A series of drought years had degraded the lucerne based pastures on a property north of Wagga Wagga. As a result the sheep enterprise relied on stubbles for summer feed and drought lots in late autumn utilising pea and canola pit silage and grain while the farm was sown to crop. The ewes went onto grazing crop once it was available and usually lambed on it. As expected with dual purpose cereal crops the sheep were removed from most crop paddocks late in the winter to enable them to recover from the grazing and produce optimal grain yields. Some of the crops were sacrificed for sheep feed and grazed through the winter and spring until stubbles were available from harvested crops.
A massive mouse plague in early 2011 resulted in the destruction of the sown and emerging seed and the expected grazing crop was not available for lambing. As a result the scanned older merino X SAMM ewes and younger Dohne x SAMM/ merino ewes all joined to Dohnes (divided into 2 pens of multiple bearing and 2 pens of single bearing) were about to start lambing in three weeks time in drought lots where the feed consisted of good quality pea/canola pit silage and ad lib weather damaged oats in feeders. No supplements (for example salt/lime) were provided. The mouse plague was still active and the feeders had numerous mice accessing the main bin and troughs. In the centre of three of the pens, dirt, faeces and spilt silage had been pushed up into mounds about 2 metres high. Water from a dam was supplied in troughs. Stock density was 500 ewes in pens 66 x 60 metres (i.e.7.9m2 per ewe). The ewes were in excellent condition.
Two sets of problems and attempted solutions are described.
On 20.06.2011 I investigated an outbreak of abortions in a pen of 500 twin bearing merino ewes due to start lambing in three weeks. The ewes had been fed dusty, weevil infested, mice damaged barley in a paddock prior to their entry into the drought lot 16.06.2011. While in the paddock a few ewes were noted to have pregnancy toxaemia and one aborted.
On Sun 19.06.2011 multiple abortions were noted and at my visit on the morning of 20.06.2011 there had been a total of 18 dead lambs. At the initial visit the sheep in the pen where the abortions were occurring were observed both standing on the mounds of dirt/faeces/silage and more surprisingly licking the mounds. I initially thought that behaviour probably related to a lack of sodium with the high grain based diet. Two of the freshest lambs were post mortemed.
At that stage there were no problems in another pen of twin bearing ewes introduced into another pen 17.06.2011.
On 21.06.2011 the owner reported 8 ewes had died, on 22.06.2011 there had been two further abortions but no more ewe deaths.
On 20.06.2011 no ewes appeared to be in ill health and there were no nervous symptoms observed.
The freshest aborted lambs had very short hair.
The joys of having the CSU veterinary laboratory on hand! I dropped off my specimens on the way back to the office and late that evening they were in contact to say that the likely culture was listeria. On 22.06.2011 they advised the culture from both lamb stomachs of B haemolytic listeria ivanovii. Antibiotic sensitivity tests revealed both isolates were susceptible to tetracyclines which had been prescribed.
The potential for a listeria abortion disaster appeared to be huge. We had an abortion storm in a small area with a mob of sheep on the point of lambing, the source of the listeria may have been feed in paddock pre feedlot entry, the silage in feeders, or the silage and dirt pushed up in the centre of the pen and the role of mice was another unknown (what would happen if they fed on aborted lambs? might they already be infected and contaminating the barley paddock fed grain or drought lot oats?)
In an attempt to control the abortion storm the owner moved the initial aborting multiple-bearing mob to a fresh site a couple of kilometres away (a new drought lot in a lane way) with the aim to remove the ewes from a potential source of contamination and break transmission with tetracycline feed medication. There is little clear advice regarding appropriate treatments in the situation described, so believing there was a very high risk of massive exposure and bearing in mind we were dealing with late pregnant ewes, I prescribed Terramycin 200 Phibro Animal Health as a feed additive in the grain. This is oxytetracycline hydrochloride (as quaternary salt) 200g/kg administered at the rate of 2.5g Terramycin 200/50kg/head/day. Regrettably it is not easy to get the dose rate accurate. The practitioner had difficulty obtaining this product, treatment was delayed until 23 or 24.06.2011 and he ultimately dispensed a similar product. Had facilities permitted it I would have preferred to go for an off-label use of a water medication like Terramycin 880 Soluble Powder which would have been easier to control the dose rate and would have not suffered the risk of inadequate intake if inappetance was associated with disease.
The other multiple bearing mob also started to experience abortions (never as many as the first mob). It was removed from the drought lot 27.06.2011 and also treated with the feed based tetracycline.
The single bearing mobs remained in two separate pens in the drought lot. Despite being on the same silage and grain and having similar piles of dirt, faeces and spoilt silage heaped up, this mob lambed uneventfully in the drought lot.
As the abortions tapered off a new syndrome of depression and death started.
The twin bearing ewes that had been involved with the initial abortions were moved a couple of kilometres to an internal laneway that could be used as a drought lot and self feeders set up. With the delays experienced getting the tetracycline feed additive it was not until the feeders were low or in some cases run out that the feeders were refilled with medicated grain (oats with an ME of 12.70 MJ/kg DM) on 23rd or 24th June.
One ewe was dead 28.06.2011 and a further 12 dull and depressed.
The 12 ewes had symptoms that included blindness, depression and terminal collapse with paddling. There was no indication of circling or facial paralysis.
A recumbent ewe was destroyed for necropsy and a classical pregnancy toxaemia seen with FS 4, fat necrosis, very pale fatty liver (floated in formalin) and twin lambs in utero. There were a few ostertagia and haemonchus visible grossly in the abomasum and the GIT had very little feed in it.
The obvious diagnosis was pregnancy toxaemia probably induced by the feeders running low but that didn't quite ad up. The feeders had not all run out and the oats was high ME as was the silage so a few hours without grain should not have triggered a problem of this magnitude.
The owner commented that this mob was consuming 1.0 kg of oats /head/day which would usually seem adequate. It's ME was 12.7 MJ/kg DM, CP 11.0 % with ad lib silage ME 9.6 MJ/kg DM , CP 18.0 %, DM 33.6 % and the intake of 1.0 kg /head/day would raise no concerns for me BUT another mob was eating 1.4 Kg grain/head/day.
Reduced appetite and pica (licking that pile of dirt and faeces in the drought lot) suggested worms so faeces were collected for a faecal egg count.
Histopathology of the liver revealed diffuse, moderate, hepatic lipidosis which is likely a result of altered fat requirement to meet increased energy requirement.
The clinical and post mortem signs, elevated - hydroxy butyrate values and hepatic lipidosis confirmed the obvious diagnosis of pregnancy toxaemia. The high egg count together with the owner's observation of depressed appetite relative to other mobs suggested that worms may well have been a contributing factor to the pregnancy toxaemia.
The mob was drenched, their appetite returned and no further pregnancy toxaemia problems were seen. There was no further evidence of listeria abortion and no nervous symptoms were observed.
The owner was contacted 26.07.2011 and he reported the mob was still being fed in the laneway. The move from the drought lot and antibiotics appeared to have successfully stopped the listerial abortion outbreak.
Confirmed listeriosis in sheep is relatively rare in the district. A search of our EZY computer records from 01.01.1995 to 31.12.2011 revealed only 7 cases. A surge in cases in several LHPAs later in 2011 associated with long feed is reported in the spring edition of Flock and Herd ( www.flockandherd.net.au ).
The source of the listeria infection is uncertain given the fact that one abortion was seen in the paddock prior to entering the drought lot. The most likely or highest risk source would seem to be the pile of silage, soil and faeces the sheep were observed licking in the pen. The predisposing reason for this behaviour which was not observed in the other mobs was most probably related to the high internal parasites burden. The potential role of mice was not investigated.
It would have been very easy to overlook the internal parasite burden without the owner's astute observation of the difference in feed intake between mobs. I believe the internal parasites did contribute to the pica leading to the ingestion of listeria and later to the pregnancy toxaemia problems.