There are some practices that happen on a dairy farm that have proven themselves effective and are confirmed by literally hundreds of research papers. But it’s a healthy idea every once in a while to revisit these practices – first to validate that they still work and second to learn if anything is new.
Feeding a diet that’s negative for dietary cation-anion difference (DCAD) is one of these practices. It’s been around for decades and has proven that, when fed during a three-week transition period, it can protect cows from metabolic disorders. Chief among these disorders is milk fever.
DCAD defined
Remember that the most stressful part of a cow’s life is the weeks leading up to and after calving. Cows experience hormonal and energy changes which lead to a significant drop in dry matter intake, followed by and including a negative energy balance as the cow transitions to high production. This period is so important to the cow’s future health and performance that only the most trusted management practices should be implemented to help her get through this critical phase.
The close-up ration helps set the stage for optimum performance in the upcoming lactation. One tool that’s been proven time and again is feeding a ration with a negative dietary cation-anion balance (DCAD) during the transition period.
Achieving a diet that has a negative DCAD involves creating a ration where milliequivalents (meq) of dietary anions (chlorine and sulfur) outnumber cations (sodium and potassium). A diet with a negative DCAD of -8 to -12 meq per 100 grams mobilizes calcium transfer from the bone to the bloodstream to create a higher blood calcium and helps prevent clinical and subclinical metabolic disorders at calving.
Achieving a negative DCAD
In order to achieve a negative DCAD diet, a thorough analysis of ration ingredients needs to take place. Start by limiting ingredients high in sodium and potassium. Key ingredients to monitor are forages. Alfalfa hay and other forages can be high in potassium, so it’s important to have forages tested before considering them for a transition diet.
The practice of feeding anionic salts is a popular and effective way to achieve a negative DCAD diet for transition cows. These ingredients are generally high in either chlorine or sulfur, or both, and tip the DCAD balance in the diet toward the negative.
Feeding straight anionic salts can be a problem. Commercial ingredients that include anionic salts in a more palatable and digestible form have been popular. Many of these ingredients also promote rumen bacterial growth that supports rumen function and provides metabolizable protein. As the term suggests, metabolizable protein is the part of the protein actually absorbed by the cow in the small intestine, providing essential amino acids needed for milk production, tissue repair and overall health.
Is it working?
The most reliable way to know if the negative DCAD diet is working is to check urine pH levels in transition cows. One common myth about negative DCAD diets is that you have to check every cow every day. That’s not the case. If you’re just starting on a negative DCAD diet, check the urine pH after three days on a negative DCAD diet to check if you’re getting the right effect. Once a baseline has been established, select a representative sample, around 10%, of cows that have been on a negative DCAD diet for a few days. pH ranges should be between 6.0 and 6.8.
Remember that the goal of feeding a negative DCAD diet is not to achieve low urine pH. Instead, urine pH values are used to indicate that the negative DCAD ration is actually working. There’s no benefit to cows with extremely low pH urine.
What are benefits of a negative DCAD diet?
A 2019 meta-analysis of 42 publications and 134 treatments shows the results of feeding a negative DCAD diet to cows three weeks prior to calving results in strong and significant reductions in total post-calving diseases per cow, including milk fever, metritis and retained placentas. Also, significant increase in parous cows' milk yield and feed-corrected milk (FCM) and tendency for increased postpartum dry matter intake.
Remember that the primary reason to feed a negative DCAD diet is to avoid metabolic disorders, especially clinical and subclinical milk fever. We know how milk fever occurs. Blood calcium drops, caused by the onset of lactation and rapid removal of calcium from the blood to support colostrum and milk production. This blood calcium drop can become severe enough to be classified as milk fever.
If the blood calcium drop is not as severe, the animals may experience subclinical milk fever. These cows do not show clinical signs and may even appear normal; however, early lactation feed intake and production are not where they should be otherwise, and the cascade of fresh cow diseases associated with low blood calcium will increase (metritis, retained placentas, dystocia, displaced abomasums, early culling and ketosis).
A typical dry period covers 60 days. In some cases, pen moves or grouping strategies don’t allow for a separate transition group. Even if it’s not possible to separate cows to a dedicated pen 21 days before calving, it’s still possible to get the benefits of a negative DCAD ration. Feeding a negative DCAD diet beginning as early as 42 days before the expected calving date yields similar health and production benefits as feeding the same diet at a shorter interval.
Even though millions of cows and hundreds of research trials have demonstrated the positive benefits of feeding a negative DCAD diet, there are always those who look for new and better ways to accomplish the goal of reducing incidence of clinical and subclinical milk fever. While those interventions do exist, it is hard to beat the proven efficacy of feeding a negative DCAD diet. After all, we know and understand the challenge (reducing milk fever) and we have a process that’s proven to work (a negative DCAD diet).
Work with your nutritionist or talk to a representative to establish a negative DCAD diet in your transition group or to assess if what you’re doing is working.
