatory cells are seen in Vit C + SDT group after 2nd sampling As previously stated, we observed vast and intense infiltration of heterophils, the avian counterparts of mammalian neutrophils, in histopathological joint samples of birds in PC group. This observation was accompanied by oxidative stress in birds of this group at first sampling as shown by an obvious increase in serum MDA levels, a primary indicator of lipid peroxidation, of PC birds compared to NC group. The increase in MDA levels was associated with increased TAC that can be considered as a compensatory response to oxidative stress. Administration of both antibacterials was not associated with a significant change in MDA levels as compared to PC birds in sampling 1, although the levels of MDA were lower in FF and VitC + FF group as compared to PC birds in sampling 2. This observation can be explained by the fact that only few heterophils were present in histopathological samples of birds in FF and VitC + FF groups at sampling 2.
In our study, vitamin C significantly lowered levels of MDA in VitC + FF group as compared to FF in sampling 1. In a study by Mosleh et al. (2018), it was reported that 5 days of vitamin C administration to broilers under chronic heat stress can significantly reduce serum MDA levels of these birds while longer administration was not associated with appreciable effects on this parameter.
In human patients with staphylococcal SA, migration of neutrophils to infected joints is followed by activated macrophages (Boff et al. 2018). Cytokines released from macrophages such as IL-6 have a major role in cartilage and bone destruction and IL-6 is also important in differentiation of T-cells (Dey and Bishayi 2017). Consistently, S. aureusdependent SA in murine knee joints has been associated with an increase of IL-6 in both blood and knee joint (Corrado et al. 2016). However, in our study, induction of arthritis did not result in significant change of IL-6 levels in synovial fluid of PC birds as compared to NC group and also no significant difference was observed among treated groups and PC birds at both samplings. This observation is consistent with the study performed by Mosleh et al. (2016) on broilers with staphylococcal arthritis. These authors also did not find a change in serum levels of IL-6 in arthritic birds. It is noteworthy that in histopathological examination of arthritic joints, we did not find many macrophages. This can at least partially describe the reason for the lack of rise in IL-6 level of synovial fluid in almost all groups with arthritis.
In conclusion, in broilers with SA, the therapeutic response to SDT is generally better than FF with regard to body weight and arthritis severity score while FF administration has better effects on oxidative stress parameters. Both antibacterials are not completely successful in treating the condition. Prophylactic administration of vitamin C does not appreciably enhance the therapeutic efficiency of antibacterials on clinical parameters of arthritis, although it decreases the lipid peroxidation and improves body weights of FF-treated arthritic birds. For SDT-treated birds, administration of vitamin C only ameliorates histopathological changes.