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CASE NOTES


Phomopsin infected lupin stubble contaminated the subsequent cereal hay crop killing sheep with lupinosis

Ellen Arney 1040 Dry Plains Rd, Finniss, SA, and Jeremy Rogers, Senior Veterinary Officer, PIRSA PO Box 469 Murray Bridge, SA

Posted Flock & Herd December 2019

Introduction

Lupinosis, a disease of sheep and cattle, is caused by the fungus Diaporthe toxica (previously known as Phomopsis leptostromiformans) that grows on the seeds and stalks of lupins. It is known to be highly toxic and most producers growing lupin crops are aware that lupin stubbles that have had rain after harvest are potentially deadly to grazing sheep.

In this case a lupin stubble paddock that had been suspected of being affected with the fungus 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, 6 lambs over a 3 day period died from lupinosis. On close inspection some lupin stubble stalks could be found in the hay, that otherwise appeared to be of good quality. Testing of the hay found it to be highly contaminated with Diaporthe toxica and unsuitable for use in any livestock.

Producers direct drilling cereals into previous lupin stubbles (a common rotation practice) should be advised of the possible risks associated with fungal contamination, and that the hay should be tested before feeding to livestock. Tests are reasonably priced and maximum recommended concentration of Diaporthe (Phomopsin) spores has been determined.

History

Due to very dry conditions, a farmer in the Murraylands area of South Australia fed his lambs 1kg cereal hay per head and whole barley in lick feeders in a confinement feeding situation. 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.

In mid-December 2018, 6 lambs were found dead at morning inspections over a period of 3 days. A local private veterinarian was contacted and performed an autopsy on one lamb and diagnosed lupinosis from the jaundiced appearance of the carcase. Laboratory tests confirmed this. 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.

The 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 direct drilled into 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, lupin stalks and other infected material was caught up with the hay.

Results

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 are shown below.

Test Result
Phomopsin (TP/043) (µg/kg) 78000

Interpretation/ Discussion

The sample of lupin stubble taken and tested from the hay had high results of phomopsin. The levels were 78,000 µg/kg, and 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 All that is needed to do a phomopsin test is half a dozen handfuls of a sample to be sent to a feed tester which may cost around $160 + GST and can be organised 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 than 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 with any symptoms showing the mob should be removed.2 When the first symptoms are present it indicates that the animal has 1/8th of the toxic dose so it may not necessarily be fatal if the stock are removed.2

Phomopsin is a fungal toxin 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 Diaporthe growth, this only applies to the growing plant, and spores can rapidly multiply in moist conditions and a high load of dead plant material. Lupinosis causes sheep to show signs of inappetence, emaciation, lethargy, jaundice and death which may continue up to two months after removal from contaminated material. There is no satisfactory treatment apart from careful management post exposure.1 Diaporthe is a stable fungus that can remain on the stubble for a long period and is thus difficult to manage.2

Management

If grazing sheep on lupin stubble it is advised that the stocking rate is no higher than 15 head/ha and sheep should be removed when there is less than 40 lupin seeds/m2.3 Several watering points will promote less condensed grazing but most important management involves monitoring the stock which may involve walking them at least 200m to observe the stragglers which may exhibit a stiff gait or reluctance to walk.1,4 Burning of the stubble is not considered as satisfactory but ideally just before pod formation the lupin crop can be made into hay 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 in any category of livestock. There was a suggestion that the hay may be suitable for compost but a composting company quoted $30 /tonne to dispose of it, not including transport costs. Since there are approximately 300 affected round bales, this represents a significant issue.

Figure 1. Stalks from lupin stubble included in hay
Image of lupin stalks in cereal hay
Figure 2. Stalks from lupin stubble included in hay
Image of lupin stalks in cereal hay
Figure 3. Lupin stalks heavily infested with Diaporthe toxica
Image of lupin stalks in cereal hay

References

  1. Hungerford, T.G., 1989. Diseases of Livestock, 9th ed., Pg 199, McGraw-Hill Book Company Australia Pty Limited
  2. Sadler, R., 2019. Personal Communication
  3. Seymour, Marion Lupinosis, Lupin Bulletin (WA Department of Primary Industries and Regional Development) www.agric.wa.gov.au and www.agric.wa.gov.au
  4. Radostits, O.M., Gay, C.C., Blood, D.C., Hinchcliff, K.W., 2000. Veterinary Medicine: A textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses, 9th ed., Pg 1695, W.B. Saunders Company Ltd
  5. Rogers, Lee, Mossop 2011 (unpublished). Deaths due to suspected mycotoxins in a group of feedlot sheep fed discoloured lupins, and a subsequent feeding trial agrifood.com.au

 


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