In mysteries, the culprit sneaks in. There’s no sign that the safe was broken into – until the money is missing.

Oetzel garrett
Professor / University of Wisconsin – Madison
Garrett Oetzel, DVM, is a professor and section chief in the food animal production medicine sec...

Subclinical hypocalcemia (SCH) is like the thief in the night – it steals from your bottom line, and you may not even be aware of it. SCH is defined as low blood calcium, but without obvious, clinical signs. Just like the loss of money from the safe, monetary losses from SCH can be substantial, because this disease affects every dairy herd and a large percentage of cows within most herds.

Cows that experience SCH have reduced opportunity for full productivity in their ensuing lactations; this steals from your bottom line.

Today’s target disease

When we speak of hypocalcemia today, subclinical hypocalcemia is the target disease. Unlike clinical milk fever, it’s a disease we cannot see. But we can monitor the prevalence of this disease by testing a select group of cows post-calving for blood calcium concentrations.

The start of each new lactation really challenges our modern dairy cow’s ability to maintain normal blood calcium concentrations. Since milk – including colostrum – is rich in calcium, the sudden calcium outflow to the mammary gland that occurs around calving is the reason SCH occurs, and why it’s the focus of our therapies and preventive strategies.


Blood calcium is essential for muscle and nerve functions – particularly functions that support skeletal muscle strength and gastrointestinal motility. This explains the association between hypocalcemia and decreased dry matter intake, as well as the increased risk for displaced abomasum, ketosis and injury.

Calcium is also essential for proper immune function. Birthing and the start of lactation are already stressful events, as evidenced by increased cortisol (a stress hormone) around calving time. Hypocalcemia increases blood cortisol concentrations even more, adding additional stress for the fresh cow. Hypocalcemia is also associated with increased risk for metritis and coliform mastitis.

Typically, every dairy herd tested has at least one fresh cow with SCH and numerous cows with SCH. When we test, we find that the average herd has more than 60 percent SCH in second-and-greater-lactation cows.

Manage one, manage them all

Because of the increased risk for subsequent diseases, even subtle declines in blood calcium can affect the profitability of lactation and a cow’s future productivity.

When a cow is low in calcium, she doesn’t eat as much. Losing that dry matter intake at the critical time around calving sets a cow up for displaced abomasum, ketosis and metritis. Calcium is also integral to helping cows recover from metritis. This is likely related to direct immune suppression from the hypocalcemia, because cows need calcium for their immune cells to work correctly.

If you take care of the hypocalcemia and ketosis, your herd’s risk for displaced abomasum will decrease. Displaced abomasum can’t be eliminated, but we can lower the risk quite a bit by paying attention to the conditions that underlie it. These are interrelated diseases, so prevention really starts with getting the calcium right.

Management solutions

Preventing hypocalcemia starts with nutrition in the pre-fresh period. We want to supplement feed with anionic salts to create acidogenic (low dietary cation-anion difference) diets where we can. We recommend acidogenic diets for herds, along with good feed management and good-quality feed ingredients. That’s our starting point.

Good feed management is required when supplementing with anionic salts, because they may be a bit unpalatable. It is also important and sometimes difficult to get the right dose of anionic salts. This requires careful monitoring of urinary pH in the pre-fresh cows and adjusting the dose of anionic salts accordingly.

However, even feeding a proper pre-fresh diet that has been optimally supplemented with anionic salts can’t prevent all occurrences of hypocalcemia. We cannot win the hypocalcemia battle by using anionic salts alone, even if we use them well. They reduce the risk for hypocalcemia, but not entirely.

It is recommended that dairy producers also help prevent this invisible disease by supplementing with oral calcium for cows that are on their second or greater lactation.

There are two options when deciding which cows to supplement with oral calcium. One approach is to identify and supplement only lame cows and cows that gave more than herd-average milk in the previous lactation. Large-scale field trials have shown that these cows have the best response.

The beauty of oral calcium supplementation is that you can target specific subgroups. It does require a little more management and effort to identify the cows most likely to respond to oral calcium supplementation, but it is the optimal economic solution.

The second approach is to supplement all second-and-greater-lactation cows with oral calcium after calving. Many herds respond better to this simpler approach, and it’s still economically beneficial.

Some cows remain hypocalcemic more than a couple of days after calving. You can identify these cows and continue their oral calcium supplementation as long as needed.

Cows that might be struggling with persistent subclinical hypocalcemia may not look right, are not eating well, are not coming up on milk as fast as they should and may have cold extremities. These cows may benefit from oral calcium supplementation.

Excellent management of fresh cows is not an easy job, and it’s important not to take it for granted. The people who work with pre- and post-fresh cows need to be well-trained, well-monitored and in touch with their herd veterinarian on a regular basis.

Managing subclinical hypocalcemia well is one of the things that separates excellent herds from average ones. When fresh cows get off to a strong start, good things follow for the rest of the lactation.

For herds to thrive economically, they need both good health and good production. Most of the things that get you there aren’t magic; they’re pretty simple. Often, the hardest part is doing the simple things correctly over and over again.

PHOTO: The sudden calcium outflow of milk and colostrum that happens at calving is the reason subclinical hypocalcemia occurs. Photo courtesy of Boehringer Ingelheim. 

References omitted but are available upon request. Click here to Email an editor.

—Submitted by Boehringer Ingelheim Vetmedica