Effects of different expander processing conditions on the nutritive value of barley and wheat by-products in pig diets

The apparent nutrient digestibility and nitrogen (N) utilization was studied to evaluate the responses of growing pigs (from 31 to 70 kg) for the expanding of barley and wheat bran-wheat middlings mixture (2:1) (WBM). In Experiment 1, four male castrates were used in a 4×4 Latin square where the effects of expanding (unexpanded vs. expanded) and WBM level (200 vs. 400 g/kg) were studied. In Experiment 2, five male castrates were used in a 5×5 Latin square where effects of steam additions during processing were studied and WBM diets were compared to a barley-soybean diet (barley-SB diet) (WBM 400 vs. 0 g/kg). WBM and hammer milled barley were expanded separately by adding 0.0, 3.0 and 6.0% (w/w) steam into the expander. WBM was included in barley-SB meal diets by formulating to the same crude protein content (163 g/kg). The effects of expanding on digestibility were very small excluding that of ether extract which improved remarkably. The calculated digestibilities (%) of dry matter, NDF-fibre, ether extract and crude protein in the WBM were 72.0, 44.0, 39.3 and 81.2 (standard error 1.8, 4.4, 5.9 and 5.8) and in the expanded WBM 69.9, 44.7, 58.3 and 78.3 (standard error 2.8, 4.7, 5.8 and 6.8), respectively. The nitrogen retention (N retention) remained the same in experiment 1, but expanding improved that in experiment 2. The steam addition during expanding improved linearly digestibility of ether extract, while digestibility of the other nutrients and N balance were unaffected. The increased WBM level from 200 to 400 g/kg depressed digestibility of dry matter, organic matter, crude carbohydrates and gross energy without affecting the N retention. Nitrogen retention and digestibilities of all nutrients excluding ether extract and ADF-fibre in the barley–SB diet were superior to those of the WBM diets. Expanding increased undigestible dietary N (UDN) excretion and decreased the percentage of bacterial and intestinal debris N of faecal N. WBM increased UDN excretion. The other effects of expanding and WBM level on faecal N fractions were contradictory between our experiments.