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This article was published in 1981
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T.B. Breakdown Herd
Bob Irvine, B.V.Sc., Veterinary Inspector, Denman-Singleton
The subject of this talk is 'T.B. Breakdown Herd' and the events began in August, 1977 when D.V.O. Newcastle was advised of a T.B. condemnation in a district dairy herd.
This was a large herd which had been brought up from the Moss Vale district the previous March.
It transpired later that this herd had a previous history of tuberculosis dating back to 1969.
Prior to movement to Singleton the herd was released from quarantine after two clean tests and came to Singleton.
On 19th September 1977, a T.B. test was read on the herd and 120 reactors taken out of 388 head. On slaughter there were 20 total condemnations, 60 localised lesions and 40 N.V.L.'s.
At this stage, it might be mentioned that the herd was on zero grazing and confined to 2 small paddocks on sandy soil. All feed was forage harvested and brought to the cows which were fed in a large shed with a concrete floor and a large central trough. In the early stages of residence, feed had been in short supply and cows would have been stressed.
This owner had heifers running on a property some 15 miles away on agistment and these were boxed with another owner's heifers. Heifers were from 12 months to springers. On test, 49 reactors were detected from 100 head of the infected herd, whilst the other owner had one reactor. Surprisingly, all reactors were in heifers under 12 months of age whilst older heifers were clear. There were 9 totals in the reactors. On 18th October 1977, 22 calves on the home property were tested with 10 positive reactors all of which were totals.
Subsequently all neighbouring properties were tested and on 3 of these skin T.B. cases were seen. Reactors were sent for slaughter from these properties but all were N.V.L.
Testing proceeded on the home herd as follows:
| 5/12/77 | 2nd Test | 15 reactors | 7 localised | 6 N.V.L.'s |
| 10/4/78 | 3rd Test | 5 reactors | 3 localised | |
| 26/6/78 | 4th Test | 5 reactors | 4 localised | |
| 25/9/78 | 5th Test | 5 reactors | 5 localised | |
| 19/12/78 | 6th Test | 317 tested negative | ||
| 5/3/79 | 7th Test | 3 reactors | 1 localised | |
| 21/5/79 | 8th Test | 11 reactors in the herd 8 with localised lesions | ||
The owner had commenced keeping calves after the negative test and a test of 18 calves gave 13 reactors. As he had some younger calves making a total of 24 head all were forwarded for slaughter. All but the 5 negative reactors had lesions and 4 were totally condemned.
T.B. testing was interrupted due to change in management and other factors.
In the meantime, cull cows were forwarded for slaughter and two old advanced cases were detected on slaughter and were spreaders.
It was realised we were dealing with a highly infectious strain of M. bovis which was also anergic.
D.V.O. consulted with C.S.I.R.O. and Tony Leper, Senior Research Scientist, suggested using a neck test as the skin of the neck is 4-5 times more sensitive than the caudal fold. P.P.D. tuberculin was used.
On the initial neck test, 24th September, 1979, 70 reactors were detected. Of these, only 3 showed lesions with one spreader. One reactor showed lesions of skin T.B., and culture from this produced mycobacteria of M. avium, intra cellulare scrofulaceum complex. Thus it was shown skin T.B. existed on the property.
Further testing using P.P.D. in the skin of the neck produced, on 3rd December, 1979 10 reactors all N.V.L. on slaughter. 12th June, 1980 9 reactors all N.V.L. cows with lesions of skin T.B. seen. 19th December, 1980 13 reactors. Some with typical skin T.B. lesions. As a result these are to be retested in April.
This herd is reported because of the type of spread and the complication of skin T.B.
I might add that Brucellosis testing was proceeding in the herd whilst T.B. testing went on and some 51 Brucella reactors were taken out. None of these showed T.B. lesions on slaughter.
During the period mentioned, some 50 cull cows were sent for slaughter on Forms 3 and only the two mentioned previously showed lesions.
All told 330 T.B. reactors were taken out of this herd.
Another factor possibly favouring the spread of skin T.B. has been the fact that because of the labour troubles etc. cows were grazed on heavy irrigated flats during last 12 months or more.