Use of metaphylactic protocols based on the risk to develop bovine respiratory diseases in feedlot cattle

EnglishBovine respiratory diseases (BRD) affect production rates negatively because it compromise health and well-being of the affected animal. The hypothesis of this study was that the use of metaphylactic protocols based on the risk to develop BRD would reduce morbidity and pulmonary lesions. For this purpose, the aims of this study were to evaluate the effect of two metaphylactic protocols on the morbidity of feedlot cattle with a known sanitary history, occurrence of pulmonary lesions at slaughter, and the possible participation of Mannheimia haemolytica, Histophilus somni, Bovine alphaherpesvirus 1 (BoHV-1) and bovine respiratory syncytial virus (BRSV) in the development of BRD. An experimental study was designed in which 3,094 adult, male, cattle, were grouped according to the risk to develop BRD: a) group without metaphylaxis (n=2,104), low-risk animals; b) metaphylaxis group with oxytetracycline (n=789), moderate-risk animals; c) metaphylaxis group with tildipirosin (n=201), high-risk animals. All cattle were immunized against pathogens associated with BRD (BoHV-1, BVDV, BRSV, PI3). The morbidity for BRD was 8.2% (253/3,094); cattle within the moderate-risk group for BRD had the lowest frequency (6.1%), followed by high-risk animals with tildipirosin metaphylaxis (6.5%) and low-risk without metaphylaxis (9.1%) (P=0.019). At the abattoir, 1.2% of lungs with lesions were found. There was a difference (P=0.036) in the frequency of pulmonary lesions between healthy animals (1.1%) and those diagnosed with BRD (2.8%). Two agents associated with BRD were identified by PCR assays in the lungs (n=37) of cattle: M. haemolytica (16.2%) and H. somni (5.4%). In addition, concomitant infections involving these pathogens were identified in the lungs of two steers. These results demonstrate that the use of metaphylactic protocols, based on the risk to develop BRD, reduces morbidity and pulmonary lesions in affected cattle. Furthermore, pulmonary lesions were more frequent in animals with a history of BRD. Key words: Histophilus somni; Mannheimia haemolytica; pulmonary lesions portuguesAs doencas respiratorias dos bovinos (DRB) afetam negativamente as taxas de producao por comprometer a saude e o bem-estar animal. A hipotese deste estudo foi que o uso de protocolos metafilaticos com base no risco de desenvolvimento de DRB reduziria a morbidade e as lesoes pulmonares ao abate. Para tanto, objetivou-se avaliar o efeito de dois protocolos metafilaticos sobre a morbidade de bovinos confinados com historico sanitario conhecido, ocorrencia de lesoes pulmonares no abate e possivel participacao de Mannheimia haemolytica, Histophilus somni, Alphaherpesvirus bovino 1 (BoHV-1) e Virus respiratorio sincicial bovino (BRSV) na DRB. Foram avaliados 3.094 bovinos adultos, machos, agrupados de acordo com o risco de desenvolvimento de DRB: a) grupo sem metafilaxia (n=2.104), animais de baixo risco; b) grupo metafilaxia com oxitetraciclina (n=789), animais de risco moderado; c) grupo metafilaxia com tildipirosina (n=201), animais de alto risco. Todos os animais foram previamente vacinados contra os principais agentes virais causadores das DRB (BoHV-1, BVDV, BRSV e PI3). A morbidade para DRB foi de 8,2% com menor frequencia em animais com risco moderado e metafilaxia com oxitetraciclina (6,1%), seguido por animais com alto risco com metafilaxia com tildipirosina (6,5%) e animais com baixo risco sem metafilaxia (9,1%) (P=0,019). No frigorifico, foram encontrados 1,2% 1,2% de animais com lesoes pulmonares. Houve diferenca (P=0,036) na frequencia de lesoes pulmonares entre animais saudaveis (1,1%) e aqueles diagnosticados com DRB (2,8%). Foram identificados dois agentes associados a DRB pela tecnica de PCR nos pulmoes (n=37) dos bovinos: M. haemolytica (16,2%) e H. somni (5,4%). Adicionalmente, infeccoes concomitantes envolvendo estes potenciais patogenos foram identificadas nos pulmoes de dois animais. Concluiu-se que o uso de protocolos metafilaticos, com base no risco de desenvolvimento de DRB, reduziu a morbidade e a ocorrencia de lesoes pulmonares nos bovinos acometidos que foram identificadas com maior frequencia em animais com historico de DRB. Palavras-chave: Histophilus somni; Mannheimia haemolytica; lesoes pulmonares