Thiago Souza Azeredo Bastos

Avermectin toxicity in bovines less than thirty days old

The present study was designed to evaluate possible adverse effects of different dosages of avermectins (abamectin and a combination of ivermectin + abamectin) administered subcutaneously in calves less than one month of age. Clinical as well as biochemical parameters of blood and cerebrospinal fluid (CSF) were evaluated for animals subjected to various treatments. Thirty-five calves were divided into seven groups of five animals each: T01 (control), T02 (abamectin 200 μg/kg), T03 (abamectin 400 μg/kg), T04 (abamectin 600 μg/kg), T05 (ivermectin 450 μg/kg + abamectin 250 μg/kg), T06 (ivermectin 900 μg/kg + abamectin 500 μg/kg) and T07 (ivermectin 1350 μg/kg + abamectin 750 μg/kg). Cerebrospinal fluid and blood samples were collected on day zero (treatment day) and on days 1, 7 and 14 following treatment. The biochemical parameters measured in blood samples were total protein and the AST, GGT and alkaline phosphatase enzymes. In CSF samples, color, aspects, pH, density, cellularity, total proteins, glucose and the CK, ALT and LDH enzymes were evaluated. No neurological toxicity or biochemical changes in the CSF or blood that could be correlated to administration of tested products were observed in this study. Though it is well known that abamectin may lead to intoxication in bovines less than four months of age, based on data from the present study, no adverse clinical effects to the CSF or blood were observed in calves <30 days old that had received up to 600 μg/kg abamectin formulations and up to 1350 μg/kg ivermectin +750 μg/kg abamectin associations. It is possible that the level and activity of the multiple drug resistance gene (MDR1 - ABCB1) present in the calves may have influenced the results obtained in this study. Future studies should be carried out.

Susceptibility of Rhipicephalus (Boophilus) microplus to fluazuron (2.5 mg/kg) and a combination of novaluron (2.0 mg/kg) + eprinomectin (0.36 mg/kg) in field studies in Brazil

The present study aimed to determine the susceptibility of 32 R. (B.) microplus populations from Southeast, Midwest and South regions of Brazil, to fluazuron (2.5mg/kg), administered topically (pour-on). Additionally, five populations (Southeast and Midwest regions) of the southern cattle tick were evaluated using in vivo field studies, regarding their susceptibility to a new combination of novaluron (2.0mg/kg)+eprinomectin (0.36mg/kg), administered subcutaneously, compared with two positive controls (fluazuron 2.5mg/kg and eprinomectin 0.5mg/kg), both administered topically (pour-on). Selected bovines were allocated to treatment groups on day 0, and block formation was based on arithmetic means of female ticks (4.5-8.0mm long) counted on three consecutive days (-3, -2 and -1). To evaluate therapeutic and residual efficacies of these formulations, tick counts (females ranging from 4.5 to 8.0mm long) were performed on days 3, 7 and 14 post-treatment, continuing on a weekly basis until the end of each experiment. Results obtained throughout this study, utilizing field efficacy trials, allowed us to conclude that four R. (B.) microplus populations (including two in the Southeast and two in the Midwest regions) could be diagnosed as resistant, or with low susceptibility, to fluazuron (2.5mg/kg). Such fact was detected in farms where owners applied products containing this active component on cattle for at least five years, with treatment intervals of 30-55days during the rainy season. Nonetheless, in vitro studies should be performed in order to reinforce in vivo results obtained on the present study. Regarding efficacy indexes obtained by the association of eprinomectin and the novel molecule novaluron against R. (B.) microplus, none of the trials managed to obtain efficacies superior to 48%. Such results, allied to data obtained by different researchers and previously published in literature, reinforce the perception that maybe these formulations containing novaluron, in the administered dosages and treatment routes, may not be effective tools for controlling R. (B.) microplus. However, future studies must be conducted in order to support such hypothesis. Additionally, all five R. (B.) microplus populations were diagnosed as resistant, or with low susceptibility, to eprinomectin (0.5mg/kg) as well. Even though fluazuron, administered topically (pour on), is still an excellent active principle to be used against R. (B.) microplus, resistance management strategies should be quickly implemented in order to keep selection pressure in Brazil at a minimum level for this compound.

Phenotypic and molecular detection of Salmonella sp. on growing, rearing and production phases in a commercial group of laying hens

This present study was developed with the objective of detect Salmonella sp. by conventional bacteriology and qPCR techniques in samples of flooring material from transport crates (meconium); raising environment (swab of cages and drinking fountains); cloacal swab; food and insects from growing, rearing and production phases in a commercial group of laying hens. A total of 864 samples were collected, among whom 248 originated from growing, 392 from rearing and 224 from production phase. Among the 864 samples, 2,8% where positives in bacteriologic technique and 15.3% in qPCR. Contamination was higher in growing and rearing phases and declined in production phase. Twenty four isolations of Salmonella where typified as Salmonella Agona (41.7%), Salmonella Livingstone (33.3%), Salmonella Cerro (16.7%), Salmonella Senftenberg (4.2%) and Salmonella Schwarzengrund (4.2%). During growing phase Salmonella Livingstone was identified. These findings suggest vertical contamination in the group. During rearing and production phases, isolated materials belong to serovars Agona, Cerro, Senftenberg and Schwarzengrund, pointing to horizontal contamination. It is possible to conclude that both vertical and horizontal contaminations are important during the cycle of commercial egg production and contamination in rearing phase is higher than in growing and production phases.