Differential Haematobia irritans infestation levels in beef cattle raised in silvopastoral and conventional pasture systems.

The use of silvopastoral systems (SPS) can be a good alternative to reduce the environmental impacts of livestock breeding in Brazil. One of the reasons for its scarce adoption is the lack of information on health and productivity of cattle raised under these conditions. The experiment reported here was designed to compare the infestation by external parasites - the cattle tick (Rhipicephalus microplus), horn fly (Haematobia irritans), and larvae of the botfly (Dermatobia hominis) - in beef cattle raised in a SPS and a conventional pasture system (CPS), evaluated for 24 months. Data on air and soil temperature, solar radiation, wind incidence and water balance were used to characterize the SPS and CPS. R. microplus adult females and D. hominis larvae were counted on the body of each animal to determine the parasites burdens, but we did not find significant differences between the two systems. Horn flies counts on animals' body, and analysis of the horn fly and its pupal parasitoids associated with the dung pats were obtained in the two systems. Horn fly infestation was significantly lower (p=0.01) in the SPS (13.17±3.46) in comparison with the CPS (24.02±4.43). In SPS and CPS, respectively, the mean densities of pupae of H. irritansin dung pats were 9.8 and 10.7; the mean density of adults of H. irritans, 3.7 and 3.5; and the density of its pupal parasitoids were 20.5 and 5.4. The effect of production system was significant (p<0.05) only for the occurrence of pupal parasitoids of the horn fly, where the greatest occurrences of these natural enemies were in the SPS. These data indicate that natural enemies were able to control, at least partially, the horn fly populations in the cattle.

Quantitative study of Babesia bovis infection in beef cattle from São Paulo state, Brazil.

The qPCR technique with SYBR Green was used to estimate the prevalence and level of Babesia bovis infection in beef cattle raised in areas endemic for babesiosis in Brazil, where the animals were continuously exposed to ticks (Rhipicephalus microplus). This is the first report in which qPCR was used to quantify and compare B. bovis DNA in blood of different cattle breeds. Blood samples were collected from 150 animals (75 cows and 75 calves) of the Angus and Nelore breeds and the first generation of an Angus and Nelore cross (AxN). Blood samples from the jugular vein were used for DNA extraction and determination of packed cell volume (PCV), while samples from peripheral veins were used for microscopic parasite detection. Although no piroplasms of B. bovis were found in blood smears, DNA amplification using qPCR revealed that all of the 150 animals, except two calves and one cow, were positive. The number of copies of B. bovis DNA was higher (p<0.05) in the Angus than in the Nelore and AxN animals, for both calves and cows, but no significant difference was found between the Nelore and AxN groups. These results suggest that a heterotic effect was present, since the results from the crossbred animals significantly deviated from the mean of the two parental groups, while closely approaching that of the Nelore group. In the Nelore and AxN groups, calves showed higher infection levels than cows (p<0.05), while for the Angus group the difference was found to be non-significant. Within each animal age group, the breed groups with higher infection levels were those with lower PCV values. However, within each breed group, no significant correlations were found between the number of DNA copies and PCV according to animal age. The qPCR method applied here allowed the observation that although there are no differences in the prevalence of infection among breed groups, Nelore and AxN cattle are able to maintain infection by B. bovis at lower levels than the Angus cattle.