Blackleg is known as an acute specific infectious disease which not only affects cattle, but also sheep.
The cause of Blackleg is an anaerobic bacillus known as Clostridium chauvoei. The bacillus lives in the soil and is more often found in soils subjected to floodings. It gains entrance into the animal's body principally by medium of abrasions to the skin, and can also be taken in by way of alimentary tract with food, but I would say that the main mode of entrance is from cuts and abrasions to the skin, and then on those parts of the body which come into contact with the soil.
Animals are frequently found dead by the owner in the paddock without previously showing any symptom of sickness, but this is due to infrequency of paddock inspections; but in other cases it is noted that there is a decided lameness in one or more of the limbs, and if examined the affected area will be found swollen and painful. These characteristic swellings contain a dark coloured blood, the skin is of a purplish hue. In cattle there is a formation of gas present which cracks, but not to be seen as a rule in sheep. The swellings are in the region of the neck, thigh, shoulder, throat, head. There is a stiffness in the gait, animals are disinclined to move or feed, they are found away from the mob. Death takes place between 24 to 48 hours.
I have described Blackleg, giving the predominating features of the disease, and now desire to relate recent mortalities in sheep which may be of benefit to members.
(1) Last November, in the Armidale District, some 800 merino weaners were shorn, and immediately following the shearing. i.e, the same day, they were dipped in a non-arsenical dip mixture. The next day the owner reported that they were dying, and he had lost twenty within 48 hours following shearing and dipping. An inspection was made. A number were noticed in the mob showing a decided lameness in one or more of the limbs, and when caught it was found that swellings were present over the seat of shearing cuts and stabs. They showed a general lassitude; a sanguineous discharge on pressure was liberated from the swelling; anorexia was present. P.M. was conducted, it being only a partial one due to the knowledge and history of the cases: but the sheep showed oedema of the musculature in the region of the wounds with blood-stained exudate. Pipettes and smears were secured from an infected cut on the tail and inside the thigh. where considerable swelling was evident. The examination showed Cl. chauvoei in purity.
No doubt the entrance of the bacillus was per medium of cuts at shearing time. The question was, where was the infection picked up—in pens, yards or sheep dip? Other sheep had been shorn before the sheep under discussion, but they had not been dipped; again, other sheep were shorn after and were dipped immediately following shearing, but then the dip had been cleaned out. So the conclusion is that the sheep in question picked up the infection in the dip, which had not been cleaned out when they were dipped. It would be possible for the bacillus to have been washed from the soil into the dip.
(2) A flock of 100 merino ewes which were grazing over a small paddock which had, some years previously, been cultivated. This paddock was subject to floodings from a creek which ran through it.
The ewes, at the period of mortality, had been lambing about two weeks, and there remained four ewes to lamb. Just prior to inspection, rains had fallen and humid weather followed.
The owner mostly found sheep dead, but he was fortunate to get one sick. Inspection was made, and symptoms were; the ewe was disinclined to move, but when made to move, showed decided lameness in both hind legs, would not eat, took no notice of the lamb, which was 24 hours old, and she paid no notice to external surroundings. The vulva showed a good deal of swelling, was dark purplish-blue colour, which extended around the perineum and over the hind quarters. Death soon intervened.
Note.—No ewe which showed the above symptoms survived longer than 36 hours. No ewe which was dry or had not lambed was affected, so it was self-evident that the infection was contracted through the vagina following lambing.
On P.M. examination, the principal changes were to be found in the vulva and surrounding tissues, musculature of the hind quarters, all of which were swollen, dark blue in colour, and engorged with a blackish fluid. The uterus was filled with a blood-stained semi-liquid material, there was congestion of the cervix and vagina, sub-peritoneal haemorrhages. The heart showed sub-epicardial petechiae; also, the musculature of the rump showed a dark blood-stained fluid and haemorrhages. Pipettes and smears were taken from uterine content exudate from rump muscles, kidney, spleen and heart blood. The examination proved Clostridium chauvoei in purity from all specimens.
The mortality was 13 per cent.