Including distillers grain with solubles (DGS) at the rates of 15% and 30% (dry matter basis) in lactating cow diets increases excreted nitrogen (N) by 3% and 16%, respectively. When compared to the currently recommended low phosphorus (P) lactating cow diet, excreted P increased by 33% and 67% for DGS inclusion rates of 15% and 30%, respectively.
If manure is applied at a N-based rate, DGS inclusion at a 15% rate will have minimal effect on a nutrient management plan for this situation and only modest impact on diets with 30% DGS. If manure is applied at a P-based rate, inclusion of DGS in the diet for the first time produces changes that must be considered in a nutrient management plan. As DGS inclusion rates increase, the increased P excretion is likely to require the long-term or strategic nutrient plan to address:
* Greater land requirement (up to 67% for 30% DGS inclusion in ration).
* Greater travel distance and time requirements for manure application, impacting labor and equipment needs as well as capital and operating costs.
* Revisions in the land treatment component of a nutrient management plan,including practices for minimizing soil erosion and runoff if fields are allowed to increase in soil P levels.
With inclusion of DGS in dairy rations, the annual plan (application rates, fields, and application methods) should also consider:
* The need for new farm-specific manure samples. Book values of manure nutrient concentration and past manure samples (prior to DGS inclusion) are not likely to be representative.
* Recalculation of application rates.
* Field selection for manure application. If manure is applied at a N-based rate, higher P application rates may result. This may lead to a higher P-Index rating (greater risk of P in runoff) and shorten the transition time for these fields to a P-based rate.
Additional information on the impact of the use of distillers grains and the impact on nutrient planning can be found at the Heartland Animal Manure Management Web site after May 1, 2008.
Author: Rick Koelsch, University of Nebraska
