The impact of environmental factors on bovine respiratory disease complex in dairy calves - a review

Bovine respiratory disease complex (BRDC) is a multifactorial disease in which, in addition to infectious agents and the individual resistance of animals, technological, management and climatic factors also play a role. Outdoor rearing in small groups has many advantages in terms of BRDC prevention. Continuous real-time monitoring of environmental factors, such as the temperature, relative humidity, air velocity, bioaerosols and harmful gases can also help to prevent damage by BRDC. Low temperatures in combination with elevated relative humidity and windspeed can lead to increased morbidity and mortality. Among noxious gases, ammonia may be of the greatest importance for respiratory diseases, as it directly damages the respiratory tract, leaving room and opening gate for pathogenic and opportunistic microbes. Bioaerosols of livestock buildings consist of feed, manure, organic matter from animals (e.g., epithelial cells, hair, urine, faeces), microorganisms, and toxins. Due to their size, particulate matter (PM) particles (PM10 and PM2.5) have important health effects, leading to severe respiratory and systemic diseases. Particulate matter formation and concentration depend on the housing and feeding conditions, species housed, stocking density, animal activity and environmental factors, but also on the sampling periods within a day. High temperature, low humidity, air movement (especially drafts), and increased activity of animals also cause the manure to dry, leading to dust formation and particles becoming airborne. With increased environmental control, the effects of the climatic factors on the calves health can be more easily identified, measures can be taken to reduce them, thus the occurrence and damage of possible diseases (mainly respiratory, BRDC) can be decreased.