Pimelea spp. are a significant cause of poisoning in cattle in southern Queensland and northern NSW. Although curved rice flower/tough-barked rice flower (Pimelea curviflora) occurs in the south western region of NSW, based on records at the Narrandera office, it has not previously been recorded as a cause of death or illness in cattle in this region.
In November 2013 cattle in the Riverina area were investigated following the owner reporting ill thrift, and submandibular oedema then death.
The cattle were extensively run on a dry-area property which had experienced a large flood in March 2012. Rainfall in 2013 was below average.
The cattle were first noticed to be affected in mid-winter 2013.'They had been treated with' ivermectin as a pour-on (ivermectin 10 mg/ml, Genesis Pour On, Ancare Australia) in October 2013. One percent of the herd of 1800 Angus cattle including cows and weaners (both heifers and steers) were noticed to be affected. Affected cows had managed to successfully rear calves. Pasture was relatively abundant and the cohorts were all in good body condition.
Clinical signs were ill thrift and significant submandibular oedema followed by death in some of the cattle after 4-6 months. Diarrhoea was present in some of the affected cattle.
Biochemistry showed hypomagnesaemia, hypoalbuminaemia and hyperglobulinaemia. The levels of magnesium present in the cows tested were: 0.52 mmol/L, 0.61mmol/L, 0.45 mmol/L. Two of the weaners had levels of 0.7 mmol/L. One of the weaners also had a non-regenerative anaemia. Serology was negative for liver fluke and pestivirus. There was no evidence of helminths on FEC.
An autopsy and laboratory tests on an affected cow revealed a suppurative cholangiohepatitis (no bacteria were cultured) and an eosinophilic enteritis (suggestive of parasitic involvement). A second autopsy of an affected weaner revealed intestinal oedema with no evidence of bacterial enteritis or any parasites of significance. There were minimal liver changes noted (which were of uncertain significance) and no evidence of peliosis hepatis associated with pimeleosis.
A search of the property was conducted for plants that might be likely to cause the clinical signs observed. The owner found plants identified as Pimelea curviflora in the lanes used to move cattle to the yards, which were also used as temporary holding lanes. The owner reported that these plants had been present for years and no previous problems had been observed.
The marked clinical signs in these chronically affected animals are in line with many seen in other poisonings associated with Pimelea spp. Kelly (1975) reported no gross changes in the intestines of calves affected by St George disease and did note oedema in the intestines as was present in the weaner autopsied. In spite of the clinical signs, the gross changes at autopsy in the weaner animal were relatively minor. The significance of the cholangiohepatitis in the older cow is not known. The significance of the biochemical findings is also not known. Hyperglobulinaemia is not normally found in animals with Pimelea intoxication (Erika Bunker pers. comm.). The hypomagnesaemia was another unusual finding in the case and appeared unrelated to the pasture available or the lactational state of the animals. Classic grass tetany is not common in this area and when it occurs, it is generally in late winter on short grass dominant pastures in stressed lactating cows.
Pimelea curviflora is not a common cause of pimeleosis and is noted to contain irritant diterpenoids, causing gastroenteritis, without simplexin (the cause of St George disease syndrome) (McKenzie, 2012). Pimeleosis has not been known to occur in this area previously.
The history of the cattle being held in laneways containing the plant during a year which had a dry start to the season could explain the uptake of a plant reported to have low palatability. The historical presence of the disease for many years before this event is unable to be explained in this case. The owner undertook to remove the existing plants after they were determined to be the most likely cause of the disease.
Alan Bolton, NSW DPI, Yanco for identification of the plant. The EMAI pathologists, especially Erika Bunker for her comments on the case. My district veterinary colleagues (especially in the north of the state) for their assistance in identifying a possible cause of disease.