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This article was published in 1948
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Losses Associated with Dipping in D.D.T.
E. SCOTT ROGERS, B.V.Sc., Inspector of Stock, Deniliquin.
On one of the larger holdings breeding stud merino sheep in the Deniliquin District, a heavy infestation of lice was found in July, 1947. As the ewes on the property were due to lamb at the end of August the owned decided to dip his sheep off the board in 0.1 per cent. D.D.T. to clean them up before lambing commenced, there being insufficient time to hold the sheep for two weeks and dip in a normal arsenical solution. Derris in carbolic had been used in the previous season with unsatisfactory results.
The following is the history of the heavy loss which occurred in Merino ram lambs following this dipping:—
On 13th August, 2,890 merino ram lambs aged 5 months, in fair condition, were brought a short distance to the shearing shed. On the following day all these sheep were shorn and 2,200 were run through a swim dip, the weather being cool and dry during the period in question. The dipping solution originally contained 0.1 per cent. D.D.T., had been mixed for five days and already had been used for the dipping of several thousand sheep. The owner changed the dip every 4-5,000 sheep and cleaned it thoroughly with a disinfectant. The dipped rams were placed in a 600-acre paddock on a creek frontage, with plenty of shelter, for the night.
On 15th August the dipped sheep were returned to the yards and drafted, then walked eight miles to an open paddock on the plain country. The following morning they were inspected by the overseer, who estimated that 200 were then dead and 1,500 of the balance were either lame or swollen in the legs. This was reported that evening and arrangements were made to investigate the mortality.
On 17th August an inspection was made, and it was noted that very few sheep were lame, although odd sheep showed swelling on the legs. The overseer reported that very few additional losses had occurred. Sheep were lying dead all over the paddock and a subsequent count when the carcases were collected for burning revealed 300 dead; all appearing to have died without a struggle. In some cases there was a discharge from the nostrils and on almost every carcase there was an oedematous haemorrhagic swelling, usually on one of the limbs. There was also a slight serous discharge from the shearing cuts, which had not dried up. The swelling could be missed easily if only a cursory glance had been given to the carcase and the early report from the overseer appeared to indicate a Hypocalcaemia. A post-mortem carried out on a ram which had died only about half an hour earlier revealed an oedematous swelling in the hind leg, with a sero-sangulneous discharge and a darkening of the muscles in the vicinity. The small intestines were very congested, with some petechial haemorrhages, and also were heavily infested with Nematodirus spp. The rest of the organs appeared normal. Two pipettes of sero-sanguineous exudate from the lesion on the leg, contents of the small intestine, and section of the jejunum with contents were forwarded to Glenfield for examination, in addition to a sample of the dipping mixture. A tentative diagnosis of Blackleg was made and it was assumed that the infection had been picked up in the dip.
Of the 2,890 rams shorn, 690 were not dipped and no losses occurred in the paddock in which these were placed. It was ascertained also that 500 ewe lambs were camped in the same 600-acre paddock after shearing as the 2200 ram lambs in which the losses occurred, but there were no losses amongst the ewes.
Glenfield reported that "the sample of ingests and smears from the small intestines showed normal intestinal flora with very few Cl. welchii organisms. The small intestines were fairly congested, but apart from this no gross lesion was detected. From the pipettes from the leg lesions an organism resembling Cl. septique was recovered. Samples of the dip have been rubbed into wounds and deep scarifications on sheep on this station, but after six days these sheep have showed no ill-effect. It appears likely that the mortality is due to Blackleg following infection of wounds after shearing." The Director of Veterinary Research further advised that "histological examination of the dip sample submitted has revealed it to be highly contaminated with a large number of different organisms. These cultures became rapidly overgrown with spreading anaerobic saprophytic organisms. It was not possible to isolate either Cl. septique or Cl. chauvoei from these samples of dip."
It is postulated that the D.D.T. in the dipping fluid caused an irritation of the shearing cuts, which became readily infected with any organism with which they came in contact, as in the Blackleg infected paddock; whereas shearing wounds which were allowed to dry did not become infected. It would appear, therefore, that there are grave risks attendant on dipping off the board in any dipping fluid which irritates shearing cuts,etc.
The final loss in this case amounted to approximately 500 ram lambs.