TB Research
Research into bovine TB in NI is being supported by DAERA, including work being done by AFBI. Recent projects include investigation of the role of passive immunity in wildlife bTB vaccination, development of the use of whole genome sequencing of the TB bacterium as an epidemiological tool, and the relevance of genetic variability in the host/ pathogen relationship.
Outside NI, research areas that could be of benefit here in the future include cattle vaccination strategies (particularly the development of a diagnostic test that could differentiate between vaccinated and infected animals), improved diagnostic tests and strategies to manage the infection in wildlife.
What is Whole Genome Sequencing?
Bacteria contain unique genetic material. Whole Genome Sequencing (WGS) is a way of characterising the DNA sequence data of the whole M bovis genome and has largely replaced genotyping. The outcome of the sequencing is that different M bovis strains can be identified, and that relatedness between the bacteria found in different animals can be analysed.
WGS has provided evidence of ongoing TB transmission between cattle and badgers at the individual farm level, and also signals of cattle to cattle spread.
What is molecular strain typing?
Strain typing refers to tools related to the TB genome to investigate TB epidemiology and outbreaks. They demonstrate local micro-epidemics, and can be useful for tracing. In NI, cattle and badger strains have been associated at regional level through molecular strain typing.
Can selective breeding improve TB resistance?
AHDB Dairy publishes the TB Advantage genetic index to allow dairy farmers to make informed decisions about breeding to improve resistance. Research, supported by Defra and the Welsh government, has taken place in the Roslin Institute (Edinburgh) and Scotland’s Rural College. Data from 87,683 cows in Northern Ireland was supplied by DAERA and added to APHA data on 650,000 cows to establish more resistant bloodlines. The index shows the degree of resistance to TB that offspring are predicted to have passed on to them. For every +1 on the index, 1% fewer daughters are expected to become infected during a TB breakdown. The TB Advantage is not believed to have a detrimental effect on any other trait, however each bull should be considered as to how its merits meet the herd’s needs.
At present TB Advantage is available for all dairy breeds but Predicted Transmitting Abilities are only available for Holsteins. Holstein females which have been genotyped are given a TB Advantage rating. Reliability averages 65% for bulls with UK daughters.
The impact of breeding using TB Advantage selected bulls will take time to have a significant impact on the control of TB, however it is an important part of the long term strategy.