Roadmap for development of disease control strategies for bTB

What are we trying to achieve and why? What is the problem we are trying to solve?

• Is there exploitable (by selective breeding) genetic variation in the risk of TB following exposure?
• Can we breed cattle with reduced TB susceptibility that won’t interfere with current testing protocols?
• Can we breed cattle for lower TB infectivity?
• If so, can industry-led genetic indices be developed?

What are the scientific and technological challenges (knowledge gaps needing to be addressed)?

• Challenging to curate and link cattle pedigree data with cattle TB data at population levels.
• Challenging to communicate and encourage adoption of TB genetic indices by industry.
• Suspect some misinformation and confirmation bias exists; initial concerns about using TB skin test results as metric investigated and allayed.

What approaches could/should be taken to address the research question?

• Exploitable heritability of TB susceptibility trait has been estimated, initially in Holsteins, followed by other dairy and beef breeds.
• Industry-led TB resistance indices are increasingly available and increasingly accurate.
• Research continues to investigate “TB infectivity” as a further trait.
• Interest in the mechanism(s) by which some cattle resist TB; relevant for diagnostics and vaccines.
• Knowledge outreach from trusted and impartial experts.
• Establish the importance of early detection and rapid removal of infected animals.

What else needs to be done before we can solve this need?

• Ensure ongoing availability and integration of animal-level pedigree and TB data to refresh genetic indices.
• Knowledge outreach from trusted and impartial experts.

Existing knowledge including successes and failures

• Evidence that taurine cattle (Bos taurus) are more susceptible to TB than indicine cattle (Bos indicus).
• Substantial quantitative genetics evidence that there is heritable and exploitable genetic variation in risk following exposure i.e., there are relatively high risk and low risk sires, depending on the TB status that follows in their daughters.
• This facilitated the development of industry-led genetic selection indexes, initially for Holstein cattle but extended to other dairy and beef breeds, allowing cattle to be bred with cumulative reducing TB susceptibility.
• Further genetic gain is achievable via genomic prediction and no significant “antagonisms” with other desirable traits are evident.
• Research is progressing to evaluate “relative infectivity” as a further TB trait.