Abstract
The anthelmintic efficiency of doramectin, fenbendazole, and nitroxynil, used individually or in combination, was determined by the Fecal Egg Count Reduction (FECR) test and cultivation of larvae of anthelminthic-treated sheep grouped as follows: G1 (doramectin), G2 (fenbendazole), G3 (nitroxynil), G4 (doramectin + fenbendazole), G5 (doramectin + nitroxynil), G6 (fenbendazole + nitroxynil), G7 (doramectin + nitroxynil + fenbendazole), G8 (untreated). In addition to individually used doramectin and fenbendazole, the helminths were also resistant to the combination of doramectin + fenbendazole; nitroxynil + fenbendazole; and doramectin + nitroxynil + fenbendazole, with their FECR rates ranging from 62-83%. The helminths showed possible nitroxynil-resistance, but had low resistance when the drug was administered in combination with doramectin. The evaluation of individual helminth species revealed that fenbendazole was fully effective against Cooperia; doramectin (G1), moderately effective against Haemonchus and insufficiently active against Cooperia; nitroxynil, effective against Haemonchus and insufficiently active against Cooperia. It was concluded from the results that herd nematodes are resistant to doramectin, fenbendazole, and nitroxynil, and that the combined use of the drugs not only fails to significantly improve the anthelmintic efficiency against Haemonchus and Cooperia, but is also cost-ineffective.
Highlights
According to the data from the Brazilian Institute of Geography and Statistics (IBGE), sheep farming in Paraná, Brazil, has been observed to be slowly increasing in recent years
The mean eggs per gram of feces (EPG) values of only those animals treated with a combination of doramectin and fenbendazole (G4) remained significantly lower (P = 0.002) than those of animals given treatment combinations throughout the experimental period
The comparison of the EPG values between the groups revealed that the animals treated with nitroxynil (G3), a combination of doramectin and fenbendazole (G4), and a combination of doramectin and nitroxynil (G5), had EPG values significantly lower than those of the control group (P = 0.22, 0.0456, and 0.0203, respectively), respectively, seven days after treatment
Summary
According to the data from the Brazilian Institute of Geography and Statistics (IBGE), sheep farming in Paraná, Brazil, has been observed to be slowly increasing in recent years. In the penultimate livestock census, in 2009, the herd size was estimated to be 599,925 head of sheep, which corresponded to 12.5% of the total sheep population in southern Brazil (IBGE, 2013). The last census estimated a 6.7% increase in the number of sheep a small increment, considering the effective increase in the sheep population over the last four years in other states of southern Brazil, which was estimated to be 12.97% and 7.72% in Santa Catarina and Rio Grande do Sul, respectively. Failure in using this method effectively has favored the emergence of resistant strains of parasites (SANGSTER, 2001)
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