The discussion about the importance of proper prepartum dietary cation-anion difference (DCAD) levels often centers around cow health, and rightly so. It’s been repeatedly shown that lowering ration DCAD prior to calving helps stave off serious health challenges, including milk fever (clinical and subclinical), reduces incidence of displaced abomasum and retained placenta, and boosts immune function.
All of these improvements increase milk component production and reproductive performance in the ensuing lactation, too.
Meanwhile, increased start-up milk and higher overall milk production as a result of lowered prepartum DCAD levels sometimes get lost in the shuffle. But it should come as no surprise, since common sense says healthy cows get off to a better start and milk more.
It’s calcium’s fault
To set the stage, here’s a little more detail on why DCAD is so important.
As you well know, the onset of lactation causes a severe and rapid drain on blood calcium required to produce milk. If this blood calcium is not replaced as rapidly as it is reduced via bone calcium release (resorption) or intestinal absorption of calcium, cows will become hypocalcemic, and many develop clinical and subclinical milk fever.
Reducing DCAD to negative values at least three weeks prior to calving has been shown by many researchers to prevent this rapid decline in blood calcium at calving.
Failure to address blood calcium losses often leads to a cascade of negative results, especially as cows get older. For example:
- Research indicates that cows with clinical milk fever produce 14 percent less milk in the subsequent lactation.
- Productive life for these cows is reduced approximately 3.4 years when compared to cows that did not experience milk fever.
- Cows that recover from milk fever have an increased risk of ketosis, mastitis (especially coliform mastitis), dystocia, left displaced abomasum, retained placenta and milk fever in the subsequent lactation.
In addition, subclinical hypocalcemia, which may be as high as 66 percent for second-lactation and higher cows after calving, is a serious concern. Just as with clinical milk fever, subclinical low blood calcium often leads to low dry matter intake (DMI) after calving, dystocia, ketosis and retained placentas.
Meta-analysis results
A study from researchers in the U.S. and Australia further reinforces this concept. In work published in 2005, a meta-analysis focused on factors that affected milk fever. These factors were identified as:
- DCAD and the individual minerals that make up the equation (sodium, potassium, chloride and sulfur)
- Other minerals (calcium, phosphorus, magnesium)
- Parity
- Breed
- Days fed the transition diet
When researchers dug further into the results this past year, they found additional data that lent credence to the argument that healthy cows produce more milk.
In research shared at the 2014 American Dairy Science Association annual meeting in Kansas City, Missouri, this summer, this meta-analysis explored the milk production impact of feeding a negative DCAD diet for at least 21 days prepartum. The meta-analysis included 15 different studies and 34 comparisons.
The results were significant and showed:
- Cows fed a negative DCAD diet during this time frame produced 2.5 pounds per day more fat-corrected milk for at least the first 65 days in milk.
- This equates to a minimum of 163.5 pounds more milk per cow per lactation.
At $22 per hundredweight (cwt), that equals $36 per-cow gross profit. When multiplied by 1,000 cows, $36 becomes $36,000. Consider that when milk prices are not as high as $22 per cwt, the impact of start-up milk is of even greater economic importance to your bottom line.
Take-home message
The occurrence of clinical and subclinical hypocalcemia is a multifactorial disease that is not solely dependent on DCAD.
However, balancing prepartum rations for negative DCAD levels has a significant impact on blood calcium, incidence of disease and metabolic disorders, and postpartum milk production, especially when higher- fiber, reduced-starch diets are fed.
In trials that have measured postpartum milk production, cows in second lactation or higher produce more milk after being fed a prepartum diet with a negative DCAD, whether milk fever occurred or not.
Ultimately, it is in your best interest to incorporate negative DCAD into prepartum diets for at least 21 days before calving. The rewards – in improved cow health, improved milk production response and resulting financial performance – are worth the investment.
For the most effective DCAD formulation, dietary sodium and potassium should be reduced as much as practically possible before adding supplemental anions. In order to avoid possible adverse effects of supplemental anions on dry matter intake while still achieving mild systemic acidosis, a DCAD of -8 to -12 mEq per 100 g is suggested. PD
References omitted due to space but are available upon request. Click here to email an editor.
Elliot Block
Senior Manager of Technology
Arm & Hammer Animal Nutrition
