Metabolismo oxidativo dos neutrófilos de bezerros das raças Nelore e Limousin nos primeiros quatro meses de vida

To study some defence mechanisms of beef calves kept on range conditions, 90 healthy calves, 45 Nelore and 45 Limousin, were bled at 24 to 36 hours of life, 15, 30, 60, 90 and, 120 days. Leukogram and neutrophil oxidative burst through the non-stimulated and the stimulated NBT tests were determined. The parasitemia with Anaplasma marginale, Babesia bigemina and B. bovis was investigated. Repeated measure ANOVA was used to analyse the age effect on leukocyte counts. Variation of positive neutrophil throughout the age was analysed through Krushkal-Wallis test. Comparisons among breeds were done using the Mann-Whithney test. The white blood cell count increased with age in both breeds, with a decrease in neutrophil and an increase in lymphocyte counts. The neutrophil lymphocyte ratio had been inverted before 15 days of life. The neutrophil oxidative burst was less effective in the newborn calves increasing with age. Limousin calves' neutrophils had higher capacity to reduce NBT in advanced ages. The observed differences between taurine and Zebu calves had no effects on calves' health and could be atributed to Anaplasma marginale natural and asynptomatic infection.