Calcium Is the Cornerstone to Transition Cow Success
Jul 03, 2014
Strategies for meeting your herd’s calcium needs.
By Glenn Holub, Prince Agri Products, Inc.
The transition period is the most challenging time during the production cycle of a dairy cow. One of the major determinants of whether a cow transitions properly is her ability to maintain normal blood calcium concentrations of more than 8.5 mg/dL.
A recent study reported more than 50 percent of cows and 25 percent of first lactation heifers have blood calcium concentrations after calving in the range considered subclinical (Reinhardt, 2011). Subclinical hypocalcemic cows are at greater risk for developing metabolic and infectious diseases postpartum, illustrating the importance of calcium status during the transition period. Fortunately, the physiology of calcium status is now more fully understood and can be effectively managed through proper management and nutrition. Through the use of these nutritional strategies, it is possible to help reduce the diseases related to low blood calcium.
The metabolic and physiological demands for calcium increase dramatically as calving approaches. The calving process, colostrum production and milk synthesis all have a requirement for calcium and collectively may exceed the available levels in circulation, leading to either subclinical hypocalcemia or clinical milk fever. Calcium is essential for normal cellular activity and function of almost all cells. Cells of the immune system have the same need, and cows that become hypocalcemic are more susceptible to infection and disease because immune cell activity is impaired.
Meeting calcium needs
There are several strategies for maintaining blood calcium concentrations to avoid hypocalcemia. Most practical and effective approaches nutritionally manipulate dietary macro-mineral ions, such as chloride, sulfur, sodium and potassium. By feeding a diet higher in the negative ions (chlorine and sulfur) and lower in the positive ions (sodium and potassium), the cow’s blood becomes mildly acidic. This stimulates the physiological processes needed to mobilize bone calcium stores and initiate dietary intestinal calcium uptake necessary for meeting the calcium demands associated with transition. This strategy is referred to as feeding a negative dietary cation-anion difference (DCAD) diet or ‘acidified’ diet.
The success of a negative DCAD nutritional strategy can be measured using urine pH prepartum and blood calcium levels within the first 24 to 48 hours of calving. Urine pH targets, when samples are tested after three to four days of feeding a negative DCAD diet, should be within the range of 5.5 to 6.0 for all breeds.
Negative DCAD diets are most effective when fed at a calculated DCAD value of -10 to -15 mEq/100g of dry matter and fed continuously for a minimum of 21 days prior to calving. Because some DCAD feed additives are not palatable, it is important to feed a product that promotes a high level of dry matter intake during this period.
Monitoring blood calcium levels
If postpartum blood calcium concentrations are monitored, values should be near or above 8.5 mg/dL. Blood calcium concentrations begin to fall two or three days prior to calving due to demand for colostrum production. During this time, a dry matter intake reduction usually takes place and exacerbates the issue of lowered calcium concentrations.
Typically, blood calcium concentrations are lowest two to three days after calving, and cows do not usually recover fully until three to four days later when normal blood calcium concentrations return to 8.5 to 10 mg/dL. Fresh cow diets containing calcium concentrations between 1.0 and 1.1 percent may provide the necessary levels to avoid prolonged subclinical hypocalcemia status. Utilizing ingredients with high bioavailability may be warranted.
In addition to feeding the proper dietary levels of anions, other nutritional adjustments need to be made to the pre-fresh negative DCAD diet to ensure optimal transition success. These include feeding dietary dry matter levels of 1.4 to 1.6 percent for calcium and 0.45 to 0.5 percent for magnesium.
Keeping a cow’s blood calcium level at or above 8.5 mg/dL throughout the transition period by feeding a highly palatable -10 to -15 mEq/100g negative DCAD or fully acidified diet will help reduce the incidence of hypocalcemia and its related cascade of diseases. Following this with a highly bioavailable calcium diet postpartum will further enhance the recovery from transition to peak milk.
Strategies for meeting your herd’s calcium needs.
Glenn Holub, Ph.D., PAS, is a dairy technology manager for Prince Agri Products, Inc. He is a former animal science professor specializing in dairy cattle nutrition and can be contacted at firstname.lastname@example.org.
Reinhardt, T. A., J. D. Lippolis, B. J. Mc Cluskey, J. P. Goff, and R.L. Horst. 2011. Prevalence of subclinical hypocalcemia in dairy herds. Vet. J. 188:122–124.