ARCHIVE FILE
This article was published in 1981
See the original document
An Interesting T.B. Breakdown
B. Unger, B.V.Sc., Veterinary Inspector, Casino
On 5/11/80 a total condemnation T.B. case was reported from Casino Abattoir. This aged cow was traced back by means of tail tag to Grady's Creek, a narrow valley in the rain forest area adjoining the McPherson Ranges of the N.S.W. - QLD. border.
The first test of this herd on 17/11/80 revealed 5 reactors out of 114 with several more doubtful which were left in the herd at this stage.
Of the 5 reactors at post-mortem examination, all had tuberculosis lesions and 3 were total condemns.
10 head of the traceback owner's cattle were agisted on an adjoining property with 65 other cattle. 2 of these 10 were reactors when the whole herd was subjected to test, both were total condemns.
Another adjoining herd, a dairy herd of 121 head yielded 1 reactor. This cow on post-mortem had lesions restricted to the head nodes but was totally condemned due to its poor, carcase condition.
PROPERTY HISTORY
This property has a history of tuberculosis dating back to a previous owner, W. Trihey. Seven totals and two others were detected at first round test in October, 1962. One with other lesions was detected at a re-test in January, 1963, and one with other lesions was detected at the third round test in November, 1965. Two subsequent re-tests and three round tests were negative up to August, 1971.
In late 1971, the property was sold to G. Green who subsequently sold it to the present owners in 1973. The present owner's herd is comprised of cattle from Trihey and Green. Green's herd had no history of T.B. with 5 negative tests over the period 6/6/62 to 2/7/71.
The present owner has been slowly building up his herd size over the years retaining many aged cows for breeding. purposes.
The present herd contained two aged cows which were originally part of the Trihey herd running on this land 9 years ago. Both have now been slaughtered, one as a reactor with lesions in the head, the other on suspicion only was an N.V.L.
HERD MANAGEMENT
Two management factors involving the present owner are thought to have contributed to the breakdown and widespread infection noted in this herd.
The herd recently has been subjected to stress, especially of a nutritional nature, as the property is overstocked and the last 3 years have been unusually dry with the last 18 months particularly so.
Even in average seasons the area is subject to feed stress in late winter-spring and the property's hillsides become very bare, grazing often being restricted to creek flats and gullies at this time,
A small group of approximately 12 head were being trough fed during the worst of the drought.
This combination of environmental and managerial conditions is thought to have contributed to the breakdown and spread in this herd. The possibility of breakdown under tuberculin testing in these conditions is also considered.
FURTHER TESTS
The owner's herd was re-tested 16/1/81 and out of 124, 14 reactors and 2 suspected on clinical/history basis were sent for slaughter. The 2 non-reactors were N.V.L. at post-mortem.
2 of the 14 reactors were yearling steers with a slight oedematous reaction to tuberculin. These too were N.V.L. at slaughter.
of the remaining 12 head; all had lesions with only 2 carcases passed and the rest totals.
At least eleven of the total of 21 reactors slaughtered to this stage were considered as active spreaders.
For example, one cow with visibly enlarged parotid and submaxillary lymph nodes had lesions at P.M. in submaxillary, parotid, bronchial nodes and extensive lung abscessation. During testing she was frequently observed coughing and when at one stage she coughed a small amount of clear, mucous sputum into the dip-yard, a sample was obtained, smeared and forwarded to R.V.L. Wollongbar. Acid fast organisms typical of Mycobacterium bovis were observed on staining these smears.
RELATION OF TUBERCULIN REACTION TO LESIONS
7 animals gave only small, slight oedematous reactions. Of these, 2 were N.V.L.'s, the young animals mentioned above. One was an aged cow with only lesions found in submaxillary lymph nodes and these were calcified, apparently inactive. The other 4 animals with slight reactions which could have easily been overlooked, had severe widespread lesions including extensive lung abscessation.
All animals sent off on the basis of history and/or clinical signs only were all N.V.L.
No animals with a reaction I described as medium to large and firm were N.V.L. All had lesions, and all but one were extensive.
The most recent re-test gave two animals with slight soft, diffuse reactions which were N.V.L. on slaughter.
At this last test 4 other animals were sent off on clinical and/or history grounds. These included 2 animals with enlarged parotid and submaxillary nodes and slight respiratory noise, 1 cow with distinct respiratory noise, mainly snoring and one 9 year old Braford cow which was the mother of 3 infected individuals slaughtered after earlier tests. All of these non-reactors were N.V.L. at slaughter.
SOURCE OF INFECTION
Extensive testing of adjoining and other holdings in this valley has revealed no further cases apart from those mentioned above i.e. 1 case on a closely adjoining property which uses a common dip facility and 2 in stock agisted on another adjoining property.
4 slight reactions in one neighbouring herd and 3 in another were all N.V.L. at slaughter.
It therefore seems reasonable to assume that infection was obtained from within this herd only.
REASONS FOR CARRY-OVER AND BREAKDOWN
The carry-over of a false-negative reactor or anergic animal from the previous herd is a definite possibility. The original owner particularly is reported usually to have left carcases of cattle dying on the property up in secluded gullies to decay away, thus providing ideal conditions for the long survival of tuberculosis organisms in damp sheltered soil.
Survival of the organism is reported as up to 18 days in stagnant water, 6-8 weeks in faeces in protected damp soil and to several months in carcases and warm, moist protected positions.
CATEGORIES OF FALSE-NEGATIVE REACTORS
1. Advanced cases of tuberculosis.
2. Early cases until 6 weeks after infection.
3. Post-parturient desensitisation - as many as 30% give false negative reactions returning to positive status 4 to 6 weeks later.
4. Animals desensitised by tuberculin during the preceding 8 to 60 days.
5. Old cattle.
Such a false-negative beast later breaking-down and shedding more T.B. organisms on dying and contaminating pasture most likely accounts for the persistence of infection on this property in spite of negative tests back in 1971 and the present position of 29 reactors and suspects or 19 tuberculosis animals so far removed from this herd of approximately 120 head.