Lupinosis, caused by a fungus affecting both seed and stalks of lupin crops, is known to be highly toxic to livestock, and most producers growing lupin crops are aware that lupin stubbles that have had some rain after harvest are potentially deadly to grazing sheep.
In this case a stubble paddock that had been suspected of being affected with lupinosis (phomopsin) was not grazed, but was oversown with a cereal crop that was subsequently cut for hay. When this cereal hay was fed to lambs in a feedlot, six lambs over a three-day period died from lupinosis. On close inspection some lupin stubble stalks could be found in the hay that otherwise appeared good quality. Testing of the hay found it to be highly contaminated and unsuitable for use with any livestock.
Producers oversowing previous lupin stubbles with cereal crops (a common rotation practice) should be advised of the possible risks associated with phomopsin contamination and that the hay should be tested before feeding to livestock. Tests are reasonably priced and maximum recommended concentration of phomopsin spores have been determined.
A farmer in the Murraylands area of SA feeds his lambs in a confinement feeding situation, due to very dry conditions, 1 kg cereal hay per head and whole barley in lick feeders. Confinement feeding of lambs and other classes of sheep is becoming more common in SA arid and semi-arid areas, especially in drought conditions and has many benefits in well-managed situations.
This producer is experienced with confinement feeding and has very good levels of management in place, with low mortality rates. However in mid-December 2018, six lambs were found dead at morning inspections over a period of three days. A local private veterinarian was contacted and performed an autopsy on one lamb and diagnosed lupinosis from characteristic appearance. Laboratory tests confirmed this clinical diagnosis. Since the sheep were not being fed lupins the hay was closely inspected and some lupin stalks observed. A sample of the hay was sent for testing and very high concentrations of phomopsin spores detected.
This hay was cut from a paddock that contained mandelup lupins grown and harvested in the summer of 2017. Sheep were not allowed to graze this stubble as previous experience had shown toxicity when stubbles had summer rain on them. A cereal crop, intended for grain/straw production, was planted over the lupin stubble using minimum tillage techniques but seasonal conditions were such that the crop was cut for hay, rather than harvested as usual. In the baling process, a certain amount of lupin stalks and infective material was caught up with the hay.
Necropsy results from the lamb autopsy confirmed lupinosis. Pathologist’s comments were:
“The histological appearance is compatible with chronic hepatotoxicosis, with extensive liver fibrosis, cholestasis, biliary hyperplasia and ongoing hepatocyte necrosis and attempted regeneration (mitotic activity). This pattern is most consistent with your primary differential diagnosis of mycotic lupinosis (phomopsin poisoning); however, other hepatotoxins, especially pyrrolizidine alkaloids, can have overlapping histological lesions. The mycotoxin (phomopsin) induces defective microtubule formation and mitotic arrest in metaphase - affected cells die during this mitotic arrest."
Phomopsin results from tested hay are shown below.
Phomopsin is a fungal toxin (Phomopsis leptostromiformis) produced by the fungus Diaporthe toxica that infects lupin plants and can cause lupinosis in livestock when eaten. Although many modern varieties have some resistance to phomopsin growth, this resistance only applies to the growing plant and spores can rapidly multiply in the right conditions of moisture and a high load of dead plant material. Lupinosis causes sheep to show inappetence, emaciation, lethargy, jaundice and death that may continue up to two months after removal from contaminated material. There is no satisfactory treatment apart from careful management post exposure.1 The phomopsin is a stable type of fungus that is likely to remain of the stubble for a long period and is thus difficult to manage.2
A sample of hay contaminated with lupin stalks was tested in this case and had high levels of phomopsin. Levels were 78,000 µg/kg, where any result greater than 300 µg/kg is considered dangerous. Hence only a small amount of the stubble had to be consumed to be poisonous.2 Phomposin testing is easy - all that is needed is half a dozen handfuls of a sample to be sent to a feed tester in a plastic bag. The test costs around $160 + GST and can be organized through companies such as Landmark. One company that conducts this testing is Agrifood Technology in Victoria.6 If the results are less than 300 ppb or µg/kg then sheep are still able to graze on the stubble without serious damage but a close eye would have to be kept on them especially if close to 300 ppb. If any symptoms are showing the mob should be removed.2 When the first symptoms appear this indicates that the animal has received 1/8th of the toxic dose so it may not necessarily be fatal if the stock are removed quickly.2
If grazing sheep on lupin stubble it is advised that the stocking rate is no higher than 15 head/ha and should be removed when there is less than 40 lupin seeds/m2.3 Several watering points will promote less condensed grazing but, most importantly, management involves monitoring the stock, which should include walking them at least 200m to observe the stragglers that may exhibit a stiff gait or reluctance to walk.1,4 Burning off the stubble may not be completely effective in removing toxic plant material but may be an option in some circumstances and lupin crops may also be cut for hay just before pod formation minimising the risk of phomopsin growth.1 There are some excellent management and preventative strategies described in the Western Australian documents cited.
In this situation dealing with infected hay is problematic, as the very high levels of phomopsin would make it unsuitable for use with any category of livestock. There was a suggestion that the hay might be suitable for compost but a composting company quoted $30/tonne to dispose of it, not including transport costs. Since there are approximately 80 affected round bales disposal represents a significant issue.