Retrospective study of the relationships between age, inflammation and theisolation of bacteria from the lower respiratory tract of thoroughbred horses

A total of 1235 tracheal aspirates taken from 724 thoroughbreds in race tra ining, aged from two to 10 years. were examined cytologically and bacteriol ogically. An inflammation scoring system on a scale of 0 to 9 was devised t o allow the severity of lower airway disease to be assessed from the cytolo gical results. The inflammation scores were closely related to the isolatio n of bacteria (P<0.001), and the most common bacterial isolates were Strept ococcus zooepidemicus, Streptococcus pneumoniae and Pasteurella/Actinobacil lus-like species. Lower airway disease was less common in older horses (P=0 .031), and the groups at highest risk were the two- and four-year-olds. Low er airway inflammation was more common in the four-year-olds at National Hu nt yards than in the four-year-olds at flat racing yards (P=0.040, odds rat io=3.80).