Abstract The objective of this descriptive study was to identify and characterize bacterial isolates associated with respiratory disease in bucks enrolled in a standardized performance test. Respiratory disease remains a significant economic burden for livestock producers. While certain bacteria have been recognized in cattle and sheep as causing respiratory disease, their roles in goats are not well defined. We hypothesized that bacterial populations at arrival will differ from those associated with respiratory disease. Thirty (n = 30) bucks originated from different regions (OK, IN, WV, AL, MS) were transported to the H. H Leveck Animal Research Center in Starkville, Mississippi, where bucks were observed for two weeks in confinement followed by ten weeks on pasture. Nasal swabs were collected upon arrival for bacterial isolation. Colonies were initially cultured on brain heart infusion agar and classified based on colony morphology (e.g., yellow-whitish, circular, and flat, and other distinct characteristics). Representative colonies were then subcultured on blood agar and shipped for identification. Throughout the trial, thoracic ultrasounds were performed weekly. Animals with pulmonary consolidations greater than or equal to 1 cm were classified as having respiratory disease. Additional nasal swabs were collected from bucks exhibiting these signs and submitted for bacterial identification. In total, fifteen different bacterial isolates were retrieved at arrival. The most frequent isolates were Staphylococcus xylosus (8/15, 53.3%), and Staphylococcus aureus (2/15, 13.3%), with other staphylococcal and opportunistic organisms recovered in small numbers. By the end of the trail, 26 of 30 bucks (86.7%) developed pulmonary lesions and a total of 28 bacterial isolates were identified over the course of the trial. Among these, Mannheimia haemolytica (7/28, 25.0%) and Streptococcus pneumoniae (5/28, 17.9%) were the most frequently isolated pathogens. Other isolates include Staphylococcus aureus (2/28, 7.1%), Pasteurella multocida (1/28, 3.6%), and opportunistic organisms. This study demonstrates that bacterial populations present at arrival differed from those associated with respiratory disease during a buck performance test. At arrival, 13 of the 15 isolates were considered normal flora of the respiratory tract, while two Staphylococcus aureus isolates were potentially pathogenic. By the end of the trial most of the bacteria were considered pathogenic. Bacteria such as Mannheimia haemolytica and Streptococcus pneumoniae were most frequently isolated from animals with pulmonary lesions, highlighting their role as primary respiratory pathogens in goats. The high proportion of affected bucks underscores the health, and welfare impacts of respiratory disease in performance testing environments. This study suggests that Mannheimia haemolytica and Streptococcus pneumoniae are key contributors to caprine respiratory disease, while staphylococcal species are more likely to be commensals. Overall, these results emphasize the importance of monitoring bacterial populations during confinement and support further research into preventive measures targeting primary respiratory pathogens in goats.
Taylor et al. (Wed,) studied this question.