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.