In situ ruminal degradation characteristics of by-product feedstuffs for beef cattle consuming low-quality forage.

Eight ruminally cannulated steers (BW = 753 +/- 48 kg) were used to evaluate in situ N, NDF, and DM degradation characteristics of by-product feeds and their application for beef cows consuming low-quality forage. Experimental feedstuffs included (DM basis) 1) extruded-expelled cottonseed meal (ECSM; 33% CP and 55% NDF), 2) extruded-expelled cottonseed meal with linters (ECSML; 25% CP and 41% NDF), 3) dried distillers grains with solubles (DGS; 33% CP and 36% NDF), 4) solvent-extracted cottonseed meal (CSM; 43% CP and 29% NDF), and 5) a blend of 76% wheat middlings with 18% CSM (WMCSM; 23% CP and 40% NDF). Steers were fed chopped prairie hay (4.8% CP, 69% NDF; DM basis) ad libitum and received 0.38 kg/100 kg of BW of WMCSM daily. In situ degradation kinetics of N, NDF, and DM components included the following fractions: A (immediately soluble), B (potentially degradable), and C (undegradable). Calculated rumen degradable protein (RDP) for ECSM was the greatest among all feedstuffs (83.8%; P < 0.01), which was composed of a large A fraction of N (41%). Similar RDP values were observed for DGS and ECSML (50.7 and 50.9%, respectively, P = 0.93). The B fraction N for ECSML was large (88.9%); however, most of this was unavailable for ruminal degradation. The amount of RDP in CSM and WMCSM was similar (78.2 and 73.5%, respectively; P = 0.12) though the A fraction of N was greater for WMCSM compared with CSM (P < 0.01). Degradability of NDF was greatest (P < 0.01) for DGS (67.4%) and was similar (P = 0.48) for WMCSM and CSM (54.5 and 57.0%, respectively). The least degradability of NDF was calculated for ECSM (29.3%; P < 0.01), attributed to greater lignin content (13.3%, DM). Degradability of DM was greatest (P < 0.01) for CSM and WMCSM (63.7 and 59.4%, respectively) and least (P < 0.01) for ECSM (36.5%) and ECSML (40.6%). Ruminal N degradation characteristics of ECSM were similar to more traditional supplements containing CSM and WMCSM. The RDP for ECSML and DGS N was less compared with other feedstuffs, indicating these feeds may need to be blended with other ingredients containing greater concentrations of degradable N, particularly in situations in which forage RDP is low.