Although this and allied conditions and their more than probable causes are recognised quite often, it is perhaps unusual that apart from the summary by Belschner (1941) there are very few references readily available to the field officer in this State. This is the more noticeable in view of the fact that treatment hitherto has not always been as effective as might have been expected. Further, while the appearance of a condition such as Trefoil Dermatitis in young merino lambs when adult sheep running with them remain unaffected can be explained by the absence of wool cover in the case of the lambs, the same age incidence of Yellow Big-head is not nearly so understandable.
During the past summer several outbreaks of Yellow Big-head occurred in young sheep of various breeds in this District. One appeared in young merino weaner lambs at Murringo grazing in an old cultivation paddock containing a fresh green growth of Panicum effusum about two inches in height. Six of the lambs in a flock of 160 running with 180 merino ewes developed the condition; while none of the adult ewes was affected. 260 points of rain fell on the property where the outbreak occurred and a fortnight later, during which period there was very hot, sultry weather, the disease appeared.
Affected lambs developed a swelling over the face and ears. Lips were swollen, some lambs were blind and a yellowish fluid was secreted from the swollen lips and ears. The swelling pitted on pressure and odd lambs were lame. Panicum effusum comprised almost the whole of the pasture on which the lambs were grazing. No mortality occurred, owing to prompt action and treatment carried out by the owner. Lamp black and grease was applied to the affected parts, and the sheep confined to adequate shade and placed on other feed.
On another holding, 19 Border Leicester lambs in a flock of 160 developed Yellow Big-head and five died. Affected lambs were three months old and grazing on a good green growth of Panicum effusum, some of which was commencing to flower. Some of the affected lambs were very swollen in the eyelids and blind, while the skin on the ears was broken, bleeding and raw; the condition being one causing severe pain and misery. So much so that the owner, rather than see the lambs suffer, destroyed two of them. On moving the lambs to another paddock of different feed with ample shade, and treating the affected lambs by applying lump black and grease to the swollen parts, most of them recovered in a few days.
This ailment, which was quite common during the past summer, had a serious effect on the growth and development of fat lambs and is one that can be prevented largely by good breeding-ewe husbandry. Specimens of Panicum effusum collected in sods were forwarded to Dr. H. R. Carne, Dean of the Faculty of Veterinary Science, University of Sydney, who advised that experiments are being carried out in an endeavour to learn something further about the photo-sensitising substances in the young stages of growth of this grass, known commonly as "Summer Grass."
Belschner, H.G. (1941). The Agricultural Gazette, N.S.W., 52 : 299.
[NOTE.—It is considered that treatment by painting affected areas with a strong solution of Potassium permanganate (Condy's) has many advantages over the use of lamp black and grease. It is more easily applied and easier to handle at application, and afterwards. It certainly is just as effective.—Editorial Committed.]