Production hypocalcaemia: when high-performing ewes run short of calcium
Hypocalcaemia is often thought of as a ‘late-pregnancy problem’ triggered by yarding, transport, shearing, sudden feed changes, crutching or grain feeding without enough limestone for six weeks or more. But that is only part of the story...
Key take-home messages for woolgrowers
- Production hypocalcaemia is a reminder that high-performing ewes need high-level nutritional support.
- For Tasmanian woolgrowers, the priority is to look closely at ewe losses, especially in older twin-bearing mobs, and investigate patterns early.
- If ewes are going down around lambing, responding to calcium treatment, or dying unexpectedly on lush feed, hypocalcaemia should be on the list of possible causes.
Hypocalcaemia is often thought of as a ‘late-pregnancy problem’ triggered by yarding, transport, shearing, sudden feed changes, crutching or grain feeding without enough limestone for six weeks or more. Those risks still matter. But according to Dr Graham Lean, Agrivet Business Consulting, Tasmanian woolgrowers also need to be alert to another presentation — production hypocalcaemia in well-managed, high-performing ewe flocks grazing lush, productive pastures.
According to Graham, production hypocalcaemia is not a problem of poor feed or poor management.
“In many cases, production hypocalcaemia is showing up in well-managed, highly productive systems where ewes are in condition score 3–3.5, grazing highly digestible pastures and carrying a heavy production load,” he said.
"In fact, you could call it a disease of good management."
Why is it happening?
Calcium (Ca) is essential for muscle function, nerve function, milk production and the ewe’s ability to cope with the demands of late pregnancy and lactation. Traditionally, hypocalcaemia has been associated with ewes going down after a stress event, particularly during late pregnancy. However, Graham has identified and confirmed a different pattern during the past 15 years through blood testing and postmortems.
This newer pattern of hypocalcaemia is often seen in ewes that are:
- in ideal body condition (i.e. 3–3.5 or higher)
- grazing lush, high-quality pastures
- close to lambing, lambing or in early lactation
- older and carrying twins.
Graham explained that as breeders and commercial producers have selected for higher reproductive rates and faster post-weaning growth rates, the ewe’s requirement for calcium, particularly in twin-bearing mobs, is outstripping supply.
“In simple terms, the ewe’s calcium demand has gone up, but her ability to access calcium has not kept pace,” Graham said.
The pasture connection
It’s not just higher animal performance that is driving the challenge. Almost counterintuitively, some high-production pastures are reducing the amount of calcium the ewe can absorb or mobilise from her bones.
“We have analysed highly productive pastures that are testing high in phosphorus (P) and potassium,” Graham explained.
“This matters, because calcium, phosphorus, magnesium and potassium are closely linked in the ewe’s metabolism.”
Ideally, ruminant diets will have a calcium-to-phosphorus ratio (Ca:P) of about 2:1. However, according to Graham some pasture tests are coming back closer to 1:1, or even lower, due to high phosphorus levels. This can interfere with calcium uptake from the intestine.
High potassium can also interfere with magnesium supply. Magnesium is important because it helps calcium move across the intestine and also plays a role in calcium release from bone.
Many of these pastures also have a high dietary cation anion difference (DCAD) — acid base balance — which also reduces the ability of the bones to release calcium and magnesium.
A seasonal conundrum
As if that isn’t enough, low vitamin D levels across southern Australia during winter can further limit the ewe’s ability to mobilise calcium from her bones.
“Calcium does not operate in isolation,” Graham said. “You need to think about the whole mineral balance — calcium, phosphorus, magnesium, potassium and vitamin D — and how they all interact.
“That is why feed testing and veterinary investigation are so valuable when it comes to managing metabolic conditions such as hypocalcaemia."
Signs of concern
Hypocalcaemia can be sudden and serious. Affected ewes may go down and die if they are not treated quickly.
Possible warning signs include:
- ewes going and staying down before lambing, during lambing or in early lactation
- ewes that respond to calcium borogluconate treatment (e.g. a 4-in-1 flowpack)
- higher losses in older, twin-bearing mobs
- unexplained ewe deaths around lambing
- increased uterine prolapse in some affected flocks.
Graham recommended woolgrowers avoid assuming ewe losses are simply ‘one of those things’ at lambing.
“If the losses are occurring in a pattern — particularly in older twin-bearing ewes — it is worth investigating,” he said.
“The most useful information often comes from combining flock records, pasture testing, blood testing and postmortems.”
Local consulting veterinarian, Dr Bruce Jackson has seen high DCAD levels in some grass-dominant pastures and has associated low calcium levels with increased newborn lamb mortalities as well as ewe mortalities.
“Sometimes when I have carried out a postmortem on older ewes their skulls have been quite easy to split because they are so decalcified," he commented.
Diagnosis, not guesswork
It is important to get a diagnosis before treating affected animals. A firm diagnosis can be made with the support of a consulting veterinarian. Blood samples, postmortems and laboratory testing can help confirm whether hypocalcaemia is involved.
Wet chemistry feed testing can also help identify paddocks carrying a higher hypocalcaemia risk, especially where lush feed is being grazed by late-pregnant or lactating ewes.
Importantly, this syndrome does not occur in all high-production systems. The risk depends on the interaction between pasture mineral balance, ewe demand, ewe age, condition, lambing status, seasonal conditions and soil chemistry.
The final word
The message is clear: measure, test and seek advice early. In a high-performing flock, small mineral imbalances can have large consequences. Finding the risk before lambing is far better than treating affected ewes after the damage has been done.
Prevention and treatment of hypocalcaemia
Ewes that are down and suspected of having hypocalcaemia require immediate treatment under veterinary guidance. Calcium borogluconate (a component of a 4-in-1 flowpack) is commonly used, but the timing and correct administration are critical.
For prevention, discuss an appropriate mineral strategy with your veterinarian or animal health advisor. In higher-risk situations, this may include a waterproof anionic lick with high magnesium and calcium levels that includes a long-acting vitamin D component.
“Home-made licks can work but are rendered ineffective if they get wet. Commercial waterproof licks are usually more effective than home-made alternatives,” Graham noted.
“The aim is to treat all ewes, from maiden ewes to mature ewes, to prevent calcium decline before younger ewes age and become more likely to conceive and carry twins.
“It’s worth remembering any adult ewe that conceives and rears a single lamb this year, is still as likely as this year’s twin-bearing ewes to conceive twins the following season.”
Dr Bruce Jackson has had success with a 1:1:1 ratio of limestone, coarse magnesium product and iodised coarse salt as a loose licks.
Bruce encourages producers to add to the mix a small quantity of a high-vitamin D magnesium loose lick (e.g. half a cup to 10 kg of mix).
“To get around the problem of rainwater leaching out the magnesium and salt, we place the loose mix in tubs (typically cut down 20 L drench drums) inside an IBC and cut some flaps to allow the ewes to access the loose lick inside the IBC,” Bruce said.
“You can also buy feeders that hang on a fence and are easy to fill from the top to protect the mix from rain.”
Image source: Dr Bruce Jackson
More information
- MMFS Hypocalcaemia fact sheet
- AWI and MLA Resource guide for sheep reproduction
- Hypocalcaemia in sheep (Agriculture Victoria)
This article has been adapted from an article written by Dr Graham Lean. Reproduction of the article is encouraged and should be attributed as follows: This article was first published in the AWI Extension TAS Newsletter.
