During 1945, whilst drought conditions prevailed in the Moree P.P. District, attention was drawn to sickness and mortalities in horses of all ages and types; though the condition was found only amongst horses actually grazing on what is known as Water Course country. Horses grazing in paddocks almost adjacent to the affected animals, but not on Water Course country, were not affected, and horses on the same property but being hand fed showed no sign of sickness.
Water Course country in the Moree District may be described as land that is flooded at regular periods, perhaps once annually; these floods being from the Gwydir River. The flooded areas retain large swamps, some continuing in existence for years, but the greater area dries up in a few months. The particular type of herbage growing where the soil is moist drys off. The flooded country is of a heavy black type of soil and has become over the years covered with Gilgais or Coolamon holes; and during the wet period these grow a large quantity of Nardoo. This plant appears much hardier than others that have grown under such conditions and makes quite good feed for months after the onset of dry conditions; and it was during such a period that the abnormal conditions in the horses was found. It might be mentioned here that on these particular areas sheep and cattle were grazing but in no instance was sickness found in these animals. It must be emphasised also, in so far as horses were concerned it was found that they were grazing continually on what may be called Nardoo country; they did not move about the paddock as sheep and cattle do and in this way obtain a more mixed diet. To give an instance, the horses would remain on the Nardoo areas to such an extent that the owner would be able to indicate the exact place to find them from day to day. It was reported by owners of affected horses that this disease had been noted about 9 or 10 years ago, and while the same conditions prevailed, but as the horses were not of much value no enquiry or investigation was sought.
In all there were seven properties belonging to different persons on which this disease appeared. Out of one hundred horses on this area at least 40 showed similar symptoms in a more or less pronounced state, and it should be noted that these particular horses were not in work; they were just grazing and had been for some time. Due to the fact that the horses were not being handled or inspected frequently it may be that some had recovered. It is known that some had died, and when this sickness was noted the deaths were attributed to it; there actually being no other reasonable cause for these mortalities. In all there were probably eight of these animals that had died from the disease.
Ante-mortem: In the early stages of this sickness in horses it was difficult to recognise unless the horses were fairly closely examined or driven; for the reason that they would continue to graze up to an advanced stage of the disease. The characteristics of the condition were similar in all affected horses; the main symptom being an extremely excitable condition. When walking or trotting the horses would show inco-ordination in all legs, the front legs and front portion of body being perhaps worse. The feet were lifted much higher than normal and this caused stumbling and an inability to maintain a direct course.
The horse, if with others, generally would move off by itself; and frequently whinnied for no apparent reason. The tail usually was elevated slightly. It did appear that affected animals were near-sighted and perhaps a little deaf. The quietest horse was difficult to catch and when cornered showed extreme nervous excitement; which would cease when a hand was placed on the horse and he was stroked. In bad cases there was definite blindness and impaired hearing. The head was held lower than normal, and a constant symptom was a nodding of the head in an arc of six or eight inches. The ears also were moved frequently. There did not appear to be any great pain and the bowels appeared normal. In this advanced stage the horse would not feed but would stumble about over anything in the yard; and if offered a drink would muzzle the water with its nose. All cases which became recumbent remained down until death occurred. In some respects horses in the advanced stage of this sickness appeared very similar to tetanus cases.
Post-mortem: Autopsies held on horses destroyed with this disease actually showed nothing that could be attributed to plant poisoning; and specimens submitted from these animals of heart, blood, liver, kidney, spleen and medulla were not helpful when examined at Glenfield.
From the characteristic symptoms it appeared that the primary effect was an involvement of the C.N.S., and not the normal type of plant poisoning. One horse in a very advanced stage of the disease, neither feeding nor drinking, apparently quite blind and in a highly nervous condition, was treated with morphine in fairly large doses for four days. With careful nursing, recovery was complete in this instance in about 14 days.
With other cases, from 250 to 300 ml. of 20% calcium gluconate was administered without any apparent result.
Actually, a diagnosis of plant (and, in all probability, Nardoo) poisoning was reached early in the investigation. All horses on the suspect country then were removed to other types of grazing. Although many of the animals were difficult to move owing to pronounced ataxia and excitability, when placed on a complete change of pasture improvement in health was obvious in a few days; with apparently complete recovery in about one week.
Marsilea drummondii is a very common plant on swamp areas in the north-west, where it grows in swards up to six inches in height. It is silvery green in colour and very similar to a trefoil in that it has a "shamrock" leaf. The seed is developed at ground level, is about the size of a pea and may be seen to form a thick covering on the ground in suitable seasons.
Hurst (Poison Plants of N.S.W.—Snelling Printing Works Pty. Ltd., 1942) describes this plant as having been suspected of causing a choreic disease of sheep and cattle in the Namoi basin (1911), at Moree (1934 and 1936) and at Burrell Junction (1938). The symptoms are described as resembling Tetanus; but there is not any reference to any effect on horses.
Following the outbreak here recorded, fairly large quantities of Nardoo plant were forwarded from Moree to Glenfield for feeding trials. It is understood that this trial gave negative results; but that a supply of Nardoo seed has been obtained with a view to conducting further feeding trials with the plant actually in the growing state.