Saturday, March 30, 2024

Managing calcium deficiency

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All farmers will recognise a downer cow by the symptoms presented and they know the disease is caused by low calcium in the blood during stress.  It is commonly called milk fever. 
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What farmers won’t always recognise is cows with clinical symptoms are just a small part of a much bigger issue. 

That is why most researchers use terminology such as hypocalcemia because the broader term better conveys the true issue of calcium deficiency and that the disease takes many forms and affects many processes critical to early lactation.

For every downer cow there will be many more cases where cows stay on their feet but suffer the wider effects of the deficiency. They commonly have calving problems, metritis, retained fetal membranes, mastitis, poor immunity, poor conception and the list goes on. Few are as dramatic as a downer cow yet are equally important.

Most feeds supply more than adequate calcium yet it is among the most poorly absorbed elements. The body controls calcium uptake very tightly because an imbalance can lead to serious complications. That is done through the release of hormones, particularly parathyroid hormone and vitamin D and calcium storage is controlled by another hormone, calcitonin. The body’s hormonal system responds quickly to manipulate the available calcium based on demand. This system works really well provided the diet is right and the cow has not been subject to longer-term deficiencies and is not under or over conditioned because such cows are not as good metabolically at regulating the hormones.

On New Zealand farms our high reliance on large amounts of pasture during early lactation presents the biggest challenge for calcium management. 

Pasture supplies very high levels of potassium, normally more than 3%, when the cow’s nutritional requirement is about 1.1%. The large over-abundance of potassium doesn’t just compete with calcium for uptake, it also seriously affects the acid/alkaline balance of the blood. Increased pH in the blood interferes with the release of the hormones required to control calcium balance. High blood pH effectively stops the release of parathyroid hormone.

Over the years farmers have used many strategies to treat milk fever with varying levels of success. Many of the common one have shown very inconsistent results and methods that prove successful in one situation can often fall totally on their face in another.

Here is a run-down on common methods used to combat calcium deficiency in dairy cows:

• Reducing the levels of calcium in the diet. This is probably the most common method used over the last 40 years. It can work well as long as no pasture is fed but to work well pasture must be almost totally removed and replaced with a feed that has low calcium, potassium and sodium. Maize silage is one of the few feeds that fits the criteria and where large quantities of maize silage have been added to the diet this approach has worked well. It is, however, important the cows are very well supplemented with extra calcium during lactation otherwise the induced calcium deficit can have serious consequences.

• Injectable calcium or calcium boroglucinate has always been used as the last line of defence for this disease. This formulation floods the bloodstream with readily available calcium along with boron, which further increases calcium absorption. In desperation some have adopted this method as their primary means of control, simply treating the cows showing clinical symptoms, giving either intravenously or under the skin. This approach never works satisfactorily. While a bottle of calcium boroglucinate usually gets a cow back on her feet she will often go down again later. In many cases when she does seem to recover she will remain sub-clinically calcium deficient throughout much of the early lactation. Another issue is many sub-clinical cases of calcium deficiency are not picked up. It can be common to have anywhere from 25% to more than 50% of cows suffering sub-clinical calcium deficiency at calving and well into early lactation. As well as producing less milk these cows will be more susceptible to mastitis and uterine infections as well as poor reproductive outcomes. Interestingly, a number of scientists report injecting calcium solutions can seriously interfere with a cow’s ability to balance her calcium status longer-term, struggling to regulate and control the calcium metabolically in subsequent seasons.

• Flooding the body with calcium in the form of lime flour is another option that has gained some traction over recent years, sometimes with large quantities of vitamin D. This approach can work on some farms, however, success is very reliant on keeping the levels of ongoing calcium supplementation very high. That can be challenging. If the levels fall below an often poorly defined point the cow will then be metabolically incapable of activating any of the calcium reserves in her body.

The high levels of lime flour have the added disadvantage of buffering the blood pH to the point where parathyroid hormone release can no longer be activated. This approach means a farmer relies solely on the body’s ability to absorb its calcium from the diet yet, because of the pH buffering of the blood, the body is doing everything it can to shut down the absorption of calcium and could be triggering calcium storage through calcitonin release.

So, is there a better option available? 

Over the last five years Agvance Nutrition has worked intensively to develop and apply its own specific version of the anionic (negative DCAD) diet designed to be practical in a NZ dairy system. We believe, based on the many hundreds of farms we formulate these blends for, we have developed a combination of the DCAD salts that suit NZ conditions and provide a better option to combat calcium deficiency.

During this time we have learned how this system can be applied to local conditions where pasture normally makes up at least part of the diet. We have also formulated ways that better match requirements based on the make-up of the diet and that target specific deficiencies more prevalent under different crop feeding situations. The poor palatability of these salts is often mentioned in the literature and removing this issue has also been given much time and effort. It is no good making up a good blend of minerals if the cows won’t eat it.

Chris Balemi is the managing director of Agvance Nutrition. 

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