Análise dos fatores de risco relacionados à resistência ao Rhipicephalus microplus e à resposta imune-humoral anti-Anaplasma marginale em bovinos leiteiros

Abstract

The study objectives were to evaluate the physiological status, seasonality, age, genetics, lactation number, milk production, vector density and stocking rate as potential risk factors for infestation by the tick Rhipicephalus microplus and the frequency of IgG antibodies against Rickettsia Anaplasma marginale in dairy cattle. For this, we randomly selected 80 cows and 20 calves belonging to the Empresa de Pesquisa Agropecuária do Estado do Rio de Janeiro through proportional stratified sampling. The animals were followed from 2008 to 2010. The evaluation of the resistance of cattle to R. microplus was performed by counting engorged or partially engorged females of R. microplus. The data were transformed into log 10 (2 `count + 1). They were then subjected to analysis of variance, Student's t test or Tukey test and linear regression. To evaluate the humoral immune response against A. marginale was used Indirect Enzyme-linked immunosorbent Assay. The frequency of seropositive animals for A. marginale was submitted to the χ2 test, and those with p <0.2 were offered to the multivariate analysis. We observed high numbers of ticks (36 ticks / animal) and a significant reduction (p <0.01) antibody titers against A. marginale during peripartum. It were considered risk factors for anaplasmosis delivery (OR 2.61, CI 1.08-7.63), physiological status (OR 4.5, CI 0.12 – 0.38), genetics (OR 3.83, CI 0.08 – 0.28), number of lactations (OR 33.7, CI 2.14 – 5.16), dairy (OR 3.9, CI 2.24 – 7.03), infestation by R. microplus (OR 10.3, CI 0.05 – 0.17) and stocking density (OR 3.22, CI 0.05 – 0.17). The calves showed prevalence of 14% at birth, 66% at 12 months and 79% at 24 months. The low prevalence of newborn calves (OR 4.90, CI 0.13 – 0.31) was a consequence of the low prevalence of the agent in cows and not by a deficiency in the transfer of colostral antibodies. Although located in an area of enzootic stability, the property was classified as unstable to A. marginale.