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Selenium/Vitamin E Responsive Myopathy in Pigs - a Clinical Trial
J.M. Wilson, B.V.Sc., Veterinary Inspector, LISMORE
INTRODUCTION
Myopathies associated with selenium/vitamin E are not uncommon in cattle and sheep in many parts of the world. In pigs, hepatosis dietetica and mulberry heart disease are associated with selenium/vitamin E, and nutritional myopathies in growing pigs have been seen as a result of dietary deficiencies of selenium and/or vitamin E. This report gives a brief account of a clinical trial in a piggery where selenium/vitamin E deficiency was suspected as a cause of myopathy in weaned piglets.
MANAGEMENT
The piggery is a modern, intensive slatted floor unit of 50 breeding sows, with a good standard of management. Sows are basically Landrace and Large White cross breed, and over the past two years the introduction of performance tested hybrid boars and gilts has resulted in a notable improvement in growth rates.
Rations for this piggery are purchased in bulk, ready mixed, from a small district feed miller. This miller is a highly skilled pig producer, and runs, in conjunction with his feed business, a 120 sow piggery with performance tested stock. He supplies his clients with identical rations to those used in his own piggery.
After weaning at 5 weeks of age, piglets are batched for two weeks, and then transferred to elevated weaning cages. They are fed a high protein ration which includes a vitamin/mineral premix. Piglets are held in weaner cages until 11 weeks of age when they are moved to grower pens where they remain until slaughter.
Because of the design of the piggery, it is necessary to drive weaners a considerable distance (up to 50 metres) when transferring them from weaner cages to grower pens.
DISEASE STATUS
The usual collection of diseases found in well managed North Coast piggeries - colibacillosis, enzootic pneumonia, parvo virus, metritis, sarcoptic mange etc., is seen from time to time in the piggery, and there have been occasional losses from E.M.C. infection.
Because of the history of E.M.C. and the interest of the Regional Veterinary Laboratory (Wollongbar) in this disease, an effort is made to investigate all sudden deaths.
HISTORY
On 24/5/83, the owner reported that while driving 30 weaners along the passageway from the weaner cages to the grower pens, several piglets had collapsed and after showing gasping respiration, two had died.
Autopsy was carried out in the field on one cadaver, while the second was taken to the Regional Veterinary Laboratory, Wollongbar for more detailed examination.
Neither heart showed discrete foci of myocardial necrosis, rather there were extensive pale areas generally between major branches of the coronary vessels. These areas contrasted with surrounding areas where the blood vessels were congested and there was some haemorrhage. The pericardial sac was distended with yellow sero-fibrinous exudate.
There were no fluid accumulations in serous cavities and the liver did not appear congested.
Small groups of skeletal muscle appeared darker than normal possibly due to haemorrhage.
Heart was fed to mice and material was submitted to V.R.S. Glenfield for E.M.C. virus isolation. Mulberry heart disease was suspected, and subsequently confirmed on histopathological examination.
Liver and kidney submitted for selenium estimation were unfortunately 'lost' at V.R.S. Glenfield.
The owner continued to have problems moving weaners, but because he avoided forcing them too hard, lost no more. However, he stated that after about three weeks in weaner cages, all piglets were tending to show muscular 'spasm' and temporary recumbency when handled or startled. After moving to the grower pens; the piglets gradually became normal after 10 - 14 days.
The piggery was visited on 12/7/83, when it was seen that 18 weaners of about 10 weeks of age were exhibiting abnormal behaviour.
Piglets became very agitated when approached, and on handling or being forcibly moved, adopted a crouching posture, with spasmodic contractions of muscles of the hind limbs, abdomen, and thorax. A gasping respiration was accompanied by a 'barking' grunt. If left undisturbed, affected piglets returned to normal within a few minutes.
CLINICAL TRIAL
It was decided to perform a clinical trial on the basis that the problem might be associated with selenium/vitamin E metabolism.
The only available product which could be obtained (borrowed from a practitioner) at short notice was MYOPATHYL INJECTION ADVANCE®. This product contains, per ml, adenosine triphosphoric acid 2.5mg, uridine triphosphoric acid 200 microgram, vitamin E 40mg, sodium selenite 500 microgram. Formulated for treatment of horses and dogs, there is no recommended dose for pigs, but an empirical dose of 1ml was chosen.
On 13/7/83, 9 of the affected piglets were given an intramuscular injection of 1ml 'Myopathy'. The remaining 9 were left untreated, and both groups were confined in identical, adjoining weaner cages.
On 19/7/83, inspection revealed that the untreated controls were all exhibiting the muscular spasms to a greater degree than when last seen. The treated group had improved to the point where considerable exercise stress had to be applied to elicit the clinical signs.
On 25/7/83, both groups were moved to the grower pens. There was great difficulty in moving the control group, several collapsing en route and having to be left to recover before moving again.
The treated group by contrast, was apparently normal, frisky, and piglets actually ran along the race of their own volition.
Both groups were clinically normal when next seen a fortnight later, but, when viewed subjectively, the treated group was about 10 percent ahead in terms of growth.
FURTHER INVESTIGATION
The feed supplier was interviewed, and it was learned that he had been experiencing a similar problem with his own weaners. Retrospective investigation of rations indicated that about a month before the problem began, he had, for reasons of economy, changed from one vitamin/mineral premix ('Grower Premix' Pfizer) to another ('Weanaid' Keymix®). Examination of the formulae of both products revealed that the latter contained no selenium.
Subsequent batches of feed were prepared using the original premix, and no further myopathies have been noted in either piggery. (The manufacturer of the second premix, 'Weanaid' now also includes selenium in the premix).
DISCUSSION
No other piggeries purchasing rations from the local miller had experienced similar problems.
The common factor in the two affected piggeries was the introduction, over the previous two years of performance tested breeding stock, and the consequent improvement in quality and growth rate.
It may be that the resultant genetic capacity for more rapid muscular development and growth has produced a pig whose selenium requirements are more critical.
Glutathione peroxidase levels in blood may have been worth determining. However, it was felt at the time that physical restraint of affected piglets for blood collection would have resulted in their death.
It was not possible to determine the effects, if any, of the A.T.P. and U.T.P, which, with selenium/vitamin E, formed a component of the 'Myopathyi'®.
However, the observation that changing from a premix without, to one with, selenium reversed the clinical signs; seems to point to a selenium/vitamin E responsive myopathy.