After a dry autumn, farmers in many parts of the country will be tight for feed going into spring and this could put ewes at greater risk of developing metabolic diseases.
Pregnancy toxaemia, hypocalcaemia and hypomagnesia can cause significant ewe losses around lambing, particularly when ewes are under stress in bad weather or yarding events.
While the treatment for each of these conditions is different, they are all related to inadequate 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.
Treatment
Early treatment is critical and 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. Managing dehydration (either orally or intravenously) and maintaining appetite is important, so where possible, leave ewes with their flocks as this can encourage feeding.
Prevention
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 reserved 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.
Treatment
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.
Prevention
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.
Hypomagnesaemia
Sheep have virtually no bodily reserves of magnesium so are reliant on dietary intake of magnesium. 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 fertilizer) 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.
Treatment
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.
Prevention
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.
Find out more
For information about metabolic diseases in sheep, see our Metabolic diseases in ewes factsheet (PDF, 50KB).