Mid-Lactation Milk Fever or Electrolyte Imbalance?

The first time I heard mid-lactation milk fever was in 2005. We got a call from a client in Hanford regarding half a dozen cows that went down. Most got up with a bottle or two of CMPK. But some had to be euthanized. Luckily we have a senior partner that has seen almost everything. Since it was a Jersey herd he suggested I take a look at the TMR. Most likely it was being sorted. It looked horrible – the dairy was trying a new mixer that was totally inadequate for a diet with alfalfa hay. The dairy went back to their own mixer and within a few days the diarrhea, the down cows, and the loss of milk were all improving. It wasn’t until the latest case of mid-lactation milk fever hit that another aspect of this problem became apparent.

The Misnamed Syndrome

Calling it milk fever often results in incorrect actions being taken. It is important to identify why they go down. Just immediately jumping to “calcium is deficient in the diet” usually ends up with getting the wrong answer. It is often a mineral/electrolyte imbalance, with magnesium (Mg) and potassium (K) more likely involved. The latest incidence of this happened on a mixed herd, with Holstein and Jersey cows going down. The dairy milks about 4,000 cows. Over the previous week 22 cows had gone down; definitely more than usual. A few cows responded to calcium but more got up after receiving potassium. Which would mean potassium is deficient in the diet – this has been the historical response. However, we wanted to dig deeper into the underlying issue. Because potassium metabolism would indicate that it is relatively hard to underfeed this macro-mineral. This newsletter illustrates how we troubleshoot nutrition related problems to get the right answer.

Background – Nutrient Requirement

Potassium requirement under ideal conditions is 1.0-1.2% in the diet dry matter; for mature cows making about 90 lbs ECM. Under most conditions the basal diet we will be over 1.2%. During summer heat stress in CA, it is common for us to be at 1.7% K or more. The diet for this herd is 1.44% K. Another way to look at nutrient requirement is how many grams per day are required. Two hundred fifty grams of K would be required. This quantity of K should easily be consumed at only 40-42 lbs of dry matter. So at the estimated average intake of 48-50 lbs, we are supplying more than adequate amounts of potassium per day.


Now back to the investigation of this case. We had to ask lots of questions to uncover a pattern to the cows going down. The intent was to identify why too many cows were going down between 120-300 DIM. No first lactation animals were impacted. Three were second lactation, 12 were third lactation, with 7 cows 4th lactation or higher. This distribution wasn’t surprising. What was of interest was the high incidence of diarrhea reported by the herdsman. Our observations didn’t indicate bad manure but we kept this in mind as we conducted our investigation. A couple cows had E coli, which often presents as down cows. After the questions and observations were done we began to rule items in or out.

  1. There appears to be adequate K in the diet. Samples of alfalfa were taken, as was a TMR sample, for confirmation.
  2. While 22 down cows is too many for a week, we must also note that there are over 3,980 that are fine. If a nutrient was deficient in the diet, more cows would be impacted.
  3. TMRs looked phenomenal. Particle size and moisture were adequate to minimize sorting.
  4. The amount of milk produced appears to have very little impact on potassium homeostasis. These cows ranged from high to mid-lactation production. The pools of K present in the body are adequate when consumption is high enough. Higher milk means higher intakes, so milk production alone will not deplete potassium.
  5. Potassium in the intracellular/extracellular pools is fairly mobile. This means the body can move potassium to where it is needed.
  6. Cows with underlying issues were identified. There are still too many that appear to have been healthy (no events before this incident).
  7. I contend that they are all impacted by the same factor. Inadequate consumption of the TMR.
    • For some reason cows are using up all their potassium reserve (E coli and diarrhea have been identified in some animals) and it is not getting replenished through eating.
  8. It is not the diet, nor the people, nor the “string/ pen”. It appears to be a cow issue – why are some cows not eating enough TMR. Individual cow investigations are much harder than herd-wide episodes.

Reasons Cows Don’t Eat

  1. Feed not available. Empty Bunk Syndrome. This dairy tries to feed to a slick bunk.
  2. Upset stomachs from various causes. Bad feed, sorting feed, slug feeding after being out of feed. This often results in variable manure in a pen.
  3. Lameness. A close look at 6 of the cows involved with this case indicated lameness.
  4. Older, slow cows. Any cow in her 4th lactation or over is probably a little tired.
  5. Timid cows. This usually describes first lactation animals, of which no cases were observed here.
  6. Crowding at either feed bunk or beds. I counted 342 stanchions and 298 beds in the free stall barns. Pen count ranged from 331 to 352 in pens where down cows were located.
  7. Stress. The biggest BS term we use. But some examples are long lock up times, handling, environment, etc.

Corrective Action: Band-aid

As soon as practical it is a good idea to get potassium up in the diet. This can be relatively easy, and inexpensive with potassium chloride. This is definitely a band-aid as the diet is likely adequate except for an intake problem. Until the underlying reduction in intake can be alleviated it is best to bump the nutrient that may be deficient.

In Conclusion

  1. The down cows in this investigation appear to be due to electrolyte depletion, likely caused by a drop in intake. One of our DairyWorks guys told me “One more pound of intake fixes a lot of problems”. How true. The reason for the lack of intake is often hard to assess.
  2. Two key factors on this herd were feeding to a slick bunk and overcrowding. While there are plenty of eating spots, cows were overstocked in relation to beds.
    • One possibility is older cows, with sore feet, are lying down longer. When they do make their way to the bunk it is often empty. They then go back to lying down for an extended period of time and therefore do not replenish potassium.
    • Alternatively, they may be slug feeding when feed is presented, get diarrhea, and lose excessive minerals via excretion.
  3. Solution 1 – reduce the crowding
  4. Solution 2 – ensure feed available for when the last cows wants the last pound of intake.

Final Thoughts

Proper investigations are required. Making assumptions too early in the process usually results in getting the wrong answer. The challenge may go away, but the underlying issue remains. For example, another dairy reported a similar scenario a couple of months ago. They milk about 3,000 in open lots. About 20 cows were reported as having gone down. The investigation uncovered a lapse in footbath maintenance resulting in a surge in heel warts and foot rot coming out of the summer heat. These lame cows under consumed the TMR due to pain overwhelming the drive to eat.

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