In the 1945 and 1946 Year Books of the Institute the writer discussed the role of the nutritional plane in Carbon tetrachloride poisoning, and successive case histories were recorded.
Four additional cases since have come to notice, the details of these being as follows:—
Case 1. In mid-August, 1946, 638 weavers to full-mouthed sheep were drenched in four mobs. They were brought in on four separate days in good weather, crutched, wigged, drenched and returned to the same paddocks the afternoon following mustering. Losses occurred in each mob and totalled 97 head in a period of a fortnight after drenching. In mid-June the sheep had been snow-bound for about a week, after which they were fed oats and molasses. At the time of drenching the paddocks were bare and almost the only feed the sheep were getting would have been new growth. The owner was emphatic that the sheep were improving at the time of drenching. Though the time of the year and casual inspection of paddocks would have, and did, lead to the impression that growth was at a standstill, the owner was able to show that among briars and fallen timber there was definite new growth. In the open paddocks the sheep were keeping this grazed very close.
Case 2. 300 six-tooth and full-mouth wethers were drenched in mid-September. 1946. They were yarded straight from the paddocks for drenching and returned to the same paddocks on the same day. More than 21 head died. Feed definitely was improving; it was beating the stock in each of the two paddocks in which the sheep were running. On the same day a mob of 400 merino wethers was drenched without loss. The country was similar but feed conditions were not as good as for the mob of 300 head.
Case 3. About 300 merino ewes in good condition, a month from lambing were drenched at the end of the first week of September, 1946. Four wethers and one hogget were running with the ewes. They were improving in condition and feed comprising barley grass, rye grass, sub-clover and native grasses was improving fast. Following wet winter conditions portion of the paddock had been under water until a week before drenching; and when the water went off a good supply of lush feed was available to the sheep. About 60 died, including the hogget and the wethers. In this case the sheep were brought in during the morning, spelled for a few hours before drenching and then turned back into the same paddock.
A second mob of 300 was drenched similarly without loss. They were a run of ewes the same as the first mob, but had received two to three ounces of oats daily for six weeks prior to drenching and were just holding their condition. Feed was very short and not of such good quality, though it could be assumed safely that the feed was growing. After drenching they were turned into a paddock of the same size (200 acres) as that from which they had been mustered for drenching, but in which feed was fresher and more plentiful. No other differences in circumstanees were noted.
Case 4. 190 very fat Corriedale ewes with 140 two to three-months-old lambs at foot were drenched following shearing and inoculation for Black Disease in October, 1946. On the 14th they were driven some four miles to the shed and spelled in paddocks adjoining until shearing on the 20th. During shearing and before inoculation and drenching they were shedded for 48 hours. Feed in all paddocks was flush barley grass and trefoil. The mob was returned to the same paddock from which it had been removed for shearing. On the 22nd, when being removed from the shed, one was left behind, unable to walk. Other than this, the first sick sheep was noted on the evening of the 23rd, when a cold change occurred in the evening. There was wind and some sleet and the temperature dropped from 58º F. to 46º F.
At inspection on the 24th six were dead. One was frothing slightly at the mouth and affected with muscular spasms. Treatment with Calcium gluconate and Magnesium sulphate brought about a marked improvement in condition, but not recovery to such an extent that the ewe could stand or walk. The remainder of the mob was scouring freely, there being blood in the scour of one at least. The outstanding lesions were severe endocardial and slight epicardial haemorrhages, constant inflammation in the caecum and inflammation of variable intensity in the small intestines.
Examination of specimens by Glenfield Research Station eliminated Entero-toxaemia and revealed that the serum Calcium and Magnesium levels of one ewe were 8.5 and 1.5 mgms. per cent. respectively. The cause of the mortality was diagnosed as tetrachloride poisoning.
Since the whole mob had been running continuously on alluvial river flats for over three weeks and there had not been any noticeable changes in feed conditions it could not be held that there was any improvement in the nutritional plane prior to drenching.
Discussion. In the twelve mortalities attributed to Carbon tetrachloride poisoning which are recorded in this series of articles, ten have been associated with a rising plane of nutrition; the data concerning one (Case No. 5. 1946) being collected a considerable time after the occurrence and apparently being unassociated in this regard; and the last recorded occurring when the nutritional state appeared to be unchanging. Eleven of the twelve cases definitely are associated with growing green feed.
This type of poisoning remains one of the field workers "headaches," to some extent damaging to prestige in that it is not possible to state with any certainty why mortality occurs, or how to avoid it. One can enumerate merely the considerable number of recommendations already established. Perhaps it is fortunate that the risk is so small; otherwise some of these recommendations soon might fall into disrepute. In this District the recommendation now made is that for greatest safety drenching with Carbon tetrachloride should be carried out as a single operation. In good weather; sheep being returned to the same paddock, and not at a time when feed is flush or improving.
The best safeguard, possibly, is to drench a trial ten per cent. of each class of sheep some four or five days before drenching the whole mob. Since it is not known for how long susceptibility to poisoning takes to develop in sheep, nor once developed how long it is retained, even this recommendation may not be well-founded in the light of knowledge which, we hope, eventually will be gained.