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Pasteur described an organism causing fowl cholera in 1880. In 134 years we have progressed from crude vaccines for Pasteurella, to some refined vaccines, to a name change (Mannheimia), to autogenous vaccines (back to crude). In the last 25–30 years, we have attempted to mitigate the problem of bovine respiratory disease with antimicrobials and subsequently have a high incidence of multi-drug resistance. All of these attempts have resulted in little if any improvement in morbidity/mortality. Is it time to focus on the animal's response or lack of response to infectious pressure? Instead of focusing on the 10–50% morbid cattle should we focus on the 50–90% that are not compromised and determine why they stay healthy under the same environmental conditions?

The North American beef cattle industry has endured many changes throughout the years but is encountering some of the most dramatic challenges in history during the first decade of the 21st century. The US beef cattle inventory increased from 1990 to a high of 103.5 million in 1996 and since has declined to a low of 94.5 million on 1 January 2009. Even though economic signals have encouraged the cow herd to increase over the last 5 years, a significant decrease occurred during 2008. It is difficult to determine the precise cost of bovine respiratory disease (BRD) to the industry but it is reported to be greater than US$500 million per year. Data from our practice indicate that losses from BRD over the last 18 years have been characterized by 5-year cycles of decreases and increases. Perhaps it is time for the industry to look for ways to reduce death loss by methods that focus on the animal's response to the pathogens instead of continuing to focus on the pathogens.

Objective—To compare concentrations of 3-methyleneindolenine (3MEIN) in lung tissues obtained from feedlot cattle that died as a result of acute interstitial pneumonia (AIP) and cattle that died as a result of other causes and to compare blood concentrations of 3MEIN in healthy feedlot cattle and feedlot cattle with AIP.Study Population—Blood samples and lung tissues collected from 186 cattle housed in 14 feedlots in the western United States.Procedure—Samples of lung tissues were collected during routine postmortem examination and submitted for histologic, microbiologic, and toxicologic examination. Blood samples were collected from cattle with clinical manifestations of AIP and healthy penmates. Histologic diagnoses were categorized as AIP, bronchopneumonia (BP), control samples, and other disorders. Concentrations of 3MEIN were determined in lung tissues and blood samples, using an ELISA.Results—Concentrations of 3MEIN in lung tissues were significantly greater in AIP and BP samples, compared with control samples. Absorbance per microgram of protein did not differ between BP and AIP samples. Blood concentrations of 3MEIN were significantly greater in cattle with AIP, compared with healthy cattle or cattle with BP. Odds of an animal with AIP being a heifer was 3.1 times greater than the odds of that animal being a steer.Conclusion and Clinical Relevance—Increased pulmonary production of 3MEIN may be an important etiologic factor in feedlot-associated AIP. (Am J Vet Res2001;62:1525–1530)

Objective—To evaluate viral and bacterial respiratory pathogens andMycoplasmaspp isolated from lung tissues of cattle with acute interstitial pneumonia (AIP) and cattle that had died as a result of other causes.Sample Population—186 samples of lung tissues collected from cattle housed in 14 feedlots in the western United States.Procedure—Lung tissues were collected during routine postmortem examination and submitted for histologic, microbiologic, and toxicologic examinations. Histologic diagnoses were categorized for AIP, bronchopneumonia (BP), control samples (no evidence of disease), and other disorders.Results—Cattle affected with AIP had been in feedlots for a mean of 127.2 days before death, which was longer than cattle with BP and control cattle. Detection of a viral respiratory pathogen (eg, bovine respiratory syncytial virus [BRSV], bovine viral diarrhea virus, bovine herpesvirus 1, or parainfluenza virus 3) was not associated with histologic category of lung tissues. Bovine respiratory syncytial virus was detected in 8.3% of AIP samples and 24.0% of control samples. Histologic category was associated with isolation of an aerobic bacterial agent andMycoplasmaspp. Cattle with BP were at greatest risk for isolation of an aerobic bacterial agent andMycoplasmaspp.Conclusion and Clinical Relevance—Analysis of these results suggests that AIP in feedlot cattle is not a consequence of infection with BRSV. The increased risk of isolation of an aerobic bacterial agent from cattle with AIP, compared with control cattle, may indicate a causal role or an opportunistic infection that follows development of AIP. (Am J Vet Res2001; 62:1519–1524)