Calcium is a key ingredient to growing up big and strong. Of course, this isn’t just limited to humans. The presence of low calcium levels in the blood, or hypocalcemia, is a serious medical condition that cows face during the lactation process.

Its prevention and treatment were the main topics of the DAIReXNET webinar, “Treatment and Prevention of Subclinical Hypocalcemia,” held on Dec. 16, 2014.

Gary Oetzel, professor at the School of Veterinary Medicine at the University of Wisconsin – Madison, presented information on the causes, prevention and treatment of hypocalcemia. The sudden calcium demand of lactation triggers hypocalcemia in most older cows soon after calving. Subclinical hypocalcemia, which is defined as calcium levels below 8.6 mg/dL of total calcium in the blood, is much more common that clinical hypocalcemia (milk fever).

In general, hypocalcemia causes serious health effects in dairy cows, including decreased dry matter intake after calving and increased incidence of secondary diseases.

According to data Oetzel reviewed at the start of the presentation, the threshold for hypocalcemia prevalence was originally believed to be any levels below 8.0 mg/dL. However, this was only an educated guess and was not derived from research studies. Following a recent 2014 study in Florida, the actual 8.6 mg/dL limit was discovered.


Subclinical hypocalcemia is associated with multiple medical problems in cows, including increased risk for metritis (3.2 times more likely), postpartum fever (2.4 times), increased post-fresh beta hydroxy butyric acid or BHBA (1.0 versus 0.7 mmol/L), and longer median days open (124 versus 109 days).

Oetzel discussed various means by which the threat of hypocalcemia can be minimized. Dietary means for reducing hypocalcemia include calcium restriction and dietary acidification by anionic salts. These reduce the risk for hypocalcemia and subsequent health problems.

The webinar also compared IV calcium preparations to oral calcium supplementation. In general, oral calcium supplementation is best for standing cows and should never be administered to down cows. In contrast, IV calcium is the treatment of choice for cows that are down.

Oral calcium is used only modestly in the industry currently for various reasons, including a lack of veterinary involvement in developing on-farm treatment protocols and perceived difficulties in administering oral calcium. The advent of oral calcium boluses has greatly improved the safety and ease of administration of oral calcium supplements. Oetzel stressed the superiority of oral supplementation for standing cows and lamented its poor image in the dairy industry.

There can be serious problems following IV calcium administration. It is simply not needed for cows that are still standing; they can safely absorb all of the calcium they need from oral supplementation. Cows given IV calcium experience poor sustained calcium support afterwards; this is likely due to the calcitonin response that follows IV calcium. Cows can also be killed by a fatal heart block while the IV calcium is being administered.

Oetzel and his colleagues at the University of Wisconsin – Madison conducted a study on the effects of oral calcium supplementation on health and production in early-lactation cows. A secondary objective of the study was to determine if different subgroups of cows responded differently to the oral calcium supplementation.

Over the summer of 2010, 927 cows were divided into two groups – those supplemented with oral calcium boluses and control cows that were not supplemented.. Both groups were fed a low DCAD pre-fresh diet. Subclinical hypocalcemia was found in 53 percent of the cows, despite feeding the low DCAD diet.

Cows that had a relatively high milk yield in the previous lactation and had received the oral calcium boluses produced 6.5 percent more milk at their first DHI test than cows in the control group. Oetzel concluded that good cows, when supplemented with oral calcium, eat more dry matter in the days after calving and are able to produce much more milk. It is interesting that the cows supplemented with the oral calcium boluses were able to give more milk without any impairment to their health. Most other technologies that increase milk yield also increase the risk for cow health problems.

Another point that Oetzel made during the conclusion of the webinar was that the highest risk cows for hypocalcemia did not always equate to the best responders for calcium supplementation. In fact, neither increasing parity nor calving difficulties had any effect on response to oral calcium supplementation. The best response to oral calcium appeared to be in healthy cows with relatively high milk yield in the previous lactation.

Of the three calcium sources out there for use, Oetzel stressed the use of calcium chloride or calcium propionate rather than calcium carbonate. Calcium chloride is considered the “gold standard” of oral calcium supplementation. Calcium propionate is more slowly absorbed and requires a higher total dose of calcium, but can work if pumped to cows. Calcium carbonate is very poorly absorbed and is not recommended as an oral calcium supplement. PD

This webinar can be viewed at the eXtension website.

David Melie is a student at the University of Illinois.