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This article was published in 1980
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Hypocalcaemia and Hypomagnesaemia of Weaner Lambs Grazing Oat Stubbles
A.G. Morton, B.V.Sc., Veterinary Inspector, Gundagai
Introduction
Metabolic disturbances of weaner lambs grazing lush cereal crops are not an uncommon occurrence in southern N.S.W. Similar disturbances when grazing cereal stubbles are less common and discussions with several other Riverina veterinarians failed to elicit any similar confirmed cases.
History
During February 1979 and 1980 three lamb weaner mortalities were investigated with similar histories and clinical signs. In each outbreak weed-free cereal stubbles had been grazed by weaner lambs for several weeks or longer late in summer, and the clinical appearance of the lambs and response to early treatment with calcium/magnesium injections mimicked hypocalcaemia of ewes.
The first outbreak involved a mixed sex mob of 200 merino wearers, and 100 crossbred weaners, all in fair condition and grazing oat stubble. There was a suggestion that the lambs may have been briefly water deprived before the outbreak. Interestingly, only the merinos were affected.
On the first day of the outbreak two lambs were found down. Post-mortem examination of one by a private veterinarian failed to yield a diagnosis. The following morning the second lamb was still down and unable to stand, eat or drink. Its temperature was normal but respiration and heart rate rapid.
On the second morning a further four lambs were found down. All had normal temperatures, rapid respiration and heart rates and flaccid paralysis. Three of the four could raise their heads and were quite bright and alert while the fourth was unable to lift its head and the owner, reported that it had passed red coloured urine. The owner had treated all four with chloramphenicol that morning without response. Intravenous treatment with a proprietary calcium, magnesium, phosphorous and dextrose solution gave some response but the lambs were still unable to stand.
The second outbreak involved 600 mixed sex crossbred lambs in fair to good conditions that had been grazing oat stubble for six weeks.
The mob was being driven when four lambs went down. Two died within a few hours, leaving two available for examination. One lamb had symptoms typical of milk fever while the second had symptoms typical of grass tetany. Intravenous treatment with a proprietary calcium/magnesium solution gave an excellent response.
As I recall post-mortem of the two dead lambs revealed no significant lesions other than scattered subepicardial petechiae.
The third outbreak involved a mixed sex mob of 500 Corriedale cross Dorset lambs grazing oat stubble and a dry grass dominant pasture and receiving supplementary cereal hay.
One sheep was found dead and two down. One of the sick sheep died within twenty four hours while the other progressively deteriorated.
On examination the sick sheep had a normal temperature and normal mucous membranes. It was unable to stand, the front legs twitched slightly while there was slight rigidity of the hind legs. Moderate submandibular oedema was apparent.
Post-mortem examination revealed very limited chronic pneumonia and moderate oedema of the mesenteric lymph nodes, brisket and submandibular tissues.
Clinical Pathology
Specimens collected from the first outbreak proved interesting.
Haematology was performed on smears and EDTA samples collected from the five weaners initially examined. The laboratory report from the Regional Veterinary Laboratory, Wagga commented:
'The leucocytes in all smears showed severe damage, particularly the neutrophils in which the nuclei stained poorly, had indistinct outlines and a somewhat foamy appearance to the chromatin. The lymphocytes were affected to a lesser degree. Not withstanding the cellular degeneration the majority of cells could be identified, although the results should be interpreted with some caution. Although white cell counts are generally regarded as of little value in diagnosis of sheep disease it appears in this case that all five sheep are showing marked reversal of the usual (neutrophil lymphocyte ratio and relative and absolute) neutrophilia. A similar blood picture (although cellular degeneration was not mentioned) has been reported in cases of oxalis poisoning in South Australia.'
Examination of the paddock failed to detect any green feed of any description. Nonetheless a kidney was submitted from a lamb which had been down for a week before it died. Histopathology of the kidney detected no oxalate crystals or damage suggestive of oxalate poisoning.
Biochemistry provided a diagnosis with all five samples deficient in calcium, one of the five low in magnesium and the remaining four samples above the normal range for magnesium.
| Serum | Ca(mg/100 ml) | Mg(mg/100 ml) |
|---|---|---|
| 1 | 6.8 | 4.7 |
| 2 | 8.3 | 3.3 |
| 3 | 8.2 | 3.1 |
| 4 | 6.8 | 4.0 |
| 5 | 6.9 | 2.0 |
From the second outbreak the only samples collected were sera for calcium and magnesium analysis. One animal had normal calcium levels and low magnesium levels, the other was deficient in calcium and had excess magnesium.
| Serum | Ca(mg/100 ml) | Mg(mg/100 ml) |
|---|---|---|
| 1 | 10.8 | 2.3 |
| 2 | 7.1 | 4.5 |
From the third outbreak a brain was collected for histopathology and two serum samples collected for biochemistry. No significant microscopic lesions were detected in the brain.
The first serum sample was deficient in calcium and magnesium, the second had normal levels of calcium and magnesium.
| Serum | Ca(mg/100 ml) | Mg(mg/100 ml) |
|---|---|---|
| 1 | 7.1 | 1.7 |
| 2 | 9.3 | 3.0 |
Subsequent History
On the first property the owner removed the sheep from the stubble and put them in a paddock with a short green lucerne pick and supplemented them with oat grain. One sheep showed symptoms the day after being shifted off the stubble. The owner treated it promptly with subcutaneous calcium/magnesium solution and it recovered. Only one of the original sheep treated recovered, the balance died approximately one week after first going down.
No further losses were reported from the second property.
On the third property the Lambs remained on the stubble for a further four to five days. The cereal hay was withdrawn, pasture hay feedad lib. (roller bales) and oats plus ground limestone fed daily. The lambs were then removed from the stubble and supplementary feeding continued. No further losses occurred.
Differential Diagnosis
The differential diagnosis in cases similar to those described above might include metabolic diseases, encephalopathy, botulism, oxalate poisoning, blue green algae poisoning and Vit. A deficiency.
Conclusion
Three outbreaks of an apparent metabolic disease affecting weaner lambs grazing oat stubbles are described. The clinical picture closely resembles metabolic disturbances of lambs grazing lush cereal crops. Treatment with intravenous or subcutaneous calcium/magnesium solutions is only successful when done early. Prevention through removing the remainder of the mob from the stubble and providing a more. balanced diet appears to be successful.