By Dr. Louisa E. Koch, Ph.D., P.A.S.
When you hear the acronym, DCAD, what comes to mind? You probably immediately thought about pre-fresh rations, right? While that is usually the first thing most people think of, DCAD is not just important for transition cow rations. It also should be considered when formulating lactating cow rations.
Dietary cation-anion difference (DCAD) is a term that refers to the difference between the positively-charged cations (cations: primarily sodium [Na] and potassium [K]) and negatively-charged anions (anions: mainly chloride [Cl] and sulfur [S]) in the cow’s diet. The DCAD value is calculated by subtracting the total dietary anion concentration from the total dietary cation concentration (Equation 1). Negative DCAD diets (more anions than cations) induces a compensated metabolic acidosis, which can lead to decreased blood and urine pH and the mobilization of calcium stores for lactation (common practice in dry cows). Positive DCAD diets promote a more alkaline (higher blood pH) metabolic state. It should be noted that feeding a negative DCAD diet to a cow in lactation is not advisable.
Sodium, potassium, and chloride are critical osmoregulators in the body, as they help to maintain osmotic balance in the tissues. For example, they maintain osmotic balance in milk and consistent moisture content (85%) in the feces. Sodium and potassium drive urine output. Ultimately, increased intake of these minerals will increase water intake in the animal. Of all the minerals, potassium has the greatest concentration in milk at about 0.15%, so there is a demand for adequate potassium through normal milk synthesis and output. Research has suggested insufficient potassium is linked to displaced abomasums, likely due to the influence potassium can have on proper abomasal muscle contraction (Constable et al., 2013).
Elevating sodium and potassium will enhance the DCAD level in your ration and is commonly achieved through the use of Silo-King® treated forages, sodium bicarbonate, potassium carbonate, and sodium sesquicarbonate. While increasing DCAD by using forages high in potassium is the most ideal approach, it may not always be feasible and you may have to supplement additional sodium or potassium through the mineral mix. However, not all ingredient sources will impact DCAD in the same manner. Table 1 shows the composition of sources commonly used to elevate the DCAD level in the diet.
No, there is no requirement for DCAD in lactating cows according to the NASEM (2021). However, a practical minimum for DCAD can be established based on the minimum requirements for potassium, sodium, chloride, and sulfur. A 1,500 lb cow producing 110 lb of milk needs at least 1.11% potassium, 0.25% sodium, 0.3% chloride, and 0.20% sulfur in her diet (NASEM, 2021). If the measured chloride and sulfur of the diet is greater than the minimum requirement, then additional potassium or sodium will be necessary. Our recommended ranges at Agri-King for DCAD are 200-300 mEq/kg, and a PCI of 700-850.
The primary responses to increasing DCAD in lactating rations are observed with intake, milk production, and milk fat yield. A 2015 meta-analysis summarized the results of 43 published articles with diet DCAD ranging from 0 to 500 mEq/kg of DM (Iwaniuk and Erdman, 2015). They found that the maximum response of DMI was 4.2 lbs, whereas milk production increased by 2.4 lb/d and did not respond to DCAD over 300 mEq/kg. Milk fat responses to DCAD were linear with a 0.08 lb/d (0.1%) increase in milk fat for every 100 mEq/kg (Figure 1).
Fat yield is the primary economic response to DCAD, and can have major profitability implications in today’s milk market. Some of this milk fat response is thought to be due to the impact on the rumen pH and improved NDF digestibility. Rumen pH has been observed to increase with elevated DCAD levels. There is also data that shows reduced production of fatty acid intermediates that are known to lower milk fat. Testing urine pH is common practice in negative DCAD dry cow programs, but it can be helpful for lactating as well. The urine pH for a lactating cow should be 8.0 to 8.1.
Optimizing DCAD in lactating rations is essential in maintaining health and production throughout a cow’s milking lifespan. By understanding the importance of DCAD to milking cows and implementing appropriate dietary strategies, you can enhance the productivity and profitability of your clients’ operations. Furthermore, DCAD may need to be elevated further as temperatures start to warm up and heat stress is a concern. Remember to test the urine pH in your milking groups to ensure that it is within the ideal range of 8.0-8.1 pH. Agri-King’s Dairy Synergy Program helps to evaluate all the pieces of a farm’s nutrition puzzle to ensure success. Inquire with the Nutrition Department if you would like to have further discussion on this topic. AK
Sources:
Constable, P., W. Grünberg, R. Staufenbiel, and H. Stämpfli. 2013. Clinicopathologic variables associated with hypokalemia in lactating dairy cows with abomasal displacement or volvulus. J. Am. Vet. Med. Assoc. 242(6):826-835. https://doi.org/10.2460/javma.242.6.826.
Ender, F., I. W. Dishington, and A. Helgebostad. 1971. Calcium balance studies in dairy cows under experimental induction and prevention of hypocalcaemic paresis puerperalis. Z. Tierphysiol. Tierernihr. Futtermittelkd. 28:233.
Iwaniuk, M.E., and R.A. Erdman. 2015. Intake, milk production, ruminal, and feed efficiency responses to dietary cation-anion difference by lactating dairy cows. J. Dairy Sci. 98:8973–8985.
National Academies of Science, Engineering, and Medicine. 2021. Nutrient Requirements of Dairy Cattle, 8th rev. ed. National Acad Press, Washington DC.