Effects of Processing on the Supplemental Protein Value of Distillers Byproducts in Forage Diets

Abstract

Five abomasal-cannulated wether lambs (25 kg) were used in a 5 × 5 Latin square arrangement of treatments to compare the supplemental protein value of unprocessed, fresh wet corn stillage (WCS) with that of centrifuge-processed wet distillers grains (WDG), distillers dried grains with solubles (DDG-S) and WCS that had been used to reconstitute and ensile early-bloom Kenhy tall fescue hay (EWCS). Each lamb received 530 g/d of dry matter (DM) as fescue hay (F) alone (negative control) or with sufficient byproduct DM to achieve daily nitrogen (N) intakes of 9.1 and 13.1 g, respectively, for the negative control and byproduct-supplemented treatments. Single degree of freedom contrasts were used to evaluate the effects of supplementation (F vs all supplements), solubles removal (WCS vs WDG), drying (WCS vs DDG-S) and ensiling (WCS vs EWCS). Apparent total tract DM digestibility was lower (P<.05) for EWCS than WCS (46.8 vs 52.5%), primarily due to lower cell wall digestibility (46.4 vs 52.6%). Supplementation increased (P<.05) abomasal flow of undegraded feed N (6.0 vs 4.4 g/d), apparent total tract N digestibility (62.3 vs 53.3%) and N retention (2.8 vs .9 g/d). Abomasal flow of undegraded feed N was greater (P<.05) and N retention was lower (P<.05) for EWCS than WCS (7.0 vs 5.4 and 1.6 vs 3.0 g/d, respectively). Abomasal microbial N flow was greater (P<.10) for WCS than processed byproduct treatments (5.2 vs 4.0 g/d); microbial crude protein synthesized in the rumen per 100 g organic matter (OM) fermented (corrected for microbial OM) averaged 9.7 g across all treatments. Ruminal degradability of feed N was similar (P>.10) among diets containing WCS, DDG-S and WDG (60.3, 57.6 and 53.1%, respectively), but was lower (P<.05) for EWCS (46.7%) than WCS. Reconstituting and ensiling forage with WCS enables long-term storage of wet byproduct and spares energy costs of producing DDG-S, but detracts from the feeding value of the same mixture blended fresh daily as evidenced by lower (P<.05) N retention in growing lambs.