Hypervigilance is the new watchword for profitable dairy farming in the 21st Century. Cow comfort in clean, stress-free environments is getting the attention and implementation that makes milk production a rewarding experience for both staff and animals. But even with this focus and continuing advances in cow management, there is one under-diagnosed disease that is linked to almost every disease that has onset around the time of calving. This disease is subclinical hypocalcemia (milk fever) and it’s sneaky, harmful and costly.
Hypocalcemia is Most Apparent in Its Subclinical Form
Recognition and treatment of milk fever (hypocalcemia) at calving is becoming well-recognized and treatment protocols are in place on well-managed dairies. Unfortunately subclinical hypocalcemia, because of its non-symptomatic nature, is not dealt with as efficiently. It’s easier for cows to get enough calcium from the food eaten when they are late in their lactation or early in the dry period. But as they get closer to giving birth, the calf’s bones are growing rapidly, and the need for calcium increases by two to ten grams a day. Subclinical hypocalcemia is defined as low blood calcium concentrations without clinical signs of milk fever.
One Out of Every Two Cows Has Subclinical Hypocalcemia
Subclinical hypocalcemia affects about 50% of second and greater lactation dairy cattle fed typical pre-fresh diets. If anions are supplemented to reduce the risk for milk fever, the percentage of hypocalcemic cows is reduced to about 15 to 25% (Oetzel, 2004). Cows with high body condition at calving also are more likely to have hypocalcemia. However, subclinical hypocalcemia does not present with recognizable symptoms, and can only be diagnosed when blood samples which must be collected within the first 1 to 2 days post-calving and blood calcium concentration is determined to be below 8.5 md/dl.
Jersey and Guernsey cattle are more susceptible to the disorder.
One reason for this is that Jersey cattle have fewer vitamin D receptors than Holstein cattle. Incidence increases with higher milk production and successive lactations. First-calf heifers rarely develop clinical hypocalcemia because they produce less colostrum and milk and can more rapidly mobilize calcium from bone in their growing skeleton. Reinhardt and co-workers at the National Animal Disease Center in Ames, Iowa, found the prevalence of clinical hypocalcemia was 1% for first-lactation, 4% for second-lactation, 7% for third-lactation, and 10% for fourth-lactation Holstein cows in a study where 1,462 cows were sampled.
Studies Show Reduced Dry Matter Intake
In recent studies used a group of induced subclinical hypocalcemic cows and a control group of normalcemic cows no differences were detected in heart and respiratory rates, rectal temperature, and white blood cell counts between the two groups. However, subclinically hypocalcemic cows had a major decline in dry matter intake, from 26 lbs of dry matter/day on the days before, to 12 lbs of dry matter/day during hypocalcemia, whereas the decline in dry matter intake in normocalcemic cows during the infusion of saline was of only 4 lbs/day.
Subclinical Hypocalcemia Is Sinking Dairy Herds
Subclinical hypocalcemia could be a contributing factor in herds with a high incidence rate of metabolic disorders. A recent study (Martinez et al., 2012) defined subclinical hypocalcemia as serum total calcium below 8.59 mg/dl during any of the first 3 days in milk. Cows with subclinical hypocalcemia in this study also had reduced pregnancy rate and longer days open. Other problems such as the following can be attributed to hypocalcemia:
- Can inhibit muscle and nerve activity and lead to increased risk of injuries due to falling and slipping.
- Subclinical hypocalcemia has a blocking effect on immune function
- Greater risk of developing milk fever, metritis, ketosis, retained placenta and pneumonia.
- Poor smooth muscle function brings on slower GI tract activity, so a cow feels full when it’s not, and eats less. The loss of dry matter intake continues to decrease calcium intakes and the cascade continues.
Check for Higher Rates of Uterine Disease
One of the most common health problems affecting dairy cows is uterine disease. It affects 20 to 30 per cent of the cows either in confinement or in grazing systems. Recently, a group at the University of Florida (Martinez et al., 2012 J. Dairy Sci. 95: 874-887) documented that cows with subclinical hypocalcemia in the first 3 days postpartum had 3-fold greater risk of developing metritis and 11 times the risk of developing metritis concurrent with fever, compared with cows with normal blood Ca after calving.
Is there Increased Incidence of Endometritis?
There were other interesting results. “Cows with subclinical hypocalcemia also had increased incidence of endometritis, a disease that is less recognized by producers and characterized by presence of pus in the uterus after 3 weeks postpartum. It is thought that the inability to eliminate the typical bacterial contamination of the uterus after calving predisposes cows to develop inflammation of the uterus and extension of the period in which pathogens remain in the uterus of dairy cows. In fact, cows with subclinical hypocalcemia had immune cells with impaired function, which is thought to explain some of the inability to eliminate the bacterial contamination with the onset of parturition.”
Compromised Reproductive Performance
Not only do cows with subclinical hypocalcemia have increased risk of uterine diseases, but they also have compromised reproductive performance. The interval from calving to pregnancy becomes extended from 109 days in normocalcemic to 124 days in cows with subclinical hypocalcemia. This means that the affected cows had more diseases and also had a 15-day delay to become pregnant. Fifteen more days means that more cows will be needed to meet production goals. There are more dry days and other logistical issues that this causes.
Subclinical Hypocalcemia Steals Profits
Oetzel at the University of Wisconsin has estimated that the economic cost of subclinical hypocalcemia in a dairy herd is four times the cost of clinical cases, thus resulting in a substantial impact on profitability of dairy operations. This increased economic cost is attributed to the greater number of cows with subclinical versus clinical hypocalcemia even though a subclinical case costs 40% of a clinical case.
The Oetzel research gives this sobering example. “If a 2000- cow herd has a 2% annual incidence of clinical milk fever and each case of clinical fever costs $300 (Guard, 1996), the loss to the dairy from clinical cases is about $12,000 per year. If the same herd has a 30% incidence of subclinical hypocalcemia in second and greater lactation cows (assuming they are 65% of cows in the herd) and each case costs $125 (an estimate that accounts for milk yield reduction and direct costs due to increased ketosis and displaced abomasums), then the total herd loss from subclinical hypocalcemia is about $48,750 per year. This is about 4 times greater than the cost of the clinical cases. (Tri-State Dairy Nutrition Conference – April 23 and 24, 2013).
Pro-Active Prevention Strategies
A general rule of thumb is that no more than 15%-20% of cows should have blood calcium levels below 8.5 mg/dl at calving. As with all metabolic disorders, prevention is the key.
- The use of anionic salts until the urinary pHs are between 6.0 and 6.3. (Jerseys, 5.5-5.8)
- An intentional strategy for oral calcium supplementation is cost-effective due to increased milk yield in supplemented cows. Most second- and greater-lactation cows should be given an oral dose at the time of calving and a second dose about 12 hours later.
- Oral calcium supplementation is the best approach for hypocalcemia in cows that are still standing, such as cows in Stage 1 hypocalcemia or who have undetected subclinical hypocalcemia (Oetzel, 2011). Cows absorb an effective amount of calcium into her bloodstream with about 30 minutes of supplementation. Blood calcium concentrations are support for only about four to six hours afterwards (Goff and Horst, 1993, 1994) for most forms of calcium supplementation.
- Blood calcium levels and urinary pH levels are inversely related. Properly acidified animals will have urinary pH between 6.0 and 6.3.
- Feeding a negative DCAD diet 21 days pre-fresh has been shown to prevent clinical (a five-fold reduction) and subclinical hypocalcemia.
- More studies are needed before extending or reducing the number of days pre-fresh anionic salts are fed in the field.
Raise the Subclinical Threshold to 8.5 Mg/dl (2.1 mmol/l)
As previously mentioned subclinical hypocalcemia occurs in dairy cows with blood calcium concentrations at or below 8.0 mg/dl (2.0 mmol/l) but not showing clinical signs. Recently, Martinez and co-workers at the University of Florida suggested that the cut-off should be raised to 8.5 mg/dl (2.1 mmol/l) because cows below this concentration were more likely to develop metritis or metabolic disorders. Using this higher criterion, Reinhardt and co-workers’ data indicate that over 65% of mature cows and 51% of first-calf heifers were below this threshold. Research suggests that subclinical hypocalcemia may be directly associated with other metabolic disorders and may be the primary or secondary cause of decreased performance.
The Bullvine Bottom Line
Prevention of hypocalcemia should go beyond minimizing milk fever after calving. It is necessary to take proactive steps to reduce the prevalence of cows that develop subclinical hypocalcemia. Even though the attack may be unseen, using prevention strategies could have a very positive and visible effect on your dairy profitability. Don’t become the next statistic of a preventable disaster. Remember the Titanic?