Looks Can Be Deceiving: Research Shows Costly Lung Lesions are Prevalent — Even in Treated Cattle

Just because calves look healthy doesn’t mean they are healthy, according to Dr. Louis Perino, a veterinarian at West Texas A&M University in Canyon.

In fact, according to research he and Dr. Dee Griffin conducted at the University of Nebraska, in cooperation with Dr. Tom Wittum and Dr. Neal Woolen, then with USDA Agricultural Research Service, there’s a better than 70% chance those "healthy" cattle were affected by some form of pneumonia sometime between birth and slaughter – even if they were properly vaccinated or treated with antibiotics.

"This doesn’t mean that vaccinations or antibiotics are without value," Perino insists, noting that antimicrobial treatment of clinically affected cattle in the study may have prevented more severe pulmonary damage, a greater reduction in growth rate or even death.

"What it does mean is that our procedures for identifying and treating cattle clinically affected by BRD (bovine respiratory disease) may not be optimal."

Walking pneumonia

The object of his concern is the presence of lesions, or scars, on lung tissue that, according to Perino, "indicates the animal had pneumonia sometime in its life."

"With a lot of these animals, we’re not talking about active pneumonia," he explains. "These cattle look fine, they walk into the packing plant and they pass ante-mortem and post-mortem inspections, so they are in good shape. The pneumonia has healed and there are just some small residual scars that we can observe."

From an economic standpoint, Perino is concerned about what this subclinical pneumonia might be doing to a producer’s bottom line.

"On average, cattle with lesions at slaughter appear to gain about 0.2 lb less per day than cattle that do not have lesions at slaughter," he says. "Those differences are statistically significant."

No clinical symptoms

Perino notes that weight gains of calves showing BRD symptoms and requiring treatment were similar to calves that were seemingly healthy. "But not all calves with respiratory tract infections have overt clinical signs of disease," he says. "Cattle with subclinical infections can develop pulmonary lesions similar to those seen in clinically affected cattle."

To determine the prevalence of lung lesions and their effect on weight gain, the University of Nebraska and USDA scientists conducted a study with 469 cross-bred steers born during three consecutive calving seasons at the U.S. Meat Animal Research Center in Clay Center, Neb. Clinical disease was monitored from birth to slaughter. Steers were weaned at approximately 6 months and entered the feedlot at 273 days. Mean daily weight gain (MDG) was monitored during the feeding period. Lungs were collected at slaughter and evaluated for gross lesions associated with active or resolved pneumonia.

Surprising results

MDG during the feeding period was 2.87 lbs and ranged from 2.56 to 3.22 lbs within individual pens. Although 35% of the steers received treatment for respiratory tract disease between birth and slaughter, 72% had pulmonary lesions at slaughter. And, among steers treated for clinical respiratory tract disease, 78% had pulmonary lesions.

"Surprisingly, 68% of the steers that were never treated for respiratory tract disease because they did not display symptoms also had pulmonary lesions at slaughter," he says.

Although the proportion of untreated steers with lesions was lower than the portion of treated steers, a substantial number of cattle with respiratory tract disease were never identified, Perino says.

"We could not differentiate between subclinical infections that developed prior to weaning from those that developed in the feedlot, though we believe conditions in the feedlot were more conducive to detection of respiratory disease," he says.

"Regardless of when these subclinical infections developed," he adds, "it is obvious there was a large number of affected steers in this population that were not identified as clinically ill. If this finding is representative of feedlot cattle in general, the use of clinical signs or treatment rates as indicators of disease status in field studies of feedlot BRD could result in a large misclassification bias."

Serology surveys help support Perino’s findings. While it’s uncommon to conduct serology on healthy cattle, a 3-year study in Ontario, Canada, showed that 41% of 290 healthy calves developed antibodies to Pasteurella haemolytica and 55% developed antibodies to P. haemolytica cytotoxin during the first month in the feedlot. Other studies have measured high titers of Haemophilus somnus in groups of apparently healthy cattle.

"Our packing house studies looking at lung lesions suggest that subclinical respiratory tract infections capable of producing long-term lung damage may be common in feedlot cattle," he says.

Solving the Lesion Puzzle

Dr. Lonty Bryant of the University of Nebraska knows a thing or two about lung lesions in cattle. As a graduate student, he studied under Perino at Clay Center and made lesions the focus of his master’s degree thesis. His work is not expected to be published for another 6-12 months, but he says it confirms his mentor’s findings in "real world" conditions.

"I spent about 3 years chasing beef calves to packing plants looking for lung lesions," he says. "What I found was between 30-90% of calves had lesions, but there was no relationship between the lesions and the animals that were either sick or had been diagnosed with pneumonia during the feeding period. Calves that had never been diagnosed with pneumonic symptoms were just as likely to carry lesions as calves that had been diagnosed with pneumonia."

So what does this say about the state of bovine vaccination and respiratory programs? "Oh brother," Bryant says chuckling, "we’ve got a lot of work to do."

Like Perino, Bryant doesn’t fault the vaccinations or antibiotics being used. "They have done a world of good for us," he says. "But if you look at the vaccination data and literature over the last 30 years, about all we’ve really done is decrease the size of the dead pile. I think there’s a lot of things we don’t understand, and that is reflected in the nomenclature – ‘shipping fever,’ ‘dust pneumonia,’ ‘bovine respiratory disease’ and so on. You can find numerous names for what is simply pneumonia. And now we call it the bovine respiratory disease ‘complex’."

No protection against lesions

Part of the problem, Bryant says, is measuring vaccine efficacy. "We have traditionally measured it with serology, because we could," he says. "But is a serologic increase after vaccination really protective? Maybe against the disease organism in controlled trials, but it’s not protective against some inflammatory conditions that cause lung lesions in field settings."

Bryant says his research confirms earlier work indicating a significant association between lesions that can be seen at slaughter and average daily gain (ADG) during the feeding period. "What I’m going to publish is a decrease in ADG of .04 lb to .50 lb/day. It varied within pens, but there was a significant reduction in ADG in all pens," he reports.

Bryant hopes his research will eventually find a way to minimize lesions and related losses in weight gain. "We all think we know what makes a good pen of calves – those from a single source that are hauled a short distance, cattle that have been exposed to modified-live virus vaccine two or three times in their life," he says. "But quite frankly, I looked at that those kinds of calves and they still had lung lesions. And lung lesions cost money."

Pressing questions

His most pressing questions: "Is there something in the genetics? Is there something with vaccination or antibiotic timing that will actually reduce these lung lesions? Should we be using an NSAID (non-steroidal anti-inflammatory drug) along with the antibiotic? Or can we identify some risk factor that’s associated with a decreased frequency of lung lesions?"

Bryant says he’s intrigued by the potential of using NSAIDs such as flunixin meglumine, which was recently approved for use in beef and nonlactating dairy cattle.

"Anytime a veterinarian perceives that cattle are suffering from fever or inflammation, or that inflammation is actually going to impair or delay healing time, flunixin could be used," he notes. "Certain bacterial infections produce endotoxin, some of which can be alleviated with this type of agent."