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Pneumonia caused by the bacterial pathogens discussed in this article is the most significant cause of morbidity and mortality of the BRDC. Most of these infectious bacteria are not capable of inducing significant disease without the presence of other predisposing environmental factors, physiologic stressors, or concurrent infections. Mannheimia haemolytica is the most common and serious of these bacterial agents and is therefore also the most highly characterized. There are other important bacterial pathogens of BRD, such as Pasteurella multocida, Histophulus somni, and Mycoplasma bovis. Mixed infections with these organisms do occur. These pathogens have unique and common virulence factors but the resulting pneumonic lesions may be similar. Although the amount and quality of research associated with BRD has increased, vaccination and therapeutic practices are not fully successful. A greater understanding of the virulence mechanisms of the infecting bacteria and pathogenesis of pneumonia, as well as the characteristics of the organisms that allow tissue persistence, may lead to improved management, therapeutics, and vaccines., (Copyright 2010 Elsevier Inc. All rights reserved.)

Well-designed immunization programs have an important role in the control of disease outbreaks in cattle. The success of these immunization programs depends on the coordinated and effective use of an efficacious vaccine along with other required control measures. Efforts to improve key characteristics of vaccines (such as onset of immunity, duration of immunity, and basic safety and efficacy) will allow greater utility of the vaccines for outbreak control., (Copyright 2010 Elsevier Inc. All rights reserved.)

Although there are few, well-characterized PIDs of food animals, these diseases are important because they tend to be severe and with no cure. Most animals with PID do not receive the intensive and aggressive care required for survival: Veterinarians may be consulted only when the animals are in the terminal stages of illness; it is generally not economically practical for livestock producers or practitioners to pay for the exhaustive laboratory tests required to detect and characterize these anomalies. Another reason for the small numbers of characterized clinical cases of PID is that they are rare. It is possible, however, that intensive artificial insemination and embryo transfer could select for heterozygous carriers of these autosomal traits. As seen with bovine leukocyte adhesion deficiency, as the frequency of an allele increases in the population, the numbers of affected animals increase. Furthermore, other immunodeficient syndromes are likely to exist. Veterinarians therefore should be aware of these disorders and should seek laboratory assistance to arrive at a correct diagnosis. Because of the inheritable nature of PID, livestock producers need assistance from veterinarians to identify carriers and establish sound breeding and control programs. One positive outcome from studies of PID is that research scientists and veterinarians learn much about immune systems from these afflicted animals. In fact, these animals may become models for gene therapy or marrow reconstruction procedures.