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How to Forage Test and Assess Feed Quality

11 March 2015

Forage testing is critical to know what you are feeding to optimise rations for specie, age and production stage.

Two Ohio State University (OSU) extension agents question how many producers know what they are feeding their animals. 

If You're Not Testing Then You're Guessing

Visual inspection plays a big role in the absence of proper forage testing, according to Ted Wiseman and Mark Landefield, county extension educators at OSU. They write that colour, texture, maturity, mould, insect and weed content can indicate forage quality. 

Visual Assessment

But they add: "A nice green color doesn't always mean it's of high quality. A nice green color would usually indicate a high protein level and vitamin content, but the hay could also be high in nitrates and low digestibility."

Hay that is soft and flexible indicates a less mature plant, compared to tough thick stems, write Mark and Ted. One can also look for the presence of seed heads of grasses indicating stage of maturity.

Hay should not smell old or musty or have the presence of dust, all of which indicates mould. Weeds and insects not only can reduce nutrient value, but some are also toxic.

If we look at three forage samples as an example, two of the samples are from first cutting and one is a third cutting hay. All three samples have a nice green color and variances in maturity when evaluating the orchard grass in these samples. There's no presence of moulds, insects, but a few weeds.

Fortunately we have sent these samples to be analyzed and the results are listed in Table 1. Looking at the results can you tell which samples might be first cutting and which one is third? You could look at Crude Protein level, Total Digestible Nutrient (TDN), Dry Matter (DM), or Relative Feed Value (RFV). Forage analyses have much more detailed information than what is included here, but that's another discussion.

Table 1. Forage Sample Analysis (reported as percentages on DM basis)

Livestock Nutrition Requirements

Next we need to know what the requirements are for the livestock we are feeding. In this example we will look at beef cows with an average weight of 1200 lbs, that have a peak milk production of 20 lbs. The three stages of production listed are for the last trimester, first month after calving and peak milk production according to the National Research Council (NRC, 1996).

Table 2. Nutrient requirements of beef cows (reported as percentages on DM basis)

If we compare the forage analysis to the requirements needed what are some of the possible deficiencies? Protein levels appear to meet requirements for all three samples. Our Energy or TDN levels for sample A and C look like they would work for the last trimester and after calving, but fall a little short for peak milk production. Sample B is low in TDN for all stages of production, but has adequate Calcium and Phosphorus levels. Sample A has low Calcium and sample C has a low Phosphorus level respectively.

Dry Matter Intake: How Much Do They Eat?

So far we have looked at the forages and requirements on a percentage basis, the only problem is that cows don't eat percentages, they eat pounds. We cannot be confident that the ration is meeting the cow's requirement unless the actual pounds of what is being fed and how many pounds the cow is actually consuming is known.

Table 3 illustrates the pounds of nutrients that a beef cow would need for each of the three stages of production.

Table 3. Nutrient requirements of beef cows (reported as pounds per day)

The following table contains the nutrients from each forage sample based upon pounds of dry matter. Feed consumed on as-is basis have also been calculated for each stage of production.

Table 4. Forage Sample A. Nutrients provided in pounds on a dry matter basis

Forage sample A appears to be sufficient in protein for all stages of production and energy for late gestation and at calving. During peak milk production energy is only 0.25 lb. low, doesn't seem like much. However, it would require 1.5 lb. of shelled corn to meet the energy level of a cow at this stage of production. Additionally be aware of the low calcium levels in this forage. You would need to make adjustments for this by adding a calcium supplement or adjusting mineral supplement.

Forage Sample B is adequate for protein and phosphorus, but calcium may need to be adjusted slightly. This sample has the lowest TDN or energy levels of the three samples evaluated. To meet the energy levels using corn it would require 2.8 lb. during late gestation, 4.9 lb. at calving and 6.1 lb. during peak milk production.

Sample C has the highest Relative Feed Value and very similar to sample A in TDN. It also contains enough protein for all three stages of production. Energy is sufficient for the last trimester of gestation, however it would require 0.3 lb. of corn at calving and 1.5 lb. of corn at peak milk production. In this sample phosphorus levels were low, and again the mineral supplement may need to be adjusted.

The samples used were collected last year from fields planted to an alfalfa, red clover, orchard grass or alfalfa, orchard grass mixture. Sample A is an established field of first cutting hay made early (mid-May), Sample B is also an established first cutting of hay made late (mid-June), and Sample C is a third cutting of a newly seeded field baled in late August. Sample C also received a 0.25 inches of rain on it after 24 hours of drying.

So I hope that this exercise helps to reinforce the value of testing your forages. As you can see, feeding protein tubs with these hay lots would not be necessary. If you would have fed protein tub(s) along with this hay, you would have spent much more money than the laboratory test cost. The tests are relatively inexpensive compared to the value of knowing what you are feeding and when it is needed.

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