CSI Dairy: Two mysteries of butterfat depression

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. In this mystery, two investigations into  unexplained butterfat depression reveal a common offender.

By Drs. Brian Perkins and Dave Ohman

The experienced dairyman’s voice rang with concern. His Holsteins were no longer producing 80-85 lbs. of milk per cow per day with 3.4%-3.5% butterfat. When butterfat dropped to 3.0% in midwinter, he increased the straw fed and decreased corn. Unfortunately, milk production dropped.


The ration contained 37% high-starch corn silage, double the normal level due to haylage constraints. With high-moisture shelled corn (HMSC) as the main grain source, the ration’s starch content totaled 26%-28%. Potential off-farm feed sources – hay or finely ground dry corn – had not been considered due to cash flow limitations.



An evaluation of risk factors related to the diet, cows and management included testing the total mixed ration (TMR) for neutral detergent fiber (NDF) and starch degradability analysis. The lab results provided a clue: The two-hour starch degradability was a startling 83%.


To reduce the ration’s starch degradability, HMSC was replaced with dry ground corn. The haylage level was increased and straw was reduced. BF increased about 0.25% and milk production increased by several pounds. The reduced starch degradability improved rumen function.

In a second situation, a Western dairyman was puzzled over why persistent low BF dogged his herd on a high-hay diet. An evaluation of the risk factors offered no easy clues.

Then results of the HMSC seven-hour starch degradability analysis provided a surprise: 76% degradability, several points higher than average for HMSC. Rumen acidosis and upsets as the offenders were likely depressing butterfat.

Not long afterwards, the dairy’s first HMSC supply ran out. It switched to a second source. Lab tests were repeated, but with different results: 70% starch degradability and some relief from acidosis.

Simultaneously, two feed byproducts were pulled that had provided small amounts of unsaturated fatty acids to the rumen; BF increased by 0.2%. A potential lead? We asked the lab to run a milk fatty acid analysis.

The test proved revealing. The ration itself had been affecting the rumen biohydrogination pathways that rumen bacteria use to begin detoxification of dietary fats. The level of “trans” fatty acids most active at depressing BF was many times higher than normal.

In addition, the analysis indicated a combination of too much unsaturated fatty acid (vegetable oils) and borderline acidosis. A milk sample taken following the ration changes indicated normal fatty acid levels.

Lab tests

Three tests help evaluate the role of dietary starch availability on rumen function:

• Ruminal starch digestibility analysis. The seven-hour ruminal starch digestibility analysis evaluates the rate of starch degradation in corn, corn silage or the TMR. It is readily available at many forage labs. As the rate of digestibility for a corn starch increases, more starch is digested in the rumen, with less digested in the intestines. Having too much or too rapid ruminal starch digestion increases the risk of sub-acute as well as acute ruminal acidosis.

• Protein solubility also closely correlates to starch availability and can be used to monitor changes in starch availability in HMSC and corn silages.

• Gas production. New and interesting technology uses gas production to understand the digestion rates of both starch and fiber. Compelling information can be gained when troubleshooting milk production and component issues.

Remember, if BF depression strikes, your forage labs have important analysis tools.



Brian Perkins, Ph.D., Dipl ACAN, Dairy Technical Service Specialist for Diamond V, serves producers in the Pacific Northwest. He can be reached via e-mail: BPerkins@diamondv.com.

Dave Ohman, DVM, Dairy Technical Service Specialist for Diamond V, serves the Central U.S. He can be reached via e-mail: DOhman@diamondv.com.

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