Ration dietary cation-anion difference, or DCAD, and dairy cow health and performance are closely intertwined. Still, the concept of DCAD isn’t always well understood, which can lead to dairies failing to obtain the best possible results from their nutrition program.
To help you avoid this pitfall, use the following DCAD details to enhance your understanding of it. Then work with your nutrition management team to ensure that you employ DCAD to its fullest extent on your operation to improve overall cow health and productivity.
DCAD definition
DCAD is calculated by adding together the milliequivalents (or charges) of dietary cations and subtracting the sum of the milliequivalents (or charges) of dietary anions. The equation looks like this:
Milliequivalents (Sodium + Potassium) – (Chloride + Sulfur)/100g or kg of DM
Some equations do not include sulfur, so it is important to know which equation was used to calculate DCAD when evaluating nutrition research and product materials.
DCAD does not necessarily impact the ration directly, but it has strong influences on the cow. When rations are properly formulated for DCAD, they can prevent or decrease incidence of metabolic disorders during the transition period, support milk and milk component production (especially milk fat production), help mitigate the effects of heat stress, increase feed intake and more.
Ration DCAD levels should not remain the same for the entire lactation.
Prepartum DCAD
Pre-calving is when rations should be balanced for negative DCAD. As the DCAD becomes more negative, the cow is forced into a mild acidosis, which is appropriate at certain stages of her life, especially the three weeks prior to calving.
Reducing DCAD to negative values beginning at least three weeks prior to calving has been shown to prevent a rapid decline in blood calcium at calving and improve postpartum health and performance outcomes.
That’s because a negative DCAD ration helps mobilize calcium from bones and prevent clinical and subclinical milk fever, as well as maintains immune function. Clinical and subclinical hypocalcaemia often lead to low dry matter intake after calving, dystocia, ketosis and retained placentas.
A ration DCAD of -8 to -12 meq/100g ration dry matter is recommended during this time to prevent or decrease the occurrence of these health challenges.
A 2014 study found that cows fed a negative DCAD diet pre-calving produced 2.5 pounds per day more fat-corrected milk for at least the first 65 days in milk.
Postpartum DCAD
After calving, ration DCAD should be positive. As DCAD becomes more positive, the cow develops more blood buffering capacity, which is desirable in fresh and high-producing cows.
Positive ration DCAD is needed postpartum when the cow is producing a significant amount of metabolic acids (high milk production, fat mobilization and increased respiration increase blood acid load). The more milk production you expect, the higher the ration DCAD should be.
Recommendations for postpartum DCAD levels are +35 to +45 meq/100g ration dry matter for high producing cows, +30 to +35 for mid-lactation cows producing less than 85 pounds of milk and +25 to +30 for late-lactation cows. Research shows that higher DCAD also optimizes milk and component production, as well as feed efficiency.
DCAD impacts milk fat production
During lactation, keeping rumen pH at a higher level, increasing ration DCAD and delivering high-quality potassium results in:
- Rapid increases in milk fat percentage and volume (fat corrected milk) compared with improper ration inclusion levels
- Corrected potassium imbalances that occur early post-calving
- Mitigated effects of rumen acidosis in the short and long term
- Improved dry matter consumption postpartum
Monitor DCAD levels
Lastly, keep in mind that seasonality and climate can affect ingredient DCAD levels, and forages and feedstuffs in the ration change. Therefore, ration DCAD levels do not remain the same either.
Regularly test forages and commodity feedstuffs by wet chemistry analysis (i.e., not by NIR), especially for mineral content, so you know ingredient DCAD levels and can adjust rations as needed based on your nutrition objectives for pre- and post-fresh diets.
Also note that ration DCAD cannot be consistently adjusted through forages alone. You must include research-proven, consistent, palatable feed ingredients in diets to accomplish ration DCAD goals. PD
References omitted but are available upon request. Click here to email an editor.
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Elliot Block
- Research Fellow
- Arm & Hammer Animal Nutrition
