|RICK LUNDQUIST is an independent nutrition and management consultant based in Duluth, Minn. You can contact him at firstname.lastname@example.org.
New research shows that increasing the dietary cation-anion difference (DCAD) in lactating cows by raising dietary potassium (K) can boost both milk production and milk fat.
We mostly hear about DCAD in connection with prefresh animals. We try to maintain a negative DCAD during the close-up dry period to reduce metabolic disorders during the transition period. But a positive DCAD is beneficial once cows freshen.
Many nutritionists increase K in summer diets to combat the effects of heat stress. Milk is high in K and cows lose K though sweat and urine, especially when it’s hot. The strategy is to replace the amount of K in the animal by feeding higher dietary K levels during hot weather. Potassium chloride (KCl) has been used extensively, but the chloride anion counters the K cation, so DCAD is not increased. However, research shows that raising the DCAD of lactating diets to between +35 and +45 milliequivalents per 100 g of dry matter has a positive effect on milk and fat.
Potassium carbonate (K2CO3) is the source of choice to increase K as well as DCAD. Sodium bicarbonate also increases DCAD, but doesn’t supply K.
Alfalfa and grasses are typically high in K. But they can also be high in chloride. High corn silage diets usually do not supply adequate K.
Test your forage for K, sodium, sulfur and chloride to accurately balance for K and DCAD. These minerals vary greatly by region. Fertilization and manure application also affect these minerals. Chloride levels can build up in soils that have had frequent manure applications.
Forage magnesium levels should also be checked. Higher dietary magnesium should be fed when K levels increase. Be sure that minerals are tested by wet chemistry rather than near infrared, because the latter method does not always deliver accurate numbers for minerals.
Milk production responses of 2 lb. to 4 lb. have been consistently shown by increasing K to 1.8% to 2.1% of dry matter (DCAD up to +45). Butterfat has also increased two to four points, even when it was over 3.8% prior to raising K levels in the diet. K2CO3 was used in these studies to increase DCAD. Studies at Clemson University indicate that added K may reduce the formation of trans fatty acids in the rumen that causes milk fat depression.
K2CO3 is expensive (currently $1,400 to $1,600 per ton). KCl is less expensive ($600 to $700 per ton) but it won’t increase the DCAD. The K2CO3 can heat in the feed mill and in a total mixed ration, especially in humid conditions. I use DCAD Plus, a commercial K2CO3 product that’s formulated to prevent heating, when I have to worry about humidity.
At current pricing, it can cost up to 35¢ per cow to increase K from 1.3% (a typical high corn silage diet) to 1.8% of the dry matter with K2CO3. Less supplemental K is required in high alfalfa or grass diets.
You need a couple pounds of milk to get a return on your investment. After years of feeding cows under heat stress conditions, I am convinced of the need for added K in the summer. I’ve seen very consistent responses of at least 2 lb. per cow per day of milk during the summer, even under field conditions where milk production responses are hard to measure.