AVA Conference Gold Coast 2020

The primary aim of the backgrounding/vaccination study was to measure the effects of respiratory vaccines for cattle placed in local backgrounding facilities then feedlots on feedlot health and growth rate. With backgrounding, cattle are placed in a facility with more space than a feedlot pen, and fed a low grain ration or pasture. Between November 2009 and February 2017, 7011 cattle entering six feedlots in Australia were allocated to eight respiratory vaccine categories, including an untreated control category, on entry to backgrounding facilities contiguous with each feedlot. The vaccines, against Mannheimia haemolytica, bovine herpesvirus 1 (BHV1), and bovine viral diarrhoea virus (BVDV), were given in various combinations at backgrounding facility entry and feedlot entry. Blood samples were taken at these times to measure BHV1 and BVDV serum antibody concentrations. Cattle were held in the backgrounding facilities for a minimum of 28 days. Results: Six of the respiratory vaccine combinations decreased growth rate during backgrounding relative to untreated controls. Overall, feedlot growth rate was not significantly affected by vaccine category (global Wald P = 0.169) but growth rate improved (P = 0.003) in response to Bovishield® and Pestigard® (against M. haemolytica and BVDV, respectively) in combination. BRD subhazard was lowest in cattle vaccinated with Bovilis MH+IBR® (against M. haemolytica and BHV1; subhazard ratio: 0.47; 95% CI: 0.27-0.83; P = 0.010). Point estimates for other vaccine combinations were consistent with reduced risk of BRD but these estimates were compatible with both beneficial and adverse effects. A high proportion (66%) of cattle were seropositive to BVDV at backgrounding facility arrival, and during their feedlot phase, 27% of study animals were exposed to the 0.28% of the study population that was persistently infected with BVDV. Only 14% of cattle were seropositive to BHV1 at arrival. During their feedlot phase, 3.7% of study animals were detected with respiratory disease. Conclusion: Accounting for vaccine effects on growth rate during backgrounding and feedlot phases, economic analysis showed that routine use of these respiratory vaccines in populations represented by this study population, with cattle held for at least 28 days in backgrounding facilities contiguous with their feedlots before feedlot entry, is not justified. Further research into the appropriate use of respiratory vaccines in cattle destined for feedlots should be directed at their administration on the farm of origin. Many feedlots use a single dose of a Mannheimia haemolytica vaccine at feedlot entry. There is no evidence to support the use of these vaccines in this way. In this study the incidence of BRD was low, and no effects of vaccination on the incidence of BRD or growth rate were observed. These findings should be considered with further research into the use of vaccines to prevent BRD and our preventative practices in the field. Mycoplasma has been found in a high proportion of cattle in hospital systems in two feedlots in an additional study, but not in cattle at induction. It is possible that Mycoplasma might be complicating our treatment of BRD and if this is a consistent effect we should consider it in our feedlot hospital management.