SHORT COMMUNICATIONS Dairy calf rearing unit and infectious diseases: diarrhea outbreak by bovine coronavirus as a model for the dispersion of pathogenic microorganisms Amauri Alcindo Alfieri1,2 & Juliane Ribeiro1 & Luciana de Carvalho Balbo1 & Elis Lorenzetti1,3 & Alice Fernandes Alfieri1,3 Received: 4 January 2018 /Accepted: 9 April 2018 # Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract Dairy calf rearing unit is a management system that is only recently being implemented by some milk producer’s cooperatives in southern Brazil. However, aspects related to the health profile of the heifer calves that arrive in the rearing unit as well as about biosecurity practices and microbiological challenges have not yet been evaluated in this rearing system in a tropical country. Diarrhea is the main and most frequent consequence of enteric infections in newborn calves. This study, through some etiological and epidemiological characteristics of an outbreak of neonatal diarrhea, has the aim to alert to the possibility of pathogenic microorganism spread in a dairy heifer calf rearing unit. The diarrhea outbreak presented some non-regular characteristics observed in bovine coronavirus (BCoV) enteric infections in dairy calves. The spread of infection was extremely rapid (1 week); the attack rate (> 50%) was much higher than that observed in calves subjected to conventional rearing; and the age range (5 to 90 days) of the affected heifer calves was much broader than that often observed in the BCoV diarrhea worldwide. These unusual epidemiological characteristics observed in this BCoV diarrhea outbreak raise awareness of the health threat present in calf rearing units as well as of the easy and rapid viral spread in a population of young animals from different dairy herds and, therefore, with very distinct immunological status. Keywords Dairy calf . Biosecurity . Risk infection . Enteric infection . BCoV Introduction One of the aims of dairy herds is the rearing of high-quality heifers for the replacement of adult animals to improve milk production which is the main activity. In order to accelerate the development of the calves and heifers and the genetic im- provement of cows, some dairy farmer’s cooperatives have adopted the calf rearing system where dairy heifer calves are re- ceived up to 5 days old and returned to the original farm as preg- nant heifer. However, calves from distinct herds with different health management and immunological status are grown in the samerearingunitwhichcanbeagreatthreatfortheoccurrenceof several infectious health problems (Walker et al. 2012). Dairy calf rearing unit is a management system that is only recently being implemented by some milk producer’s cooper- atives in southern Brazil. Aspects of management and nutri- tion of dairy heifer calves in this rearing system are being evaluated with relative frequency in Brazil. However, regard- ing the health status, very little is known about biosecurity practices and the microbiological challenges in Brazilian calf rearing units. Neonatal diarrhea is considered as an important health problem in calves worldwide (Ammar et al. 2014; Lorenzetti et al. 2013; Park et al. 2006). Calf diarrhea is a multifactorial syndrome with predisposing factors (age, genetics, nutritional, and immunological) and mainly the causal agent such as virus, * Amauri Alcindo Alfieri