Biofuel co-products as livestock feed - Opportunities and challenges

Utilization of wet distillers grains in high-energy beef cattle diets based on processed grain 67Roughage concentration and sourceThe proportion of traditional roughage sources added tofeedlot diets is typically low because this optimizes G:F anddecreases problems with handling and conveying bulkymaterial. Indeed, the small amount of fibre supplied bythe roughage component of feedlot diets is thought toprimarily help performance by maintaining a healthy rumenand minimizing digestive disorders like acidosis and bloat.Despite low inclusion rates, roughage concentration andsource can significantly affect feedlot performance, primarilythrough changes in DMI. Arelovich et al. (2008) reportedpositive linear relationships between dietary NDF and DMI(r 2 = 0.96) by feedlot cattle. In addition, dietary NDF concentrationand NE for gain (NEg) intake were closely associated(r 2 = 0.86) in feedlot beef cattle diets that ranged from7.5 to 35.3 percent total NDF. Given that NEg intake is keyin determining performance, when the price of roughage islow, increasing dietary NDF concentration through changesin roughage concentration can increase DMI and therebyADG by cattle. Moreover, with differences in physical orchemical characteristics of NDF among roughage sources,changing the roughage source at a fixed dietary roughageconcentration can result in similar effects to changes inroughage concentration (Galyean and Defoor, 2003). Basedon their meta-analysis, Arelovich et al. (2008) suggestedthat roughage sources could be exchanged on an equalNDF basis to achieve equal DM and NEg intakes, a recommendationthat is generally supported by the literature(Marshall et al., 1992; Theurer et al., 1999). Nonetheless,the possibility of unique physical characteristics related toparticle size, density and fibre composition (i.e. physicallyeffective NDF) probably need to be considered.With observed relationships between DMI and NDF(Arelovich et al., 2008), one might expect DMI to increasewhen DG is added to feedlot diets; however, this expectationhas not been observed consistently in practice. Forexample, adding 15 percent wet sorghum DG to the DMof feedlot diets did not affect DMI in either DRC- or SFCbaseddiets (Leibovich, Vasconcelos and Galyean, 2009),despite decreased ADG. Similarly, Vander Pol et al. (2009)observed no effects on DMI with inclusion of up to 40 percent(DM basis) maize DG in DRC-based feedlot diets, andDepenbusch et al. (2008) reported no effects on DMI whenmaize DG (0 or 25 percent of dietary DM) was added toSFC-based diets. Indeed, Drouillard et al. (2005) reporteda linear decrease in DMI as sorghum DG concentrationincreased from 0 to 40 percent of the dietary DM.Recent results of our collaborative studies in feedlotsteers suggest that both roughage concentration (Mayet al., 2011) and source (Quinn et al., 2011) need to beconsidered in diets containing wet DG. May et al. (2011)evaluated two dietary concentrations of wet DG (15 or30 percent of the DM; DG was approximately 90 percentmaize and 10 percent sorghum) and alfalfa hay (7.5, 10 or12.5 percent; DM basis) plus a non-DG control diet thatcontained 10 percent alfalfa hay. No DG × alfalfa hay interactions(P >0.12) were detected, and final shrunk BW, ADG(P >0.15), and DMI (P = 0.38) did not differ between thetwo DG concentrations over the feeding period. Increasingalfalfa hay concentration tended (P