Effects of parenteral or intranasal modified-live virus respiratory vaccination and revaccination on day 14 in auction-derived feedlot heifers

Auction-derived beef heifers were received in 12 arrival blocks and randomized to 4 treatment groups: 1) parenteral MLV vacci­nation on d 0 (INJ), 2) intranasal MLV vaccination on d 0 (INT), 3) parenteral MLV vaccination on d 0 and revaccination with intranasal on d 14 (INJ-R), 4) intranasal MLV vaccination on d 0 and revaccination with intranasal on d 14 (INT-R). Pen was experimental unit, with 12 pens/treatment and 65 to 76 heif­ers/pen in a randomized complete block design. Performance, health, carcass traits and BRSV and H. somni frequency of car­riage in the nasopharynx of revaccinated groups on d 0 and 60 was determined. Morbidity (P = 0.95), mortal­ity (P = 0.80), and other health variables (P > 0.74) did not dif­fer. However, an improvement in gain-to-feed (G:F) (P = 0.04), increased ribeye area (REA) (P ≤ 0.01) and percentage of edible livers (P ≤ 0.01) was observed for INJ and INJ-R. The BRSV (P = 0.09) and H. somni (P < 0.01) frequency of carriage in the naso­pharynx increased with time but no treatment effect (P ≥ 0.23) nor treatment x day interaction (P ≥ 0.29) existed. Revaccina­tion with an intranasal MLV did not impact health or growth, and arrival intranasal vaccination (INT and INT-R) resulted in less G:F and REA concomitant with increased liver absces­sation, compared to parenteral (INJ and INJ-R). Detection of H. somni in the nasopharynx was frequent on d 60, suggesting important prevalence of this bacterial pathogen in the south­ern U.S. cattle population.