New Data on Negative DCAD Diets
Decades of research clearly demonstrate that multiparous transition cows do extremely well when fed a negative DCAD diet. A meta-analysis of published research in the March Journal of Dairy Science shows that in addition to reducing milk fever, negative DCAD diets also reduce subclinical hypocalcemia, retained placenta and metritis. They also increase milk production and fat-corrected milk in multiparous cows, Santos et al., (2019).
Despite all the known benefits from feeding negative DCAD diets, some questions still remain. That’s why researchers continue to ask questions. New research from the University of Florida and the University of Illinois provides some answers.
How Long Should I Feed Negative DCAD?
How cows are fed during the 45- to 60-day dry period makes a big difference on how successfully they transition into lactation. In the last decade controlled-energy diets, also called the “Goldilocks” diet, have emerged as the most beneficial diet choice for dry cows. (Please see “‘Goldilocks’ Diets Still Just Right for Dry Cows” in the May 2018 issue)
Negative DCAD diets are another piece of the puzzle for healthy and productive transitions. Negative DCAD diets that metabolically acidify cows to achieve a urine pH of 5.5 to 7.0 work well. But how long should cows be metabolically acidified—the entire dry period or just the last 21 days? That’s the question University of Florida researchers recently answered.
Research by Lopera et al., (2018) examined the effects of feeding a negative DCAD diet for either the last 21 days of gestation or the last 42 days of gestation. Two different diets, -70 mEq/kg of DM and -180 mEq/kg of DM, were each fed to the short- and long-duration groups. After calving, all 114 Holstein cows enrolled were fed the same diet. Long-duration cows, fed either level of DCAD, had two days shorter gestation lengths, produced 5.5 lbs less milk per day in the first 42 days of lactation and tended to have increased days open. There were minor differences in ionized calcium (iCa) and measures of acid-base status pre- and postpartum between short- and long-duration cows. Researchers also identified differences between cows fed -70 and -180 mEq/kg of DM, regardless of the duration of feeding. Prepartum cows on the more acidogenic diet ate 2.4 lbs less feed per day. Those cows were also in a more negative energy balance and produced less colostrum. However, after calving there was no difference in yields of milk, milk components, health or reproductive performance compared to cows fed the -70 mEq/kg of DM diet.
Researchers reached two conclusions: 1. Feeding acidogenic diets beyond 21 days might be detrimental to dairy cows, and 2. There was no benefit to reducing DCAD from -70 to -180 mEq/kg of DM. Read the full study in Journal of Dairy Science.
How Much Calcium to Include?
Researchers at the University of Illinois presented six abstracts at last summer’s ADSA meeting that sought to zero in on how much calcium should be fed in negative DCAD diets. The research team, led by James Drackley, professor of dairy nutrition, fed 81 Holstein cows one of three diets: Control +6 mEq/kg of DM with 0.4% calcium DM, Low -24 mEq/kg of DM with 0.4% calcium DM (40 grams/day) or High -24 mEq/kg DM with 2% calcium DM (220 grams/day). All cows were fed a high-forage, low-energy (“Goldilocks”) diet at the start of the dry period until enrolled in the feeding trial at 28 days before expected calving date.
Findings of interest include: All cows fed a negative DCAD diet, with either low or high calcium, had greater iCa concentrations at calving (1.10 and 1.11 mmol/L) and at 24 hours after calving (1.11 and 1.05 mmol/L) when compared to control cows (0.98 mmol/L). There was no difference in immune function measurements between diets.
All cows fed a negative DCAD diet, with either low or high calcium, had lower postpartum BHB (0.91 and 0.88 mmol/L) at 24 hours post calving compared to cows fed the control diet (1.47 mmol/L). A BHB ˃1.0 mmol/L at 24 hours after calving indicates subclinical ketosis. There was no difference in NEFA levels.
Dry matter intake was higher in prepartum cows fed the control diet compared to cows on the low or high calcium acidogenic diets—26.6, 22.1 and 24.2 lbs/day respectively, says Drackley. But after calving, cows fed low or high calcium diets had greater DMI (41.7 and 43 lbs/day) and greater milk yield (98.3 and 99.6 lbs/day) than control cows (37.5 and 92.6 lbs/day).
In the study, researchers were feeding to achieve a mean urine pH of 5.7 for cows on the low calcium and high calcium negative DCAD diets. The actual mean urine pH achieved was 8.12 for cows fed the control diet, 5.76 for cows fed the low calcium diet and 5.67 for cows fed the high calcium diet, says Drackley. They also examined the amount of calcium excreted in urine. All of the cows fed the acidifying diets excreted more calcium in urine than control cows did prepartum. Total calcium excreted was 8.4, 13.4 and 1.0 grams/day for low calcium, high calcium and control diets. Cows fed the low and high calcium acidifying diets all successfully created a calcium sink in the prepartum period to help prepare cows for the high calcium demand of calving.
On most of the parameters measured, the resulting difference from feeding a low or high calcium level was small, says Drackley. His current recommendation on calcium in the prepartum diet would be 0.9% to 1.0% calcium in the total diet DM (80 to 120 grams/day) if feeding a partial or moderate DCAD diet. If feeding an aggressive negative DCAD (fully acidifying) diet he recommends about 1.6% calcium or above in the total diet DM (˃180 grams/day).
While current research has not revealed the optimal level of calcium to feed prepartum, it has shown that feeding a “Goldilocks” diet combined with a negative DCAD diet during the close-up period can produce healthier, more productive cows for many farms. As more research and meta-analysis are completed, the calcium question will eventually be answered.