1 January 2011

7 minute read

Introduction

Benefits of DGS as a ration ingredient include increased availability and competitive pricing relative to other ingredients. Feeding DGS will potentially increase nitrogen (N) and phosphorus (P) excretion in manure and require changes in a nutrient management plan (NMP)1. An increase in excreted N and P is expected to not only increase costs associated with land application of manure but also the value of the manure (if sufficient land is available). This publication will summarize:

• the implications of using DGS on an NMP,
• the costs associated with its implementation, and
• the changes necessary to comply with environmental regulations.

Manure nutrient excretion other than American Society of Agricultural and Biological Engineers (ASABE) and Natural Resources Conservation Service (NRCS) book values are estimated using a mass-balance procedure based upon the specific dietary and animal performance assumptions for each diet evaluated.

Inclusion of DGS in a lactating dairy diet is a practice receiving increasing attention from researchers. DGS inclusion rate of 20 percent (Schingoethe, 2006), and 26 percent (Linn and Chase, 1996) of total ration dry matter base was reported. Schingoethe and co-workers also suggested including more than the 20 percent of the ration as DGS for diets containing higher proportions of corn silage. For other dairy cattle, a DGS inclusion rate of 15 percent is recommended for replacement heifers while distillers grains are not commonly recommended for calves less than 6 months old.

In most studies, milk production remained the same or showed a small increase in response to DGS inclusion (Schingoethe, 2004). A drop in feed intake, milk yield, and milk protein concentration was reported for DGS inclusion rates greater than 30 percent of the dietary dry matter. Most recently Kleinschmit and co-workers (2006) reported that feeding DGS at 20 percent did not significantly decrease the concentration of milk fat, but significantly reduced milk protein percentage. Reduced dry matter intake and reduced milk production were also reported at DGS rates exceeding 25 percent of the ration dry matter. Other positive impacts of feeding distillers grains to dairy cattle could be protection against acidosis, laminitis and liver abscesses. However, feeding high levels of DGS may inhibit some fiber-digesting bacteria normally found in the rumen, which could lead to depressed milk fat, a component used to make butter.

In deciding the inclusion of DGS in dairy feed, producers have historically evaluated the variability of DGS nutrient content, ingredient costs, and issues related to on-farm storage and handling of DGS. The following information will allow the impacts of DGS use on the Nutrient Management Plan to also be considered.

DGS Inclusion Effect on Manure

Current Natural Research Council recommendation for lactating dairy cows range from 0.30 to 0.40 percent P in the diet, depending primarily on milk production (NRC, 2001). Corn grain commonly has 0.3 percent P. This is further concentrated by the removal of starch during ethanol processing by a factor of about three. With the inclusion of DGS, the ration P concentration will commonly increase. Ration crude protein concentrations may also increase with inclusion of DGS. The additional nutrients are not retained by the animals which results in more N and P in the manure.

To estimate the change in N and P excretion, and subsequent changes in the NMP, four rations were evaluated for two case-study farms, a 200- and 2000-head lactating dairy herd. The low P baseline diet (0 percent DGS) was formulated for a crude protein and P concentration of 18.5 percent and 0.33 percent, respectively. This diet was modified to allow a 15 percent and 30 percent DGS inclusion rate. Diets were formulated with DGS substituted for corn silage, corn, hay and haylage, soybean and soy supplement. The 30 percent DGS inclusion rate exceeded recommendations at the time of this publication but was considered within the realm of possibility for the near future. A high P diet (0.5 percent P) is more representative of past feeding practices and was included for comparison. Assumptions made in this study are summarized in Table 1.

Excreted and crop-available N increased due to an inclusion of DGS in dairy diet. Excreted N increased by 3 percent and 16 percent, respectively, for DGS inclusion rates of 15 percent and 30 percent (Table 2). When compared to the currently recommended low P baseline dairy diet formulations, excreted P increased by 33 percent and 67 percent for DGS inclusion rates of 15 percent and 30 percent, respectively. However, when compared to a traditional high P diet, phosphorus excretion was 33 percent and 17 percent for 15 percent and 30 percent inclusion rates, respectively. The extent of the observed change depends on which comparison is used, the traditional high P diet or the low P baseline diet.

Book values traditionally used to estimate manure N and P excretion are based on blanket average value and are not accurate in estimating excretion . Natural Resource Conservation Service book value estimated only half the N excretion on feeding DGS while the ASABE commonly over-estimated P excretion.

Impact of DGS Inclusion on Nutrient Plan DGS inclusion at a 15 percent rate will likely have minimal effect on an NMP for a manure system that conserves N. The moderate increase in P excreted might have some implications for systems less conservative of N than the manure system modeled for the case study. Phosphorus may become the limiting nutrient in these situations and determine land requirements. However, for the N-conserving manure management system modeled , N was the limiting nutrient at 15 percent DGS inclusion. With inclusion of DGS in dairy rations at 30 percent, the strategic (or long-term) plan will benefit by considering:

• Greater land requirement,
• Greater travel distance and time requirements for manure application impacting labor and equipment needs as well as capital and operating costs,
• The land treatment component of an NMP including practices for minimizing soil erosion and runoff for fields receiving higher P content manure should be reviewed, and
• Book values for manure excretion are often inaccurate in estimating land requirements. With inclusion of DGS in dairy rations at 30 percent, the annual plan (application rates, fields, and application methods should consider:
• Book values of manure nutrient concentration and past manure samples (prior to DGS inclusion) are not likely to be representative. New, farm-specific manure samples will be needed,
• Application rates will need to be recalculated,
• If manure is applied at an N-based rate, field selection for manure application may need to be reconsidered due to higher P-application rates. Some fields with a higher P-Index score may need to transition to a P-based rate immediately. The transition time for most fields to a P-based rate will be shorter.

Significant reductions in dietary P recommendations have reduced excreted P since the 1990s. These changes should have produced significant modification in NMPs over the last 10 years. However, many planners have not had the tools necessary for such adjustment in the past. Thus, current NMPs for farms feeding a recommended P level or some level of DGS are likely to contain errors overestimating land requirements and the potential need to transition to a P-based manure application rate.

Summary

The results found in this publication apply to manure handling systems that conserve N- manure storage systems with minimal treatment and land application by injection or direct incorporation. The important points from this evaluation of the effect of feeding distillers grains on an NMP of a dairy farm include:

Including DGS at 15 percent did not increase land requirement for field manure application under the assumptions of this case study and should not require a change in the NMP provided initial excretion estimates for the plan were accurate.

DGS inclusion rate of 30 percent increases the land requirement and application time, requiring adjustments to labor and equipment need for manure application

. Farm-specific animal performance and feed pro- grams should guide estimating manure nutrient excretion, not book values. Using book value to estimate excretion leads to erroneous results for the dairy. The discrepancy can be worse for diets including DGS.

Farm-specific and current manure analysis should be used in estimating the amount of nutrient (N and P) in manure. Manure application rates should be adjusted to those samples.

The use of DGS increases the value of the manure and has the potential for offsetting increases in land application costs.

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