The most common of these diseases are pregnancy toxaemia, hypocalcaemia and hypomagnesaemia and while the treatment is different for each of them, they are all related to nutrition and all require early treatment to minimise losses.
Pregnancy Toxaemia (sleepy sickness)
Pregnancy Toxaemia is more common in multiple-bearing and older ewes, especially where there has been a sudden restriction in feed intake due to weather, yarding, lameness, teeth issues, internal parasites or increased competition.
Ewes appear depressed, are reluctant to move, may appear to be blind, stagger, display neuromuscular symptoms such as the twitching of facial muscles and frothing at the mouth. Eventually they become cast and die.
Early treatment is critical. Once the ewe displays severe clinical symptoms kidney failure has probably occurred and recovery is unlikely.
Treatment includes the provision of carbohydrates such as oral propylene glycol or intravenous dextrose and a dose of calcium borogluconate, given under the skin, is also recommended. Managing dehydration (either orally or intravenously) and maintaining appetite is important, so where possible leave ewes with their flocks as this can encourage feeding.
Avoid unnecessary stress or sudden changes in diet. Bad weather raises ewes’ energy requirements which highlights the importance of shelter and having supplementary feed available, particularly during or immediately after storms.
Hypocalcaemia (milk fever)
This is caused by insufficient intake and absorption of calcium into the blood. To meet the demands of the developing foetal skeleton, a heavily pregnant ewe will need to mobilise some of her own skeletal calcium to meet her calcium requirements. Additional calcium goes into milk production.
The amount of calcium a ewe uses from her skeletal reserves depends on her diet. Lush, actively growing pasture, wheat or concentrates that contain low calcium and high phosphorous may predispose ewes to hypocalcaemia. Others factors that predispose a ewe to hypocalcaemia include sudden changes in feed type, sudden increases in green feed, yarding or handling and access to sorrel or other oxalate-rich plants.
Ewes initially stagger and appear hyperactive and then become cast and comatose. They will often bloat and regurgitate their stomach contents. Left untreated, ewes with hypocalcaemia can die within 24 hours.
Calcium borogluconate administered under the skin will result in a rapid improvement (15-30 minutes) and the ewes will get up and start grazing. Low blood magnesium is also common in ewes with hypocalcaemia so treatment with magnesium sulphate and glucose may be warranted.
Avoid stressful situations in late pregnancy and early lactation, slowly introduce sheep to green feed crops and give calcium supplements to grain-fed animals, especially during drought conditions when pasture is not available.
Sheep have virtually no readily-metabolisable reserves of magnesium so are reliant on constant dietary intake. Magnesium requirements go up during lactation. The absorption of magnesium is influenced by a number of factors including decreased saliva production, increased potassium levels (due to the use of high rates of potassic fertiliser) and decreased sodium in the rumen.
For example, changing a sheep’s diet from hay to lush pasture can cause hypomagnesaemia simply because there is a reduction in the amount of chewing and salivating needed to digest the feed.
But the most common cause of hypomagnesaemia is inadequate feeding relative to energy demand.
Ewes affected with hypomagnesaemia are typically found dead. However, in the early stages, ewes will appear dull, stop eating and if disturbed, may display twitching and muscle tremors.
In later stages, the ewe will be collapsed with her head thrown back, suffer sever convulsions while paddling her legs and froth at the mouth.
Early treatment includes the administration of magnesium sulphate and calcium borogluconate under the skin. If the sheep responds, then she may also be drenched with magnesium oxide.
Other sheep in the flock may also be suffering sub-clinically with low magnesium levels so it is advisable to administer magnesium oxide at 10 grams/sheep/day.
Increasing the amount of hay the flock consumes can also help, as this increases salivation and the sodium/potassium ratio in the rumen.
To prevent further cases in subsequent seasons, attention should be paid to increasing the intake of dietary magnesium, especially in older, multiple-bearing ewes.
Magnesium can be given to sheep as either calcinated magnesite (in powder form) or Causmag which can be sprayed onto hay – although it can affect palatability. Pasture can be tested for magnesium content and fertiliser applications adjusted accordingly.
For information about metabolic diseases in sheep, see our Metabolic disease in ewes factsheet (PDF, 50KB).