Spring Calving and Lactation: Why Minerals Are So Important | North Queensland Registry
CATTLE are more susceptible to tetany than any other domestic animal, in part because ruminants are less efficient at absorbing magnesium than non-ruminants.
Among domestic ruminants, cattle are three times less able to absorb magnesium than sheep or goats. The reason cattle are more likely to be deficient in magnesium is that the primary site of absorption is in the rumen.
The body depends more on daily intake of magnesium than on body reserves. The circulating levels of magnesium in the system are greatly affected by daily food intake.
Fasting causes serum magnesium levels to drop rapidly. This is why transportation and bad weather can be triggers for the onset of tetany symptoms.
The chemical environment of the rumen environment is crucial for the absorption of magnesium in cattle. Magnesium is absorbed by active transport through the cell wall against an electrochemical gradient.
The additional potassium in the rumen increases the potential difference, thereby reducing the absorption of magnesium. On the other hand, the presence of sodium in the rumen decreases the potential difference, facilitating the absorption of magnesium.
So, in essence, sodium improves the absorption of magnesium while potassium blocks it.
Rumen pH is also important because the solubility of magnesium is highly pH dependent. Magnesium must be dissolved in the rumen contents to be absorbed. Magnesium is most soluble at a slightly acidic pH.
Too much nitrogen in the diet can negatively influence magnesium absorption by creating excess ammonia which in turn increases rumen pH and allows less magnesium to dissolve in rumen contents.
Colostrum contains up to three times more magnesium than “normal” milk, drastically increasing the need for magnesium during calving. However, even though “normal” milk is not a rich source of magnesium, the concentration is not influenced by the cow’s diet.
Lactation will continue to drain maternal reserves in the event of a diet deficient in magnesium or interference in absorption. On the other hand, an increased intake of magnesium does not increase the amount of magnesium present in milk.
Onset of tetany
The rate of occurrence depends on the degree of deficiency. Lactating cows may experience rapid decline while undernourished and non-lactating cattle (both sexes) may experience slower development of symptoms.
Symptoms include: extreme excitability, muscle twitching, frequent urination, grinding of teeth, a staggering, uncoordinated and stiff gait, and possibly collapse with convulsions with conventional “paddling”. Death usually follows quickly. Progression can be a matter of hours or can span several days.
Treatment and prevention
Animals showing symptoms should be treated immediately. Because calcium deficiency often accompanies magnesium deficiency, administration of both magnesium and calcium is a common treatment.
Prevention is best achieved with a combination of daily intake of a palatable supplement containing sufficient magnesium and proper management. From a management point of view, make sure the cattle are not losing too much weight or becoming malnourished. Also, don’t allow them to run out of hay or supplement.
– Toby Doak is a ruminant nutrition specialist at Alltech Lienert Australia.
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The story Spring Calving and Lactation: Why Minerals Are So Important first appeared on Queensland Country Life.