Manage feed to reduce risk of milk fat depression

By Stacy Nichols, Vita Plus dairy technical specialist

As we enter the summer months, we face a higher risk of milk fat depression caused by several factors.  One of those factors can be the increased availability of starch and corn oil in well-fermented corn silage and high moisture corn (including high moisture ear corn and snaplage).

When corn silage and high moisture corn are harvested, the starch in many hybrids is contained within a matrix of prolamin (or zein) protein.  This protein encapsulation of starch can be a contributing factor to fall milk slump on dairies where corn silage and high moisture corn are fed soon after harvest due to inventory needs.  Fortunately, fermentation acids from ensiling dissolve the prolamin protein during storage, giving the cow’s rumen bacteria more access to the starch.  Dairy producers have recognized the need to improve processing of the kernels of corn silage and high moisture corn during harvest to increases the surface area for access to the starch matrix by the fermentation acids and, ultimately, the rumen bacteria and the cow.

The increasing starch availability during storage can be seen on lab analysis with an increase in soluble protein.  The soluble protein of fermented corn increases as the prolamin protein matrix is dissolved by the fermentation acids.  The Miner Institute suggests that well-fermented corn silage will reach 85% of its final starch availability after six weeks in storage.  This is a good minimum guideline for when to open a silo.

Unfortunately, the increased availability of the starch in corn silage and high moisture corn also is directly related to the availability of the corn oil.  As this corn oil is metabolized by rumen bacteria, there is a risk of milk fat depression due to undesirable (trans-10) fatty acid intermediates of the oil.

This challenge is worsened by very wet corn silage (moisture greater than 68%) or high moisture corn (moisture greater than 36%) because the starch matrix becomes so available that the rumen bacteria very rapidly ferment it, resulting in more acid production and lower rumen pH that favors the production of the undesirable fatty acid intermediates.  Paying attention to the harvest moisture can go a long way to avoid major milk fat depression challenges.

For dairies that have normal moisture corn silage and high moisture corn, the increased availability of starch and oil can still be a challenge.  A few nutritional and management changes can be implemented to help:

1. Improve heat stress abatement.  A cow will have a lower rumen pH during heat stress due to an increase in standing as she tries to cool.  Standing causes decreased rumination that buffers the rumen.

2. Implement feeding management changes to encourage smaller, more frequent meals that help avoid slug-feeding and improve rumen pH.  This can include adding a feed delivery, changing the timing of feed delivery, and increasing the number of feed push-ups.

3. Work with your Vita Plus dairy nutritionist to optimize your ration for summertime feeding.  Recommendations may include:

• Decrease vegetable oil sources, primarily corn byproducts.
• Improve rumen pH conditions by:
  • Increasing the amount of hay-crop silage
  • Increasing the amount of buffer fed
  • Adding water or a liquid feed to reduce ration sortability
  • Decreasing the amount of starch fed
  • Bringing in finely ground dry corn to replace some high moisture corn to improve rumen pH
• Utilize feed additives that have research-proven ability to decrease milk fat depression.

Table 1. Target dry matter/moisture content of various silages.

Note that these are dependent on the silo structure. For example, bag silos are typically drier than bunkers.