Deaths and staggers in weaner heifers were investigated on a Narrabri district property. This herd was experiencing staggers, recumbency and deaths in heifers as they were being returned to a paddock 10 km from the yards where they had been weaned.
Of eight heifer mobs (1263 head) moved on different days from 9 April to 27 May, 1999 three mobs were affected. Of the 596 heifers in the affected mobs there were 26 cases. Of these five died (four on day of movement and one overnight) and another two were euthanased after three days of recumbency.
Cases were more prevalent the further from the yards they had been driven.
The steer mobs were only moved a short distance post-weaning and were not affected.
The syndrome was described by stock staff having three different signs; knuckling of hind limbs, hind limb ataxia and a forelimb problem where scapula attachments loosened and dorsal edge of scapula became higher than dorsal midline. This syndrome is commonly referred to as flying scapulas in the literature. Most animals had only one sign prior to becoming recumbent.
With the exception of the scapula animals two heifers) the heifers that did not die fully recovered in the paddock.
Following the third affected mob a private practitioner examined the heifers that had been left behind recumbent the previous day. They had risen and showed aggression and charging. One that could be caught had a temperature of 41°C.
Thirteen normal weaners and a steer showing flying scapulas (only steer affected and only animal noticed affected on movement to yards) from the next weaning mob brought in were examined.
Temperatures ranged from 39.1° to 40.2°C (the latter scapula steer). Six weaners had temperatures above 39.5°C. There was no difference in heifer and steer temperatures. No weaner showed any obvious nervous signs.
The temperatures were taken after a suggestion by Chris Bourke of the NSW Orange Veterinary Laboratory that the syndrome may be ergotised rye caused hyperthermia.
Autopsy of a heifer that had remained recumbent found extensive haemorrhaging of myocardium. Histopathology was negative.
These finding suggested a mycotoxin caused hyperthermia that was only causing problems when the stock were driven a distance. Freshly weaned heifers returning to paddock are likely to gallop along while a cow and weaner mob would move much slower. This would explain the limitation of the problem to the weaner heifer mob.
Paddock inspection confirmed that in keeping with the usual pasture species in the district, rye grass did not occur on the property.
All heifer mobs came from different paddocks. Most paddocks on the property are similar in that they are heavy black clays with open areas along with wooded areas of Bimble Box (Eucalyptus populnea) / Belah (Casuarina cristata ssp. cristata) communities along waterways. Some paddocks have been developed so that the open areas are sown to Purple Pigeon grasses. Affected mobs came from both Purple Pigeon grass (Scuola incrassata) and no Purple Pigeon grass paddocks.
The previous winter of 1998 was very wet (wettest since 1950 reputable) and water lay in most paddocks. Summer was moderately wet but autumn was dry with the only significant rain between Christmas and June at Easter.
The "couch" formed a carpet in the open interspersed with Blow Away Grass (Chloris truncata) in the open areas and with Warrego Summer Grass (Paspalidium spp probably P jubiflorum) in the wooded lower areas. The "couch" was more prevalent this year than usual, no doubt due to the wet winter.
On closer inspection the "couch" consisted of two species. One was common couch (Cynodon dactylon) the other Rat Tailed Couch (Sporobolus mitchelli).
With reference to the cattle grazing habit. As conditions have dried out it is apparent that their first preference was the "couch" which has grazed to a close carpet with seed heads very rare. The next preference was the Blow Away Grass and Rat Tailed Couch, which had been mostly eaten out with seed heads uncommon. The grass that the cattle had been most recently turning to was the Warrego Summer Grass, the seed heads of which they were consuming at the time of the problem.
No ergotised seed heads were seen.
Chris Bourke provided a possible solution with the information that a Balansia spp, an endophyte fungi that has been associated (with) a hyperthermia syndrome, was isolated from Warrego Summer Grass at Mungindi in November 1990 as part of the Flood Plain Staggers investigations.
Unfortunately finding endophyte colonised plants is difficult. The only sign that a plant may be infected is the occasional dark seed. The next step is to inspect the paddocks once the seed heads have all dried out and see if Balansia or another mycotoxin can be isolated.
It should also be acknowledged that hyperthermia causing mycotoxins can also occur in other species present, namely couch and panic species (there was the occasional plant of the latter).
Post Script: Inspection of the paddocks once the Warrego Summer Grass seed heads had dried failed to find any endophyte colonised plants.