Efficacy of amprolium and toltrazuril in chicken with subclinical infection of cecal coccidiosis.

Sir,

Coccidiosis is a significant problem in the poultry industry throughout the world. It is responsible for 6–10% of all broiler mortalities.[1] In subclinical coccidiosis, minor damage of the intestinal wall will lead to deteriorated performance. In such cases, the farm owners are complaining poor performance of the chicken. The diagnosis of coccidiosis is carried out promptly at the laboratory during routine parasitological examination. Under these conditions, broiler chickens are continually exposed to coccidial oocysts found in litter. Thus, at one time we could expect overlapping parasite cycles in which more than one parasitic stage will be present. Therefore, under these conditions, the anticoccidial efficacy will depend on the ability of drug to affect broad range of parasitic stages. This is typically occurring in subclinical coccidiosis, in which we expect different stages of a parasite at one time. In this study, the efficacy of amprolium and toltrazuril was investigated in cases of subclinical coccidiosis, in which the drug is given after the oocysts shedding started.

Floor-pen studies were carried out to simulate field conditions. Chicken were divided into three groups, either infected nontreated or infected and treated with 150 ppm amprolium (AMP) or 25 ppm toltrazuril (TOL). Chicks were infected with 1000 oocysts of a prepared E. tenella field strain isolated from a commercial Egyptian farm. Oocysts shedding was confirmed at day 6 post-infection. The chicken received the medications after an interval of 4 days during which no treatment was administered.

The highest oocyst output occurred at 7 day after infection [Figure 1, Table 1]. The average oocyst excretion for the duration of the study was 229 × 103 oocysts per gram of feces (OPG) in the control group, while it was reduced in the AMP group (218 × 103 OPG) and was as low as 92 × 103 OPG in the TOL group [Table 2]. In control group, the oocyst shedding was continuous all over the study. In AMP-treated group, the oocysts shedding remained high on most sampling days, even it significantly exceeded the values of control nontreated group between day 10 and 18 post infection. In TOL-treated group, the oocysts shedding remained significantly low throughout the treatment (P < 0.05).

Figure 1

Oocyst count from the control group or receiving 25 ppm toltrazuril or 150 ppm amprolium

Table 1

Oocyst count mean ± (standard deviation) from the control-infected nontreated group or receiving 25 ppm toltrazuril or 150 ppm amprolium (n = 3)

Table 2

Effect of amprolium and toltrazuril treatment on final body weight of broiler chicken on the average oocysts output (× 103) in chicken infected with E. tenella

In all groups, there was no change in appetite and the fecal score remained low until day 16 post infection. On day 17 post infection, the control group showed diarrhea tinged with blood, similar to the clinical coccidiosis. AMP group showed soft excreta, sometimes tinged with blood. TOL group showed normal fecal score throughout the test period.

Body weight in the AMP- and TOL-treated birds significantly exceeded that of the control nontreated group at the end of the observation period. Mean difference in body weight was higher in the TOL group (+216 g) and the AMP group (+200 g) compared with the control infected nontreated group (P < 0.05).

The test drugs failed to completely stop oocysts shedding. This indicates that there is lowered sensitivity for TOL and AMP once oocysts shedding begin. This can be explained by the inability of the test drugs to cover all the parasitic stages under these conditions.

Toltrazuril's spectrum of efficacy covers all intracellular developmental stages excluding oocysts, as has been demonstrated for Eimeria species in poultry and have strong anticoccidial action against all types of coccidiosis in chicken, rabbit, pigeon, calves, and lambs.[2-4] The anticoccidial action against most stages is probably the reason for the comparatively better efficacy of toltrazuril in our study. The significantly high oocyst outputs of the amprolium treated birds could be attributed to altered sensitivity for the drug. Similar findings were reported by Guo et al., who reported an increased oocysts count of maduramicin-treated birds compared with the nontreated control.[5]

The reduced oocysts shedding with toltrazuril contributes to the reduction of oocysts accumulation in the litter, thus reducing the parasitic pressure and appearance of clinical coccidiosis. However, there was a peak of oocysts shedding (during the days 20-22 post-infection). The oocysts shedding with toltrazuril treatment is expected to approach zero within several days of treatment. In contrast, the delay of treatment until oocycts shedding begin, will affect the oocysts shedding with toltrazuril. This indicates that some stages escaped from the effect of toltrazuril under subclincal conditions.