Feed Enough Potassium in Dairy Lactation Diets

It is widely accepted that excessive amounts of potassium (K) fed to a pre-fresh dairy cow may lead to a high-incidence of milk fever at calving. However, many people don’t realize that once she calves, high milk producing cows require lots of dietary potassium, because lots of research since the 1960s has actually proven that high dietary levels actually promote good dry matter intake and rumen digestibility, which together leads to better milk production.

That is why; well-balanced dairy diets should be reviewed for potassium content. And if there isn’t enough, potassium; supplementation is easily justified and implemented.

Consequently, potassium is classified as a vital macro-mineral for dairy cows. It is similar to calcium and phosphorus. It is required in grams per cow per day as compared to essential trace-minerals such as copper and zinc - required in milli-grams per head (mg = 1/1000 gram). According to NRC (2001), a typical dairy cow needs about 1.0% potassium of her daily diet (dm, basis) in order to perform vital functions, namely: osmotic balance at the cellular level, nerve transmission and of course – good milk and milkfat production.

The funny thing is that a good body of research suggests that 1.0% potassium is too low in the lactation diet. This K deficiency causes high-producing dairy cows to become marginally deficient in potassium, especially during their first-ten weeks of lactation.

These scientific papers point out that dairy cows naturally lose a significant amount of potassium every day, just through milk production, alone. That’s because milk contains about 0.15% potassium (compared to 0.10 % calcium and 0.08% phosphorus), which secretes 25 – 40% of daily potassium intake, depending upon feed intake and milk yield.

Since, there is little storage capacity in the cow’s body (such as bones for calcium and phosphorus); a significant amount of potassium must be consumed in the lactation diet everyday in order to meet body maintenance and production requirements.

As a dairy nutritionist, I read many of these research papers, which recommend that all potassium requirements of lactating dairy cows can be met with at least 1.3 – 1.8% potassium formulated in early lactation diets (dm, basis). For example, I have seen a first-hand case of a possible K-deficiency in a 120-milking cow operation that took this advice with positive results.

Last year, this dairy producer told me that he was having milk production issues with his early lactation cows from 50 – 90 days in milk. Upon review of his lactation diet – adequate amounts of energy (44 Mcal/head), protein (17%) and enough calcium (200 grams)/phosphorus (110 grams) were being fed.

Upon review of the dietary potassium level, it seemed low (0.90%). So, I felt that we should increase it to 1.4%, respectively.

I did this by increasing the potassium-enriched alfalfa hay portion of the diet (2.88% K) by 2 kilos, while substituting out an equivalent amount of corn silage (1.1% K). Plus, I added 40 grams/ head of potassium chloride to their grain-mix, which was added after the forage in their TMR. No other di- etary changes were made and within about two weeks of introduction; average dry matter intake of the cowherd increased from 25.7 to about 26.2 kg per head, daily. And milk production followed from 33.8 kg to about 34.7 kg per cow per day. Milkfat remained unchanged at 4.2%.

At first, I was hesitant to increase the potassium levels in this diet by 40%, since high levels of potassium are known to interfere with another macro-mineral; magnesium.

Researchers at Ohio State University showed that for every 1% unit increase in dietary K above the 1.0% NRC recommendation in the lactating diet; 20 – 30% more magnesium is needed to meet the cows’ respective requirement. That’s because high levels of dietary potassium inhibit magnesium absorption in the cow’s gut. Therefore, I made sure that this new lactation diet met a critical ratio of 4:1 (K to Mg) to avoid antagonistic problems.

I am not sure, why we focused solely upon the potassium levels of this lactation diet in the first place. It might have been that I implemented a 1.4% potassium level in most of my dairy feeding program for some time. I also think that I am balancing more dairy TMRs containing corn silage, which in itself contains relatively lowpotassium and often need Ksupplementation.

In either case, it’s a good lesson to me; review every lactation dairy diet that I come across and make sure that enough potassium is being fed.