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This article was published in 1994
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A Severe Outbreak of Lupinosis in Sheep
John V Evers, District Veterinarian, Young
This short article records a severe outbreak of Lupinosis in sheep in the Young District during early Winter 1993. It records some of the peculiar features contributing to this occurrence and emphasises the animal husbandry and agronomic practices required to avoid the risk of further outbreaks.
1. LUPINOSIS IN YOUNG DISTRICT
Lupinosis is seen in sheep and occasionally cattle throughout the Young District. When Lupins were first grown in the early 1980's there were some horrendous crashes as locals embarked on another learning curve. These losses can be largely attributed to:
* use of varieties not resistant to Phomopsis infestation
* the almost non-seasonal rainfall pattern (around 50mm per month)
* heavy stocking rates.
While many learnt to cope, grazing of non-resistant stubbles was difficult and Lupin sowings were decreasing until resistant varieties like Gunguru and Merit were released. Since then, grazing of stubbles has been much safer with only sporadic outbreaks - mainly in sheep, with mortality rates generally no more than 2% - 3%.
The normal seasonal pattern of losses (1986-91) was illustrated in a previous paper on Mycotoxicoses (DV's proceedings 75, p.46, 1992). This demonstrates peak outbreaks in March, terminating by June, and another small peak in winter. Careful grazing with mature sheep at modest stocking rates (10-20 per HA) has generally yielded trouble-free utilisation of lupin stubbles from harvest in December until the end of February. Most stubbles are then re-worked for a winter cereal rotation so late-season grazing is not extensively practised.
2. PROPERTY PROFILE
The property on which this outbreak occurred is a very well-managed mixed farming enterprise. It is a family farm of 800 ha located 30km north-west of Young running 4,000 Merino wethers in conjunction with a rotational cropping program. Much of the grain is used to drive a very modern 300 sow piggery. Lucerne rotations are an important part of the pasture/cropping program. Wheat crops are undersown with Lucerne and Sub-clover in the final year of the cropping phase.
3. PRELUDE TO 1993 OUTBREAK
On 9/6/1993 the property in question contacted me about mortalities in a mob of 3 & 4 year old merino wethers. On visit to the farm I found 12 dead, 10 sick ex 1,500 sheep grazing 80 ha of Lucerne. Stock had been in the paddock for 3 weeks and losses had occurred over 3-4 days. I noted occasional dried Lupin stalks which were dead self-sown plants originating from a crop stripped in December 1991. These were obviously contaminated with fungus.
* P.M. findings - Toxaemic Jaundice.
* Diagnosis - Toxaemic Jaundice precipitated by acute/subacute Lupinosis.
* Recommendation - immediate removal and drench with Molybdenum if losses continue.
* Further grazing of this and other similar paddocks with caution.
* Lab results - severe chronic Lupinosis and normal copper levels.
4. THE OUTBREAK
Owner rang me 29/6/93 after finding a lot of sick and dead sheep in another mob of young wethers that had grazed a similar Lucerne paddock for one week (18-25/6/93) without apparent problems. Losses started 24-48 hours after removal and on my first visit tallied 74 dead/120 sick ex 1,450. Aggregate rainfall to this point was 176mm (63% of normal figures) and only 15mm for June.
* P.M. findings - Acute Lupinosis.
* Recommendation - dig a pit and prepare for the worst; feed grain/cereal hay and avoid high-protein feed (e.g. more Lucerne).
* Lab results - most severe case of acute Lupinosis ever observed at RVL, Wagga.
At a further visit on 6/7/93 the situation was 470 dead/700 sick ex 1,450 and no relief in sight. The mob had been put into an unimproved timber paddock with natural grasses, some Phalaris and fedad lib. Triticale hay. The owner commented that about 50 stragglers originally left in adjoining Lucerne paddock seemed to be recovering and as no grain was available (oats) several hundred more were put on the Lucerne. By 16/7/93 the tally was 630 dead/30 sick ex 1,450 and a marked improvement in those on the Lucerne diet. All sheep were then placed on the Lucerne and hand-feeding discontinued.
The mob slowly recovered and by the end of July losses totalled approximately 700 head (48%) and I observed a total of about 100 (13%) in the remaining 750. My recommendation was culling of the entire mob to abattoirs after shearing in Spring 1993. This [w]as not done, but wool cuts were down 20% compared to other mobs and from past experience I would expect long-term decreased productivity and increased annual mortality rates.
5. THE PADDOCK
The paddock associated with this severe outbreak was 25 ha of lucerne approx. 15cm high prior to grazing. It had been sown to Gungura Lupins in 1991, wheat 1992 (+ Lucerne/Subclover). Self-sown Lupin plants were estimated to be no more than 200/ha i.e. 5,000 plants killed 700 sheep. The remaining stalks appeared moderately affected by fungus. Note that the stocking rate was around 60 d.s.e/Ha.
6. DISCUSSION
Heavy losses of sheep and cattle have previously been seen in the Young District. These sort of losses have not been seen on resistant varieties, although these are not regarded as being safe. Likewise, the extreme potency of Phomopsis toxins is well-recognised and outbreaks on self-sown 'crops' and litter are recorded. I have certainly seen small outbreaks on non-resistant varieties the following year. The main points worth consideration is this debacle are:
* Phomopsis resistance is relative to rainfall, time elapsed since plant maturity, etc. All stands should be regarded as potentially highly toxic by Autumn (March April).
* Self-sown plants in dense pasture stands like lucerne may be exposed to greater fungal challenge in that particular microenvironment.
* It may be prudent to include several cereal grain rotations before returning to pasture phase where lupin cropping is included in a program.
* Are varieties genetically stable - Lupin breeders assure me they are - or are the self-sown survivors reverting to susceptibility?
* Alternate paddock feed is not necessarily protective and Lucerne monocultures are not always highly palatable despite their superior nutritional qualities.
* While confirming the risks associated with heavy stocking rates and late-season grazing, this particular outbreak does nothing to elucidate the reasons why so many other producers graze high-risk stubbles with apparent impunity.
* The response to low-protein diet in clinically-affected animals was inferior to that on high-quality Lucerne (and most terminal clinical cases I saw did show symptoms of hepatic encephalopathy).
The difficulty posed by extreme cases like this is an advisory conundrum - we can play safe and recommend nil grazing under certain circumstances. However, many will ignore our warnings and suffer no losses so our advice becomes suspect or discredited. If our advice is taken on board, many hectares of valuable feed would be wasted each Autumn. I still believe if the normal precautions are taken, outbreaks like this one will be rare.
REFERENCES
Blood & Radostits - 7th Ed.
Animal Health in Aust. - Vol. 2
Proc 75th DV Conference P.G.F. Proc No. 103 - JG Allen