Weather conditions have been close to ideal in recent days for flocks that are currently lambing.

However, there is a significant drop in nighttime temperatures on the horizon, with Met Éireann forecasting temperatures dropping to as low as -2°C and widespread frost on Saturday night. It will be a similar situation on Sunday and leading into at least early next week.

Flock owners need to be mindful of a potential increased risk of grass tetany. The disease is caused by low blood magnesium levels and is most common in spring during early lactation when a ewe's system is under considerable pressure to produce milk.

Poor ability to store magnesium

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

The level of magnesium absorbed from forage is depressed by a number of factors, including high nitrogen fertilisation, rapidly growing swards, high potassium levels in the soil and the rapid transfer of leafy grass material through the animal's system.

It was particularly prevalent in 2019 where ewes were grazing reseeded swards during adverse weather.

A significant dip in temperatures from day to night could act as a trigger for tetany hitting

The disease is generally triggered when the above conditions combine with factors that put animals under stress such as a nutritional intake deficit, changes to their diet, difficult weather conditions or any other factor that unduly increases stress levels.

As mentioned above a significant dip in temperatures from day to night could act as a trigger for tetany hitting.

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.

Feeding concentrates during high-risk periods will help increase the dry matter of the diet and slow down the rate of digestion and, in turn, help increase absorption of magnesium.

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. Take note also that magnesium bullets or boluses typically have a short period of cover.

Supplementation should be introduced two to three days in advance of the high-risk period

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 out of sheds after a long housing period and being transferred onto 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 occurs 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

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 intravenous is essential to improve the chances of a successful recovery.