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Target ration DCAD levels, not urine pH results

Ruby Wu for Progressive Dairyman Published on 29 September 2017
Nutrition Professionals

Balancing rations for dietary cation-anion difference (DCAD) prepartum is a valuable nutrition strategy in pursuit of reducing costly metabolic challenges like hypocalcemia, metritis and ketosis during the transition period.

We know these health challenges have multiple causes and are not solely dependent on DCAD balancing.

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But rations appropriately formulated for DCAD, and other considerations such as metabolizable protein and energy, offer significant preventative benefits while enhancing cow performance and productivity – especially during the transition period.

Dairies understandably focus on this critical time frame because cows that do not navigate the transition period well often result in the loss of 4 to 9 kilograms of peak milk, which could represent 900 to 1,800 kilograms of unrealized milk yield.

What to watch?

There has been much attention paid lately to monitoring urine pH levels as a measure of transition cow health. Since urine pH will drop with blood pH, urine pH is an indicator of blood pH and helps to assess the effectiveness of the negative-DCAD program on cows’ acid-base status.

In some instances, however, urine pH monitoring has become the focus of the nutrition management program rather than the desired outcomes related to health associated with rations adequately formulated for DCAD.

Such was the lesson learned by a 1,300-cow dairy in the southwest U.S. The farm embarked on an aggressive weekly urine pH testing protocol. However, the herdsman and his team conducted tests at random times.

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They tracked results but couldn’t seem to find a discernable pattern – inconsistency of results was the rule rather than the exception. Urine pH levels fluctuated from 5.8 to 7.5 in the Holstein herd, averaging 6.0 some weeks, 7.1 other weeks and everywhere in between.

This inconsistency could be attributed to the irregular testing protocol, overcrowding, feedbunk management or mixing as well as the variation that occurs naturally within an animal. Still, the dairy decided to reduce prepartum ration DCAD even further to keep urine pH levels consistently below the desired 6.8 threshold.

In fact, the farm added more product to the ration in hopes of pushing urine pH below 6.3 and keeping it there. The dairy accomplished this goal, but there was no measurable improvement in transition cow health. The feed bill increased, though.

Calculations show for every 2 points of DCAD you decrease in the diet, you add approximately 5 cents to ration cost (4 to 7 cents depending on product price).

For example, if you only need a ration DCAD of -10 but are over-formulating for -14, then you are wasting 10 cents per cow per day with no added benefit. We also know as DCAD decreases, you may be sacrificing critical feed intake for this stage of the animal’s life cycle.

To avoid this pitfall, aim for a ration DCAD of -8 to -12 meq per 100 grams of dry matter for at least 21 days prepartum. This practice adequately acidifies cows and helps reduce the risk of clinical hypocalcemia and subclinical hypocalcemia postpartum.

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Ultimately, the dairy backed off on its goal of very low urine pH levels as an assessment of nutrition success. It tightened the timing of the monitoring program so urine pH samples were taken at the same time.

It also reformulated rations to -10 meq per 100 grams of dry matter with the objective of simply acidifying cows. This change immediately cut the farm’s transition group feed cost by 12 cents per cow per day while maintaining cow health.

Clinical and subclinical incidences of hypocalcemia and other transition challenges as determined by desired outcomes remained in check.

It’s all about animal health

Instead of debating how high or low urine pH levels should be, or what fluctuating urine pH levels mean, your strategy must aim higher than that.

The larger concern is what you are trying to accomplish when formulating rations for DCAD. That is, what job are you really trying to get done by formulating rations for DCAD?

The number one purpose of feeding a negative-DCAD diet prior to calving is to have healthier cows with less time in the sick pen along with higher start-up milk and peak yields.

When rations are properly formulated for negative DCAD, more of the total blood calcium becomes available in ionized form. This reduces the risk of subclinical hypocalcemia, milk fever, metabolic diseases associated with transition cows and subclinical hypocalcemia, as well as start-up and peak milk.

Furthermore, cows that recover from milk fever have an increased risk of ketosis, mastitis (especially coliform mastitis), dystocia, left displaced abomasum, retained placenta and milk fever in the subsequent lactation.

Reducing transition health challenges by lowering prepartum ration DCAD accomplishes this aim. Plus, this strategy helps elevate reproductive performance and cow productivity in the following lactation.

As for dealing with the minutiae of urine pH monitoring, it should be of lesser concern than the overarching objectives of improved animal health and performance.

Still, it makes sense to develop and follow a specific protocol to obtain the most useful results. Once urine pH is less than 6.8, the job of acidifying cows is done.

Testing parameters

When setting up a testing program, consider the following:

  1. Understand there will be some fluctuations in urine pH due to the cow’s biology. These variations are normal and no cause for alarm.

    Changes in urine pH can also be related to overcrowding, mixing and sorting challenges, feeding times or other management actions.

  2. Take samples at the same time to take some of the inconsistency out of your sampling program.

    If 80 percent of cows tested are not consistently within range, this should trigger further exploration, beginning with overstocking, bunk management, mixing and sorting issues.

  3. Don’t focus on getting and keeping urine pH levels to extremely low levels.

If urine pH is below 6.8 for each Holstein or 6.5 for each Jersey monitored, you will reap the health and productivity benefits of a prepartum negative-DCAD diet.

Focus on the outcome

There appears to be no justification for trying to achieve lower urine pH values based on postpartum health and production responses. Formulating rations with increasingly negative DCAD values only increases feed cost and can drive down feed intake.

Dairies do not attain the performance payback they desire from this strategy; there are no compounding efficiencies or increases in health or milk production to be gained from further acidifying the rumen.

That noted, you may periodically record urine pH values below the target values during monitoring since some variation is normal based on the cow’s biology and behaviour. But there is no reason to strive for consistently, extremely low urine pH values as a goal.  end mark

References omitted but are available upon request. Click here to email an editor. 

Ruby Wu
  • Ruby Wu

  • Technical Services
  • Manager – Ruminant
  • Arm & Hammer Animal Nutrition

DCAD HINT

To make sure rations are accurately formulated for DCAD, be sure to test your water supply to determine chloride levels, which can vary by water source and could affect DCAD levels. Also, obtain DCAD forage analysis by wet chemistry since forage mineral levels can vary as well, also affecting ration DCAD levels.

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