How to Pick the Right Close-up Diet
No one likes to treat a sick cow. And having to treat a sick cow following calving means something in your transition period system failed. Hypocalcemia, both clinical and subclinical, occur all too often, but they are highly preventable. When you prevent low blood calcium you also minimize the health problems that often follow.
Milk fever increases the risk of eight other periparturient diseases and is often considered the “gateway” disease process for poor transition performance, explains Robert Van Saun, extension veterinarian at Penn State University. Decades of research have demonstrated the negative effects of hypocalcemia. And it’s not just clinical milk fever you have to be concerned with; newer research indicates that subclinical hypocalcemia predisposes multiparous cows to less milk production, more disease risk and increased risk of involuntary culling. But it doesn’t have to be that way.
Take for example, a Pennsylvania dairy that had milk fever prevalence upwards of 15% in multiparous cows. Blood analysis indicated a >50% prevalence of subclinical hypocalcemia (<8.0 mg/dl) in multiparous cows. An investigation revealed a change in the forages fed to the dry cows and that the dairy was using a mixture of nutritional practices including a partial DCAD diet and feeding high dietary calcium. To correct the problem forages were tested for mineral content, then the dietary DCAD was calculated at 0 mEq/kg dry matter, dietary magnesium was increased and dietary calcium was reduced to 0.95%. The prevalence of all periparturient diseases was dramatically reduced—milk fevers declined to <5%. Intervention was warranted in this case because of the high prevalence of milk fever in the herd.
Every dairy should evaluate their transition cow program and ask if they can do better. Many nutritionists today report that they can achieve <3% milk fever prevalence and <20% subclinical hypocalcemia in well managed herds using negative DCAD diets.
PICK YOUR STRATEGY
Transition cow nutrition is not one-size-fits-all. Nutrition for transition cows should be tailored to each dairy. You must consider the forages available, the management level of the dairy, capabilities of the staff and feeding system to provide consistent mix and delivery of feeds—especially if using an anionic supplement, the facilities available for grouping dry cows, how many cows will calve per month and the potential for overcrowding or increased stress during the transition period, says Van Saun. All of these factors impact the success or failure of a transition cow program. You also need to identify which metabolic diseases occur during the transition period and their prevalence. The nutritional remedy for milk fever and ketosis are not the same. That’s why you need a good understanding of which problems occur in transition cows before making a nutritional change.
For dairies with clinical and subclinical hypocalcemia, research and on-farm use has clearly shown the many benefits of feeding negative DCAD diets to close-up cows, says Van Saun. Three nutritional strategies for DCAD have emerged for close-up dry cows:
- Not feeding an anionic supplement, instead focusing on lowering the DCAD by feeding low potassium and low sodium forages.
- Feeding enough anionic supplement to reduce the calculated DCAD to about zero.
- Feeding enough anionic supplement to create a negative DCAD diet and induce a state of metabolic acidosis in the cow.
Producers in areas that can grow low potassium and low sodium forages may opt for just reducing the dietary potassium load, with no anionic supplement. With this strategy, you need to keep the dietary calcium level as low as possible, meaning little or no high-calcium forages, and no calcium supplements. This results in a calculated DCAD of about +100 mEq/kg of DM which results in a urine pH of 8.3 to 8.5. This strategy may reduce clinical milk fevers, but subclinical hypocalcemia often remains above desirable levels.
Adding some anionic supplement, sufficient to reduce the calculated DCAD to about 0 mEq/kg DM, should result in a urine pH of about 7.5 and is a good intermediate step in the right direction toward reducing some transition cow issues. However, recent research by Koszewski and Goff (2018) suggests that transition cows don’t start experiencing benefits from added anions until the urine pH drops below 7.5. Keep added dietary calcium to a minimum, and keep dietary phosphorus at 35 grams/day or less. Increase magnesium to 0.45%. This strategy is a small step that allows people to try anionic supplements and see some reduction in clinical milk fevers.
However, feeding an even lower DCAD diet that creates a mild, compensated metabolic acidosis with a urine pH of 6.0 to 6.5 is the strategy that yields the most benefits to the cow. For this strategy, the calculated DCAD is about -50 to -100 mEq/kg of DM. Some supplemental calcium is advisable, although the exact amount has yet to be firmly established by researchers. Anywhere between 60 and 120 grams per day should be sufficient, without negatively impacting feed intake. In addition, keep phosphorus intake under 35 grams per day and increase magnesium to 0.4 to 0.5%. Urine pH should be checked weekly and DCAD supplementation adjusted if needed.
These strategies are a progression from no negative DCAD to a level of negative DCAD sufficient to create a mild metabolic acidosis. Each strategy is unique. To get good results you must adhere to the strategy selected. Do not try to mix the nutritional aspects of two different strategies, stresses Van Saun. For example, do not feed high dietary calcium to cows that are not metabolically acidified. If you start with one strategy and don’t see the results you want, then you must follow all of the steps of the next strategy you select.
Each of the three strategies requires a little bit more in terms of labor and management. That’s why it is important to understand the day-to-day requirements, cost and potential benefits of each before you try. Talk to your veterinarian and nutritionist about which strategy would be best to improve calcium homeostasis and transition cow success on your dairy.