Effects of vaccination in backgrounded feedlot cattle.

Summary

The primary aim of this study was to measure the effects of respiratory vaccines administered to cattle in local backgrounding facilities on feedlot health and growth rate. 7302 cattle across 6 sites in Australia were allocated to 8 respiratory vaccine groups, including negative controls, between November 2009 and February 2017 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 background entry and feedlot entry according to label recommendations. 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.

A high proportion (66%) of cattle were seropositive to BVDV at background facility arrival with more cattle seropositive in western Queensland than in sites south of this. 0.28% of the study population was persistently infected with BVDV. Only 13.5% of cattle were seropositive to BHV1 at arrival. With the exception of the M. haemolytica vaccine, Bovishield®, all other respiratory vaccine combinations decreased (P < 0.001) growth rate during backgrounding. Overall, feedlot growth rate was not affected by vaccine group (global Wald P > 0.05) with one point estimate improvement (P = 0.003) in response to Bovisheild® and Pestigard® (against BVDV) in combination. BRD risk was lowest (P = 0.010) in cattle vaccinated with Bovilis MH+IBR® (against M. haemolytica and BHV1; subhazard ratio or SHR: 0.47; 95% CI: 0.27-0.83), but other vaccine combinations had effects with the confidence limits overlapping nil effect.

Accounting for respiratory vaccine effects on growth rate during backgrounding and feedlot phases, financial analysis showed that routine use of the respiratory vaccines in this study, administered on entry to backgrounding and entry to the feedlot, with cattle held for at least 28 days in backgrounding facilities contiguous with their feedlots, is not warranted. Further research into the appropriate use of respiratory vaccines should be directed at their administration on the farm of origin.