PSXII-22 - Analysis of the upper respiratory tract microbiome in newly-received feedlot heifers according to subsequent incidence of bovine respiratory disease

Abstract: This study compared the relative abundance of bacteria in the upper respiratory tract (RT) of newly-received feedlot heifers according to incidence of bovine respiratory disease (BRD). Angus-influenced heifers (n = 76) were transported for 1,100 km (11 h) to the feedlot (d -1). At feedlot arrival (d 0), heifers were weighed [initial shrunk body weight (BW) = 234 ± 15 kg] and a nasal swab collected for analysis of the upper RT microbiome. Heifers were ranked by arrival BW and allocated into 6 pens on d 1 where they remained until d 55. Heifers were evaluated daily for BRD signs (d 0 to 55), and a final shrunk BW was recorded on d 56 (16-h feed and water deprivation). Heifers were classified according to number of antimicrobial treatments for BRD received (0, 1, or ≥2), or according to time of first incidence of BRD signs [no incidence (NOBRD), early incidence (EARLY; 4.1 ± 0.1 d), or late incidence (LATE; 18.5 ± 9.6 d). All data were analyzed using heifer as the experimental unit, the PROC MIXED procedure of SAS and Satterthwaite approximation to determine the denominator degrees of freedom for tests of fixed effects. The first model statement included the number of BRD treatments received, the second model statement included the time of first incidence of BRD signs. Average daily gain decreased linearly (P = 0.04) according to number of BRD treatments and was less (P = 0.04) in LATE and tended (P = 0.08) to be less in EARLY compared with NOBRD heifers. The abundance of the phyla Tenericutes increased linearly (P < 0.01), while the abundance of Firmicutes, Bacteroidetes, Actinobacteria, Verrucomicrobia, Spirochaetes, Euryarchaeota, Chlorobi, and Chloroflexi decreased linearly (P ≤ 0.05) according to number of BRD treatments. Heifers classified as EARLY had greater (P = 0.01) abundance of Tenericutes and less (P = 0.03) abundance of Firmicutes compared with NOBRD, as well as less (P ≤ 0.03) abundance of Euryarchaeota and Chloroflexi compared with both NOBRD and LATE heifers. The abundance of the genera Mycoplasma increased linearly (P < 0.01) while the abundance of Corynebacterium, Blautia, Jeotgalicoccus, Clostridium, and Dietzia decreased linearly (P ≤ 0.03) according to number of BRD treatments. Heifers classified as NOBRD had less (P = 0.01) abundance of Mycoplasma compared with EARLY, and greater (P ≤ 0.05) abundance of Corynebacterium, Jeotgalicoccus, Dietzia, and Planomicrobium compared with EARLY and LATE heifers. Collectively, heifers that developed BRD had altered upper RT microbiome at the time of feedlot arrival compared with heifers that remained healthy, particularly increased prevalence of Tenericutes phylum and Mycoplasma genera. Such differences in upper RT microbiome were heightened in heifers that developed BRD shortly after arrival, or that required multiple antimicrobial treatments.