Like all well-run businesses, the management team of a well-run dairy operation will know and understand the key parameters that make them successful. When it comes to cow performance, these may include early postpartum health events, peak milk yield, total lactation milk yield, somatic cell count (SCC) and reproductive performance, just to name a few. To effectively manage these items, they must be measured.

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Animate Product Manager / Phibro Animal Health
Ken Zanzalari has a Ph.D. in animal science from the University of Tennessee and is an ARPAS boar...

The primary reasons for collecting, analyzing and understanding data are to:

1. Make sure processes and procedures are being followed within defined standard operating procedures

2. Be certain changes can be measured

3. Allow for review of performance results in order to make better decisions (i.e., reduce fresh cow health events, lower SCC, increase milk yield, etc.)


Serum total calcium concentration, taken sometime shortly after calving or within the first 48 hours post-calving, is one of the more important biological parameters that provides insight into transition cow health and performance.

Importance of serum calcium status
During the last decade, the importance of serum calcium concentrations in transition cow health and performance has been overlooked.

New research demonstrating calcium’s importance in maintaining proper immune function, minimizing metabolic and infectious diseases and allowing the cow to express her milk yield potential are reasons why monitoring serum total calcium concentrations, at least periodically, can have significant payback to profitability.

Arguably, there is no more important nutrient responsible for the well-being of a recently fresh dairy cow than calcium. The sudden demand for calcium in milk at the onset of lactation often exceeds the mechanisms the cow uses to maintain normal serum calcium concentrations, which can lead to clinical or subclinical hypocalcemia.

Clinical hypocalcemia (milk fever) typically occurs when serum total calcium concentrations fall below 5.5 mg per dl. At concentrations below this threshold, cows are lethargic and may become down cows.

When cows become clinically hypocalcemic, immediate calcium therapy is necessary to keep the cow alive. Although clinical hypocalcemia may occur at high incidence levels (more than 8 to 10 percent of fresh cows) in some herds, it can be managed to a low incidence rate most of the time (less than 2 percent).

The real economic impact
While the critical nature and importance of clinical hypocalcemia should not be overlooked, subclinical hypocalcemia is more economically important. Cows are defined as subclinically hypocalcemic when serum total calcium concentrations fall below 8.5 mg per dl.

Research and surveys have documented that more than 50 percent of all fresh cows, regardless of lactation number, are subclinically hypocalcemic beginning either at the time of calving or within seven days post-calving.

Furthermore, it has been estimated that the herd-level cost of subclinical hypocalcemia is four times greater than the cost of clinical hypocalcemia simply because many more cows in a herd are affected by the subclinical disease.

The annual lost revenue of subclinical hypocalcemia per 1,000 cows, including only lost milk income and cost of displaced abomasums, is approximately $24,000. Factoring in the lost revenue associated with metritis for subclinically hypocalcemic cows doubles the lost revenue.

Therefore, it pays to know the incidence rate of subclinical hypocalcemia (determined by periodic serum calcium sampling) and to make the necessary corrections to the management of these transition dairy cows.

Serum calcium testing
An initial snapshot of a herd’s incidence rate of subclinical hypocalcemia starts with sampling approximately 13 to 15 fresh cows. Ideally, these samples should represent the age makeup of the herd and include parities 1, 2, 3 and 4 and higher.

There are two important considerations to keep in mind when sampling for serum calcium status. First, which laboratory method will be used to determine serum total calcium? Generally, samples are analyzed through either a veterinary diagnostic laboratory or through the herd’s veterinary practice.

Differences in serum total calcium concentrations between the analytical methods used by each of these locations have been observed and reported, which may impact the interpretation of the results.

Second, at what time should blood samples be taken to obtain the most accurate reflection of herd calcium status? Most of the data utilized to establish serum total calcium concentration thresholds of fresh cows was determined using samples taken within the first 12 hours post-calving and through three days in milk.

Obtaining a serum calcium sample within the first 12 hours post-calving is most convenient as fresh cows are routinely handled within this time period. However, this time may not be the most ideal for all herds.

Research has shown that the nadir (time when serum total calcium concentration is lowest) may not occur until 48 to 72 hours post-calving. Herds not utilizing a negative dietary cation-anion difference (DCAD) prepartum diet, herds utilizing a partially acidified diet and herds feeding low dietary calcium irrespective of prepartum DCAD concentration should start with obtaining samples within 12 hours post-calving.

For many herds, taking a sample at this time will be sufficient to establish herd incidence of subclinical hypocalcemia. For herds feeding a partially or fully acidified diet with moderate to high dietary concentrations of calcium (90 to more than 140 grams of calcium), the 48-hour post-calving window may be more beneficial for establishing herd incidence of subclinical hypocalcemia.

To completely understand the dynamics of fresh cow calcium status and obtain the most meaningful data, it may be best to take samples three times: at pre-calving, at or within 12 hours post-calving and 48 hours post-calving. By taking samples at these three times, the true dynamics of fresh cow calcium status can be determined for two reasons:

  • The effects of hypocalcemia are determined by the magnitude of the decrease in serum calcium concentrations following calving.
  • The rate at which normal serum total calcium concentrations return following the nadir, which sometimes occurs immediately following fresh cow milking.

Recent field trials utilizing the three time points have been successful in either confirming or disproving several theories on negative DCAD diet feeding to prepartum dairy cows either alone or in conjunction with routine fresh cow calcium therapy.

Your first step
If fresh cow health and performance is not meeting your standards for excellence, consult with your nutritionist and veterinarian to determine if monitoring fresh cow calcium status can be beneficial to improving your herd’s health and performance. PD

Ken Zanzalari has a Ph.D. in animal science from the University of Tennessee and is an ARPAS board-certified nutritionist with Prince Agri Products, Inc. specializing in transition cow management and nutrition.

References omitted due to space but are available upon request. Click here to email an editor.

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Ken Zanzalari
Dairy Technology Manager
Prince Agri Products