There have been more reports of grass tetany in ewes and cows in recent days. The significant change in weather, with showers, heavy rainfall and a sharp variation from daytime to nighttime temperatures, is the likely trigger.

Animals at the greatest risk are aged and young ewes suckling strong multiple lambs and facing a nutritional challenge.

Animals grazing reseeded ground which has received a high nitrogen input are also high-risk and particular care should be taken over the next few days.

The disease is caused by low blood magnesium levels and is most common when a ewe's system is under considerable pressure to produce milk.

Animals have a poor ability to store magnesium and must ingest sufficient levels on a daily basis to prevent a deficiency.

Pre-empting problems

Prevention centres on ensuring animals achieve their daily magnesium intake. This can be achieved through supplementing a ewe's intake of magnesium, while reducing the rate of forage digestion will also help.

Supplementation can take many forms, including offering ewes access to high-magnesium lick buckets, feeding concentrates containing magnesium, administering magnesium bullets or the addition of magnesium to water.

The latter is less reliable in periods of heavy rainfall, while another option of dusting pasture with calcined magnesite is also less viable.

Supplementation should be introduced two to three days in advance of the high-risk period to ensure that blood magnesium levels are adequate and can withstand challenges that may present in the following days.

Grass supplies are sufficient, in most cases, to sustain a ewe's nutritional appetite, but it may be worth feeding concentrates for a couple of days in cases where ewes are coming from a period of nutritional stress and being transferred on to lush grass.

The risk is particularly high if animals are grazing swards which have received slurry or are high in P and K.

Symptoms and treatment

The onset of disease is rapid, with ewes often found dead in the morning or afternoon without exhibiting any clinical symptoms.

Cases sometimes occur after ewes and lambs are moved from bare pasture to lush leafy swards with high nitrogen and potassium levels.

Characteristic signs include animals isolating themselves from the flock, muscle tremors and animals stretched out and kicking due to the muscle tremors.

Ewes suckling multiple lambs and in poorer body condition or overfat are also at a higher risk due to higher nutritional stress.

The risk is also heightened where ewes are reaching peak milk yield and possibly under the greatest nutritional stress.

As the onset of disease is so rapid, prevention is the best cure. Where animals are identified, swift treatment by administering magnesium is essential to improve the chances of a successful recovery.