New Meta-Analysis Reveals The Whole Truth About Negative DCAD

“We knew well that acidogenic diets reduce milk fever and that hypocalcemia is linked to other disease during the transition period,” explains José Santos, professor of animal sciences at the University of Florida. “But we did not know, or had not documented scientifically, whether acidogenic diets would reduce diseases other than milk fever. This meta-analysis shows that.”

Results showed reduced retained placenta and metritis in all cows and improved lactation performance in multiparous cows.

A total of 42 published experiments were included in the meta-analysis. Data from 1,803 cows (151 first-calf heifers or nulliparous) were included. The DCAD of prepartum diets ranged from -246 to 1,094 mEq/kg and concentrations of dietary calcium (0.16 to 1.98%), phosphorus (0.18 to 1.58%) and magnesium (0.09 to 0.68%) had wide ranges that allowed for evaluation of their associations with production and health. Diets were fed prepartum for an average of 21.9 days for nulliparous cows and 25.6 days for multiparous cows.

DRY MATTER INTAKE

As DCAD decreases, so does dry matter intake in all cows.

Researchers found as DCAD decreased, so did prepartum intake in both nulliparous and multiparous cows. Reducing the DCAD from 200 to -100 mEq/kg resulted in a 1.5 lb/day and 0.9 lb/day decline in prepartum DMI for nulliparous and multiparous cows. The concentration of calcium, phosphorus and magnesium in the diet did not influence DMI.

Researchers also determined that the decline in DMI prepartum induced by diets supplemented with acidogenic products did not differ regardless of the source of strong ions fed. Research by Zimpel et al., 2018, showed that the depression in DMI prepartum caused by acidogenic diets is the metabolic acidosis, and not the source of strong ions. If prepartum cows are metabolically acidified, dry matter intake declines a bit. If the acid-base status is not altered, DMI is not expected to decline.

However, in spite of the decline in DMI prepartum, feeding a prepartum diet with negative DCAD drives an increase in intake after calving for all cows. Both nulliparous and multiparous cows that were metabolically acidified prepartum increased postpartum feed intake by about 2 lbs/day compared to non-acidified herdmates. Likely, the improved postpartum intake is linked to the better postpartum health when cows are fed acidogenic diets.

MORE MILK FOR MULTIPAROUS COWS

Results from the meta-analysis clearly show that “multiparous cows respond positively to acidogenic diets with increased yields of milk and milk components,” says Santos. The expected milk yield response in multiparous cows fed an acidogenic diet with -100 mEq/kg prepartum was 3.75 lbs/day compared with cows fed a diet with 200 mEq/kg.

However, nulliparous cows fed similar negative DCAD diets tended to have reduced yields of fat-corrected milk and protein, and reduced milk fat content. Milk yield was not influenced. Diet concentrations of calcium, phosphorus or magnesium prepartum did not affect yields of milk or milk components.

It should be noted that only five studies reported data on nulliparous cows, so the data are quite limited. More research is needed to understand what level of DCAD in prepartum diets is best for nulliparous cows.

HEALTH BENEFITS

While most recognize the benefits of feeding prepartum cows negative DCAD diets to minimize milk fever, the meta-analysis clearly demonstrates that other health and production benefits also occur. With individual studies it can be difficult to demonstrate such effects because of the limitations in the number of cows one can enroll in an experiment with individual feeding, explains Santos. A meta-analysis provides a thorough examination of all of the research on a specific topic, and in this case, it found that feeding negative DCAD diets prepartum delivers additional health benefits—less retained placenta and less metritis in all cows.

In the analysis, when prepartum DCAD was reduced from 200 to -100 mEq/kg, the predicted incidence of milk fever in multiparous cows dropped from 11.7% to 2.8%. The incidence of metritis dropped from 34.4% to 12% in nulliparous cows and from 16.3% to 9.9% in multiparous cows. The incidence of retained placenta declined from 12.7% to 3.5% in nulliparous cows and from 17% to 9% in multiparous cows. The number of disease events per cow declined by half in all cows.

NEGATIVE DCAD WORKS

Prepartum cows should be fed a negative DCAD diet (somewhere between -50 to -150 mEq/kg), says Santos. These diets reduce milk fever, subclinical hypocalcemia, retained placenta and metritis. These diets also increase yields of milk and fat-corrected milk in multiparous cows.

The metabolic acidosis induced by negative DCAD diets is expected to slightly depress DMI in prepartum cows. Feed intake declines because the cows have been metabolically acidified. But, these cows respond with increased feed intake after calving.

The ideal DCAD to optimize health and production has not yet been identified, but it is likely somewhere between -50 to -150 mEq/kg for multiparous cows. But there are still questions to be answered. “We do not know if dietary calcium content of prepartum diets when between 0.5 and 1.6% of the diet dry matter makes any difference for postpartum health and production,” says Santos. “We also do not know if primiparous cows should be fed acidogenic diets to the same values as multiparous cows.”

But negative DCAD diets do work extremely well in multiparous cows if you manage them. Analyze forages and byproducts, select ingredients that are low in potassium and sodium, supplement with an acidogenic product or salts to reach your target value of DCAD and then monitor urine pH and incidence of milk fever. If producers and nutritionists do these steps, then negative DCAD is a recipe for transition success.

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