Of all the different illnesses that can affect cattle, one syndrome far and away outdoes the others:  bovine respiratory disease (BRD).  This disease complex accounts for 75% of health problems in cattle today. 

The term “complex” aptly describes how this disease occurs.  It’s not just one bacteria or even one class of infectious agent.  Rather, viruses such as BVDV, IBR, and BRSV become involved in conjunction with bacteria such as Mannheimia, Pasteurella, and Mycoplasma.  Oftentimes these pathogens don’t cause any problems unless stresses such as weaning, transportation, or weather come into play. 

The profile of BRD has changed somewhat over the past decade or so, with less of the classic “shipping fever” type events 7-14 days after arrival, and more illnesses later into the feeding period: 40-50 days on feed or longer.  Often these illnesses are more subtle and chronic in nature.  Bacterial issues such as Mycoplasma or Histophilus may be more common in these later-onset cases. 

The shift to more subtle problems in feedlot cattle, away from the acute outbreaks, doesn’t make it any easier for us to detect calves that need treatment.  No one has to question whether the calf with droopy ears, separated from the rest of the group, breathing hard and coughing, needs to be treated.  But what about more subtle cases?  What about that calf that’s just a little slower than the rest but still comes up to the bunk?

The task of detecting calves in need of BRD treatment may be more daunting than we think.  For those of us who think we’re pretty good at picking these calves out, several published studies might make us question our abilities.   

These studies compare treatment records (calves identified as sick enough to be pulled and treated) with the extent of the actual lung problems seen in those calves’ carcasses at slaughter.  One would hope that the number of calves with lung damage would be similar to or fewer than the number of calves treated.

The studies show a different story, though.  One study (Wittum, 1996) characterizes a group in which 35% of the calves were pulled and treated, but 72% had evidence of BRD at slaughter.  This observation is repeated in more recent studies (Thompson, 2006) in which 23% of calves were treated but 43% had evidence of pneumonia at slaughter, and one (Schneider, 2009) in which 8% of calves were treated but 62% had lung lesions.  It would appear that despite our best efforts, we are still missing a substantial number of claves that may benefit from BRD treatments. 

Such information might frustrate cattlemen trying their best to identify calves that need attention.  But on the other hand, it should spur us to heighten our detection skills.   

What some would call “sickness behavior” is often the physical result (“side effects”) of the action of certain chemicals released by cells of the immune system.  While these substances are meant to mobilize the rest of the immune system in response to an infection of the respiratory tract, for example, they also have physical effects on the behavior and appearance of the affected calf. 

Some of these changes include lethargy, reluctance to move with the group, droopy ears and lowered heads, lack of appetite, piloerection (or fuzziness of the hair coat), a tucked-up abdomen, and a tendency to want to lie down.  All of these can be explained in terms of calves wanting to conserve energy for their immune system’s fight against the pathogen. 

Making the situation tougher is the fact that calves, having evolved a prey species, try to hide these signs from others. As such they will work to blend in with the rest of the group as much as possible. 

The bottom line is that nothing has yet proven to be a substitute for careful experienced observation of calves.  In our rush to get things done and get on to the next job on our list, we run the risk of missing calves that may be in much worse shape tomorrow.  Take time to spend time observing your calves this fall.

Source: Russ Daly