Ewes have a different pattern of calcium demand than cows.
ON many tablelands farms ewes and cows are either close to or have lambed or calved. We all know that the developing foetus needs calcium to build bones and that milk is rich in calcium.
So should we supplement late pregnant and lactating livestock with calcium to help them through this time of high demand?
Unfortunately, this is not a simple question. Dairy researchers decades ago showed that a high calcium ration prior to calving resulted in more cases of hypocalcaemia (milk fever) than if cows were fed a low calcium ration pre-calving.
Cattle and other animals have mechanisms to increase calcium supply by absorbing more through their intestines and kidneys and by pulling it from their reserves in the skeleton. However, these mechanisms take about 4-6 weeks to switch on.
These mechanisms are encouraged when cows are fed a low calcium ration whereas on a high calcium ration, the cow’s metabolism recognises no need to be ready to increase calcium supply. Therefore, cows not adjusted to extracting calcium efficiently from feed and bones are caught short and collapse with milk fever.
This also occurs in sheep but ewes have a different pattern of calcium demand than cows.
Cows face a predictable massive increase in calcium demand close to calving as the udder fills with milk. This is when cows usually suffer from milk fever. However, ewes face a bigger calcium demand well before lambing, as they need calcium to build the new bones of multiple foetuses over a shorter gestation.
This means that ewes, and especially mature multiple bearing ewes are in a precarious state for calcium from about six weeks before lambing until six weeks after lambing.
Hypocalcaemia (milk fever) is rare in beef cows although we sometimes see it in association with low magnesium levels in grass tetany. So I don’t think cows need calcium supplementation prior to calving or during lactation except under three circumstances.
Calcium may help prevent grass tetany so the addition of lime to a magnesium supplement is warranted. Secondly, cows on grazing cereals can suffer hypocalcaemia and grass tetany and should be supplemented with lime, salt and magnesium oxide. Thirdly, as cereal grains are low in calcium, cattle should be supplemented during periods of prolonged grain feeding.
We most commonly see hypocalcaemia in ewes if they are held off feed close to lambing. Producers who shear or crutch pre-lambing always run this risk (plus the risk of pregnancy toxaemia) and therefore need to move heavily pregnant sheep in and out of yards as efficiently as possible. Farmers should also have flow packs of calcium and energy on hand for emergencies.
Otherwise, we rarely see hypocalcaemia in ewes leading me to consider that in general we don’t need to supplement pregnant and lactating ewes with calcium. As with cattle, some exceptions apply. Grazing cereals (especially grazing wheats) are low in sodium, magnesium and sometimes calcium. Pregnant or lactating ewes on cereal crops should be supplemented, as should sheep fed grain for prolonged periods.
If it is your practice to supplement ewes with calcium, I advise that you should not do this in early pregnancy (in ewes) and during pregnancy at all for cows to enable the bodily mechanism to switch on to absorbing more calcium from feed and bones. However, late pregnant and lactating ewes and lactating cows may benefit from calcium supplementation.
Finally, it is not always easy to tell whether ewes are suffering from pregnancy toxaemia compared to hypocalcaemia or some other condition close to lambing. Pregnancy toxaemia only occurs before lambing whereas milk fever can occur before lambing (especially if ewes are held off feed) or during lactation.
Ewes with pregnancy toxaemia remain on their feet for a day or two but seem blind and vacant. Ewes with milk fever, at least in the early stages of the disease remain bright and alert but collapse and are too weak to stand.
In advanced cases, pregnancy toxaemia can resemble milk fever but can also look similar to ewes sick from other conditions such as mastitis or bearing a dead lamb. As the management of these conditions is quite different, a diagnosis is important.
