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What's up with first cutting hay?

Jim Salfer
Extension Educator
July 26, 2014

The springs of 2013 and 2014 presented challenges throughout much of the upper Midwest. Harvesting high quality first cutting forage this spring has been a particular challenge. The cold wet spring delayed harvest by several weeks in most areas. When we did get a harvest window with no rain forecasted, the fields were often not dry enough to carry the harvesting equipment; there was a lot of mud resulting in large ruts in the field.

Based on forage analysis results, this year's first cutting may also present some feeding challenges. Most forage samples are showing a large difference between the relative feed value (RFV) and relative forage quality (RFQ). The RFQ is much lower than the RFV. After communicating with lab personnel and Dr. Undersander, University of Wisconsin forage agronomist, this appears to be a common occurrence in this year's first cutting throughout the entire upper Midwest. Many samples have RFQ that is 30 to 50 points lower than the RFV.

Let's review the difference between RFV and RVQ. Relative feed value was developed over 30 years ago and was designed as a single number index to predict the potential digestible dry matter intake of a sample. The two lab measurements that went into the RFV calculation were acid detergent fiber (ADF) and neutral detergent fiber (NDF). As researchers discovered factors that better predicted fiber digestibility and as labs became able to better evaluate the digestibility of the fiber portion of forages, University of Wisconsin developed RFQ as a replacement for RFV. This new index (now over 10 years old) was designed to better predict animal performance when feeding a particular forage. When evaluated across a large number of samples, the average values of the two indexes should be similar.

Based on growing conditions, this big difference would not be expected in first crop feed. Under cool growing conditions you would expect that the fiber portion of the forage would tend to be more digestible. So, why the big difference this year? According to Dan Undersander and lab managers these might be the reasons:

  1. It is possible that more leaves fell off than in previous years. I am not sure this is true, because many of the samples are very high in crude protein relative to the RFQ. Typically with a lower leaf to stem ratio you would expect a lower crude protein percent.
  2. There may have been more leaf disease resulting in more leaves falling off before harvest. Again this may not be correct with the high crude protein content of the forage.
  3. One of the likely culprits is a larger amount of dirt contamination of the forage. One sample I saw contained over 20% ash (minerals and dirt). Typical alfalfa hay samples with minimal dirt contamination should average 8 to 12% ash. This could easily be part of the explanation since harvest took place in extremely muddy conditions.
  4. Some other growing season effect that we don't totally understand.

In reality, it really doesn't matter why there is a big difference. What does matter is how feeding these forages may affect animal performance. Below are some ways to maintain animal performance when feeding this year's first cutting forage:

  1. Evaluate your first cutting forage for RFQ. Quantifying the problem is half the battle. If you typically do not request a forage test that calculates RFQ, re-analyze the sample or request a test that calculates RFQ.
  2. Examine the forage analysis for ash content. Consider anything over 11% in a hay sample to contain excess dirt contamination. If a producer is feeding 15 pounds per day of dry matter from a forage that contains 20% ash, the cows will be consuming 1.2 pounds of dirt per day. Not only does the dirt take up valuable dry matter space, it may also contain higher numbers of clostridia spores increasing the risk of butyric acid in the forage. There may also be a slight risk of increased health problems caused by organisms present in the soil. Observe cows closely and report and discuss any health concerns with your nutritionist and veterinarian.
  3. We would not expect these forages with low RFQ values to feed as well as forages with higher values. Relative forage quality is an estimate of the potential dry matter intake and available energy of the forage. Measure dry matter intake and work with your nutritionist to adjust rations accordingly.
  4. Because the NDF portion of the forage is not as digestible, consider adding fibrous by-products that are high in digestibility. Some examples include corn gluten feed and soybean hulls. These feeds are not good at stimulating rumination, so work with your nutritionist to ensure that your ration contains adequate amounts of long particles.

This spring has been a challenge in many areas throughout the upper Midwest. This may just be one more challenge to overcome. Analyze forages for RFQ and work with your nutritionist to adjust diets and closely monitor cows' milk production, milk components and health.

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