• Jin Gan

Fluctuations In Silage Digestibility


Depending on how much silage you stored, you may be considering making the switch to new-crop silage soon. When making the switch, it is crucial to keep a close eye on starch content and digestibility.

When storing the corn silage, amount of starch would not vary much but the digestibility of the starch would increase as the ensiled time increases.

Take note of starch digestibility

  • When transitioning from fall to summer, the increase in starch digestibility makes a huge difference on ration balancing.

  • Not having a good pulse on starch digestibility will lead to lower feed intakes and milkfat depression if there is an overload of starch digestion in the rumen.

  • One way to combat this is to measure the changes in starch digestibility at regular intervals.

  • Best tool to measure any change is a starch digestibility test.

  • Test would enable you to know how much starch will be available in the cow's rumen from the corn silage before formulating any ration.

  • There are many ways to test for starch digestibility. However, the most important thing is to make sure the results are quick and accurate for you to apply them in the ration.

  • When taking the sample for testing, it is encourage to take it over time rather than just one time. Testing should then be continued every two weeks.

Economics for your herd

  • It is crucial to know the starch digestibility of corn silage so that adjustments to the ration can be made while at the same time considering prevailing inventory and economics in order to have high milk production and profitability.

  • For example, if you are able to plant sufficient corn for a high corn silage ration diet - 22 pounds of corn silage dry matter (DM) per cow but due to a great growing season, the resulting tonnage becomes enough to feed 25 pounds of silage DM per cow.

  • Assuming the average starch content of the current corn silage being fed is around 35% with ruminal digestibility of around 75%.

  • By summer, starch digestibility is around 90%.

  • This will thus increase ruminal digested starch by 1.3 pounds, creating and overload of starch for the cows.

  • Most farmers would opt to reduce amount of corn silage in the diet but with so much inventory available, it is not the most economical choice since it has been paid for and difficult to sell.

  • Assume average dry matter intake (DMI) to be 55 pounds per cow throughout the year, the ration would most likely contain an additional 8 pounds of hay DM, 8 pounds of high protein supplement DM and 6 pounds of ground corn DM, leaving 8 pounds of DM to be filled.

  • The cheapest solution is to fill that with corn but it is not advisable for our example as the additional starch would make the starch overload worse.

  • It is best to fill the last 8 pounds of cow's ration with a combination of high-fiber (low-starch) byproducts and available forages.

  • Adding available forages for the last 8 pounds of diet can only work provided it does not exceed rumen fiber fill limits.

  • Beyond that, you need to incorporate byproducts with little or no starch content to fill the remaining pounds.

  • Byproducts such as soyhulls or corn gluten feed is recommended but it will increase purchased feed costs.

Planning for the future

  • It is important to plan for the next planting season to ensure optimal animal performance.

  • Planning for a different forage program could give you more option to fill the final 8 pounds as mentioned in the above example.

  • Consider switching some area assigned to corn silage to other highly digestible, lower-starch forages.

  • Generally, it is cheaper to grow own forages as compared to buying from other sources.

  • Discuss with your nutritionist and do some calculations after harvest to determine the starch and fiber digestibility limits on a wide variety of diet scenarios.

  • Make sure to keep an open when formulating ration by having more options.

  • Measure the starch and fiber digestibility of ensiled corn silage in a ration regularly to avoid unwanted negative effects of starch overload such as reduced dry matter intake or milk production.

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