The cost associated with a case of milk fever — whether it rises to clinical level or not — can be upward of $150. That’s plenty incentive to follow the time-tested strategy of feeding prefresh cows a dietary cation-anion difference (DCAD) diet, but like all protocols, this one’s susceptible to drift. Additionally, research over the years has indicated that when it comes to DCAD, details matter: According to a recent University of Wisconsin dairy extension article, DCAD diets bring other benefits to the table, such as reduced risk of retained placenta and metritis. If it’s implemented for heifers before freshening, studies have associated the DCAD diet with reduced postcalving uterine disease instances, another check in the “pros” column. But crucially, the authors noted that farmers who feed a DCAD diet to cows during the entire dry period (rather than restricting it to the prefresh period) run the risk of reduced milk production. Striking just the right balance in the window of time can make all the difference, they wrote.

Reviewing the rudiments

DCAD is a matter of equilibrium through and through: The calculation is used to find the sweet spot between positively and negatively charged ions in the diet, offering producers the opportunity heighten calcium availability through feeding anionic minerals — those that trigger two important mechanisms. Minerals such as chloride and sulfur will lower blood pH, which boosts bone and kidney response to parathyroid hormone (PTH). This hormone stimulates release of calcium from bone stores and triggers the digestive tract (via signals from the kidneys) to augment dietary calcium absorption. At the same time, urine pH goes up, which spurs the kidneys to flush more calcium through urine — a response that the authors note may seem counterintuitive to the goal of getting more calcium but in reality is another signal for bones to release more of the mineral into the bloodstream.

Refining the realities

Implementing a DCAD diet for prefresh cows involves more than just finding the right balance between anions and cations. The article offers some practical considerations for prefresh cow success:

Palatability – To avoid a potential dry matter intake (DMI) dip, the authors recommend finding a DCAD product that your cows will accept. A workaround is to add the DCAD product to a total mixed ration (TMR) instead.

Urine pH – Ideally, a DCAD diet should yield urine pH of 5.8 to 6.8, and the only way to make sure you’re in the pocket is through consistent monitoring. It takes about 48 hours from implementation of the DCAD diet for urine pH levels to reach that zone, so allow for that cushion and then implement regular testing.

Forage mineral levels – To get accurate readings, request a wet chemistry analysis with DCAD mineral package for your forage samples. This deep-dive testing will offer you the most accurate results; once you know the baseline of what you’re feeding your prefresh cows, you can better adjust the DCAD additions to their diet.

Stressors – The authors recommend overall stress mitigation to ensure that carefully balanced DCAD mix is getting to the cows. Limiting pen moves and overcrowding, as well as addressing environmental stressors such as cold and heat will help. As always, access to fresh and plentiful water are key factors in reducing stress potential.

While DCAD diets have been a conventional option for reducing the risk of milk fever, the authors mentioned there’s a newer option: Supplementing the dry period at 30 days or less to calving with zeolite A, a molecule that binds well to phosphorus and triggers bone-stored calcium release in the form of calcium phosphate molecules. Details on emerging research and recommendations can be found here.

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