Butterfat depression

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The following case was handled by Martha Baker, a dairy nutrition specialist with Purina Animal Nutrition LLC.. 


The problem of milk fat depression can have multiple causes, and because it can take 3-5 weeks to see the impact of a ration change, it can be a time-consuming process to fix.

I was called to a 700-cow Pennsylvania dairy, averaging 85 pounds of milk. The herd had a strong reproduction program and, in general, herd health was good.

The herd was fed a heavy corn silage diet: The ration’s forage portion consisted of 80% corn silage and 20% haylage.

Like many other dairy producers, the herd manager incorporated commodity byproducts into the ration, including cottonseed, dried distillers grains and tallow, in an effort to control costs.

Monensin was also fed at a rate of 400 milligrams, and the diet’s poly unsaturated fatty acid (PUFA) levels were running in excess of 450 grams.

Despite trying several strategies, the herd was struggling with its butterfat levels.

Independently, diet starch had been reduced for fear of rumen acidosis. When no improvement in butterfat occurred, the starch was added back into the ration.

Next, monensin was pulled out of the diet. There was no change in butterfat, so it  was added back into the ration.

The PUFA level was then lowered; no butterfat response resulted.

For each step the herd manager waited two to four weeks before adding the feed ingredient back into the ration. Not only did each independent step not fix the problem, but the herd lost milk production when starch was lowered and when monensin was pulled.

Conceptually, every step taken to evaluate the cause of the milk fat depression was correct. However this herd needed to hit the “reset button” on the cows’ rumen environment.

To reset, monensin was pulled from the diet and PUFA levels were lowered simultaneously. No adjustments were made to the starch level.

Starch was monitored using a rapid rumen degradable starch test, and we were able to rule out starch out as one of the potential milk fat depression causes.

PUFA levels were lowered by reducing the combination of cottonseed, distillers grain and tallow in the ration.

The volume of fat bringing energy into the diet was replaced by a saturated fat.  We needed to utilize the most economical source that delivered the right amount of net energy. There were no concerns that intake would be impacted.

This saturated fat  also comes in a physical form that is easy to handle, with no concerns of the melting point or that it would cake in the bin or auger. It was late summer when these adjustments were being made and with some saturated fat products, temperature can be an issue.

Components started ticking upwards within three weeks after ration adjustments, stabilizing within six weeks. The herd regained 4 points on butterfat, going to a 3.5 to 3.7 butterfat, without adversely affecting milk production.

The herd manager shifted his philosophy away from “lowest” feed cost, focusing instead on “best” feed cost to maximize milk production and components.

As we learn more about fatty acids there is no reason a herd should lose milk production to gain a higher butterfat level. This herd was able to successfully maintain milk volume and improve components, while still maintaining good reproduction and herd health.



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