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This article was published in 1942
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
SOME SPECTACULAR HORSE MORTALITIES
By K. BYRNE. B.V.Sc.
The following consists of a summarised history and description of post-mortem appearances in a series of mortalities in horses, all of which took place in one particular area in the writer's district. In all important respects these cases were identical and the writer is of opinion that they had common cause, although efforts to find such a cause have not so far been successful.
During investigation of these mortalities it became evident that they have been taking place in this district for many years, and the experiences of some owners have been so unpleasant that they have reached the stage of debating whether they should continue to take the risk of keeping hones on their properties at all. The need for shedding some light on the matter is, therefore, considered to be most urgent, and it is hoped that, if any mortalities of this type are encountered by other field officers earnest endeavours will be made to uncover the cause. However. there would seem to be a reasonable possibility that these losses are not widespread, as even in this district all recorded cases have been on irrigated country, those actually encountered by the writer being within a radius of four miles. There have been seven of the latter extending from September, 1940, to July, 1942, and these have been as follows:—
(a) September, 1940: Twelve Clydesdale horses, in good condition, running on a resting paddock carrying rice stubble. All apparently in good health the previous evening and, on being driven up from the resting paddock in the morning, all started off in good spirits. However, after travelling a few hundred yards one horse, to use the owner's words. "staggered, fell down, appeared to be gasping for breath, and died in two or three minutes." After the balance had travelled about half a mile, another horse fell down and died in the same manner.
(b) October, 1940: Ten Clydesdale horses, in good conditions, running on a rice stubble resting paddock. Three horses died at intervals of a week all in exactly the same manner described by the owner as follows; "Apparently in normal health when approached in the resting paddock, but after travelling a short distance towards the stables commenced to rush about, to turn head as if trying to bite flanks, whinnied, fell down, made forced respiratory efforts, stiffened the limbs and died within five minutes."
(c) July, 1941: Ten Draught horses, in good condition, running on a young oat crop. Three horses died at weekly intervals, two having been found dead without any previous period of illness, and one having died as described above whilst being driven from resting paddock to stable.
(d) July, 1942: Twenty-four Draught horses running on excellent green feed consisting of self-sown wheat and trefoil. Two died on same morning in manner already described whilst being driven from resting paddock to stables, and two more found dead a week later.
(e) July, 1942: Fifteen Draught horses running on excellent green feed in the form of a young oat crop. Two horses found dead within a week. Owner stated that he had lost 12 horses in similar fashion in the last eight rears all in the same paddock, some of which had been seen to die in the manner described.
(f) July, 1942: Twenty Draught horses running on rice stubble resting paddock. Three deaths in 48 hours. One died whilst working in a plough team, although had appeared to be in normal health when being harnessed and had been working satisfactorily for several hours. In owner's descriptions the animal "appeared to choke down, fell over and died in a few minutes, being apparently unable to get his breath."
(g) July, 1942: Fifteen Draught horses running on excellent green feed consisting of trefoil and self-sown wheat. Two horses were found dead within 48 hours. The owner then harnessed his pony to a sulky and drove a few miles to a neighbour to discuss the matter. The pony, as he was being unharnessed after his return, fell dead in the usual manner. Another horse was brought to drag the carcase away but, after travelling a few hundred yards, this animal also fell dead.
Post-mortem examinations were not carried out in all these cases, as in three of them information was only received indirectly several days after the losses actually occurred. In the other instances the losses were directly reported and the carcases were examined. In all these, decomposition had been very rapid, the carcases being very distended with putrefactive gasses within a few hours (two or three) of death and smelling most offensively. The post-mortem changes noted were also very similar in all cases, the chief of these being as follows: Inflammation of glandular portion of stomach wall, marked injection of blood vessels of small intestine, petechial haemorrhages in kidneys, fatty liver, congested and emphysematous lungs, cardiac haemorrhages and blood tinged fluid in the epicardial sac.
These appearances and general history and symptoms have suggested to the writer that the losses are due to an entero toxaemia of anaerobic bacterial origin, but laboratory examinations hare not so far secured any evidence in support of that theory. Some negative information has, however, been obtained by the latter, as blood smears have in all cases been negative for anthrax, and examinations of stomach contents have not revealed the presence of any form of poison. Moreover, there are a number of features, both in the history and post-mortem picture which are, in the writer's opinion, uncharacteristic of losses both from anthrax or poisoning whether by poisonous plants or other means. With regard to the latter possibility the most obvious feature is that the post-mortem appearances are suggestive of these seen in deaths from an irritant poison, such as arsenic, whereas the symptoms shown are those which are to be expected in a death from a massive dose of a narcotic poison such as hydrocyanic acid, and it seems unlikely that a poison of the latter class could have caused the post-mortem changes seen, or that one of the former type could have been responsible for death after death with the usual symptoms so little in evidence.
In the absence of any more definite knowledge the only advice that has been given to the owners concerned has been to change the paddock and administer a purgative drench to the survivors. Generally, the latter has not been done, but fortunately, in all cases losses have ceased following the change of pasture, even in some cases where the new paddock has presented little obvious difference to the former one. This, of course, is a frequently noted feature with bacterial stock diseases generally.
It might be mentioned, also, that the worst period for this type of loss during the writer's, sojourn in the district (July of this year) coincided with the height of a wave of stock loss from the activity of anaerobes (chiefly Entero Toxaemia and Blackleg), and that no further losses took place after this wave showed signs of subsidence.