When converting as-fed to dry matter, what is the dry-matter basis crude protein for 10 lb of corn with 85% DM and 8% CP on a DM basis?

When converting as-fed to dry matter, what is the dry-matter basis crude protein for 10 lb of corn with 85% DM and 8% CP on a DM basis?

• A. 0.80 lb DM corn
• B. 0.68 lb CP (as-fed)
• C. 8.5 lb DM corn
• D. 0.68 lb CP (DM basis)

Answer: (D)

The key idea is to express crude protein on a dry-matter basis, so you remove moisture first and then apply the CP percentage to the dry matter. First find how much dry matter is in the 10 lb sample: 10 × 0.85 = 8.5 lb DM. Then apply the CP on a DM basis (8%): 0.08 × 8.5 = 0.68 lb of crude protein in the dry matter. So there are 0.68 lb of crude protein on a dry-matter basis. The other figures come from either using the as-fed weight (0.8 lb CP) or just giving DM mass (8.5 lb) without the CP calculation, which isn’t the requested DM-basis value.

The key idea is to express crude protein on a dry-matter basis, so you remove moisture first and then apply the CP percentage to the dry matter.

First find how much dry matter is in the 10 lb sample: 10 × 0.85 = 8.5 lb DM. Then apply the CP on a DM basis (8%): 0.08 × 8.5 = 0.68 lb of crude protein in the dry matter.

So there are 0.68 lb of crude protein on a dry-matter basis. The other figures come from either using the as-fed weight (0.8 lb CP) or just giving DM mass (8.5 lb) without the CP calculation, which isn’t the requested DM-basis value.