Nutrient digestion and performance by lambs and steers fed thermochemically treated crop residues

Five studies were conducted to determine nutrient digestibility and performance of lambs and steers fed thermochemically treated crop residues and distillers dried grains with solubles (DDGS) as a corn replacement pellet (CRP; 75% residue:25% DDGS, DM basis). Fifteen Hampshire, Suffolk, or Dorset wethers (BW 33.3 +/- 5.0 kg) were utilized to evaluate nutrient digestibility of the unprocessed native (NAT) and CRP [Exp. 1: wheat straw (WS); Exp. 2: corn stover (CS); Exp. 3: switchgrass (SWG) and corn fiber:wheat chaff (CFWC)] when limit fed (Exp. 1 and 2: 1.8% of BW daily; Exp. 3: 2.5% of BW daily) compared with a 60% corn diet. In Exp. 4, 56 individually fed Dorset-cross wether lambs (BW 32.0 +/- 1.4 kg) were utilized to compare performance and digestibility of WS, wheat chaff (WC), corn fiber (CF), a 3:1 blend of corn fiber:wheat straw (CFWS), a 3:1 blend of CFWC, and SWG-CRP fed for ad libitum intake compared with a 45% corn diet. In Exp. 5, 32 individually fed Holstein steers (BW 185.2 +/- 0.9 kg) were used to evaluate performance and digestibility of diets containing corn, WS-CRP, CFWC-CRP, or NAT-WS fed for ad libitum intake. Crop residues were processed with 5% calcium oxide (DM basis) and 35% water in a double-shaft enclosed mixer (Readco Kurimoto Continuous Processor, York, PA) and subsequently pelleted with DDGS to form CRP. Feeding lambs WS-CRP (Exp. 1) or CS-CRP (Exp. 2) increased digestion of DM, NDF, and ADF compared with NAT (P < 0.05). In Exp. 3, feeding CFWC-CRP increased total tract NDF digestibility and ADF digestibility (P < 0.05). Experiment 4 final BW were greatest for control lambs and least for lambs fed CFWS-CRP or SWG-CRP. Body weight gains for lambs fed CRP averaged 15.9% less than control (P < 0.05). Lambs fed CRP diets had greater (P < 0.05) NDF and ADF intake and output. In Exp. 5, steers fed the corn or 2 CRP diets gained similarly and faster (P < 0.05) than those fed the NAT-WS diet. Steers fed the control corn diet were more efficient (P < 0.05) than steers fed other treatments. Steers fed the corn diet, CFWC-CRP, and WS-CRP had greater (P < 0.01) DM digestibility than NAT. The results confirm benefits for nutrient digestion and subsequent animal performance when crop residues are thermochemically processed. Processed crop residues may be fed in combination with DDGS to partially replace corn in ruminant diets.