Over the past several years, respiratory disease in pre-weaned calves on pasture has been increasingly identified in beef herds. These outbreaks tend to be unpredictable, occurring in well-managed herds as well as in not-so-well-managed herds. As such, they are frustrating for cattle producers and veterinarians alike.
Based on submissions to the SDSU veterinary diagnostic lab, the infectious agents associated with summer calf pneumonia cases are similar to those implicated in typical post-weaning bovine respiratory disease complex. Bacteria such as Mannheimia haemolytica, Histophilus somni, Pasteurella multocida, and sometimes Mycoplasma bovis are found in summer pneumonia calves. Viruses implicated include Infectious Bovine Rhinotracheitis Virus [IBRV] and Bovine Respiratory Syncytial Virus [BRSV]. Bovine coronavirus has frequently been found in nasal swabs from affected calves, but much more needs to be known about the role it plays in summer pneumonia.
Despite this knowledge, a specific diagnosis in an outbreak isn’t obtained all that often. For one thing, calves aren’t always available to post and work up for diagnosis. This is because typical summer pneumonia outbreaks do not exhibit high death losses. In light of this, veterinarians will often take nasal swabs from affected calves to isolate infectious agents. These results need to be interpreted with caution, however. Bacteria and viruses present in the nasal passages might not accurately reflect what’s going on down in the lungs.
Signs of respiratory disease in pre-weaned calves do not always include breathing problems such as cough or rapid respirations, although those signs may become more obvious when the herd is trailed or otherwise moved. Sluggishness, a reluctance to keep up with the herd, and drooping of ears are commonly noted. Many affected calves will have high fevers.
Most producers and veterinarians report that treating calves with summer pneumonia is frequently successful. A variety of antibiotics and anti-inflammatory medications have been used with good recovery rates. While these treatments enjoy a high degree of success, they are of course difficult to apply to individual calves in pasture situations. In cases late in the grazing season, pre-weaning vaccinations, along with antibiotics, can be administered to all calves if a high proportion of the herd is affected.
Compared to the post-weaning bovine respiratory disease encountered by animals entering the backgrounding lot or feedlot, little is known about the risk factors that predispose calves to pneumonia while on pasture. Some of the factors that have been speculated include:
- Poor colostrum intake as a newborn calf
- Exposure of calves to older calves (such as feedlot animals) shedding high levels of infectious agents (but not necessarily sick themselves)
- Dusty conditions that interfere with the respiratory tract’s normal defense mechanisms
- Adverse weather conditions
- Crowding and separation from mothers for prolonged periods of time, such as during breeding or synchronization.