Following the turnout of ewes to grass post-lambing, close attention must be paid to the health of the flock during what is an important time for lambs to thrive.
These lambs are reliant on their mothers, and the loss of a ewe will cause the problem of the farmer dealing with orphaned lambs.
According to Teagasc advisor, Damian Costello, one of the most common causes of death in ewes post turnout is hypomagnesaemia, or grass tetany, as it is more commonly known.
The disease is caused by low magnesium (Mg) levels in the blood and if not detected early and treated promptly, it is frequently fatal.
Costello has advised farmers to put prevention measures in place early, before they are presented with a case of grass tetany in their ewes.
Grass tetany in ewes
The main factors likely to trigger grass tetany in ewes include:
- Poor weather, in particular high rainfall periods, has a negative impact on both the utilisation and intake of available grass as well as a reduced capacity of the ewe to take up nutrients from the grass;
- The level of Mg potentially absorbed from forage is reduced in swards containing rapidly growing lush grass;
- Take care with fields recently reseeded along with areas receiving high levels of nitrogen (N) fertiliser and in particular high spring applications of potash (K).
Costello added that additional factors that cause stress to ewes including weather conditions, any underlying health issues, poor nutrition at peak lactation (four to six weeks post-lambing), is a time when ewes are particularly vulnerable, but animals do succumb to the disease outside this window also.
Symptoms and treatment
In many cases, the first symptom can be a dead ewe, but affected sheep that are still alive will be observed twitching, staggering or as the condition progresses lying on the ground kicking.
The Teagasc sheep specialist detailed that grass tetany treatment involves administering a subcutaneous injection of 100ml of a 25% Mg sulphate solution “as quickly as possible”.
For optimum absorption, Costello said the solution should be delivered at body temperature, splitting treatment across five to six different sites on the ewe’s body.
He added that success is dependent on the condition not having progressed too far before being treated.
Prevention measures
Costello detailed that sheep have no capacity to store magnesium in their body, meaning they need to ingest a continuous supply of the element.
During adverse weather and times of stress, the ewe’s ability to absorb Mg into the bloodstream can be halved – therefore, the recommended rate of supplementation for ewes is 3-5gMg/head/day.
The following are the main options to provide this:
- Supplementary feeding ewes at grass with a sheep ration or nut containing 1% or 10kg calcined magnesite (Cal Mag)/t of feed;
- Always ensure that rams are not fed concentrates containing Cal Mag due to the risk of them developing urinary calculi;
- High Mg lick buckets, usually containing either 10% or 15% Mg, are convenient where ewes are on a grass-only diet post turnout.
Costello advised farmers to use a product specific to sheep as the cattle version may contain levels of copper which would be unsafe for sheep.
It is important that there is free access to buckets or licks – generally three to four per grazing group should be provided.
On farms known as high risk for grass tetany, Costello said feeding 0.5kg concentrates/ewe/day for one to two days prior to and for the few days of adverse weather conditions, can complement lick buckets and further safeguard the flock.