Why early-lactation cows may need a higher DCAD

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During the olympic games this summer, the subject of lactic acid would occasionally come up whenever a runner or a swimmer suddenly fell behind. Athletes are known to “hit the wall” when too much lactic acid builds up in their blood.

The same analogy holds true for high-performing dairy cows. When cows are milking hard, they expend a lot of energy. And, that can lead to an acid buildup, which inhibits performance.

That is part of the reason why lactating cows — and early-lactation cows in particular — may need more potassium in the diet, thus creating a higher dietary cation-anion difference (DCAD). A higher DCAD will help neutralize the acid that builds up in the blood of these animals.

Consider feeding your early-lactation cows higher DCAD levels than what you’re feeding to mid-lactation or late-lactation cows.  

Still speculative

Most of the research on DCAD has been done on cows in mid- to late-lactation. Until recently, no one looked at early-lactation cows. In a paper to the 2005 Tri-State Nutrition Conference, Michigan State University dairy scientist Dave Beede noted “there are few reports of experiments with very high-yielding and (or) cows in the first trimester of lactation; such studies under these circumstances would be useful.”

Since that time, a couple of studies have looked at early-lactation cows. This past summer, at the American Dairy Science Association annual meeting, researchers from Washington State University said early-lactation cows had higher milk production, milk fat percent and feed efficiency when fed a diet of 42 milliequivalents (meq) compared to one of approximately 25 meq/100 g of DM. Cows fed the higher-DCAD diet yielded an additional 3.3 pounds of milk (or 8.58 pounds of 3.5-percent fat-corrected milk) per day.

The only difference between the two diets was the inclusion of potassium carbonate. 

Early-lactation cows may need a higher DCAD level than mid-lactation cows, points out Joe Harrison, dairy scientist at Washington State University, because they have relatively high milk production in relation to feed intake, and there are a lot of things going on in these cows metabolically.

Much of the speculation on higher DCAD for early-lactation cows has to do with potassium. (Potassium is a cation, so adding more of it contributes to a higher DCAD level.)

Potassium’s role

Potassium is important for several reasons. It appears to play an important role in insulin production and protein metabolism. It also helps control “cell pumping” so that the mammary secretory cells can take in nutrients and produce the energy needed for milk production and other useful functions.

High-producing cows lose potassium through milking and other everyday activities, so it must be replenished through the diet.  

The need is particularly acute for early-lactation cows, since they are often operating on an energy deficit. Cows in an energy-deficit will mobilize fat for energy, but fat has very little potassium, points out Ron Kincaid, animal scientist at Washington State University. “Hence, if fat is being mobilized to support milk, then added dietary (potassium) is needed during this energy-deficit time period,” he adds.

Neutralize acid buildup

As mentioned earlier, acid can build up in the blood of high-producing dairy cows.

Elliot Block, senior manager of technology at Arm & Hammer Animal Nutrition, points out that lactation is an acid-producing function:

  • High activity in the mammary and liver cells leads to increased respiration and depletion of blood buffers.
  • Non-esterified fatty acids in the blood increase.
  • Keto acids in the blood increase.

In an experiment a few years ago, Block and researchers from the University of Illinois found that blood pH was higher (or less acidic) among early-lactation cows when fed a diet of 47 meq instead of   - 3 meq or 22 meq (at the same levels of crude protein). Higher blood pH, higher blood bicarbonate and decreased net acid excretion suggested that the acid-base status of the cows improved with increasing DCAD, the researchers reported in the July 2007 edition of the Journal of Dairy Science.

That particular study also found significant increases in dry matter intake and fat-corrected milk production with higher DCAD levels among early-lactation cows. For example, 4-percent fat-corrected milk was 7.3 pounds per day higher at a DCAD of 47 meq compared to 22 meq (both at 16 percent crude protein).

Block says the optimal DCAD for early-lactation cows may be in range of 35 meq to 45 meq.

Certainly, the research bears watching. The last thing you need is to have your early-lactation cows “hit the wall” at a time when they should be gearing up and producing lots of milk.

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