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A project funded by AWI is looking at whether more widespread supplementing of lambing ewes’ diets with calcium and magnesium can improve lamb survival.
Professor Michael Friend is the principal researcher on the project at the Graham Centre for Agricultural Innovation at Charles Sturt University.
“We know when a ewe goes down with metabolic disorders such as hypocalcaemia (milk fever) or hypomagnesemia (grass tetany) the effects are very obvious,” he said.
“But what this project is more interested in is subclinical metabolic disorders, which is when there are no visual signs that the ewe is in trouble but her magnesium and calcium levels are actually below requirement.”
The researchers began the project by conducting a comprehensive literature review which indicated that, while there were strong indications that magnesium and calcium can play an important role in lamb survival, there was a knowledge gap about when the ewe shows no visible sign of metabolic disorders (a subclinical effect).
EVIDENCE OF SUBCLINICAL METABOLIC DISORDERS IN LAMBING EWES
The researchers then, in 2016, undertook a study of predominantly twin bearing Merino ewes from 15 flocks from across southern Australia.
They tested the calcium and magnesium status of the ewes and found that even in mobs that do not show signs of metabolic disorders, a large number of ewes across the flocks were deficient in calcium and magnesium.
“These farms had the type of pastures that you wouldn't ordinarily think would have low levels of calcium or magnesium,” Professor Friend said.
“However, once the animals had been grazing on the pasture pre-lambing, we took blood and urine samples that indicated ewes in a majority in the flocks had calcium levels that were deficient, and to a lesser extent magnesium as well.
“It certainly showed that, despite the fact that the pastures were telling us that things are okay (the calcium and magnesium levels in pasture tested as adequate), something metabolically was happening in the ewes.
“Interestingly there was a strong association between high phosphorus levels in the pasture and lower calcium levels in the ewes, so on farms that had higher levels of phosphorus fertilization there was an indication that there might be more of a problem.”
MINERAL SUPPLEMENTS IMPROVE EWE AND LAMB HEALTH
PhD student Forough Ataollahi is part of the research team and she conducted a controlled study to evaluate the effect of calcium and magnesium supplements on twin bearing ewes and their lambs.
“The results showed that feeding calcium and magnesium supplements had a beneficial effect on the immune systems, energy profiles and mineral profiles of both the ewes and lambs,” she concluded.
“Ewes supplemented with calcium and magnesium regulated their energy more efficiently than ewes not supplemented, which has many implications for the prevention of pregnancy toxaemia (twin-lamb disease) and the improvement of ewes’ reproductive performance.
“Lambs of ewes supplemented with minerals had better weight gain at one month of age and they had a better ability to fight against pathogens compared to lambs from non-supplemented ewes.
“Moreover we observed that, while ewes underwent a period of immune suppression at the time of lambing (which is normal), supplementation improved the immune system of the lambs at this time.”
WHAT ABOUT LAMB SURVIVAL?
Professor Friend said Forough’s work showed that calcium and magnesium supplementation is likely to put the late pregnant ewes into a better metabolic state and this is likely to lead to some improvements in lamb survival.
“However her study was a relatively small trial with about 40 sheep and we wouldn’t expect to see differences in lamb mortality in such a small trial, so we needed to test it on a larger scale,” he said.
Therefore, further similar research to monitor lamb survival on 400 ewes from each of five of the farms in the 2016 study was undertaken – the results are currently being analysed.
“We know that there are good rational reasons why calcium and magnesium supplementation should improve lamb survival, but we'd like to conclusively prove it,” he said.
ADVICE TO WOOLGROWERS
Professor Friend says the research indicates that, even in flocks that one wouldn’t think have any problems, many lambing ewes could be deficient in calcium and magnesium.
So he says that if woolgrowers are concerned about the calcium and magnesium status of their lambing ewes, they should offer them some supplement.
“The cheapest supplement is typically a loose lick of calcium carbonate (lime), magnesium oxide (Causmag) and salt. Salt is added as it improves not only the uptake of the magnesium but also the palatability of the supplement to the sheep.
“I recommend this cheap supplement option because we know it has some production benefits and the evidence is mounting that it is likely to have, particularly in some cases, a significant impact on lamb survival.”
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