Evaluating bacterial and viral colonization of the upper respiratory tract of neonatal beef calves during the first 24 hours of life

Little is known regarding the timing of initial establishment of bovine respiratory disease complex (BRDC)-associated bacterial and viral pathogens. The objective was to evaluate the presence of BRDC-associated bacteria and viruses in the upper respiratory tract of newborn calves within the first 24h of life. Commercial beef cows (n = 26) were allocated to indi­vidual pens before calving. A left nasal swab (LNS), right na­sal swab (RNS) and vaginal swab were collected from each cow immediately following parturition (0h). Calf (n = 26) LNS and RNS sampling occurred at 0h, 6h, 12h and 24h post-calv­ing. Samples were submitted to a diagnostic lab for bacterial culture (n = 26 pairs) and real-time PCR (rtPCR; n = 10 pairs) to isolate and identify bacteria and to detect bacterial and viral nucleic acid. While we were unable to isolate bacteria of interest using culture, rtPCR yielded some success. At birth, Histophilus somni (Hs) was detected in 4/30 dam swabs and 1/20 calf swabs, Mannheimia haemolytica (Mh) in 1/30 dam swabs and 1/20 calf swabs, Mycoplasma bovis (Mb) in 4/30 dam swabs and 1/20 calf swabs, Pasteurella multocida (Pm) in 2/30 dam swabs, bovine herpes virus type-1 (BHV1) in 1/30 dam swabs, and bovine respiratory syncytial virus (BRSV) in 1/30 dam swabs. In 6h calf swabs, Hs was detected in 3/20, Mb in 1/20, and BRSV in 1/20. Associations of bacteria and viruses be­tween dam and offspring remain unclear as establishment of the neonatal microbiome appears complex and more sensitive methods may be needed.