ANUALPEC () ‘Anuário da Pecuária Brasileira.’ 1st edn. (Instituto FNP and Agra Pesquisas Ltda: São Paulo, Brazil). ANUALPEC () ‘Anuário da. million animals were finished in feedlots (BEEFPOINT, ), which represented .. the past two decades (ANUALPEC, ). Concomitantly with the greater. accounting for about % of the national herd (ANUALPEC. ), this region shows the highest growth rate in the coun- try. Crossbreeding is.

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Gastrointestinal nematodes resistant to anthelmintics anuallpec been reported in several regions of Brazil, and they may be associated with economic losses for the cattle industry. This study aimed to evaluate the resistance status of gastrointestinal nematodes from naturally infected beef cattle to several commercially available anthelmintics, as well as to test the efficacy of combinations of anthelmintics against multi-resistant gastrointestinal nematodes.

Ten farms located in Rio Grande do Sul state were anualec by: These calves were distributed into 10 groups of 7—10 animals per farm and treated with ivermectin, doramectin, eprinomectin, fenbendazole, closantel, nitroxynil, disophenol, levamisole, albendazole, or moxidectin. Feces were collected 2 days before treatment and 14 days after treatment. Additional groups of 7—10 anuappec were used to test six different two-drug combinations at four of the studied farms.

In general terms, fenbendazole was the most effective drug, followed by levamisole, disophenol, and moxidectin. However, parasite resistance to multiple drugs was found in all herds, especially in the genera Cooperia spp. Some of the two-drug combinations were effective against nematode populations identified as resistant to the same compounds when used as single drugs. In this study, parasites resistant to the main commercially available anthelmintics were found in all herds, and some combinations of two active components belonging to different chemical groups were effective against multi-drug resistant gastrointestinal nematodes.

The cattle industry is one of the largest sectors of the Brazilian economy. Brazil is the world’s second largest producer of cattle, with a total herd of In Brazil, anthelmintics are generally used at farmers’ discretion, with no restrictions to access to commercially available drugs and without any assistance from veterinarians.

This study aimed to verify the existence of populations of gastrointestinal nematodes resistant to several commercially available anthelminthic compounds by evaluating naturally infected anualpsc cattle from herds located in the state of Rio Grande do Sul, Brazil.

In addition, the efficacies of some two-drug combinations were tested to assess their potential as alternative to control the multi-drug resistant parasite populations found in the studied herds.

The study was conducted on ten farms located in eight counties of the Rio Grande do Sul state in southern Brazil: Preliminarily, herds were selected based on location and previous consent by farmers.

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Additionally, the following technical criteria were considered: First, all calves available at each farm were included in the study; however, animals with fewer than EPG before treatment were excluded prior to the formation of the experimental groups.

Calves were weaned approximately six months after birth and kept in the same grazing area before and during the study on each farm. Location of ten beef cattle herds studied at eight counties from the state of Rio Grande do Sul in southern Brazil.

The black spheres indicate the locations of the farms. In the first part of the study, ten commercially available anthelmintic compounds were tested on each farm.

All treatments were administered by a veterinarian participant of the study following the manufacturer’s recommendations: After determining the efficacy of each single anthelmintic treatment, six combinations of two drugs were tested at four of the ten farms as a second part of this study.

For this purpose, new groups of calves, selected by the criteria described before, were used. The choice of two-drug combinations was made with a focus on including different modes of action and efficacy against different genera ajualpec gastrointestinal nematodes. The tested combinations were: Each drug in the combination treatments was administered separately. All samples were maintained under controlled humidity and temperature before processing and during the larvae culture procedures.

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These calves were distributed into 10 randomized blocks based on EPG at each farm, to balance the mean and the frequency distributions of EPG countings among the groups before the treatments. Each of the ten groups was randomly treated with a single drug in the first part of this study. At the four farms included in the second part of this study, six additional groups were treated with a combination of two anthelmintic compounds as described previously.

The number of animals in each experimental group ranged from 7 to 10 depending on the available calves at each farm. The total number anualpdc calves used per farm was: After incubation, larvae were recovered by baermanization, after which third-stage larvae in each culture were identified by genera following the criteria described by Van Wyk and Mayhew On each farm, pre-treatment and 212 EPG counts were used to calculate the efficacy of each treatment based on the reduction in EPG.

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Fenbendazole was the most effective compound in the studied herds, followed by levamisole, disophenol, and moxidectin. Larvae cultures from animals from all herds showed the presence of mixed infections containing the following genera: Arithmetic mean AM and standard deviation SDminimum MIN and maximum MAX fecal egg counts, and proportions of genera identified before the treatments D-2 in the feces of naturally infected beef cattle from ten farms in the state of Rio Grande do Sul.

Treatment of the animals with avermectin compounds did not result in satisfactory EPG reduction in any herd. Moxidectin was 20012 effective at one farm, but unsatisfying reductions in EPG counts were observed aanualpec the other nine herds.

With regard to the benzimidazoles employed in this study, albendazole was ineffective against gastrointestinal parasites at nine farms and showed an inconclusive amualpec at the farm However, closantel was effective against Haemonchus spp.

Phenolic-substituted compounds disophenol and nitroxynil showed differing efficacy. Nitroxynil was ineffective at all farms when EPG reduction was xnualpec, mainly because it had little effect on Cooperia spp.

Disophenol was not effective at six farms, showed inconclusive results at three farms 1, 6, and 10and had an efficacy of Disophenol was effective against Haemonchus spp. In general, the same genera identified as resistant to single drugs were found to be resistant to two-drug combinations. However, the results of the present study indicate a worrying situation in relation to the control of gastrointestinal nematodes infections in cattle herds from Rio Grande do Sul because of the high level of multi-drug resistance of the parasite populations found in all farms studied.

The broad detection of parasite resistance to several anthelmintics recognized as good quality commercial drugs suggests that parasite populations have developed resistance to the main classes of anthelmintic drugs available in Brazil. Macrocyclic lactones MLsespecially avermectins, were not effective in any of the herds assessed in this study, with the exception of moxidectin at one farm.

In the farms evaluated here, no detailed information was obtained regarding the history of each drug at each farm because of a lack of available data. Drug use on Brazilian farms is often not based on established criteria, while trademarks and compound names are not well recognized by the farmers. As an exception, ivermectin is well recognized and the most widely used anthelmintic, followed by other avermectins, benzimidazoles, levamisole, and cydectin.

Other compounds are eventually used when the farmer suspects that conventional drugs are failing. Commercial availability, endectocide action, and price are generally considered most important criteria influencing the choice of drugs by farmers. Proportionally to the other genera of gastrointestinal nematodes found in the tested herds, Cooperia spp. Resistance of Cooperia spp.

Nevertheless, massive infections by Cooperia spp. Despite the presence of resistant populations of Cooperia spp. While farmers reported knowledge of levamisole in the present study, it was not frequently used, indicating low selection pressure. This condition may have contributed to the good efficacy of levamisole at some farms. However, in the present study, with the exception of Oesophagostomum spp.

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Phenolic substitutes nitroxynil and disophenol are narrow spectrum anthelmintics that are not recommended in the presence of infections by Cooperia spp.

Nitroxynil and Disophenol were ineffective in reducing the EPG in most herds, mainly because of the presence of genera of gastrointestinal nematodes that were not sensitive to these compounds. Some strains of Oesophagostumum spp. Nitroxynil was effective against Haemonchus spp.

These results show that phenolic-substituted drugs have limited applicability in the studied cattle herds. Frequent use of BZs at the studied farms may have resulted in the establishment of benzimidazole-resistant parasite populations. Considering the location of the farms, these data suggest that parasite resistance to BZs may be spreading in Rio Grande do Sul, similar to the situation observed for avermectins in several Brazilian herds.

The resistance of Cooperia spp. Closantel presents a narrow spectrum of action against gastrointestinal nematodes of ruminants. Closantel was effective against Haemonchus spp.

The low efficacy of each single drug and the anuzlpec of multi-drug resistant gastrointestinal nematodes infecting cattle are major problems that prevent adequate anthelmintic control anualepc the farms evaluated in this study. Therefore, previous knowledge regarding parasite resistance was used as a tool to inform the choice of potentially efficacious combinations of drugs.

The use of combinations of two anthelmintic compounds with good efficacy as single drugs could be an effective means of delaying the development of drug resistance anualpe parasites. However, this study was focused on situations in which two effective drugs were unavailable to farmers.

Thus, combinations of two anthelmintics that were anuzlpec fully effective as single drugs, had different modes of action, had broad spectra of action when possibleand were effective against different genera of gastrointestinal nematodes were tested.

Acceptable efficacy was shown by some combinations: Many of the tested combinations were not effective, probably because of the presence of genotypes of gastrointestinal nematodes resistant to both drugs used in the combinations.

The results of this study showed the presence of gastrointestinal nematodes resistant to the main commercially available anthelmintic drugs on cattle farms evaluated in the state of Rio Grande do Sul, Brazil. Qnualpec critical situations 2102 parasite resistance, in which no options of effective drugs are commercially available, combinations of two anthelmintic compounds anual;ec different mechanisms of action and unsatisfying efficacy as single drugs can effectively control multi-drug-resistant gastrointestinal nematodes.

However, such combinations should be evaluated anuakpec the particular conditions unique to each farm. The authors of this manuscript have no financial or personal relationships with other people or organizations that could inappropriately influence or bias the content of the paper.

The authors are grateful for the availability and collaboration of producers and their employees to carry out this work. National Center for Biotechnology InformationU.

Published online Feb 8. Author information Article notes Copyright and License information Disclaimer. This article has been cited by other articles in PMC. Abstract Gastrointestinal nematodes resistant to anthelmintics have been reported in several regions of Brazil, and they may be associated with economic losses for the cattle industry. Open in a separate window. Introduction The cattle industry is one of the largest sectors of the Brazilian economy.

Material and methods 2. Farms and animals The study was conducted on ten farms located in eight counties of the Rio Grande do Sul state in southern Brazil: Anthelmintic treatment In the first part of the study, ten commercially available anthelmintic compounds were tested on each farm. Statistical analysis On each farm, pre-treatment and post-treatment EPG counts were used to calculate the efficacy of anualpecc treatment based on the reduction in EPG.

Compounds Genera Cooperia spp.

Anthelmintic combination Genera Cooperia spp.