In a previous article, the importance of the fundamental concept of dry matter (DM) was discussed, along with how to price feedstuffs on a cost per unit of DM basis. While understanding the impact of feedstuff DM is critical for making informed management decisions, we also must consider how differences in nutrient composition, in addition to DM, influence feedstuff cost scenarios. Remember, the term DM is commonly used to refer to the feed left over when the moisture or water from a sample of any given quantity is completely removed through drying.
Recognizing that practically all feeds have both a dry and a moisture component and varying nutrient levels, we can evaluate the price adjusted to both the moisture level and nutrient composition to allow for the most direct comparison of feeds. This approach builds upon the previous article’s discussion and is most practical when evaluating options for sources of a feedstuff to supply protein or energy (TDN) to the diet as necessary.
Think back to our previous example using wheat silage harvested this past spring. If we have it priced in the bunker at $30 per ton on an as-fed (AF) basis, that would equate to $111.11 per ton on a DM basis if the silage is 73% moisture or 27% DM ($30 per ton AF basis ÷ 0.27 = $111.11 per ton DM basis). If through a feedstuff analysis we determined the TDN content of the silage to be 55% on a DM basis, then the cost per ton of TDN on a DM basis would be $202.02 ($111.11 per ton DM basis ÷ 0.55 [TDN content of silage, decimal form] = $202.02 per ton of TDN DM basis). Keep in mind that the cost per unit of any nutrient will always be higher than just the cost per unit itself because we are accounting for the quantity of nutrient within that feedstuff, which is nearly always less than 100% for most feeds. So if the silage tested 60% TDN (DM basis), how would that impact the cost per unit of TDN?
Think about the amount of nutrient represented in the silage for each scenario:
- $111.11 per ton DM basis, at 55% TDN, equals $202.02 per ton of TDN DM basis ($111.11 ÷ 0.55)
- $111.11 per ton DM basis, at 60% TDN, equals $185.18 per ton of TDN DM basis ($111.11 ÷ 0.60)
Remember the following concepts:
- Price per unit of any nutrient will always increase if nutrient content decreases.
- Price per unit of any nutrient will always decrease if nutrient content increases.
As discussed in the previous article, as the DM content for a given feed increases, the cost per unit on a DM basis decreases because that same total cost is spread out over more units of DM. This holds true provided the AF cost stays the same as the DM changes. However, the cost per unit of nutrient will depend on the relationship of both DM and nutrient level (Table 1). Continuing our prior example with the prices for wet distillers sources A and C in Table 1, and assuming we needed to supply 1.89 pounds of crude protein (CP) equivalent in the diet, that would be a difference of approximately 22 cents per head per day just between the two sources. In order to feed 1.89 pounds of CP from wet distillers A, we would need to feed 23.3 pounds AF basis (1.89 pounds CP ÷ 0.27 = 7 pounds DM ÷ 0.30 = 23.3 pounds AF).
Now, because wet distillers C is drier, only 20.6 pounds AF basis is needed to be fed to provide the same 7 pounds of DM (7.0 ÷ 0.34 = 20.6). However, the CP content of source C is 30%, so we would actually only need to feed 18.5 pounds AF basis to meet the CP deficit (1.89 pounds CP ÷ 0.30 = 6.3 pounds DM ÷ 0.34 = 18.5 pounds AF). In the previous article, the difference in DM content impacted the cost of the feeding program by 12 cents per head per day. Taking the CP content of the sources into account along with DM, the difference between the two to supply the same amount of protein is even greater:
- WDGS A: $1,111 per ton of CP DM basis ÷ 2,000 pounds per ton = 56 cents per pound of CP DM × 1.89 pounds CP = $1.05 per head per day
- WDGS C: $882 per ton of CP DM basis ÷ 2,000 pounds per ton = 44 cents per pound of CP DM × 1.89 pounds CP = 83 cents per head per day
Pricing feedstuffs on a cost per unit of dry TDN or CP basis can translate to meaningful differences in diet cost on a per-head, per-day basis. While this method is useful for comparing any feed ingredient to another, it is particularly beneficial when evaluating different sources of similar ingredients with varying moisture levels and nutrient composition. A subsequent article will review how changes in feedstuff DM impact diet composition and feeding amounts.
