Milk Fever and Dyscalcemia in Dairy Cows: Nothing to Sneeze At

Welcome to Ricky’s Rumen-ations, a blog where I occasionally jot down my thoughts on scientific research that catches my eye. Look for me to rumen-ate () on dairy cow health, especially transition cow health, hypocalcemia, subclinical hypocalcemia, dyscalcemia, milk fever, body condition, and much more.

If you’re in the dairy cow business, you’re already aware of clinical hypocalcemia, a common disease in dairy cows also known as milk fever. It means the cows are down and require calcium treatments to recover. But you may not be as familiar with dyscalcemia, which is a shame because it also affects the health of the cow, and it is preventable!

I’ll admit it: I’m a dairy science geek. I love to read studies and glean nuggets that I use to help dairy producers and nutritionists keep their cows as healthy and productive as possible. Issues like dyscalcemia and milk fever are always on the reading list. If my wife can’t find me, it’s usually because I’ve gone down a rabbit hole learning something new that caught my eye or uncovering research that helps explain what we’re up to.

That’s how I learned of the fascinating work in the July 2023 study “Considerations in the Diagnosis and Treatment of Early Lactation Calcium Disturbances” by Jess McArt and her colleagues at the McArt Dairy Cow Lab at Cornell University. This research does an exceptional job of explaining dyscalcemia as a distinct form of subclinical hypocalcemia.

Strategies to avoid milk fever have been around for years, and the dairy industry has figured out ways to prevent it that are effective, but not without cost and hassles. Dr. McArt and her team posed a relatively new train of thought for many (but not us): what about subclinical hypocalcemia, the pre-symptom stage just before hypocalcemia? Does that affect overall cow health and milk production?

Conventional wisdom says that the cow’s calcium levels are low with subclinical hypocalcemia but not low enough to show obvious symptoms. However, that’s not all there is to it.  Calcium homeostasis (maintaining a constant level of calcium in the blood) is crucial because calcium plays a vital role in numerous bodily functions in dairy cows, including muscle contractions (the “real” rumenation), nerve impulses, blood clotting, and bone health.

Thanks to Dr. McArt and her team, we now have a more nuanced explanation of subclinical hypocalcemia. For example, not all subclinical hypocalcemia is bad. Transient hypocalcemia, which happens right after freshening (when a cow gives birth and begins to produce milk), leads to increased milk production and decreased health risks. If subclinical hypocalcemia becomes persistent and delayed, trouble is on the way.

Dr. McArt identified that period (persistent and delayed subclinical hypocalcemia after the normal and desired transient hypocalcemia) as dyscalcemia, which occurs when blood calcium levels at 4 DIM are less than 8.8 mg/dL.* Dyscalcemia leads to reduced milk production, poor reproduction, and higher health risks including milk fever.

Fast-forward and spoiler alert: We CAN and we HAVE! One of things I hope to do with some of my Rumen-ations is to unpack more about dyscalcemia – including how to identify it, what symptoms to look for, and how to prevent it. Stay tuned!

*Curious about Dr. McArt’s research related to subclinical dyscalcemia and clinical milk fever? We’ve got you covered. You can read a summary of the study here if you’re as into this as I am.