The influences of age in calves' immune system are described in their first phase of life. We hypothesized that variations that occur in the main mechanisms of lung innate response can help to identify periods of greater susceptibility to the respiratory diseases that affect calves in the first stage of their life. This study aimed to evaluate the innate immune system. Nine healthy calves were monitored for 3 mo and 8 immunologic evaluations were performed. Bronchoalveolar lavage samples were recovered by bronchoscopy. The alveolar macrophages in samples were identified by protein expression of cluster of differentiation 14 (CD14) and underwent functional evaluation of phagocytosis (Staphylococcus aureus stained with propidium iodide and Escherichia coli). Data was assessed by one-way ANOVA (unstacked and parametric) and the Mann-Whitney test (nonparametric). Functional alterations in CD14-positive phagocytes were observed, with punctual higher intensity of phagocytosis in the third week and its decrease starting at 45 d of life. A gradual increase in phagocytosis rate was observed starting at this date. It is concluded that from 45 d of life on, alveolar macrophages have less phagocytic capacity but more cells perform this function. We suggest that this occurs because lung macrophages of calves start to maintain their immune response without passive immunity influence. Until 90 d of life, calves did not achieve the stability to conclude the maturation of local innate immune response.

RESUMO.-A citologia é um importante exame complementar utilizado para a detecção de alterações no perfil celular do trato respiratório e auxílio no diagnóstico de doenças. No entanto, como os primeiros meses de vida compõem o período de adaptação à vida extrauterina resultando em possíveis alterações das populações celulares, é essencial a padronização das características comuns aos animais sadios, possibilitando a identificação e análise de qualquer mudança no quadro esperado. O objetivo desta pesquisa foi caracterizar o perfil celular por citologia do lavado broncoalveolar obtido semanalmente por broncoscopia de dez bezerros durante os três primeiros meses de vida. A análise estatística foi realizada utilizando-se o software Minitab ® 15.0, empregando-se o teste T pareado para as amostras paramétricas e Mann-Whitney para as amostras não paramétricas, considerando nivel de significância P≤0,05. Os resultados obtidos apontaram que o perfil celular do lavado broncoalveolar de bezerros hígidos durante os primeiros 90 dias de vida apresentou predomínio de macrófagos, com média geral de 63,17%, seguido de 33,69% de neutrófilos. Porém observou-se diminuição significativa na porcentagem de macrófagos (P=0,04) e aumento de neutrófilos Cytology is an important supplementary test used for the detection of changes in the mobile profile of the respiratory tract and aid in the diagnosis of diseases. However, as the first few months of life make up the period of adjustment to extrauterine life resulting in possible changes in cellular populations, it is essential to the standardization of the characteristics common to healthy animals, enabling the identification and analysis of any change in the expected frame. The objective of this research was to characterize the cellular profile by cytology of bronchoalveolar lavage obtained weekly for bronchoscopy of ten calves during the first three months of life. Statistical analysis was performed using the Minitab ® 15.0 software, using the paired T test for parametric samples, and Mann-Whitney for nonparametric samples, considering significance level as P≤0,05. The results obtained showed that the profile of bronchoalveolar lavage of healthy calves during the first 90 days of life showed a predominance of macrophages, with medium average of 63.17%, followed by 33.69% neutrophils. However it was observed significant decrease in percentage of macrophages (P=0.04) and increased neutrophils (P=0,05) over the times, proven by the strong negative correlation between percentages of macrophages and neutrophils along the times. There was no difference between the percentages of giant cells, epithelial cells, lymphocytes, eosinophils and basophils during the experiment. Although the results are influenced by environmental factors and management, the results of this research provide subsidies for the identification of critical changes in cell profile of calves affected by respiratory diseases.INDEX TERMS: Cattle, calf, respiratory disease, bronchoalveolar lavage, bronchoscopy.