This study eva‎luated the effect of feeding by-products-based concentrates instead of concentrates relying on great amounts of cereal grains on intake, feeding behavior, nutrients digestibility, ruminal fermentation, milk production, and feed conversion efficiency in the diet of high-producing dairy cows. Twelve multiparous Holstein cows (116.7 ± 8 DIM; milk yield= 42.7 ± .08 kg/d; BW= 665 ± 77 kg) were assigned to 1 of 4 squares and used in a replicated 3 × 3 Latin square design with 21-d periods (15 d for diet adaptation and 6 d for sampling and data collection). Cows were fed a TMR contained a low-forage diet (wheat straw, barley silage, and alfalfa and 1 of 3 experimental concentrates: the control concentrate was based on cereal grains (corn and barley) and soybean meal; (C-SBM), whereas the other two dietary by-product-based concentrates included: (1) pectin-rich feedstuffs (beet pulp, citrus, molasses, and canola meal); (P-BY), (2) cereal grain by-products (rice bran, corn germ meal, wheat bran, barley sprout, and broken corn); (CG-BY). All diets were formulated to be isoenergetic and isonitrogenous, and the ratio of forage to concentrate in all diets accounted for 40 to 60% of diet DM. The human-edible fractions of each dietary feedstuff were calculated according to Wilkinson (2011) in terms of human-edible energy (HEE) and human-edible protein (HEP) inputs. Accordingly, the HEE and HEP outputs were determined as amount of grass energy and true protein in the milk. The feed conversion efficiency in the sense of HHE and HEP was computed as output per input of each dietary ingredient. The dietary starch content decreased given replacing G-SBM with C-BY and P-BY from 33% to 21 and 11.5%, respectively. Our results showed that substitution of both by-product-based concentrates for grains increased neutral detergent fiber intake (10.88 and 11.03 kg/d for F-BY and P-BY vs 8.78 kg/d for the G-SBM) and neutral detergent fiber digestibility (55.6 and 56.9 for F-BY and P-BY vs 44.6% for the G-SBM), whereas starch intake (9.27 kg/d vs 5.34 and 3.31 kg/d for the G-SBM vs F-BY and P-BY, respectively), HEE (162 vs 40 and 38 MJ of grass energy/d), HEP (1.67 vs 0.39 and 0.40 kg/d) for the G-SBM vs F-BY and P-BY, respectively, decreased. Milk production and DMI were decreased when cows were fed the C-BY diet while there were no differences between P-BY and C-SBM diets. The ECM production increased when cows fed P-BY diet in comparison to CG-BY (36.23 vs 34.34 kg/d, respectively), but CG-BY diet increased FCE for ECM production compared to two other treatments. Although the eating time and sorting for fine particles increased when cows were offered the P-BY diet, all dietary treatments did not affect chewing activities, or ruminal pH at 4 h after feeding. CG-BY and P-BY diets increased significantly milk fat content compared to the CG diet (3.30 and 3.23% vs 3.01%, respectively). Similarly, cows fed with CG-BY and P-BY diets compared to G-SBM dietary had a greater performance in terms of he-FCE for protein (1.19 and 1.17 kg/d vs 0.32 kg/d, respectively) and for energy (2.51 and 2.77 kg/d vs 0.61 kg/d, respectively). In conclusion, the complete substitution of both by-product-based concentrates decreased starch intake, HEE and HEP inputs while neutral detergent fiber intake and digestibility, milk fat content, and he-FCE for protein and energy increased. In addition, milk production and DMI were affected based on by-product concentrate type and decreased when cows were offered C-BY diet rather than P-BY and G-SBM diets.

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