Larry C. Hollis, DVM., M.Ag. Extension beef veterinarian,
One of the most frustrating things that can happen to a cow/calf producer is to have a set of healthy growing calves start developing pneumonia during mid-summer while the calves are still nursing the cow. With some operations, this is an annual event, while with others it only happens sporadically. Summer time pneumonia generally happens when the passive immunity (antibodies) from the dam’s colostrum naturally diminishes, and the calf’s own immune system has not had any exposure to the viruses or bacteria that usually cause this pneumonia that would result in production of active immunity. We know that the primary bacterial species involved, Mannheimia haemolytica and/or Pasteurella multocida, are passed from the nasal cavity of the cow to the nasal cavity of the calf at a very early age. However, these bacteria rarely cause disease merely by being present – there usually has to be some sort of stressor that triggers the onset of pneumonia.
Stressors such as a sudden cold rain, hail storm, extreme heat, dust, aggravation from massive fly populations, dry pasture conditions that suddenly cause their dams to drop in milk production, etc., can be all it takes for pneumonia to be initiated. Also, viruses such as IBR, BVD and BRSV, that are carried by some cows in the herd and shed intermittently (IBR, BRSV) or continually (persistently infected BVD carriers), can establish an infection once colostral antibodies wane in the calf. The presence of internal parasites can also weaken the calf’s immune system, making it more susceptible to these pneumonia-causing organisms.
Where there is a history of summer pneumonia, vaccinating the calves with a 5-way respiratory viral vaccine (IBR, BVD types 1 and 2, PI3, and BRSV) along with a Mannheimia haemolytica bacterin/toxoid may be warranted. If the cow herd has been previously vaccinated with a modified live virus (MLV) form of viral vaccine, then it is usually advantageous to use a MLV version on the calves as well. If the cow herd has not been previously vaccinated with a MLV form, then 2 injections of a killed form of these viruses 3 weeks apart is in order. To have a chance for any of these viral vaccines or bacterin/toxoids to be effective, the final dose should be administered 2-3 weeks prior to the historical time of the summer when the pneumonia outbreaks have been known to occur.
If summer pneumonia is experienced for the first time, or prevention efforts fail, early detection is critical to treatment success. There are many antibacterials that can be used to effectively treat the bacterial portion of the disease if treatment is initiated early enough. However, if sick calves are detected too late in the course of the disease, damage to the lungs may be so extensive that the calf becomes chronically affected or dies. With the heat of summer, undetected pneumonia will usually progress much faster than pneumonia cases that arise during the cooler months.
Normally, most cow/calf producers expect everything to be on “cruise control” for the summer. The tendency may be to get a little lackadaisical. However, pneumonia in suckling calves is one disease problem that requires vigilance to keep from experiencing devastating losses during the summer months.