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ABSTRACTS
Histologically, demyelination was the constant lesion encountered, and all grada-
tions of change ranging from small foci to a total loss of myelin were present. In some
cases, where no naked eye changes had been observed, small foci of demyelination were
visible, often confined to the centrum ovale of the occipital lobes. In the cortical gray
matter, the nerve cells generally preserved their form and it was only in the most severely
affected cases accompanied by gross liquefaction of the white matter that early dege-
nerative changes (shrinkage, vacuolation, displaced pyknotic nuclei, chromatolysis)
were noticed, especially in the red nucleus. Neuronophagia, inflammatory cellular
infiltration and inclusion bodies were absent. Gliosis was never intense : the cells con-
cerned in this reaction appeared to be the fibrous astrocytes. In Marchi-Busch pre-
parations, degenerated fibres could occasionally be traced through the capsules and mid-
brain to the medulla and cord. Identical histological changes were observed in brain
sections from four Australian lambs examined by the authors.
Ewes which give birth to ' swayback ' lambs appear to be healthy and may give
birth to healthy or affected lambs. No significant lesions were noticed in six such lambs
autopsied. Bacteria or viruses could not be incriminated in the causation of this disease.
It is neither hereditary nor developmental in nature, though the disease process seems to
be antenatal.
Biochemically, low serum phosphorus values were obtained in a few ' swayback '
lambs and ewes. The suggestion is made that ' swayback ' may be due to a disturbance
of copper metabolism, as chemical analyses of the blood of ' swayback ' lambs and
their mothers showed lower copper values compared with suitable controls. A con-
firmation of this view is sought for in the success which has attended the prevention of
' swayback ' by feeding copper to the pregnant ewes in Australia and England. This
disease, however, is not a copper deficiency per se, as pasture analyses did not reveal a
deficiency of this element.
The possibility that lead is concerned in some way with the development of the
disease cannot be excluded at present. [R. N. M.]
The influence of a moderate worm burden on the growth and health of lambs.
D. ROBERTSON and A. H. FRASER (1940). Emp. J. Exp. Agri.8,
323-5
E ARLIER observations showed that a prime fat lamb may harbour 3,000—4,000
stomach worms (mainly Ostertagia). No appreciable pathogenic effects could be
ascribed to these parasites when present in such numbers. Whether the lambs
would not have thriven better with a lower worm burden, or if the deleterious effects
on the growth and health of lambs, however inappreciable in individuals, would not
assume economic importance in respect of the whole flock, was next investigated :
Forty lambs were taken at birth and reared by hand. Half of the animals were
kept worm-free, and the other half were given repeated doses of a mixed infection of
larval helminths obtained from faecal cultures. The first infective doses were given to
the lambs when they were 2 to 4 weeks of age. The experiment lasted 147 days, and
finally the lambs were slaughtered and their worm counts made. In the infected group,
the average worm infestation per animal was 1,840 and the maximum reached in one
lamb was over 4,000.
The authors do not consider the faecal cultures obtained for
infective purposes as sufficiently massive. In spite of the lightness of infection, the
results obtained were found to be statistically significant. The infected groups showed
decreased live weight (147 days period) and carcass weight, fall in haemoglobin per-
centage of blood (Haldane's method) and loss of condition. [S. C. A. D.]
GIPD-S1—256 IC of AR—12-1-43—500.