Over the past week, I spent some extra time in our sample prep department. I saw a lot of samples with a lot of dirt. This coincided with several phone calls from forage producers wondering why their relative forage quality (RFQ) was so much lower than relative feed value (RFV). Upon closer inspection of their reports, we discovered that what producers had recently noticed as a discrepancy in forage quality was actually a soil contamination issue.
When we think about forage quality, we often think of RFV and RFQ, crude protein content, and fibers. So, most of what we read and talk about when it comes to improving forage quality is increasing protein, decreasing fiber and improving digestibility. However, this season, I have been observing more samples with high ash content bringing down RFQ values in comparison to RFV.
First, let us think about what ash is on a feed report. Ash is the total mineral content of a feed and has two sources. Endogenous ash is from the plant and is bioavailable, providing micronutrients to the animal. Exogenous ash is from soil contamination of the feed. Roughages and forages range between 8%-10% ash with 4%-6% representing the endogenous portion. Extremely soil-contaminated roughages could contain as much as 25% ash. So, one-quarter of the dry matter in that forage is just dirt.
Looking back at samples from 2021 and 2022, only about 2% of samples had what I would consider to be abnormally high ash (greater than 15%). Figure 1 shows that samples with greater than 15% ash typically had a lower RFQ than samples with less than 15% ash. Additionally, samples with greater than 15% ash had a lower RFQ value than RFV. In samples with less than 15% ash, RFQ is higher than RFV, especially in grass forages. This is not surprising because RFQ considers the ash content of the forage while RFV does not.
The ash content is only a small part of the RFQ equation. It is a part of the non-fiber carbohydrate calculation, which then is incorporated into RFQ. This parameter plays a very nuanced role in forage quality.
So what causes soil contamination of harvested forages? One common reason soil can end up in our stored forages is dry conditions. When field conditions are dryer, it is easier for the rake to pull up soil particles and incorporate them into the bale. Unfortunately, here in Nebraska, as corn harvest drew to a close, we saw drought conditions right when many producers were planning to bale cornstalks. Cornstalks are a forage that we see commonly contaminated with soil.
What can we do to prevent soil contamination of our stored forages? Here are four tips to prevent contaminating stored forages with soil:
- Cut forages 3-4 inches off the ground. This can help optimize forage quality by not incorporating the most fibrous portion of the plant. More importantly, this practice will leave more ground cover and give some protection from soil erosion.
- Rake as little as possible. I have known some producers who live in climates where humidity is an issue, and they rake the windrows to turn them to ensure the hay is completely dry. Avoid this practice unless it is absolutely necessary to achieve optimal hay moisture within a specific time frame.
- Pay attention and adjust your equipment. Prior to cutting or baling, ensure your equipment is properly adjusted to prevent unnecessary disturbance of the ground. Also, if you are seeing a trail of dust, stop and adjust things to reduce the amount of soil being incorporated into the bale.
- Graze. Forgoing the harvesting process will ensure animals have the ability to choose the forage they consume and eliminate the possibility of consuming a lot of dirt.
If you analyze your forage and see high levels of ash impacting forage quality, it has the potential to negatively affect livestock health as well. The problem with soil-contaminated feeds is that the soil could cause compaction within the omasum, abomasum or beginning of the small intestine. An impaction would not allow other digesta to pass through. An impaction could cause cattle to go off feed, if it is serious enough. The more likely issue would be a decrease in performance due to the dry matter intake (DMI) the ash is taking up. Because cattle typically consume 2% of their bodyweight in dry matter, consumption of soil-contaminated feed can result in a considerable amount of ash as DMI with no nutritional value, thereby resulting in decreased performance for the animal.
In addition to the risk of impaction, soil contamination can also affect mineral nutrition. Aside from high ash, high iron levels can also indicate soil contamination. Iron can interfere with copper absorption at 250 parts per million. However, the bioavailability of minerals from the soil is low.
So if you are feeding a forage high in ash, mix it with feeds that have a low ash content to minimize impaction risk and performance losses. Furthermore, if high iron levels are present, increased copper supplementation might be necessary.
In conclusion, ash is an often-overlooked parameter on forage reports. However, at high levels, it can indicate a soil contamination issue. Soil in forages can reduce forage quality and have a negative impact on livestock health. Monitoring ash levels in forages can be important in identifying areas for forage production improvement as well as ensuring forages are managed and fed out to ensure top-tier nutrition and health for our livestock.
This is an example of soil content in chopped cornstalks. Photo provided by Rebecca Kern-Lunberry.
