Science and animal husbandry practices come together at this time to produce results that make dairy farms sustainable and profitable in the worst economic times. It is common practice on most dairy farms to feed a negative dietary cation-anion difference (DCAD) diet to assist the cow in maintaining calcium homeostasis by the utilization of calcium pools available in her body when she needs them. While every high-producing cow is going to become hypocalcemic or low in serum calcium for at least a few hours after calving, the utilization of a negative DCAD diet will shorten the duration and prevent it from becoming a problem.
Subclinically affected hypocalcemic cows, which cannot compete at the bunk, have lowered gut motility and reduced muscle coordination, and may be more prone to transition diseases related to this condition including clinical milk fever, mastitis, metritis, retained placentas, ketosis, etc.
Producers who avoid these pitfalls pay special attention to the following common areas that challenge negative DCAD diet success in the pre-fresh pen:
- Adequate anions in diet
- Target at least 21 days in pre-fresh pen
- Maintain high dry matter intakes (DMI)
- Proper physical mixing of DCAD diets
- Avoid unexpected sources of cations
Feeding the proper amount of anions is critical. DCAD is a number in ration formulation that should be negative, but one DCAD number does not fit all farms. The DCAD level that gets cows properly acidified on one farm will be completely different from another farm. The only way to determine success is by obtaining urine pH values that are consistently uniform and on target (between 5.5 and 6.0, as an example). A negative DCAD diet should produce urine pH target ranges within three to four days after the cows are exposed to the diet, and the cows should be kept in the target range for the duration of the pre-fresh period. Yo-yoing in and out of the target range may cause transition diet failure. Target the urine pH, not a DCAD number.
Exposure to the negative DCAD diet should be at least 21 days in length. While it only takes a few days to make a cow respond to a negative DCAD diet, research has shown that if the cow is on this diet less than 21 days, she is more prone to transition diseases and lower milk production in early lactation. Many managers choose to shorten this time in the pre-fresh pen to prevent overcrowding, but if cows calve too early, they will not fully benefit from the negative DCAD diet. On many farms, this becomes a no-win situation as they choose to avoid the bigger challenge of overcrowding.
Maintaining DMI in the pre-fresh pen is often not realized because of several factors. If the DMI of your pre-fresh pen is not 30 pounds or higher, several factors may be contributing. The harshness of the anionic product is usually the largest challenge. Many salts or acids used in achieving negative DCAD diet formulation do not allow for such intakes. Find ones that do. In addition, this is not a time to feed low-quality feedstuffs that may not be palatable. Freshness of feed, amounts of feeds offered, timing of feeding and bunk space can all limit DMI.
Maintaining DMI is important, but the physical mixing of the DCAD diet is also very important. A properly mixed total mixed ration (TMR) delivers uniform feed across the bunk, not a buffet of the different ingredients. Of upmost importance is the chop length of the forages. These should be chopped to a maximum length of 2 inches. If the TMR has a hairy appearance, it is too long, and the cows will use that opportunity to sort the TMR. This defeats the purpose of the TMR in the first place, and all cows will eat a different diet. The TMR should be mixed adequately so all ingredients are dispersed throughout the ration. TMRs should be about 50% moisture, unless weather conditions dictate otherwise.
Testing all potential feed sources, especially forages, before inclusion in the pre-fresh diet is important. The antagonist of a negative DCAD diet is the addition of unknown strong anion (potassium and sodium) sources to the diet, which makes the diet more positive in DCAD. This could be due to feeding from the wrong stack of hay, an untested forage source or the wrong mineral formulation. A successful DCAD diet can immediately become unsuccessful if this is not quickly detected. Weekly urine pH sampling can help detect the addition of unplanned sources of cations into the ration should it occur. Training of employees who feed will also allow them to understand that close attention to feeding this group of cows is of utmost importance.
When a farm is failing with the transition of cows, and managers claim they are following the requirements of a successful DCAD diet, pre-fresh pen overstocking can unravel everything they are doing right. Cows should not have to compete for bunk space, shade, lying space, water and other comforts at a time when they need it most. Two of the most critical factors in pre-fresh pen stocking density are allowing cows at least 30 inches of bunk space (limit stocking density to 80% of headlocks) and water availability in several places. Many pre-fresh pens fail these two requirements.
There is a lot to monitor in the pre-fresh cow pen. At a minimum, weekly urine pH values and DMI should be recorded along with routine recording of health events of fresh cows and early milk production. All will indicate the level of challenges of the DCAD diet and transition cows on the farm. It may take a little more time or attention to detail, but this is the time when the cow can either become a healthy, productive cow or a resource-draining problem. Your success depends on it. 
References omitted but are available upon request. Click here to email an editor.
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Glenn Holub
- Senior Dairy Technology Manager
- Phibro
- Email Glenn Holub
