Effects of different grinding methods and particle size of barley and wheat on pig performance and digestibility

The effect of grinding method of barley and wheat on total tract digestibility of barley-soyabean meal and wheat-soyabean meal diet, N-balance (experiments 1 and 2) and pig performance (experiments 3 and 4) was studied. Cereals were ground by four mill types and there were two degrees of grinding fineness within each mill type. Mill types were a hammer mill (HM, sieve size 3 and 5 mm), a crimping roller mill (RM1, gap between rolls 0.5 and 0.8 mm), a flattening roller mill (RM2, gap between rolls 0.15 and 0.35 mm) and a triple roller mill (RM3, gap between the Ist and 2nd roll 0.2 and 0.65 mm, gap between the 2nd and 3rd roll was fixed at 0.65 mm). Data were analysed in a nested design, mill type as the main treatment tall 4 mill types in experiments 1, 3 and 4, mill types HM, RM1 and RM2 in Experiment 2) and fineness of grinding (fine and coarse) as the subtreatment within each mill type. Digestibility and N-balance experiment with barley was conducted with eight castrated male pigs (25.9-91.9 kg) in a 8 x 6 cyclic change-over design (Experiment 1) and with wheat, using 12 castrated male pigs (31.2-83.8 kg) in two 6 x 6 Latin square design (Experiment 2). A growth experiment was conducted with 160 growing-finishing pigs (25.2-101.5 kg) housed per pair tone female and one castrated male per pen, 10 pens per treatment) with barley (Experiment 3) and an other 160 pigs (25.2-100.3 kg) with wheat using the same procedure (Experiment 4). RM1 depressed digestibility of crude protein (p < 0.05 and p < 0.10, with barley and wheat) and ether extract (p < 0.01 and p < 0.05, with barley and wheat) in both cereals and improved digestibility of NDF (p < 0.01) and crude carbohydrates, which were defined as total organic matter - (ether extract + crude protein) (p < 0.05) in barley compared to the other mill types. Coarse grinding within RM1 decreased all measured digestibilities (p < 0.05) in both cereals, except for NDF in barley, compared to fine grinding. The mill type had no effect on N retention g/day, but the proportion of faecal N excretion was increased with RM1 and RM3 barley (p < 0.05) and with RM1 and RM2 wheat compared to hammer milling (p < 0.10). Coarse grinding within RM1 increased the proportion of faecal N excretion with both cereals compared to fine grinding. RM1 increased the total feed consumption with barley and depressed the daily gain and feed conversion ratio (p < 0.10) compared to the other mill types. The coarse grinding within RM1 and RM3 increased barley based feed consumption (p < 0.10) and depressed daily gain and feed conversion ratio (p < 0.05), but neither mill type nor fineness of grinding had any effect on carcass quality with barley. The mill type had no effect on feed intake, pig performance or carcass quality with wheat. It was concluded that mill type had no effect on dry matter and gross energy digestibility in barley and wheat. Also, pig performance with rolled barley and wheat was equal to that obtained with hammer milled cereals, if the total feed consumption was not influenced by the grinding method. (C) 2000 Elsevier Science B.V. All rights reserved.