Economic impact of Bovine Ephemeral Fever Virus in Extensive Northern Beef Herds, Phase 2

Summary

Bovine Ephemeral Fever (BEF) is a familiar disease to Northern Australian cattle producers. Economic losses are experienced through rapid loss of body weight, slow recovery, temporary infertility in bulls, temporary to permanent cessation of lactation in cows, low levels of mortalities and delayed station mustering. The virus is transmitted by biting insects (vectors), which are more prevalent after seasonal rain. Overwintering of the virus has allowed the evolution of seasonal epidemics and sporadic outbreaks with occasional severe widespread epidemics. There is little to no ability to predict the timing or severity of outbreaks. 
Vaccination for ephemeral fever has been available in Australia since 1986. The viral strain used in the vaccine is efficacious in conditions of experimental challenge and has shown a sixfold reduction in the number of serologically confirmed ephemeral fever cases in commercial trials. In this study, undertaken over the period 2003 to 2009, vaccination of animals in a number of extensive northern herds was tested; growth, carcass and reproductive variables were measured and compared with control counterparts. The project was carried out under normal extensive cattle station management and regular cattle finishing and slaughter regimes.
During these years no significant differences were found between vaccinated and control animals for the variables measured. Confounding factors include unknown prior immunity of recruited weaners, inability to measure mortalities, efficacy of vaccine against wild viral strains and unknown exposure levels of control animals throughout the project. The occurrence of sporadic BEF outbreaks was recorded anecdotally during the trial. However, these years would be regarded as low incidence years for BEF in terms of sentinel herd seroprevalence information. Economic modelling using the data set as a source of herd production indices was undertaken. Break even cost to vaccinate, using the current commercial vaccine and a hypothesised next generation single dose vaccine, was calculated as the most industry appropriate outcome. For both vaccines, a break even situation was achieved if steer sale prices increased by 5.5%.