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Managing mineral nutrition when grazing cereal crops

  • By: Farm Tender "Prime"
  • Oct 13, 2017

Our Australian sheep flocks are showing increasing calcium deficiency issues. We’ve moved from running a primarily Merino based system carrying single lambs, to one of larger framed ewes, often well fed and carrying multiples. That puts additional nutritional pressure on the ewe, especially as gestation advances and during early lactation. In addition, we are keeping older ewes in our flocks, in response to lower ewe numbers and a desire to produce more lambs with good lamb prices.

Early sown cereal crops such as wheat, barley, triticale and oats, grow rapidly and fill the winter feed gap with quality feed, supporting weight gain and increased stocking rates.

However, cereal crops contain potassium (K) levels excess to stock needs, adequate magnesium (Mg), adequate to low sodium (Na), and calcium (Ca) levels are low for animals with high calcium demands (eg. twin bearing ewes). A high ratio of K:Na lowers the absorption of Mg and Ca across the rumen. Other important ratios between these cations affect the blood and urine pH, blood levels of Ca and the ability of the kidney to make vitamin D3 which assists in Ca uptake. Together these mineral balance ratios can point to the risk posed by cereal crops, and the need for calcium and magnesium supplements.

Calcium issues in sheep
Several of the diseases seen more frequently now with sheep grazing cereal crops, particularly pregnant ewes, relate in part or fully to these mineral imbalances including hypocalcaemia (milk fever, low Ca), dystocia or lazy lambers (difficulty birthing), pregnancy toxaemia (low energy), hypomagnesaemia (low Mg), and uterine prolapse. This is also true for Autumn lambers, when ewes have been fed a lot of cereal grain which is inherently low in calcium, and not enough limestone.

If there is interference with the absorption of nutrients (worms) or calcium metabolism (copper deficiency), lambs may suffer from osteomalacia (rickets or soft bones). Carotenes (vitamin A) in green feed can have an anti-vitamin D effect. Since UV irradiation form the sun is a precursor to Vitamin D synthesis, overcast weather means production will be lower, especially if grazing pastures with low Ca levels (oats).

Older ewes require higher levels of calcium from the diet as their bones are no longer as good at supplying calcium when required, and are at risk of osteoporosis and hypocalcaemia.

To manage calcium in pregnant ewes and lambs:

  * Avoid causing stress and taking sheep off feed for long periods – this includes mustering, transporting and yarding.
  * Provide hay or straw to encourage cud chewing, which aids in calcium absorption.
  * Supply a 1:1 limestone: salt mix when feeding sheep on grains. Even better, add limestone at 1.5% to grain to ensure all animals ingest the Ca.
  * When you put sheep onto growing winter cereals, introduce carefully and add Mg –> becomes a 2:2:1 Causmag (MgO): limestone: salt mix.
  * Don’t take Ca off ewes in late pregnancy – that is only for dairy cows.
  * Imprint lambs on lick feeders and mineral supplements before weaning so they take to the supplements quickly.
  * Monitor livestock daily and treat ewes that are staggering or down with an injection containing calcium borogluconate.