Association of seroconversion with isolation of agents in transtracheal wash fluids collected from pneumonic calves less than three months of age

Abstract

The potential association between seroconversion to respiratory disease agents and isolation from transtracheal wash fluids (TTW) was investigated in pneumonic dairy calves <3 months of age. Naturally infected calves from 18 commercial dairy farms were used. At least one respiratory pathogen was cultured from the TTW of each calf. Blood samples were collected at the time of diagnosis and 3 weeks later. Most calves had evidence of maternal antibodies at 2 days of age to the same pathogens isolated from the TTW at the time of respiratory disease diagnosis. Evidence of an active immune response (seroconversion) to the organism in the TTW was a specified rise in titre between paired serum samples. False-negative results, i.e. failure to seroconvert to the organism isolated in the TTW, were seen in 8 of 9 (89%) calves with bovine diarrhoea virus in their TTW, 43 of 75 (57%) calves with Mycoplasma spp. in their TTW, 20 of 53 (38%) calves with Pasteurella multocida, 4 of 16 (25%) calves with Pasteurella haemolytica, and 5 of 13 (38%) calves with Haemophilus somnus isolates in their TTW. Reliance on paired-serological testing to identify the respiratory pathogens present in the respiratory tract of clinically pneumonic dairy calves <3 months of age is not recommended.