Ruminal degradability and intestinal digestibility of crude protein in sorghum distillers dried grains compared to soybean meal and corn co-products

Abstract Text:   Our objective was to determine dry matter (DM) and crude protein (CP) ruminal in situ degradability and intestinal in vitro digestibility of sorghum distillers dried grains compared to soybean meal and other corn co-products.  In situ measurements were conducted using three mid-lactation, multiparous, ruminally-cannulated Holstein cows (BW 797.3 ± 77.8 kg). Five feedstuffs were evaluated: sorghum distillers dried grain (SDDG), corn distillers dried grains (CDDG), reduced-fat corn distillers dried grains (RFDDG), corn gluten meal (CGM) and soybean meal (SBM).  Duplicate samples were weighed into nylon bags and incubated in the rumen for 0, 2, 4, 8, 16, 24 and 48 h.  Rumen degradation constants for DM and CP were estimated using the NLIN procedures in SAS version 9.3. Six additional replicates from each feedstuff were ruminally incubated at 16 h and residues were used to determine in vitro intestinal digestibility of CP. Residues were incubated in a Daisy II incubator (Ankom Technology, Inc. Macedon, NY) with pepsin and pancreatin solutions for 1 h and 24 h, respectively. Intestinal protein digestibility (IDP), intestinally absorbable dietary protein (IADP = RUP × IDP), and total digestible protein (TDP = RDP + IADP) were evaluated using MIXED procedures in SAS with feedstuff as a fixed variable and cow as a random variable in the model. Ruminally degradable DM (RDDM) was less in CGM and greater in CDDG, RFDDG SBM compared to SDDG.  Ruminally degradable protein (RDP) was greater in SBM, CDDG, and RFDDG compared to SDDG and CGM.    Conversely, ruminally undegradable protein (RUP) was greater in SDDGS and CGM than in SBM, CDDG, and RFDDG.  Estimated IDP, IADP, and TDP were least in SDDG compared to the other feeds. Results indicate CP from SDDG was less ruminally degradable and intestinally digestible compared to CDDG, RFDDG, and SBM.  Concentrations of RDP and RUP were similar in SDDG and CGM; however, CGM had more total CP, IDP, and TDP.   

Item	SDDG	CDDG	RFDDG	CGM	SBM	SEM
CP, % DM	39.3	33.0	32.8	74.0	51.1	-
RDDM, % of DM	46.8c	56.6b	58.6b	33.3d	74.4a	0.94
RDP, % of CP	35.5c	48.7b	50.2b	31.8c	70.0a	1.04
RUP, % of CP	64.5a	51.4b	49.8b	68.3a	30.0c	1.04
IDP, % of RUP	37.5d	65.3b	66.0b	53.4c	95.4a	2.48
IADP, % of CP	24.2c	33.5ab	32.9ab	36.5a	28.6bc	1.65
TDP, % of CP	59.8d	82.2b	83.1b	68.2c	98.6a	1.17

^abcdValues with unlike superscripts differ by P < 0.05.

Keywords: sorghum distillers dried grains, rumen degradation, intestinal digestibility