Increasing DCAD value in ruminant diets. Always the best option?

1. The term DCAD stands for Dietary Cation Anion Difference. DCAD is an index of the relative balance between the principle cations (potassium and sodium) and the principle anions (chloride and sometimes sulphur) in the cow’s diet (Erdman & Ewaniuk, 2015).

2. Reducing DCAD may acidify blood and aid calcium turnover from bone. Increasing DCAD may increase blood pH and induce a more positive acid-base balance.

3. DCAD values of diets are normally used to determine what effect the diet will have on the acid-base balance. However, based on the results of 13 published article, the average responses in acid-base status to NaHCO₃ or MgO supplementation are relatively small (Erdman et al, 1988).

4. Increase in DCAD levels of the diet may increase DMI and milk production, but not necessary improve feed efficiency (Hu & Murphy, 2004).

5. Replacing 204 g Na-bicarbonate / cow / day with 87g Acid Buf / cow / day reduced the DCAD value of early lactation dairy TMR from 28 to 17 (mEq/100 g of DM). This improved the FCR over time (Bernard et al, 2014).

6. Replacing 194 g Na-Bicarbonate / cow / day with 93 g Acid buf / cow / day reduced the DCAD value in mid lactation dairy TMR from 25 to 16 (mEq/100 g of DM). This resulted in a significant reduction in time the rumen pH is below 5.5. Both milk fat yield and feed efficiency were significantly improved (Cruywagen et al, 2019).

7. Replacing 158 g Na-Bicarbonate / cow / day with 76 g Acid buf / cow / day reduced the DCAD value in fresh / mid lactation dairy TMR from 23 to 15 (mEq/100 g of DM). This resulted in a significant reduction in time the rumen pH is below 5.5. Both milk protein yield and feed efficiency were significantly improved (Neville et al, 2019).

8. Supplementing 225 g Na-bicarbonate / cow / day to a fresh cow diet increased the DCAD value of the diet from 19.5 to 27.6 mEq/100 g DM). This significantly increase the milk fat %, but significantly decreased milk production, with no difference in DMI. Dry matter digestibility was significantly decreased (Rauch et al, 2012).

9. Supplementing 364 g K₂CO₃ sesquihydrate / cow / day to a fresh cow diet increased the DCAD value of the diet from 16.6 to 37.8 mEq/100 g DM. This significantly reduced milk MUN levels. Fat corrected milk, milk fat yield and milk protein yield were numerically reduced (Alfonso et al, 2017).

10. Based on 42 published trials, increasing the DCAD value of dairy diets by predominantly supplementing Na-bicarbonate to a negative control, significantly improved the feed efficiency. However, the correlation between increase the diet DCAD and improvement of feed efficiency was very low, r² = 0.11 (Iwaniuk & Erdman, 2015).

11. Increased levels of sodium bicarbonate and sodium carbonate in ruminant diets increase the DCAD value of the diet. This increased the liquid dilution rate in the rumen by more than 50%, increased acetate by 28% and decreased propionic acid by nearly 50% (Thomson et al 1978).

Reducing the prepartum DCAD reduced intake prepartum but improved intake postpartum in both parity groups. Reducing the DCAD from +20 to −10 mEq/ 100 g DM could increase blood total Ca on the day of calving from 1.86 to 2.04 ± 0.05 mM, DMI postpartum 1.0 kg/d, and milk yield 1.7 kg/d in parous cows (Santos et al, 2019).