Clinical and endoscopic study to estimate the incidence of distal respiratory tract infection in thoroughbred foals on Ontario breeding farms.

This research aimed to determine the incidence of distal respiratory tract infection (DRTI) in Thoroughbred foals on Ontario breeding farms. The study used specific clinical criteria to identify infections, finding an approximate incidence of 82% and highlighting that most clinical DRTI occurrences were noticed in the months of July and August.

Objective and Methodology

• The main purpose of this study was to understand the frequency of distal respiratory tract infections (DRTIs) in Thoroughbred foals on breeding farms in Ontario, Canada. Prior to this study, no evaluation had been conducted on this topic.
• As a preliminary step, the researchers conducted a pilot study to establish clinical factors that could help differentiate between foals with and without DRTIs. These factors included abnormal lung sounds, nasal discharge, cough, fever, tachypnea (rapid breathing), and lethargy.
• The research team used endoscopy, a non-surgical procedure used to examine a person’s (or animal’s) digestive tract, to confirm whether the foals in the pilot study indeed had DRTIs.

Findings from the Pilot Study

• Based on the outcomes from the pilot study, the researchers identified foals with DRTIs by their significantly higher bronchial lavage total cell count and neutrophil concentration (evidence of inflammation), more frequent observation of mucopurulent exudate (a sign of infection), bronchial erythema (reddening of the bronchi suggestive of irritation), and more frequent recovery of intracellular cocci (a type of bacteria) from bronchial lavage samples.
• The pilot study findings indicated that these clinical criteria could reliably identify foals with DRTIs.

Main Study and Findings

• Using the clinical criteria identified in the pilot study, the researchers then examined a cohort of 219 Thoroughbred foals from May 1 to October 30, 1991.
• The overall incidence of DRTI, adjusted for grouping, was estimated to be around 82%. Further, the majority of clinical DRTI episodes (74%) occurred during July and August, suggesting a seasonal impact on the incidence of the disease.
• Interestingly, DRTIs were noticed equally in weaned and non-weaned foals, leading to the conclusion that weaning status did not significantly affect the occurrence of DRTIs.
• Of the 178 identified cases, 66 were further examined using endoscopy and bronchial lavage. The majority of these cases (60%) showed grade-II pharyngeal lymphoid hyperplasia, a type of abnormal tissue growth, while 21% had an auditory tube diverticulum discharge. Guttural pouch infection was confirmed in 6 out of 7 foals examined endoscically.

Conclusion

• The research provides valuable insight into the high incidence of DRTIs in Thoroughbred foals in breeding farms in Ontario, as well as the timing and some common associated conditions.