Effects of grinding versus steam-flaking on feeding value of blending barley and corn in low-forage diets fed to dairy cows Kh. Safaei1, G.R. Ghorbani1, M. Alikhani1, A. Sadeghi-Sefidmazgi1 , W.Z. Yang2*, Mahdi Saebi-Far1 #596 1 Department of Animal Sciences, Isfahan University of Technology, Isfahan 84156-83111, Iran; 2Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, AB, Canada Background Results Table 2. Ruminal fermentation characteristics and sorting activity Starch-rich feeds meet nutrient requirements of high-producing lactating dairy cows. The extent and rate of ruminal carbohydrate digestion can be manipulated through processing. Barley-corn blend is common to feed to dairy cows in Iran. There is no data about the effects of grinding vs. steam-flaking in barley-corn blend diets on dairy cows performance.   TreatmentsA Item GBGC SBSC SCGB SBGC SEM P-value Ruminal fermentation pH 6.5 6.6 6.3 6.4 0.07 0.14 Total VFA, mmol/L 83.6 87.2 83.1 84.8 5.45 0.64 Acetate, mol/100mol 54.5 56.8 56.7 58.8 1.44 0.06 Propionate ,mol/100mol 24.1 23.5 22.7 21.9 1.23 0.27 Butyrate, mol/100mol 15.7 14.7 15.5 14.2 0.53 0.11 Acetate: propionate 2.3 2.5 2.6 0.19 0.31 Sorting activity 19.0 mm 97.8c 101.3a 99.2ab 98.7bc 0.506 <0.01 8.0 mm 98.9b 104.8a 102.9a 0.806 1.18 mm 103.2a 96.5b 99.6c 98.5c 0.678 <1.18 103.8 99.6 102.1 101.2 2.83 0.76 Table 1. Effects of grain processing on performance of lactating dairy cows   TreatmentsC Item GBGC SBSC SCGB SBGC SEM P-value Intake of DM, kg/d 24.4 23.1 23.8 0.92 0.06 DDTT, %A 70.3b 73.9a 73.4ab 71.5ab 1.09  0.04 Milk yield, kg/d 45.1 44.3 44.6 1.79 0.46 Fat , % 2.8 2.9 0.15 0.91 Protein, % 2.7 0.64 Lactose, % 4.6 4.7 0.67 Milk yield/DMI 1.85 1.93 1.90 1.84 0.05 0.10 Objective To investigate the effect of grinding vs. steam-flaking in barley-corn blend diets on performance and rumen fermentation of lactating dairy cows. A DDTT = Dry matter digestibility in the total digestive tract . CGBGC= blend of ground barley and corn, SBSC = blend of steam-flaked barley and corn, SCGB = blend of steam-flaked corn and ground barley, and SBGC = blend of steam-flaked barley and ground corn. Material and Methods Grains were either ground 3 mm sieve or steam-flaked with densities of 390 and 360 g/L. Animal: 8 dairy cows (88± 12 DIM, 44.0± 1.5 kg milk/day). Design: a 4 × 4 Latin squaren (21 d/period). Diet: 25% corn silage, 15% alfalfa hay and 60% concentrate (DM basis). Treatments: 1) ground barley and corn (GBGC), 2) steam-flaked barley and corn (SBSC), 3) steam-flaked corn and ground barley (SCGB), 4) steam-flaked barley and ground corn (SBGC). Ruminal pH, VFA profile and Sorting activity (Table 2) Ruminal pH, total VFA and molar proportions of VFA were not affected. Molar proportion of acetate tended (P < 0.06) to be greater with SBGC. Cows fed GBGC diet sorted against particles on 19- and 8-mm sieves. Cows fed SBSC diet sorted in favor particles on 19 and 8-mm sieves. A GBGC= blend of ground barley and corn, SBSC = blend of steam-flaked barley and corn, SCGB = blend of steam-flaked corn and ground barley, and SBGC = blend of steam-flaked barley and ground corn. Conclusions Feeding cows with blend of steam-flaked barley and corn is beneficial to improve DM digestibility and milk efficiency. Rumen pH and fermentation characteristics were little impacted with grain processing Results Intake, DM digestibility and milk production (Table 1) Intake of DM tended (P<0.06) to be less with SBSC than others Digestibility of DM in the total digestive tract was greater (P<0.04) with SBSC and SCGB than GBGC. No treatment effects on milk yield and milk composition. Milk efficiency tended to be improved with SBSC vs. GBGC or SBGC. Acknowledgements We acknowledge Isfahan University of Technology (Isfahan, Iran) for financial support and Chavdaneh CO. (Isfahan, Iran), for grain processing.