Identification of some new risk factors was one of the key outcomes from an important study into Bovine Respiratory Disease discussed during the feedlot industry’ recent BeefWorks forum held on the Darling Downs.

Researcher Tim Mahony from University of Queensland presented some of the key outcomes from the National Bovine Respiratory Disease Initiative project.

He said the results from the project supported the view that effective BRD management will require greater cooperation between all sectors of the Australian beef industry.

BRD is consistently ranked as the number one health issue of feedlot cattle in Australia and indeed, across the world. The development of BRD is a result of a complex interaction of animal factors, environmental factors and exposure to infectious agents which can all increase the likelihood of disease.

In order to understand how these factors contribute to BRD development a study has been undertaken over the past five years to confirm and quantify these risks, and try to determine what factors, including potential new ones, pre-dispose some cattle to contracting BRD.

The purpose of quantifying factors that put cattle at greater risk of developing BRD is to allow feedlot operators to identify strategies for their enterprises that reduce these risks, and ultimately to minimise the economic impact of BRD.

The large project involved 14 feedlots in five states, and more than 35,000 cattle in 170 cohorts (pen groups).

As is seen fairly typically across lotfeeding operations, about 18 percent of the animals in the study contracted BRD at some point. About 97pc of the BRD cases were seen in the first 50 days. About 77pc of cases identified resulted in pulls. BRD-related mortality was 0.66pc.

While there has been some talk around the industry of a ‘second wave’ of BRD occurrence around day 70-80, this research trial showed little evidence of it.

Blood samples and nasal swabs were collected at the time of induction from each animal, and again if an animal was hospitalised with BRD during the time on feed. A second blood sample was also collected for all study animals after six weeks on feed.

Where possible, tissue samples from deaths considered to be BRD-related were also collected.

A subset of the collected blood samples were tested to determine how exposure to viral pathogens contributes to BRD, while nasal swabs were used to determine what viruses were present in cattle when they were sampled at induction and when pulled for BRD.

Management data were collected for all study animals from the participating feedlots for the time cattle were on feed. Where possible, owners of directly-sourced feeder cattle were surveyed regarding the weaning and other management procedures and practices utilised prior to sale.

Additionally, in a world first, NLIS records were obtained for all cattle in the study to track the life-time movements from property to property, using property identification codes (PICs), to feedlot arrival. These records were also used to determine when cattle had been mixed prior to arrival at the feedlot, whether they had passed through a saleyard, and to estimate transport time to the feedlot. Data was also collected on weather patterns that might have influenced outcomes.

All of this collected information was used to try to determine what might affect animals getting BRD.

A variety of risk factors, both new and existing, were identified:

Breed

Dr Mahony said it came as no surprise to learn from the study that breed-type is linked to BRD performance.

Using Angus (representing 56pc of cattle in the study) as a reference point, Herefords were shown to be twice as likely to contract BRD, while tropical breeds (15.8pc of the cattle in the study) and European crosses were less likely to get BRD. A surprising finding was the Murray Grey cattle were less likely to get BRD compared to Angus, although they represented only 2.6pc of the study population.

Weaning method

Completed surveys from cattle breeders supplying the feeder cattle were obtained for 10,693 animals, representing 31pc of the overall numbers. Yard weaning was shown to reduce the risk of BRD compared to paddock-weaned cattle, in this group.

Induction weight

The weight of cattle at induction was shown to affect the likelihood of cattle developing BRD. Cattle with induction weights less than 425kg were more likely to get BRD compared to cattle weighing 425-450kg. In contrast, cattle weighing + 450kg were less likely to get BRD compared to the immediate lighter group.

Mixing of cattle – on-property

The research found no evidence of any impact on BRD risk if cattle are mixed on the property of origin.

Mixing of cattle – Saleyards

In contrast, the analysis completed so far indicated that saleyards can affect the BRD risk:

• Saleyard transit prior 27 days to feedlot induction decreases risk, while
• Saleyard transit within 27 days of feedlot induction increases risk.

“However further analysis is required to determine if the observed effects on BRD risk are over and above the effects of mixing alone,” Dr Mahony said.

The NLIS data were utilised to track the lifetime movements of cattle and to identify whether cattle had been mixed with others from a different PIC within particular time periods prior to the cohort being filled (i.e. no more cattle added to the feedlot pen).

Cattle at lowest risk of BRD were:

• Cattle that had not been mixed within 27 days of the pen being filled, regardless of whether they had been mixed earlier and;
• Cattle that had been mixed at least 28 days prior and were then only mixed with 2-3 group13 animals prior to the cohort being filled. (‘Group13’ referred to animals in a group with 50 animals or more at least 13 days before induction.)

Two common mixing patterns associated with high risk were:

• Cattle that had never been mixed prior to 13 days before going on feed and were then mixed with 4 or more Group13s prior to the cohort being filled and;
• Cattle that had been at least 28 days prior and were then mixed with 4 or more Group13s prior to the cohort being filled

‘Group13’ animals were at reduced risk of BRD. The BRD risk was reduced if the ‘Group13’ groups contained more than 100 animals.

Transport time

Cattle transported for six or more hours within a day of induction were shown to be at a slightly increased risk of BRD compared to those transported for less than six hours.

Delayed induction after arrival

Animals transported to the feedlot at least 28 days before feedlot induction were at reduced risk of getting BRD.

Pen filling

Cattle in study cohorts where the pen was filled in a single day were less like to get BRD compared to pens filled over a number of days. The time it took to fill cohorts also affected the BRD risk of cattle with the last cattle to enter a cohort having a higher risk of BRD compared to those inducted earlier.

Season of induction

Animals inducted in summer, autumn and winter were at greater risk of getting BRD compared to spring inductions. Risk was similar in both summer and autumn with animals inducted in these seasons being at least twice as likely to get BRD compared to those inducted in the spring.

Pen features

Cattle in pens with shared water were at higher risk of BRD compared to cattle in pens without shared water. The number of adjoining pens did not affect the risk of BRD. The effect of shade in pens was inconclusive and required additional investigation, Dr Mahony said.

Feedlot region

For reasons yet unexplained by researchers, cattle in feedlots in southern regions were at considerable higher risk of contracting BRD than those further north. This increased risk – one of the highest risk factors identified in the study – was over and above what could be explained by differences in breed type, weight, weather and other factors.   

 

Risk factors not shown to be associated with BRD risk

A number of potential risk factors assessed in the study did not produce any association with BRD. For example various factors relating to diet were examined with risk factors such as percentage grain in the diet at start of time on feed and after 21 days. Other factors not associated with BRD risk were dentition and vitamins A, D, E at induction.

Nor could any determination be made regarding the efficacy of the various vaccines that are currently used in the industry.

“The purpose of this study was to determine how various risk factors affected the likelihood of cattle to get BRD as observers,” Dr Mahony said.

“To determine the impact of vaccination on BRD, a randomised vaccination/control trial would be required where the vaccines are applied to random to one group, and not another. However as feedlots in the study tended to either use or not use vaccination no comparative analyses could be performed.”

 “The timing of mixing of animals from different PICs relative to feedlot induction and the time of the move to the feedlot were shown to be very important. Moving and mixing of cattle too close to feedlot induction may increase the likelihood of BRD development,” Dr Mahoney said.

Collectively the results indicated that mixing of cattle has an important impact on BRD risk, with the mixing of cattle well before feedlot induction tending to lessen BRD risk.

“Possible reasons for this are that cattle are able to establish a stable social group and are possibly exposed to pathogens in a less stressful environment compared to the feedlot,” Dr Mahony said.

The importance of weaning method and cattle mixing/moving in BRD development indicated how producers/vendors can impact on BRD outcomes in feedlots.

The results supported the view that effective BRD management may require greater cooperation between all sectors of the Australian beef industry, he said.

“There are many factors which influence the decision to buy cattle for feedlot finishing and it might be that the risk factors identified in this study are out of the control of a cattle buyer. An example of this would be the strong association with season which certainly can’t be changed by an operator.”

 

BRD decision-making tools on the horizon?

Similar to other industry issues, the purpose of understanding the positive and negative risk factors associated with BRD is to understand what the BRD risk in purchased cattle is for feedlot buyers.

“If a group of purchased cattle are deemed to have a high risk profile for BRD, it might be possible to adjust standard operating procedures to account for this,” Dr Mahony said.

While the analysis of the project outcomes are continuing, the project team is now considering how best the complex results might be delivered to industry.

Suggestions so far have included the development of a ‘BRD decision-making tree’, the development of a ‘BRD App’, and a ‘BRD Risk calculator’ similar to the industry’s heatload Risk Analysis Program (RAP).

A BRD decision-support tool could be divided into two sections:

• Decision to purchase: What do you know about cattle before purchase? What could you find out? What would alter your decision to purchase?
• Decisions on management after purchase: If increased risk is identified, what would be required to reallocate resources?

 

The final project report will be submitted to MLA later this month, and is expected to be released to industry early next year.