ONCE in a great while, I find a research trial summary in a peer reviewed journal that really speaks to me. To be perfectly honest, at times, it is a struggle to stay connected through a research paper. I often read the abstract, a bit of the introduction, and then skip to the summary or discussion. However, I get to associate with people who really like the middle part of these papers and are nice enough to tell me if any of the minutia is important for me to know.
I saw a mention of a recent paper in the Journal of Dairy Science from researchers at Cornell University that concerned different strategies in building rations for prefresh dairy cows. When I saw that the question being answered was one that I have to think about regularly, I was hooked.
I can relate
So, what is this important topic and what are the two simple questions being asked? First, when feeding a dietary cation-anion difference (DCAD) diet, how low should you go on DCAD and on expected urine pH? I have seen various approaches and confirmed DCAD wet chemistry lab analyses indicating success at different points along this spectrum.
This trial looked at two formulated levels of negative DCAD. The most negative, called full acidification, was -10.3 DCAD. This would be a normal level for me. The other treatment was called partial acidification and was formulated for -2.6 DCAD. I see this low-negative result at times on lab analyses, and the usual response would be to raise the acidification to get the measurement back down closer to -10. It was convenient that these two levels are nearly exactly the same ones I deal with on routine close-up cow diet reformulations.
For the second question, they picked an even more interesting and frequently disagreed upon topic of how much calcium to add into an acidified/DCAD diet. A cow senses a huge need for calcium just after calving. At times, she is unable to get calcium out of her bones quickly enough to maintain blood calcium levels. In this case, she will likely have milk fever.
By adding acidifying minerals like chloride and sulfur into the prefresh diet before calving, changes happen in the animal that cause her to lose calcium in the urine. If the calcium spigot is dripping in the urine, adding more into the diet is wise. We have cussed and discussed this for 25 years. Some say add more, and others say it is not needed. Although calcium is likely the cheapest nutrient in the ration, it is still not free.
Differing opinions
I have some specific memories on this topic over the years. Twenty or more years ago, when we were being taught how to use DCAD diets, the smartest people in the dairy nutrition space were not sure that adding extra calcium was important.
Around 10 years ago, I had the opportunity to start working with a new and very successful client. Not long after starting there, we had some milk fever issues. This dairy also had a well-respected veterinary consultant from a neighboring state. I recall a meeting where I was compelled to raise the grams of calcium even higher than levels discussed in those previous industry meetings. I did as I was told and the transition cows seemed to do surprisingly much better. I did it in stride but was still confused by the mixed signals on this topic from reputable researchers and practitioners.
The last memory is one of the most interesting to tell. One of my largest and longest-term clients hired a new dairy operations manager for their multi-site dairy. Upon first being introduced to the new employee, during the handshake, he asked me how many grams of calcium were in the close-up diet. “Well,” I stammered. “I usually think about it in percentages,” a response helpful to buy some time to assess the situation. In a minute or two, I calculated the grams for a close-up cow eating 33 pounds of dry matter (DM).
I found out later that this new manager had not only significant nutrition training, but also experience, and I could quickly tell where he fell on the question on whether he fed high or low calcium in his diets. To this day, I still have the pleasure of fostering the relationship with this producer 10 years and many discussions later.
What about calcium?
The second question asked in the Cornell trial was related to using a high or low calcium approach in the acidified close-up diet.
The parts of the trial design and commentary about grouping the cows, number of days on the close-up ration, checking urine pH, and other details were exactly the topics we cover when implementing and evaluating transition diets in the real world. Of course, they were able to do things that we could never do, like assigning cows to treatments based on 305 mature equivalent (ME) and body condition. They fed the diets for 26 days using expected calving dates of the 98 cows participating in the trial.
The previously mentioned DCAD levels were around -10 and -3. The corresponding expected urine pH from these two levels would be 5.5 to 6 for the full acidified diet, and 6.5 to 7 for the partially acidified diet. The measured urine pH fell in line with expectations. The table of pH results looked like what I would expect, and the cows did as was expected of them. It should be noted that the DCAD change was accomplished only by adding more chloride to the diet. Potassium, sodium, and sulfur levels were kept mostly constant. Now, what about the calcium levels?
I remember in one of these discussions with the vet, we talked about 200 grams of calcium, which equates to about 1.5% calcium in the ration. The 2021 National Academies of Sciences, Engineering, and Medicine (NASEM) suggests the proper calcium level in a DCAD diet is “not known,” with successful results in the published literature ranging from 0.65% to 1.7%. In the Cornell study, in a 2x2 factorial with two levels of DCAD, the two calcium levels were 1.5% and 0.70%. After feeding the cows; checking urine pH; weighing; calving; checking blood minerals, including calcium; and finally measuring the quantity and composition of both colostrum and milk, what were the results?
Defying the norm
Cows fed the higher calcium had higher intakes in the fresh pen and also higher milk yield. Also, the cows with a full acidification program and urine pH results between 5.5 and 6 had improved intakes in the fresh pen and experienced less body weight loss. This study helps us confirm what we have come to observe: Urine pH less than 6 is okay.
So, it turns out that the vet was right about 200 grams of calcium. Previous concerns about urine pH between 5.5 and 6 may be unfounded as well. Avoiding cows that were just moved into the close-up pen can help us better manage this 5.5 to 6 range goal.
The link to the paper is below, and I encourage you to take a minute to read it. There are other papers on this topic that more closely address the potential role of calcium in the rumen and reasons why some DCAD programs seem to struggle with reduced intakes.
Link to Journal of Dairy Science: on.hoards.com/dcadforcows
