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Rain and Mud - A pain in the ash value

Jim Linn and Mary Raeth-Knight

Published in Dairy Star October 2007

The weather forecast of rain, rain and more rain is perfect for making mud pies, puddle jumping, and mud-dogging. If you’re feeding dairy cows however, all this rain may be causing you to feed a significant amount of dirt in your dairy ration.

How do I know if I’m feeding dirt?

To determine if you are feeding dirt, analyze your forages or total mixed ration (TMR) samples for ash content. Ash represents the total mineral or inorganic content of the sample. It is analyzed as the residue remaining after the sample has been burned in an oven at 500°C for 2 hours.

Forages are a good source of minerals, such as calcium and potassium. Dairy cow rations are also typically supplemented with salt, macro and micro-minerals. Therefore, a certain level of ash in forages or TMR is normal. Pat Hoffman (University of Wisconsin) evaluated the distribution of ash in 1000 legume-grass silage or hay, corn silage and TMR samples and determined normal ash values on a dry matter (DM) basis were as follows: legume-grass silage or hay = 9.0% , corn silage = 5.0% and TMR = 9.0%. This is “good ash” or ash that will help meet the mineral requirements of the cow. If the ash value is abnormally elevated, this indicates soil contamination or “bad ash” as soil mineral primarily consists of silicate minerals that are poorly digested.

How much dirt could I be feeding my cows?

If forages or the TMR are significantly contaminated with soil, you could be feeding anywhere between 1 to 4 pounds of dirt per cow on a daily basis. For example, there was a recent phone call from a producer who was concerned about his corn silage which had an ash value of 10.0% (DM basis). If his ration was a high corn silage ration where cows would be eating about 25 lbs of corn silage DM per cow per day, total ash intake from corn silage alone would be 2.5 lb/d (25 x .1). Assuming Hoffman’s normal corn silage ash value of 5% and this corn silage was twice the normal value, half of the ash intake (1.25 lb) would be coming from dirt. While this is a lot of dirt, Hoffman reported ash values of TMR samples up to 17% of the DM. If 9.0% ash is normal, at 50 lb of TMR DM intake cows would be eating 4.0 lbs of dirt.

Impact on performance

We don’t know the exact impact of soil intake on lactating dairy cow performance. However, dirt does not provide any energy or nutrients to the cow. Therefore, high levels of soil intake could be detrimental to high producing dairy cows that need to maximize nutrient intake and are limited by rumen fill.

For animals with lower DM intakes however, little negative impact of soil intake has been shown. Miller et al., (1977) fed non-lactating Holstein cows clay at 0, 4.2 or 8.0% of the diet DM (up to 2 lbs per day) for 21 days. The consumption of clay had no impact on total DM intake (avg. = 24 lb/d) or apparent digestibility of organic matter. However, clay intake linearly decreased the digestibility of protein (60.9 to 57.2%) and potassium (90.9 to 68.6%). Digestibility of fat however, increased from 56.7 to 67.4%. It was unknown why this occurred.

In an unpublished study conducted by Dr. Robbi Pritchard at South Dakota State University, yearling steers fed a high concentrate finishing diet consumed 0.5 lb soil per day. There did not appear to be any negative impact on DM intake or performance.

How am I getting dirt in my ration?

There are a variety of ways in which dairy cow rations can become contaminated with soil. Prior to harvest, soil contamination can occur due to dry and windy conditions, during flooding or any condition resulting in plant lodging. According to Hoffman, during hay harvesting, hay-bines that use negative air pressure to lift forages may simultaneously draw soil into the forages. Corn silage stored in bunkers or piles can become contaminated with soil during filling due to muddy machinery used to fill and pack the bunker. Feed-out can result in a significant amount of soil contamination on farms that do not have feed stored on concrete or asphalt slabs.

Other concerns with dirt contamination

Another reason to avoid soil contamination of feeds is that soil is a natural source of mold spores. Microbial contamination from soil may result in poor fermentation of ensiled feeds and introduce undesirable organisms like clostridia into the feed.

In summary

Although especially challenging during the last few months, make an effort to minimize the amount of dirt in your dairy cow ration. Remember, dirt does not contain any nutrients or energy and may be increasing the risk of mold and potentially mycotoxin contamination.

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