Avaliação do sistema integrado de controle parasitário em uma criação semi-intensiva de caprinos na região de Santa Catarina

Genetic parameters for worm resistance in Santa Inês sheep using the Bayesian animal model

Objective

The objective of this study was to estimate the genetic parameters for worm resistance (WR) and associated characteristics, using the linear-threshold animal model via Bayesian inference in single- and multiple-trait analyses.

Methods

Data were collected from a herd of Santa Inês breed sheep. All information was collected with animals submitted to natural contamination conditions. All data (number of eggs per gram of feces [FEC], Famacha score [FS], body condition score [BCS], and hematocrit [HCT]) were collected on the same day. The animals were weighed individually on the day after collection (after 12-h fasting). The WR trait was defined by the multivariate cluster analysis, using the FEC, HCT, BCS, and FS of material collected from naturally infected sheep of the Santa Inês breed. The variance components and genetic parameters for the WR, FEC, HCT, BCS, and FS traits were estimated using the Bayesian inference under the linear and threshold animal model.

Results

A low magnitude was obtained for repeatability of worm-related traits. The mean values estimated for heritability were of low-to-high (0.05 to 0.88) magnitude. The FEC, HCT, BCS, FS, and body weight traits showed higher heritability (although low magnitude) in the multiple-trait model due to increased information about traits. All WR characters showed a significant genetic correlation, and heritability estimates ranged from low (0.44; single-trait model) to high (0.88; multiple-trait model).

Conclusion

Therefore, we suggest that FS be included as a criterion of ovine genetic selection for endoparasite resistance using the trait defined by multivariate cluster analysis, as it will provide greater genetic gains when compared to any single trait. In addition, its measurement is easy and inexpensive, exhibiting greater heritability and repeatability and a high genetic correlation with the trait of resistance to worms.

Status of benzimidazole resistance in intestinal nematode populations of livestock in Brazil: a systematic review

Background

Benzimidazoles (BZ) are a class of drugs widely used in veterinary and human medicine, creating a great selection pressure and the emergence of BZ resistance. We conducted a systematic review to assess the status of resistance and/or effectiveness reduction of BZ drugs in animal nematodes in Brazil, and make information accessible to the scientific community, as many studies are published in Portuguese. PubMed, SciELO Brasil, LILACS/Bireme, GNTD database, and Google Scholar were searched with no language restrictions.

Results

A total of 40 studies met our eligibility criteria (from the year 1989 forward). Sheep was the host most frequently analysed, and albendazole was the most frequently drug studied. The majority of studies (75.7%) showed that BZ drugs are insufficiently active (FECRT <80%) against nematode parasites of livestock. The mean FECRT for fenbendazole, thiabendazole, albendazole, mebendazole, oxfendazole, and ricobendazole were 71.8%, 71.8%, 58.6%, 53.9%, 46.9%, and 41.5%, respectively. It was observed through linear regression that FECRT is significantly reduced over time between 2007 and 2014 (R = −0.653 p = 0.021) for the treatment of cattle with BZ, suggesting progressive loss of effectiveness and increased resistance for these hosts.

Conclusions

The scenario of BZ resistance in nematode populations in Brazil is not favourable. Given the high cost of drug discovery and development, it is urgent to implement control measures and to monitor the effectiveness/resistance to nematodes in livestock in Brazil.

Multiple anthelmintic resistance in Southern Brazil sheep flocks

Gastrointestinal parasites represent an important cause of reduced productivity of sheep worldwide. As anthelmintic are still the main control tool for these parasites, this work evaluated the efficacy of commercially available active principles in 22 sheep flocks in the southern region of Rio Grande do Sul, Brazil. In each farm 10 sheep were randomly distributed in seven groups with the following treatments: abamectin; albendazole; closantel; levamisole; monepantel; trichlorphon and no anthelmintic (control). All flocks showed resistance to at least three anthelmintics and in 20 farms only two products demonstrated efficacy for parasitic control. In two farms, there was no susceptibility to the six active principles tested. The results of this study provide evidence that the common commercially available anthelmintic are not assuring effective chemical control of gastrointestinal parasitic infections in ovine flocks in the southern region of Rio Grande do Sul. Monepantel, the newest introduced drug in the Brazilian market was not effective in 18% of the flocks tested, confirming that the parasitic resistance can be established quickly after the introduction of new molecules mainly when alternative program of parasite control is not performed.

Manejo de anti-helmínticos no controle de infecções gastrintestinais em cabras

RESUMO Objetivou-se com este estudo avaliar a eficácia do princípio ativo oxfendazole e da associação deste com o levamisol, na redução de ovos por gramas de fezes (OPG) e de larvas de helmintos nas fezes de cabras sem padrão racial definido (SPRD) criadas em pasto sob pastejo contínuo de Capim Colonião (Panicum maximum), bem como o tempo de ação após a aplicação dos medicamentos. Os tratamentos experimentais foram: animais não desverminados (ND); animais desverminados com oxfendazole (DO); e animais desverminados com associação de oxfendazole e levamisol (DOL). Entre os grupos tratados, o grupo em que as cabras foram submetidas à associação dos princípios ativos (DOL) mostrou-se 16,75% mais eficaz comparado ao grupo tratado com oxfendazole (DO). Houve um pico de redução de larvas de Haemonchus eTrichostrongylus no terceiro e nono dia, respectivamente, após a aplicação do anti-helmíntico, em relação ao dia da vermifugação. Apesar disso, até o nono dia não foi observado eficácia acima de 95%, podendo considerar uma provável resistência aos princípios utilizados. Embora não tenha atingido a eficácia esperada, esta associação foi mais eficaz na redução de larvas do gênero Trichostrongylus, quando comparado à utilização do composto químico isolado, podendo ser uma alternativa à recomendação da associação de anti-helmínticos no controle de infecções gastrintestinais em cabras criadas em regime de pasto.