Backgrounding study targets BRD

Drilling down into the effects of backgrounding cattle with and without the use of vaccines is the focus of a ground-breaking study underway to help tackle the feedlot sector’s biggest health cost - bovine respiratory disease (BRD).

Meat & Livestock Australia (MLA) is supporting a long-term study led by Associate Professor Paul Cusack of Australian Livestock Production Services in Cowra, NSW. The study aims to determine the effect of backgrounding vaccination regimens on feedlot performance and health.

Dr Cusack said while the Australian industry has access to a range of BRD vaccines for use in either the pre-feedlot situation or at entry to the feedlot, no vaccine or combination of vaccines is going to eliminate BRD altogether.

“This study is designed to separate the physiological and behavioural effects of backgrounding from the effects of vaccination and to evaluate them both separately and in combination,” Dr Cusack said.

“It will refine our knowledge of the effects of backgrounding with and without the use of vaccines, and will clarify the most appropriate use of BRD vaccines to optimise animal health outcomes and financial returns.”

The study has been underway for the past two years at sites in Queensland, NSW, South Australia and Western Australia.

A total of 10,800 cattle will be involved in the study, with eight different treatment combinations being tested.

“There’s a range of combinations of vaccines we’re examining including Bovilis MH; Bovilis MH plus IBR; Bovi-Shield MH and Pestigard,” Dr Cusack said.

“We are pooling cattle from various sources into the backgrounding facility, where they must be for at least four weeks.

“There are two reasons for that. The first is that it gives us the opportunity to get a proper secondary immune response to vaccines that require two shots, on entry to backgrounding and on entry to the feedlot.

“It's also based on findings from the National BRD Initiative, which found that mixing cattle from various sources in a backgrounding environment, rather than putting them straight into the feedlot, actually reduced the incidence of BRD subsequently if they had at least 28 days in backgrounding.”

The backgrounded cattle are also being compared with contemporary cattle of the same market specification that have been placed directly in the feedlot, but held in separate pens.

Dr Cusack said outcomes being measured included morbidity or treatment, mortality and growth rates, to give feedlot operators objective measurements.

Full analysis of the data will be conducted once the study is completed in autumn 2017.

“It’s too early for us to draw any conclusions yet, but we’re making some interesting findings regarding previous exposure to pestivirus and bovine herpesvirus 1 (BHV-1), the virus responsible for infectious bovine rhinotracheitis (IBR),” Dr Cusack said.

“There are some apparent regional differences which are likely to have effects on responses to vaccines. So far we’ve found with pestivirus, that there’s a high proportion of seropositive cattle through Queensland and in western Queensland particularly. A seropositive status means they’ve previously been exposed to the virus and mounted an immune response.

“So if there’s a high proportion of cattle seropositive to a given virus arriving for backgrounding, you’re unlikely to get a response from a vaccine against that virus.

 “It’s variable through Central West NSW and low, but variable through SA. What was quite striking was the very low proportion of cattle seropositive to pestivirus in WA.

 “With the BHV-1 serology, that’s a very different picture. Throughout Queensland, Central West NSW and SA, there was a very low proportion of cattle that were seropositive.

“But with a backgrounding time of at least four weeks, a very high proportion mounted an immune response to that virus. That means by the time they come into the feedlot, a lot of them have developed immunity, whether they’ve been vaccinated or not.

“And in WA, similarly, we had a low proportion that was seropositive on entry to backgrounding. In general, there were smaller mobs entering backgrounding in WA, and a low proportion of these seroconverted to BHV-1.

“But if a lot of cattle seroconvert to this virus in larger backgrounding systems from other regions then you’re less likely to get a response.”