Urine pH and Negative DCAD:  Don’t Overthink the Science

A negative DCAD ration (-DCAD) is used to prevent post-calving hypocalcemia in dairy cows both at the subclinical level (increased health risk) and at the clinical level (obvious milk fever).  Simply put, the -DCAD ration works by feeding the cow disproportionate amounts of negatively charge minerals, especially chlorine, for about three weeks pre-calving.  This shift to more negative minerals in the diet causes mild metabolic acidosis in cows.  This then turns on calcium mobilization from bones before the cow calves, thus limiting calcium-related problems after she calves. 

The beauty of this technology has always been that there is an easy way to determine if metabolic “acidification” is working and that is a simple urine pH test.  A reasonable range for average urine pH is 6.0 to 7.0 which should indicate that the close-up cows are, on average, properly acidified.  Unfortunately, there is sometimes a tendency to over-analyze the process of urine pH measurement.  We talk about pH ranges for a reason, because lots of things in cow management and biology can vary.  Nutritionists attempt to control the ration but sometimes forage mineral information (especially potassium) is not 100% accurate or ration mixing is simply poor.  The cows themselves vary biologically.  Cow metabolism varies and some cows simply have bigger appetites and eat more total -DCAD mineral.  Reading pH paper color changes can vary from the paper brand itself to the ability of the reader.  One in 12 men are colorblind and struggle with close color matches.  All of this is perfectly okay.  Our biological goal is to basically make sure the close-up group is simply “within range”. 

Unfortunately, there are suppliers of -DCAD products and some specialists in the field that promote very low urine pH (less than 6.0) and seem to imply that disaster might strike if average pH creeps up into the mid-6 range.  None of this is true.  Cows need at least two good weeks on the close-up ration.  If we are good at projecting calving dates and feeding management is reasonably good, all cows will have acceptable acidity.  A little variability in urine pH is going to occur and slight tweaks in -DCAD feeding rate (up or down) may be needed.  Only clinical milk fever or a spate of other possibly calcium-related health problems should really get our attention.  Our goal should occasional spot checking the program, especially if there has been some kind of ration change, such as with the forage.  Test 10 or so cows and discard the highest and lowest pH values.  If the average is between 6.0 and 7.0, then we have achieved our goal of moderate metabolic acidification.  Acidification does take a few days, so skip testing cows that have just arrived at the close-up pen. 

Sometimes examples are the best teacher.  Barentz Animal Nutrition has been manufacturing an extruded, soy-based -DCAD product called MegAnion™ for more than 10 years.  MegAnion™ has more than 22% chloride and the highest -DCAD level in the market.  We have a wonderful distributor in Latin America that has been importing MegAnion, almost since its inception.  Most of the client herds of this distributor have milk production levels that look very similar to those of upper Midwest farms in the United States.  This distributor offers support for both ration formulation and feeding management for close-up programs.  Uniquely, however, they also offer monitoring of post-calving ionized calcium to help determine how well the program is truly performing.  They randomly test recent calvers (maybe 5 or 10% of the cows) by pulling blood samples within 4 to 8 hours after calving.  These blood samples are then tested on the farm using a portable ionized calcium meter.  Depending on the goal of the producer, the herd is then tracked on the percentage of cows that may be drifting toward subclinical hypocalcemia.  In almost all cases, herds that track ionized calcium also have a good program in place to monitor urine pH.  It is a great object lesson to see, basically in real time, how much urine pH can vary at the same time that blood ionized calcium holds steady.  The vast majority of these herds try to keep pH around 6.5 and only consider tweaking the ration when average urine pH clearly exceeds 7.0.  These farms are wonderful examples of how effective practical pH monitoring can be for achieving the post calving goal of no problemas metabolicas.  As a final point, we should never lose site of the fact that pushing urine pH to very low levels (less than 6.0) costs us money.  More importantly, if urine pH is chronically close to 5.5, it is almost a certainty the feed intake of the cows will be negatively affected.