Table 1. Modes of detection for bTB breakdowns in Northern Ireland and predicted effects on breakdown size.

Mode of detection	Predicted effect on breakdown size	Reason
AHT – annual herd test	baseline
LRS – lesions found at routine slaughter	−	Slaughter usually more frequent than AHT therefore less time for infection to spread.
LCT – lateral check test (herds sharing a boundary with infected herd are tested)	−	Less time for infection to spread since last herd test than under annual testing.
BCT – backward check test (source herds of cattle bought into focal herd are tested)	+	Onward spread to another herd has occurred so likely to be a large number infected in the source herd.
CTS – check test status (individual animals withID or movement queries tested)	+	Animals bought in with unknown disease status potentially increase risk to the remainder of the herd
FCT – forward check test (destination herds of animals that left focal herd immediately prior to a breakdown)	−	Short period since potentially infectious animal(s) moved in to herd and so little time for large outbreak to develop.
CTT – check test trace (forward trace of individual animal)	−	As above.