Respiratory Microbiome Monitoring in Beef Heifers

Fourteen Angus × Herford heifers, approximately 8 months of age with an initial body weight of 290 ± 25 kg, were sourced from a research farm that was established in 1984 and free of the following pathogens: the herd was tested annually for bovine viral diarrhea virus, bovine herpes virus-1, Leptospira (serovars Canicola, Pomona, Hardjo, Grippotyphosa, and Copenhageni), Anaplasma phagocytophilum, bluetongue virus, and Brucella abortus, biannually for Mycobacterium avium subspecies paratuberculosis and bovine leukosis virus, and every five years for Mycobacterium bovis. Cattle positive for any of the above disease agents were removed from the herd. None of the cattle used were administered antimicrobials or vaccines prior to or during the study. Calves were weaned 41 d prior to study enrollment (day −41) and were bunk-fed an alfalfa-barley silage mixed diet in pens. On day 0, calves were transported to the feedlot (distance of 20 km).
Upon arrival at the feedlot, the heifers were not mixed with cattle from other sources and were fed alfalfa-barley silage mixed diets similar to the ones at the disease-free farm. Nasopharyngeal samples were collected from each calf in the study on days 0 (at the disease-free farm prior to shipment), 2, 7, and 14 according to Timsit et al. [3 (link)]. Prior to sampling, the nostril was wiped clean with 70% ethanol. Extended guarded swabs (27 cm) with a rayon bud (MW 124, Medical Wire & Equipment, Corsham, England) were used for sampling (Additional file 1: Fig. S1) and swabs were transported to the lab on ice for processing, within one hour of collection. Animals used in this study were cared for according to the guidelines set by the Canadian Council on Animal Care [13 ] and all experimental procedures involving cattle were approved by the Animal Care Committee of the Lethbridge Research Centre.