Ovine Pregnancy Toxaemia (Twin Lamb Disease) and Hypocalcaemia

Ovine Pregnancy Toxaemia (Twin Lamb Disease)

Most commonly seen in low-ground flocks, affecting older ewes carrying 3 or more lambs during the last month of gestation. On farms which rely upon pasture-based systems, with little or no supplementary feeding, OPT is seen in severely under-fed twin-bearing ewes. The disease comes into effect following a period of severe energy shortage; which can be attributed to poor roughage quality, inadequate concentrate allowance or high foetal demand. The onset of clinical signs can be encouraged by a sudden stressful event such as adverse weather, handling, vaccination or housing.

·         Early clinical signs: at first it is noticeable that affected ewes are disorientated, leading to isolation from the flock, becoming increasingly dull and depressed and easily caught due to blindness. Head pressing into the corner is common. During later stages, fine muscle tremors may be seen around the muzzle and ears. Ewes become recumbent, hind legs held out behind and the inability to stand may lead to urine scalding of the skin and fleece.
In order of events: does not feed, isolated, dull, blind, head pressing, muscle tremors, recumbency… death.

·         To treat OPT the earlier the signs are detected the more successful the treatment. That being said, if the ewe is still able to stand, general success rates are only roughly 30%. Offering more palatable foods to promote appetite and providing fresh water can help. Administering propylene glycol, IV glucose injection and glucocorticoid injection is the best course of action.

·         Ewes with OPT must be checked at least twice daily for signs of abortion/lambing because they may be too weak to expel the foetus/lambs and therefore the material may remain inside, becoming rotten and releasing poisons into the ewe, causing death. Recovering ewes are rarely able to nurse a single lamb and should be culled after condition has improved. Wool slip occurs commonly in recovered ewes, 4 – 6 weeks after abortion/lambing.

·         To prevent OPT, ewes at risk of being affected should be fed appropriate amount of high quality roughage and supplementary concentrate feed in order to prevent twin lamb becoming a problem. This feeding regime is most important during the last 6 weeks of pregnancy.

Hypocalcaemia

Affected sheep are usually older and carrying 3 or more lambs while pasture grazing during late gestation. Occasional sporadic cases can occur during early lactation. The disease is often observed when ewes are brought down off hill grazing onto improved pastures prior to lambing. “Outbreaks” can occur resulting from inaccurate home-mix rations, incorrect mineral supplementation, stress related events (dog-worrying) or movement on to good pastures prior to lambing, or following housing.

·         Affected ewes are depressed, weak and unable to stand even when supported. There is considerable rumen stasis leading to the development of bloat. Passive reflux of the rumen contents may occur with green fluid present at the nostrils and around the lower jaw. Without appropriate treatment, come and death follows 24-48 hours later.

·         There is a rapid response to slow IV administration of 20 – 40mls of 40% Calcium Borogluconate solution given over 30 – 60s. Eructation (burping) usually follows around a minute later, followed by standing up, urinating and wandering back to the flock.

·         The response to subcutaneous injection of 60 – 80mls of the same solution may take up to 4 hours when injected over the thoracic wall behind the shoulder. Especially if the solution had not been warmed to body temp beforehand.

·         Additions of appropriate minerals during pregnancy and throughout mixing are essential to prevent this disease.