Using Bluegrass Straw to Modulate the Elevated Dietary Crude Protein and Phosphorus Caused by Including Distillers Grains and Solubles in Dairy Diets

Project Overview

Project Type: Graduate Student
Funds awarded in 2008: $14,914.00
Projected End Date: 12/31/2009
Grant Recipient: Washington State University
Region: Western
State: Washington
Major Professor:
Ronald Kincaid
Washington State University

Annual Reports


  • Animals: bovine
  • Animal Products: dairy


  • Animal Production: feed/forage, feed formulation, winter forage
  • Crop Production: continuous cropping
  • Education and Training: demonstration, extension
  • Farm Business Management: budgets/cost and returns, whole farm planning
  • Production Systems: holistic management


    The impact of partially substituting bluegrass straw (BGS) for alfalfa hay to reduce N and P intake in early lactation cows was determined. Cows were fed a control ration or a ration in which 10% of alfalfa hay was replaced by BGS. Feed intakes were higher for the BGS ration whereas in vitro digestibility, feed costs, income-over feed cost, fecal P and N, and feeding behavior were unaffected. Milk yield and income was reduced but not income-over-feed costs. Thus, BGS in diets of lactating cows reduced the %P and %N, N intake, and aided nutrient management.


    The greatly accelerated production of ethanol in the U.S. increased prices of feed grains but also increased the availability of distillers grains & solubles (DGS) for livestock feeds. Because DGS contains comparatively high fiber content, most DGS is fed to cattle. The high phosphorus (P) and crude protein (CP) content of DGS challenges existing nutrient management plans for dairy farms, most of which already have excess P imports and face increased scrutiny concerning ammonia emissions. Feed ingredients containing low concentrations of P and N need to be included in rations to offset the high P and N in the DGS. Recently, bluegrass straw (BGS) was added to diets of cows entering their final 100 days of lactation without affecting milk yield or composition (O’Rourke et al., 2007). In addition, incorporating BGS into diets instead of field burning the bluegrass seed residue reduces particulate emissions, which can reach 159 kg PM2.5 per acre (Johnston and Golob, 2004).

    Environmental stewartship involves developing and adopting sustainable agricultural practices that must be economicaly viable. Currently, a challenge to environmental stewardship is incorporating the available DGS from ethanol production into livestock diets without overloading soils with P from livestock manure, thus significantly increasing P in surface water and increasing ammonia emissions from dairies. When corn grain is used for ethanol production, approximately 1 kg of dried DGS is produced from 3 kg of corn, thus as ethanol production and the availability of DGS increase, the availability of corn as a feed grain decreases. Because DGS contains more than 0.65% P and nearly 30% CP (Stein et al., 2006), replacing 5 kg of corn with DGS increases the concentration of CP in lactation diets by 4% units and P by 0.08% units. Accordingly, a basal diet that contained 16% CP and 0.4% P contains 20% CP and 0.48% P when DGS is substituted for about half of the corn. These dietary levels of CP and P (20% and 0.48%, respectively) are unacceptably high from the standpoint of P loads and ammonia emissions.

    Perhaps the best way to lessen the impact of dietary DGS on N and P excretion of cattle is to increase use of feed ingredients that contain low CP and P concentrations. For example, BGS contains only 8% CP and 0.19% P. O’Rourke (2007) found when BGS partially replaced alfalfa hay, the %CP in the lactation diet was reduced from 18.9% CP in the Control diet to 17.8% in the diet with 10% BGS, and 17.5% CP in the diet with 15% BGS. This equates to a daily reduction of 57 g of N/cow/day or an annual reduction of over 20 kg of N/cow/year. Dairy cattle producing 41 kg of milk/day and fed diets with 19% CP excrete about 0.5 kg N/cow/day (Nennich et al., 2005), emit about 170 kg of ammonia/cow/year (Rumburg et al., 2004), of which 55 kg of ammonia is lost via an open anaerobic dairy waste lagoon (Rumburg et al., 2008). Reducing N intakes of cows is the most effective way to reduce N excretion and ammonia emissions. Similarly, the low concentration of P in BGS can be used to offset the high concentration of P in DGS (Lemenager et al., 2006).

    O’Rourke (2007) found feeding 10% BGS as a partial replacement for alfalfa hay reduced daily feed costs by about $27/day for 100 cows or nearly $10,000 per year for 100 cows. In addition to reducing feed costs for dairies, use of BGS in lactation diets gives bluegrass seed growers an additional market for their bluegrass straw and reduces particulate emissions from field burning. In the Pacific Northwest there are about 152,000 acres of Kentucky bluegrass grown (Holman and Thill, 2005). Total emissions from burning the residue on bluegrass fields are estimated at 13.6 to 56 kg of PM2.5 per acre in eastern Washington to 159 kg of PM 2.5 per acre in northern Idaho (Johnston and Golob, 2004).

    The results of a previous Western SARE Graduate Student Fellow Grant (O’Rourke et al., 2007) with using BGS in lactation diets were: 1) bluegrass straw can be added at levels up to 15% (in replacement of alfalfa hay) of diets fed to lactating cows in late lactation (219 days-in-milk at the start of the study) without affecting milk yield or milk composition; 2) partial replacement of alfalfa hay with bluegrass straw reduced the %CP in diets, thus reducing N excretion; and 3) partial replacement of alfalfa hay with bluegrass straw reduced feed cost without adversely affecting milk yield or composition. Likewise, in the previous study (O’Rourke et al., 2007), partial replacement of alfalfa hay with bluegrass straw had a larger effect of reducing N excretion than P excretion because the difference in CP between BGS and alfalfa hay is much larger than the difference in P between BGS and alalfa hay. Because the results of the previous study showed BGS can be added to diets of lactating cows without affecting milk production, there is justification to expand the use of BGS in dairy diets. This proposal extends previous work of feeding BGS to late lactation cows and proposes to use BGS to reduce N and P excretion of cows in mid-lactation fed diets contains DGS. The proposed study also considers income over fee costs. Thus, the hpothesis is that BGS in diets will reduce N and P excretion in early to mid-lactation cows fed DGS and improve net income of dairies.

    Project objectives:

    • The objectives are to determine if:
      1. bluegrass straw can be used in diets to offset the increased excretion of nitrogen and phosphorus of cattle fed distillers grains & solubles;
      2. bluegrass straw can be fed to cows in early to mid-lactation without affecting milk yield and composition; and
      3. income over feed costs is affected when bluegrass straw is incoporated into lactation diets.
    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.