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Research Note

DCAD Detail to Help Douse Heat Stress

Hot, humid weather day and night can aggravate effects on cows experiencing changes in forages and other feeding and management factors. There’s greater risk of milk fat decline (MFD).

Tweaking ration formulation for DCAD (dietary cation anion difference) can help mitigate MFD. The cation potassium (K) is critical and its form in the ration affects outcomes.

Rumen imbalance

Factors that may cause MFD include low rumen pH, too much saturated fat, too much grain, improper feeding, overcrowding, etc. Physiological and behavioral changes can lead to suboptimal rumen conditions, even sub-acute rumen acidosis (SARA). Then rumen microorganisms over-produce trans fatty acids, particularly conjugated linoleic acids (CLA), as well as lipopolysaccharide (LPS), and so inhibit milk fat synthesis in the mammary gland.

Clemson Emeritus Professor Tom Jenkins points out that there’s a high correlation between MFD and a rumen that is out of balance in terms of biohydrogenation (BH) intermediates.

Maintaining rumen balance can be more challenging under heat stress conditions, especially in the transition period.

DCAD, rumen pH, K balance

Dr. Jenkins reminds us that the charge balance of the major cations (K and Na) and anions (Cl and S) determines the diet’s DCAD, which impacts blood acid-base balance. As a rule, we want negative DCAD prepartum and increasingly positive DCAD postpartum to maintain cow health and production during lactation. 

Potassium (K) is key. It supports many other vital functions in addition to maintaining the blood acid-base balance through DCAD. First, the cow stores little K and she requires it more than other mineral cations. While she loses it naturally through the milk, there is a greater risk of negative K during heat stress as she sweats it out. 

Avoiding negative K balance during lactation is especially important because, besides upsetting milk synthesis, it affects the concentration of milk components, including milk fat.

Which K source buffer?

Considering the advantages of a K source rumen buffer, what are the options?

  • K chloride (DCAD-neutral with no effect on rumen pH and little effect on rumen fermentation and biohydrogenation)
  • K bicarbonate (offers lower K content)
  • K carbonate (available in two forms, however…)

Anhydrous K carbonate generates excessive heat mixed with water, whereas K carbonate sesquihydrate (K2CO3 – 1.5 H2O) offers good pH and DCAD increase.

The sesquihydrate form costs more, but offers multiple advantages in adjusting DCAD to help mitigate MFD.

Questions?

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