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This article was published in 1951
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

Enzootic Ataxia of Lambs

E.G. Lowe, Inspector of Stock, Coonamble

Almost 20 years ago Bennets (1932) first described this condition in lambs in West Australia, and 10 years later defined, with Beck (1942), its relation to Copper deficiency. In the latter year McDonald (1942) referred to the occurrence of Enzootic Ataxia in West Australia and Victoria, and described its incidence in South Australia. Nevertheless, it appears that the cases now reported comprise the first recognised occurrence of the disease in New South Wales; though, as so often is the case, the history indicates that the condition has been present on the particular property for perhaps ten years.

This property is situated some 30 miles east of Gulargambone; and consists in general of a rich flat, but merging into the foothills of an isolated low mountain range. The opinion has been expressed that in the somewhat distant past this flat had been scoured out and the native soil replaced by a fine silt. A survey showed that the plant and tree population was normal for the particular area; though Heliotrope (Heliotropium europaeum) was present in considerable quantity after recent flooding, and may have introduced a complication. In the past the water supply was obtained from wells approximately 30 ft. deep; but the present watering is by bores which go down to about 215 feet. Both well and bore water has an appreciable "hardness." Licks, of both the block type and rocksalt, as well as ground limestone and salt, have been supplied regularly.

The normal stocking of this 300-acre holding consists of approximately 400 sheep; these including both Merino and Border Leicester-Merino lambs. Either type may be affected, and the condition usually appears at from 2-4 months of age. The history indicates that the usual incidence is in the vicinity of 5%, but in the bountiful season of 1950 this rose to almost 10%. In this regard it is of interest that when supplementary feeding has been practised during dry seasons the condition has not appeared. From the onset of symptoms the disease normally continues over a period of some months before death ensues. In the few cases which do not terminate fatally the affected animal does not return to normal.

Initially, the symptoms consist of a quick, "proppy" gait, with a slight swaying from side to side; this latter gradually becoming more marked until finally the lamb goes down with a pronounced muscular tremor. All power of the hind limbs is lost, but complete control of the front quarters is retained; the lamb being seen at times to sit up "dog fashion." In the final stage the hind legs are stretched backwards in a "straddled" position. Affected lambs maintain condition quite well and are eager for food, which apparently they can take quite readily. Sight and hearing appear to be normal throughout.

When the condition was reported and investigated during September, 1950, no abnormalities were detected on post-mortem examination. A very few stomach and intestinal worms (Ostertagia, Haemonchus and Trichostrongyles) were present, but definitely not in sufficient numbers to cause trouble. The ventricles of the brain may have been slightly larger than normal. It was considered that the disease condition was associated primarily with the central nervous system, and appropriate specimens were forwarded for laboratory examination.

The Director of Veterinary Research later advised that:-

1. Examination of sections of the medulla showed demyelination lesions typical of Enzootic Ataxia; and that so far as was known this was the first definite case recorded in this State. (Dr. H. W. Bennetts, of West Australia, later had an opportunity to examine these sections, and confirmed the diagnosis.)

2. Two (2) live affected lambs subsequently forwarded to Glenfield presented a clinical picture consistent with that of Chronic Enzootic Ataxia.

The District Veterinary Officer, Orange, later examined three affected lambs on the property; and referred to the fact that in each case there was definite evidence of steely wool at the tip of the staple, indicating that at least during the early weeks of their life these lambs had been on a copper-deficient diet.

It might be mentioned that in this case there could not be any question of an hereditary condition. since the ewes and the rams had originated from entirety different sources. A copper-rich lick now has been made available to the sheep on the property, and a regular drenching programme with copper sulphate (4%) is being put into operation. The results well might be the subject of a later report, when more definite information has been obtained as to the effects of preventive treatment.

References

Bennetts, H. W. (1932)—Aust. vet. J., 8:137
Bennetts, H. W., and Beck, A. B. (1942)-Bull. Coun. sci. industr. Res. Aust., No. 147
McDonald, I. W. (1942)—Aust. vet. J. 11:165