pHix-up & Dietary Cation-Anion Diﬀerence (DCAD)
Dietary cation anion diﬀerence (DCAD) depicts the relative balance between the most important cations (K, Na..) andthe most important anions (Cl, S..) in dairy rations.
DCAD has an important eﬀect on the acid-base status of cows. A positive DCAD is desirable for lactating cows.However, the use of DCAD as a proxy for the acid-base status of the animal is inaccurate.
First, DCAD equations are not consistent among nutritionists and nutrition software used to formulate rations. Most ac- count for Na,K, and Cl, some include S, and a few include Ca, Mg, and P. Thus, very diﬀerent DCAD values can be obtained from diﬀerent software. However, including the multivalent minerals such as Ca, Mg, P, and S in the DCAD calculation faces the challenge of including a large variation from the bioavailability of these ions compared with that of Na, K, and Cl. Thus, nutritionists need to be aware of the drastic diﬀerence in DCAD values that are reported in formulation programs (based on the way DCAD is calculated).
Also, because acid-base is only aﬀected by those cations and anions that are ultimately absorbed, it depends not only on DCAD but also on rumen pH and bioavailability of minerals in the ration. For this reason, the best option to assess acid-base in ruminants is to monitor urine pH (an ideal urine pH in lactating cows would be ≥7.70).
Manipulation of dietary cation anion diﬀerence has been an important tool for dairy cattle rations. The most important and well deﬁned role of DCAD is associated with its eﬀect during the close up period, while negative DCAD is used to reduce the incidence of hypocalcemia (milk fever) after parturition (1).
In contrast, research concerning the lactation period has focused on the beneﬁts of having a positive DCAD. However, the role of positive DCAD and targeted values are not well understood nor well established. For example, a common strategy to increase DCAD in the diet is adding sodium bicarbonate or potassium carbonate. The most relevant conclu- sion was that the tendency towards increased milk yield and the increase in feed intake were most likely due to changes in ruminal pH, feed digestibility, and ruminal volatile fatty acid concentrations.
With regards to targeted DCAD in a lactating cows diet, the literature has indicated that production beneﬁts correlate with having aDCAD ranging from 25 to 30 mEq/ 100 g dietary dry matter. As Several studies indicate that a DCAD above 25 to 30 mEq/100g of DM have no further beneﬁts on feed intake.
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