Hypocalcemia is a costly disease to the dairy industry, particularly the subclinical form (SCH) since it affects more than 50% of cows in a herd. Cows with SCH produce less milk, are more prone to other metabolic and infectious diseases and have impaired fertility. Conservative estimates for lost income due to SCH range between $125 and $150 per case, so preventing SCH should be a high priority on every dairy.

The best approach to reducing the incidence of SCH (and clinical milk fever (MF)) is through prepartum feeding of a negative Dietary Cation Anion Difference (DCAD) diet. Most industry people agree on that point, but differ on the dietary recommendations of the ration. One of the primary points of difference revolves around the proper calcium level to feed prepartum.

Q: Why the confusion on high or low calcium?

A: For decades, the proper level of calcium for prepartum dairy cows has been researched and debated by the dairy nutrition community. A wide range of transition dairy cow research reveals why there are many perspectives:

• Work demonstrates that very low levels (< 15 g/cow/d) of calcium intake prevent clinical MF.

• Research substantiates the benefits of using either a low (< 0.70% DM) or high (> 1.5% DM) level of dietary calcium.

• The various treatments utilized across many experiments in prepartum DCAD studies have been inconsistent, which has led to a wide range of strategies.

Q: Can feeding a low dietary calcium diet prepartum work?

A: The answer is yes, if success is measured by reducing MF. Low dietary calcium diets work if calcium intake is restricted below the requirement of the late-pregnant dairy cow. Research has demonstrated that this level must be below 15 grams per cow per day.  

Interestingly, in one study, although the low dietary calcium (8.2 g/cow/day) treatment eliminated MF cases compared to the control diet (41 g/cow/day), two-thirds of the animals fed the low calcium diet experienced SCH as determined by total blood calcium concentrations below 8.0 mg/dl. Thirty-eight percent of the cows fed the high calcium diet (41 g/day) had MF and 75% of the non-clinical cows had SCH. 

Q: If controlling SCH through feeding a low dietary intake of calcium is unattainable, what about high dietary calcium intake?

A: One meta-analysis revealed that for every 0.25% increase in dietary calcium concentration from 0.50 to 2.0%, an approximate 30% reduction in the incidence of MF could be expected. For cows fed a very cationic diet (non-acidified), research demonstrated a reduced rate of MF, from 80 to 23%, using a high versus low dietary level of calcium.

While very low dietary calcium intakes can reduce MF in practice, this strategy becomes almost impossible to accomplish through normal diet formulation and is not a recommended approach to controlling both MF and SCH. The most practical and effective method to control both is with a negative DCAD diet, prepartum.

Q: High versus low dietary calcium concentrations in negative DCAD diets, which is better?

A: One of the frequently asked questions regarding a negative DCAD diet prepartum is what level of dietary calcium should be fed. This is a great question, and one that can be addressed by reviewing the research conducted in this area.

• A foundational study involved two levels of DCAD (+33 or -13 mEq/100g) and one level of calcium (~ 0.65%) fed beginning 45 days prior to expected calving date. No MF incidence was observed in the cows fed the negative DCAD diet and these cows produced more milk (1,070 pounds vs. control) in the subsequent lactation. 

• Another study examined the effects of feeding three levels of DCAD (+15, 0 and -15 mEq/100g) with differing calcium concentrations (0.50% and 1.50%) prior to calving. Results showed that mature cows fed the -15 mEq/100 g diet, with 1.5% dietary calcium, had significantly higher plasma ionized calcium concentrations both before and on the day of calving, compared to cows fed the 0 mEq/100 g diet with 0.50% dietary calcium.

• Another study showed cows fed a negative DCAD diet prepartum (-7.5 mEq/100g) with 1.16% dietary calcium compared to cows fed the same negative DCAD diet with 0.59% dietary calcium had a similar low incidence of MF. However, cows fed the higher dietary calcium concentration had significantly less SCH (16.7 vs. 41.6%).

Q: What are the take-home points from these studies?

A: Clinical MF can be reduced if dietary calcium intakes are restricted below the daily requirement of the prepartum dairy cow (<15 g/cow/day). However, the incidence of SCH may not be affected.

When negative DCAD diets are fed prepartum, the level of dietary calcium will impact the effectiveness of these diets, particularly as measured by serum calcium concentrations, incidence of SCH and responsiveness of calcium metabolism. Feed a minimum of 1.5% calcium (DM basis) or the dietary concentration necessary to provide at least 180 grams of calcium per cow per day.

Feeding a fully-acidified diet (urine pH between 5.5 and 6.0) with dietary calcium intakes at or above 180 grams per day will help maintain calcium balance in the transition dairy cow and may result in enhanced fresh cow health, increased milk yield and better reproductive performance.

For more information about feeding a fully-acidified diet, visit Animate-Dairy.com.

Author: Ken Zanzalari, Ph.D., Dipl. ACAN Ken.Zanzalari@pahc.com