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0107 PD: A quick test for adjusting silage feeding rate

Richard J. Norell, Joel H. Packham and Stuart C. Parkinson Published on 10 January 2007

Rainfall or runoff from melting snow can impact a feeder’s ability to correctly feed dairy cattle. Added water from precipitation or runoff decreases silage dry matter (DM) content. In these situations, more silage must be fed to meet an animal’s nutrient requirements for production. Failure to adjust feeding rate has potential economic consequences, especially when high levels of silage are fed and substantial amounts of water has been added. First, dry matter intake (DMI) decreases because the ration includes more water and less actual feed nutrients. Second, average milk production decreases because of reduced energy intake from the ration. Third, milk fat may decrease because of altering the forage-to-concentrate ratio (less fiber from forage and proportionately more concentrate in diet).

Producers have several methods available for measuring DM content at the farm level. The two most common methods are microwave ovens and Koster moisture testers. Both on-farm tests provide reliable estimates of DM but require significant time to conduct the test. Average testing times are 10 to 15 minutes with a microwave oven and 30 to 40 minutes with a Koster moisture tester.

There is a need for a quick test at the farm level for measuring changes in silage DM content. Extension faculty at the University of Idaho developed a quick test based on change in silage density. Water has a higher density (1,000 grams per liter) than corn silage (235 to 431 grams per liter) or haylage (189 to 376 grams per liter). Added water increases the density of silage and decreases the dry matter content (see Table 1*).

This “quick test” involves measuring the density of normal silage and the test silage with added water. A scale and a shallow, flat container (1 liter in volume) are needed to conduct the test. Simply fill the container and weigh. The container should be filled level full with moderate compression on the silage. Feeding adjustments are predicted by an equation from the change in silage density (test silage density minus normal silage density). The same prediction equation can be used for both corn silage and haylage. Estimated feeding adjustments are shown in Table 2* (next page) for several different changes in density.

Applied example
Joe Dairyman measures the density of his corn silage on a monthly basis. He fills a shallow 1-liter container with corn silage and weighs it on a scale. The density of Joe’s corn silage averages 350 grams per liter. Joe observes considerable snow melt around the silage bunker today and also notes the presence of pooled water on the bunker floor. He removes silage from the bunker face with a bucket loader and then scoops a bucket load of silage. Before adding it to the mixer, he takes four 1-quart samples from the loader bucket and mixes them together in a pail. Joe fills his 1-liter container with this wet silage and weighs it. The new sample has a density of 450 grams per liter. Given this change in silage density, what feeding adjustment is required?

Joe subtracts the normal silage density from today’s measurement (450 – 350 = 100). According to Table 2*, the correct feeding adjustment for a 100-gram increase in silage density is 1.37. Joe normally adds 2,000 pounds of silage to his TMR mix. He calculates the adjusted feeding amount by multiplying the feeding adjustment (1.37) times his normal feeding rate (2,000 pounds). The adjusted feeding rate for today is 2,740 pounds (2,000 lbs x 1.37 = 2,740).

Adjusting for a different size container
This study was conducted with a shallow 1-liter container. You may not have a similar size container but still want to conduct the test. Let’s say you have a half-gallon container. How do we rescale the change in density to reflect the new container size?

To solve, we first need to determine the number of liters in our half-gallon container. A metric conversion to remember is 1 quart equals 0.946 liters. The correct metric conversion for a half-gallon container is 1.892 liters (2 quarts times 0.946 liters/quart = 1.892). To adjust the table for a larger container, multiply the change in density times the volume in liters. For example, a 50-gram change in density in a 1-liter container is equal to 95-gram change in a half-gallon container (50 times 1.892 = 94.6 grams). Rescaled adjustments in density for a half-gallon container are shown in Table 3*.  

Added water from direct precipitation or runoff can dramatically lower DM content in bunker ensiled forages. Failure to adjust feeding rates can result in reduced feed intakes and lower milk production. Our test provides a quick means for making feeding adjustments when loading the TMR.  The benefits of running this test are likely to be greater for small dairies since they typically remove minimum amounts from the bunker face daily.  Larger dairies will remove more silage from the bunker and have proportionately less added water than small dairies.  PD

Tables omitted but are available upon request to .

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