Frequently Asked Questions
Hypocalcemia is a disorder in dairy cows caused by lower than normal blood calcium concentrations. There are two forms of the disorder, clinical and subclinical. Clinical hypocalcemia, more commonly referred to as clinical milk fever, is defined by total blood calcium concentrations below 5.5 mg/dl. Subclinical hypocalcemia (SCH) or subclinical milk fever is defined by total blood calcium concentrations between 5.6 and 8.5 mg/dl.
The sudden calcium requirement for milk production at calving places an enormous demand on the cow’s ability to maintain normal blood calcium concentrations. In addition, cationic dry cow diets (resulting mainly from feedstuffs containing high levels of potassium) can predispose the cow to hypocalcemia by reducing the effectiveness of the mechanisms the cow relies upon to balance her calcium status around the time of calving.
Regardless of age, all prepartum dairy cows are susceptible to hypocalcemia due to the rapid increase in calcium requirements at calving. Cows which are hypocalcemic have increased odds of developing retained placentas, metritis, mastitis and displaced abomasums which can lead to reduced lactation milk yields and decreased fertility. Feeding a negative DCAD diet to cows prior to calving helps reduce the risk of developing hypocalcemia.
Negative DCAD diets work by causing a mild, compensated metabolic acidosis. This is accomplished by feeding elevated levels of anionic minerals containing chloride and/or sulfur. The metabolic acidosis (lower blood pH), through the actions of parathyroid hormone and vitamin D, enhances the cows’ natural physiological mechanisms for maintaining normal blood calcium concentrations. These include dietary calcium uptake by the gut, bone release of stored calcium and urinary excretion of calcium.
While some nutritional feeding practices may help reduce the incidence of clinical milk fever (MF), those practices will have very little impact on the subclinical form of the disease.
Cows affected by SCH are less productive and profitable, with an estimated cost to dairymen of approximately $125.00 per case. Since more cows are affected by SCH (> 50%) than MF (typically < 5%), SCH has a larger negative impact on dairy profitability.
(Oetzel, G.R. 2012. An update on hypocalcemia on dairy farms. Proceedings of Four-State Dairy Nutrition & Mgmt. Conf.)
The best approach is to test for serum calcium by obtaining blood samples from fresh cows between 24 to 48 hours post-calving. The test is easy, fast and an effective method to determine the prevalence rate of SCH in dairy herds.
Estimates have shown that implementing a properly balanced negative DCAD diet may return greater than a 4 to 1 payback as a result of fewer metabolic diseases, increased milk production and better reproductive performance.
To achieve the maximum benefit from feeding a negative DCAD diet, cows should be fed for a minimum of 21 days prepartum. However, feeding longer than 21 days is recommended for optimal results.
Yes, and it may be better to do so. Studies have documented the safety and effectiveness of feeding a negative DCAD diet for up to 42 days prepartum, ideal for one-group dry cow programs.
Prefresh diets should be formulated to provide between -10 to -15 mEq/100 g DM. Ultimately, monitoring urine pH will be the guide for determining if cows are optimally (fully) acidified. Targeting a urine pH range between 5.5 and 6.0 will result in cows being fully acidified and in optimal calcium metabolism.
Testing urine pH of cows is an effective and practical way to monitor the level of acidification. Proper acidification will result in urine pH values between 5.5 and 6.0. Urine pH will typically fall between these values when the DCAD of the prefresh diet is formulated between -10 to -15 mEq/100g.
The best time to test urine pH is between 4 to 6 hours post-feeding, as sampling relative to time of feeding will impact urine pH values.
Phibro recommends a properly balanced negative DCAD diet based on the nutrient specifications listed below.
|% of diet DM||grams/day*|
|Calcium:||1.52 to 1.60||180 to 190|
|Phosphorus:||0.36 to 0.42||42 to 50|
|Magnesium:||0.45 to 0.50||53 to 59|
|Sodium:||0.10 to 0.20||12 to 24|
|Chloride:||0.80 to 1.00||94 to 118|
|Sulfur:||0.40 to 0.47||47 to 55|
*Recommendations are calculated on 26 lbs. of dry matter intake
Animate is a thoroughly researched and field tested anionic mineral supplement proven to help reduce the incidence of hypocalcemia which can have negative effects on health, production and fertility. Because it is highly palatable, Animate can be fed in a fully acidified program without decreasing dry matter intake, an important consideration when choosing an anionic mineral supplement.