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This article was published in 1956
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
CURLY CALVES
I. R. LITTLEJOHNS, B.V.Sc., Veterinary Research Station, Glenfield.
The term Curly Calf has been applied to a condition which has recently been recognised and investigated by Messrs. J. M. Whittem and D. C. Blood of the University of Sydney, Faculty of Veterinary Science. Studies on the pathology of the condition have been concluded for the present, and this report is designed to bring the condition to the notice of Inspectors of Stock in order that members of the Institute can assist with further investigations into the aetiology and field aspects of the condition.
The disease is basically a congenital degeneration of nerve tissue and presents itself in two fairly distinct forms, with a third intermediate group. When the condition occurs it commonly reaches outbreak proportions throughout a district and these three forms are seen in fairly strict chronological sequence.
(1) The typical curly calf; the animal being presented, commonly as a dystocia, with one or more of the limbs having some of the joints rigid in flexion or extension. The rigidity is not due to ankylosis but movement is restricted by the muscles and peri-articular ligaments. On post-mortem examination the affected muscles are seen to he pale or even fatty and their section allows some, but not full, movement of the joint; some restriction due to the peri-articular ligaments remaining. When the spinal cord is examined, there may or may not be macroscopic abnormality of the ventral horn. However, in all cases some degenerative changes in the neurones of the ventral horn can be recognised microscopically; and on the basis of the histology of the spinal cord and muscles the neuronal degeneration is considered to be a primary lesion.
(2) Later in the season animals are found similarly affected, with additional evidence of cerebral deficiency as in the third form.
(3) The final form is that in which imbecile calves are born with limbs structurally normal. The animal is blind and quite senseless in its behaviour. Slight doming of the head may be noted but there is no true hydrocephalus. On opening the cranial cavity the cerebral cortex is found to be almost completely absent and the membranous remnant is usually reflected with the meninges; allowing fluid to gush out and exposing the basal ganglia. The posterior brain is complete in most cases.
From studies on the pathology of the disease it has been concluded that the cerebral cortex has not failed to develop, but has degenerated after development.
These calves can be kept alive for a limited time, from days to several months, by suitable nursing and hand feeding.
One might expect stockowners to contact practitioner veterinarians where limb involvement with dystocias occurs; while Departmental officers might be expected to see more of the third form. Interrogation might reveal a history of the deformed limb manifestation.
With respect to aetiology, the available evidence indicates that there are no genetical factors involved, and the condition appears to be due to some factor interfering with the development of the foetus at a critical stage. There does not appear to be any particular type of country or soil involved.
Three broad groups of possible aetiological factors are suggested:
I. Infection: Examples of viruses which have little effect on the mother but produce gross abnormalities in the offspring include that of German measles and lapinised Swine Fever virus. Bacterial infection does not have this type of support by analogy, but any bacterial disease interfering with foetal nutrition either by direct effect on the placenta or indirectly by interference with maternal metabolite levels might bear consideration.
II. Toxins might present a challenge to the foetus by direct and indirect action in a similar manner to infections. At the present stage of knowledge this group should be allowed to cover a wide scope and such things as the effect of excess hormones, which might be produced under certain conditions or obtained from plants, might be considered.
III. Nutritional deficiency may be a primary cause. The condition bears a strong resemblance in some respects to enzootic ataxia and similar lesions occur in rats fed certain anti-vitamins.
A few interesting points have been raised regarding the epidemiology of the condition. As mentioned before, it appears at fairly widely separated points as an explosive outbreak; suggesting that the cause acts suddenly over a wide area, such as do weather conditions, in contra-distinction to the spread of an infection from a centre. Further, it has been noted in several areas that, where the incidence has been heavy, the preceding summer has been a particularly good season, and it seems likely that seasonal conditions with heavy pasture growth may be of some importance in the aetiology of the condition.
To date curly calves have been seen in large numbers in South Coast and Hunter Valley areas and to a less degree in the Western highlands and slopes.
The main incidence occurs in the July-October period; except in the Hunter Valley, where most cases are seen from January to March.