Some combinations are simply meant to be. Can you imagine Abbott without Costello? Lucy without Rickie? Laverne without Shirley? Likewise, dietary anion-cation difference (DCAD) and metabolizable protein (MP) must both be considered in formulating successful dairy rations.
The two work so well in tandem to promote cow health and productivity, it’s easier and more intuitive to simultaneously consider both of these key ration nutrients.
Prepartum role of DCAD
First consider DCAD’s beneficial impact during the transition period – both before and after calving.
Dairies, nutritionists and veterinarians have learned over recent years that feeding a negative DCAD diet (-8 to -12 meq/100g ration dry matter) for the three weeks prior to calving improves cow health and performance in the following lactation.
Reducing DCAD to negative values at the onset of this timeframe has been shown to prevent a rapid decline in blood calcium at calving and improve postpartum cow health and performance outcomes.
For instance, research presented at the 2015 American Dairy Science annual meeting demonstrated that:
- Feeding the ration with negative DCAD levels reduced the prevalence of subclinical hypocalcemia at day zero and day one days in milk (DIM) (20.0 percent and 34.3 percent) compared with the ration with positive DCAD levels (69.3 percent and 76.5 percent) on day zero and day one in milk (p less than 0.05).
- Incidence of clinical hypocalcemia (milk fever) was 0 percent in the ration with negative DCAD levels compared with 23.1 percent for the ration with positive DCAD levels (p less than 0.05).
The research confirms that feeding a negative DCAD diet prepartum positively impacts cow blood calcium status after calving. That’s because a negative DCAD ration helps mobilize calcium from bones and prevents clinical and subclinical hypocalcemia, or milk fever, as well as maintains immune function.
Since clinical and subclinical hypocalcemia often lead to low dry matter intake after calving, dystocia, ketosis and retained placentas, steps taken to prevent this disorder positively influence cow health.
In addition, and not surprisingly, the improved health status of the cows in this research trial allowed them to produce about 8 pounds more energy-corrected milk.
Adjust postpartum DCAD
Of course, ration DCAD strategies should change following calving, with rations switching from negative to positive DCAD after parturition. A wealth of research and on-farm experiences show feeding a positive DCAD ration post-calving also benefits cow health and performance.
That’s because a properly formulated positive DCAD ration can help neutralize blood acid load caused by high milk production, ketone development and free fatty acids from body fat mobilization.
Plus, increasing the potassium component of DCAD will help replace levels of this vital nutrient that are lost through increased milk production and heat stress.
Aim for a dietary potassium level of at least 1.7 percent of the total dry matter during non-heat-stress periods, and 2 percent immediately before and during heat-stress periods of the year.
Postpartum ration DCAD levels depend on lactation stage. Recommendations are:
- +35 to +45 meq/100g ration dry matter for high-producing cows
- +30 to +35 meq/100g ration dry matter for mid-lactation cows producing less than 85 pounds of milk
- +25 to +30 meq/100g ration dry matter for late-lactation cows
Keep in mind that seasonality and climate can affect feedstuff DCAD levels. Be sure to test silage and other feed ingredients regularly with wet chemistry analysis to ensure proper levels of DCAD are being fed.
Don’t forget about metabolizable protein
However, DCAD is only part of the equation. Simply focusing on prepartum negative DCAD levels alone – in the absence of accounting for MP – does not result in optimal rations. You’re missing a key component of your team.
When you omit MP from consideration, you leave opportunity on the table since cows will not perform to their potential if it’s not included in rations at proper levels. MP is a combination of rumen bypass protein and bacterial protein that reaches the intestines.
This represents the total MP available for absorption and is what the animal needs.
MP matters because it is the true protein that is digested post-ruminally, and includes the amino acids that are the components of protein absorbed by the small intestine. Absorbed amino acids are used for the synthesis of proteins essential for an animal’s growth, body condition maintenance, reproduction and milk production as well as supporting fetal growth.
These are vitally important tasks, and help explain why proper nutrition in the transition period helps lay the groundwork for a successful next lactation.
If prepartum transition cows do not receive enough MP, they will break down muscle and other protein sources in the body. It’s important to remember that early-lactation cows have an inability to consume sufficient protein to meet the mammary and nonmammary amino acid requirements, as well as replenish protein losses that occurred prepartum caused by insufficient MP without formulating diets for excessively high protein levels.
That means prefresh diets should be formulated to supply about 1,100 to 1,200 grams per day of MP.
When cows receive adequate levels of MP during this timeframe, you’ll see benefits after calving. Research shows that MP fed in the close-up period was positively related to milk protein yield in early lactation as long as cows were fed more than 75 percent of their MP requirement in early lactation.
Therefore, look for nutritional solutions that help address the full spectrum of cow needs, especially during transition. Don’t focus on DCAD to the exclusion of MP, because while you can certainly lock in DCAD levels, you can’t fully unlock your herd’s potential without MP’s key. 
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
- Email Elliot Block
