CSI-Dairy: A cow-side investigation into the mystery of milk fat depression & healthy cows

Each month, DairyBusiness Communications will check the case files of lead dairy ‘investigators’ to uncover another ‘CSI-Dairy’ mystery.

Numerous ‘culprits’ exist on dairy farms, robbing herd performance and injuring the dairy’s bottom line. Identifying and arresting the offender isn’t always easy, and often requires a full investigation, gathering and analyzing evidence on the farm and in the lab. One mystery was widespread in 2010: Milk fat depression in herds of healthy cows.

By Elliot Block

The first phone call came at the most unexpected time. A dairy producer I had worked with for 10 years, Gary, called with desperation in his voice. I struggled to hear Gary through the crackling connection. It was then I heard his cry for help.

“You won’t believe what’s happening at the dairy,” Gary gasped at the other end of the phone. “My milk tester was here last week; butterfat levels continue to fall and I can’t figure out why. We need your help now!”

I could sense the tension in his voice and knew Gary was not my only producer client watching milk fat levels head south. Grabbing my investigation cap, I headed to Gary’s dairy operation.

The investigation: Not the normal culprits

Gary met me in the farm office with his DHIA records, a printout of the lactating ration and his latest forage analyses. After reviewing the records we walked pens, inspected the ration and conducted a Penn State shaker box test to evaluate ration particle size. While I could sense Gary’s frustration, the cows looked healthy and the ration looked good. I too, was a little stumped.

Based on previous encounters with low milk fat tests, we tweaked the ration slightly by:

• Decreasing ration starch levels. High dietary starch levels can reduce rumen pH and shift volatile fatty acid (VFA) production, reducing acetate and increasing propionate. Acetate is responsible for half of the fat destined for the udder.

• Evaluating free fatty acid levels in the diet. High levels of corn byproducts can have high and variable amounts of free fatty acids that can quickly contribute to milk fat depression.

Just to be safe I took a new ration sample and submitted it for dietary cation-anion difference (DCAD) analysis. I told Gary I’d be back in two weeks to check in.

The follow-up visit: Time for a change

When I arrived at Gary’s operation two weeks later, I had a sneaking suspicion things hadn’t improved. Gary looked even more frustrated; he still hadn’t found the culprit and milk fat levels were wavering.

Just as I sat down to review the ration one more time, a piece of mail fell on the floor. It was the DCAD balancing testing results. And it was then we had our breakthrough.

The DCAD analysis showed high levels of chloride in the diet. Chloride, I explained to Gary, is one of the two anions that lower DCAD levels. A positive DCAD of +35 to +45 is important for lactating diets to maintain milk and component production. Also, new research is showing that potassium – one of the two cations that increase DCAD – could help increase milk fat production.

By the time I left that evening, we had decreased all unnecessary dietary chloride sources (all but chlorides found in the forages) and began feeding a high-quality potassium carbonate source to boost ration DCAD to just over +35.

Mystery solved: Milk fat climbs

My most recent visit to Gary’s dairy showed our ration changes were beginning to alleviate the problem. DHIA records showed milk fat levels increased from 3.3% to 3.7% in just 14 days. The increase led to additional Income Over Feed Cost for Gary. And another mystery solved.


Elliot Block is Senior Manager, Technology, Arm & Hammer Animal Nutrition. Contact him via phone: 609-279-7517; e-mail: Elliot.block@churchdwight.com; or website: www.AHDairy.com.

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