Research shows that negative DCAD diets are important for the health of pre-fresh dairy cows. But how much dietary calcium should be fed to late-gestation cows to prepare them for lactation? Is more calcium better? And does that vary by operation?
How much dietary calcium do transition cows really need?
- Recommendations for the amount of dietary calcium vary widely depending on the source.
- Research has found that even extreme differences in calcium intake made no difference in immune function or milk production.
- It’s safe and practical to stick with a solution that delivers proven results— a negative DCAD diet with a moderate amount of calcium.
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Research and on-farm studies have proven that a negative DCAD diet for late-gestation cows has a consistent and profound effect on calcium metabolism.
Yet that same research does not show that feeding different amounts of calcium has much impact on actual calcium metabolism or positive impact on transition cow health or milk production.
“The amount of calcium in negative DCAD diets may be one of the least important factors for success,” says Tim Brown, director of technical support for SoyChlor.
“At a time when intake is depressed and every bite a cow takes needs to be nutrient-dense, do we really want to waste ration space on limestone if it isn’t necessary—if it doesn’t benefit the cow?” he says.
Maintaining Blood Calcium Levels
A cow’s body attempts to maintain blood calcium within a certain range, roughly between 8 and 9 mg/dl.
With non-acidified dry cows (fed no anionic supplement or salts), the metabolic calcium demand is very low. When the cow suddenly starts making colostrum, calcium demand spikes and the mammary gland pulls the calcium it needs from the blood. The body tries to meet the increased demand but because the metabolic demand was previously so low, there is a lag time in response, which results in hypocalcemia.
However, when dry cows are fed a negative DCAD diet, the resulting mild metabolic acidosis helps the cow’s body prepare to meet calcium needs even before colostrum production begins. Extra calcium is already being mobilized. If there is too much extra calcium, the kidneys remove and excrete it in urine. That’s why urinary calcium excretion increases when cows are fed a negative DCAD diet.
When the cow’s metabolic machinery is already activated, the lag time is reduced. The cow is less likely to develop hypocalcemia at calving, and hypocalcemia that does develop may be less severe, and/or persist for a shorter time.
Meta-Analysis Confirms Results
A meta-analysis by Santos et al. (2019) reviewed years of research and found that cows that are metabolically acidified during the last 21 days of gestation have reduced incidence of milk fever, subclinical hypocalcemia, retained placenta and metritis. In addition, in multiparous cows, feeding negative DCAD diets prepartum also increased milk production and fat-corrected milk.
The researchers concluded that negative DCAD diets work, but that manipulating dietary calcium content had little or no effect on health or performance of metabolically acidified cows.
A Deeper Dive Into Calcium Research
The reason DCAD isn’t a one-size-fits-all solution is that cows and herds are unique. “For example, when it comes to calcium metabolism, metabolically acidified and metabolically alkalotic cows are two totally different animals,” explains Brown. Data obtained with alkalotic cows is rarely applicable to acidified cows, and vice versa.
Several recent studies have used cows fed negative DCAD diets with differing levels of dietary calcium.
- Melendez and Poock (2017) reported that blood total calcium level within 24 hours after calving was the same (2.11 mM/l) for metabolically-acidified cows fed a diet with either 0.94% or 1.3% calcium.
- Diehl et al. (2018) concluded that feeding diets with 1.8% calcium increased blood ionized calcium (8.1 vs. 7.5 mg/dL, respectively) only on day 1 post calving compared to feeding diets with 1.3% calcium. Cows fed the diet with more calcium also consumed less feed prepartum, and produced lower quality colostrum.
- Lean et al. (2019) analyzed previous research and concluded that, “the lower-DCAD diets markedly reduced the risks of clinical hypocalcemia, retained placenta, metritis, and overall disease in the periparturient period. There was no evidence to support a particular level of calcium intake.”
- Glosson et al. (2018a) reported no difference in blood-ionized calcium (iCa) of cows fed a negative DCAD diet (urine pH 5.7) with either 0.4 or 2.0% dietary calcium. Actual calcium intakes averaged 44 grams/day and 226 grams/day for the low- and high-calcium diets, respectively. The same trial also measured the amount of calcium excreted in the urine. Cows fed the higher-calcium diet excreted more calcium in the urine (13.4 grams/day compared to 8.4 grams/day) than cows fed the low-calcium diet. Despite the extreme difference in calcium intake, no differences in immune function or milk production were found.
- Goff & Koszewski (2018) fed negative DCAD diets with either 0.46 or 0.72% calcium in the diet DM. They also fed a positive DCAD diet with 0.46% calcium. Cows fed the negative DCAD diets had higher blood total calcium on day of calving than cows fed the positive DCAD diet, but the amount of dietary Ca did not affect blood calcium concentrations of these moderately acidified cows.
Given this new research, why do some still recommend supplementing cows with extreme amounts of calcium in the diet? Currently there is little or no scientific evidence that the amount of dietary calcium affects transition cow health or performance.
Perhaps future research may reveal otherwise, but until then, it is safe and practical to stick with what delivers proven results—a negative DCAD diet with a moderate amount of calcium.
To learn more about using SoyChlor, a proven negative DCAD supplement, please visit with your Dairy Nutrition Plus representative or get in touch with us here.
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