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Why did my DCAD program fail?

Tim Brown for Progressive Dairy Published on 15 October 2019
Cows at feedbunk

Feeding a negative DCAD diet works. Science and on-farm application have proven time and again that feeding negative DCAD diets to pre-fresh cows prevents milk fever and helps minimize other common postpartum problems.

So why then do some producers report that negative DCAD failed on their farm? I have had opportunities to work with farms struggling to achieve the beneficial results they were looking for from negative DCAD diets. And the majority of the time, the problem can be traced to one of two things – failure to acidify cows or insufficient bioavailable magnesium in the diet.

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First, let’s define DCAD failure. Most would agree DCAD failure means not seeing a decrease in the incidence of clinical milk fever. Failure could also be defined as having an uptick in milk fevers and other common postpartum problems after having seen beneficial results from a negative DCAD diet. Producers often express a feeling of “something is not right; the cows are sluggish.” Both would be correct, but generally it is not the anionic supplement or salt used that is to blame. Something is not right with how the negative DCAD diet is being managed.

Urine pH

Oftentimes when a producer calls about DCAD failure, the problem is that the cows are not metabolically acidified. A slight metabolic acidosis restores tissue sensitivity to parathyroid hormone (PTH) and allows calcium mobilization from bones to proceed. New research shows that to receive beneficial results from feeding negative DCAD diets, the average urine pH of pre-fresh cows must be 7.5 or less. (Normal urine pH is 8.0.)

The first question I ask is, “Have you checked urine pH?” Many times the answer is no, and urine pH tests show that the average urine pH of pre-fresh cows is 8.0 or higher. The cows are not metabolically acidified. Adding a little more anionic supplement and rechecking urine pH can quickly eliminate the problem. Cows must be metabolically acidified (7.5 or lower) to receive noticeable benefits from negative DCAD diets. Once the cows are metabolically acidified, then, if you suspect DCAD drift from a change in ingredients, you can test minerals and reformulate the diet if needed.

Always use urine pH test strips that you have verified as accurate in the range being tested. Research conducted at Michigan State University in 2015 showed that many pH test strips are not accurate in cow urine. Nine brands were tested in cow urine. Only one brand of pH strip, pHion Balance, was suitably accurate in the pH range of 5.68-7.76. It is not uncommon to find a difference of one full pH unit between brands of pH test strips.

Magnesium

Magnesium plays two important roles in negative DCAD diets. Magnesium helps block absorption of some potassium in the rumen. It also is needed for metabolic signaling to occur between endocrine mechanisms and the bones to instruct them to release calcium to improve calcium homeostasis.

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Unlike other divalent minerals, magnesium is absorbed in the rumen, not the small intestine. That means it must be very soluble (bioavailable). Magnesium chloride and magnesium sulphate are very soluble and both work well in pre-fresh diets. But magnesium oxide, which is cheaper and more concentrated, often lacks solubility. Cows can be perfectly acidified, but if they lack adequate magnesium in the diet, calcium mobilization from the bones will not occur because metabolic signaling was impaired. Pre-fresh cows need a minimum of 0.4% of bioavailable magnesium in the diet.

When troubleshooting a problem, first check if cows are properly acidified. Next, check the amount and type of magnesium in the diet, or if your premix supplier has changed the magnesium source used.

Other factors

While lack of metabolic acidification and insufficient soluble magnesium in the diet are the top two causes of DCAD failure, they are not the only ones. Sometimes, producers are doing these two things right and they still don’t see beneficial results, or after seeing noticeable improvements in cow health, they suddenly see an increase in transition-cow problems. In these cases, the answer is often found in cow or feeding management.

Anything that prevents all of the cows in the pre-fresh group from getting their fair share of the anionic supplement can have negative effects. Overcrowding of the pre-fresh pen, inadequate feed mixing and distribution, and too much time without feed all can negatively affect pre-fresh cows. A change in forage – new hay crop, different field, new bunker or bag of corn silage – can alter the total DCAD of the diet. If either urine pH or forage mineral analysis reveals a change in mineral composition of the forage, adjust the diet to return to your desired level of metabolic acidification.

Feeding a moderate negative DCAD diet to pre-fresh cows and getting beneficial results is not difficult. Lots of producers see beneficial results each and every day. But if problems do arise, start with the basics. Are the cows metabolically acidified with a urine pH of 7.5 or less? Are the cows receiving adequate magnesium that is bioavailable? Does my feeding management or cow management prevent cows from consuming enough anions?  end mark

PHOTO: Cattle at the feedbunk. Staff photo.

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Tim Brown
  • Tim Brown

  • Director of Technical Support
  • SoyChlor

References omitted but are available upon request. Click here to email an editor.

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