Not so many years ago little attention was paid to non-parasitic respiratory diseases of cattle because they seemed of minor importance. However, in the past twenty years, as the number of cattle kept on any farm unit increased under economic pressures, there has been a concomitant rise in the prevalence of respiratory illness. Investigations into cattle respiratory diseases have become a significant part of the research effort in most countries of Europe. Initially much work went into finding, like the alchemist's stone, the orgdnism responsible for causing cattle respiratory disease. Many viruses were isolated and over the years a long list of those recovered from the respiratory tract of cattle has been prepared. Unfortunately, few of these viruses on their own are recognised as proven pathogens and no single virus provides the complete aetiological answer to bovine respiratory disease. More recently, perhaps in despair, g eater attention has been directed to the role of mycoplasma and, additionally. a revival of interest has taken place in the significant part played by bacteria in the later stages of res- piratory disease. Now, phrases such as "multifactorial disease" are being commonly used to describe the complex situation with respiratory disease.
