•DMI was not affected by supplementation either with starchy or fibrous concentrates.•Supplementation did not affect microbial N supply and its efficiency.•Ruminal pH of heifers supplemented with starchy or fibrous concentrates was similar.•Soyhulls supplementation enhanced NDF digestion respect to starch supplementation. The objective of this study was to evaluate the effects of supplementation with starchy or fibrous concentrates to heifers fed temperate pasture silage on intake, digestibility, ruminal environment, microbial N supply and plasma glucose and insulin concentrations. Twenty-four Hereford heifers (average BW = 224.2) were assigned to 4 dietary treatments in a completely randomized design. Experimental diets consisted in pasture silage alone (S), pasture silage supplemented with soyhulls (S + SH), pasture silage supplemented with barley (S + B) or pasture silage supplemented with corn (S + C). Concentrates were offered prior to forage at 10 g DM/kg BW once daily. The inclusion of supplements depressed daily forage intake (6.60 vs. 5.13 kg/d, P < 0.001), but supplemented animals ate enough forage to reach a forage:concentrate ratio of 70:30.Supplementation tended to increase total DM daily intake (6.60 vs. 7.40 kg/d, P = 0.072) and increased total OM intake (5.73 vs. 6.63 kg/d, P = 0.015). Non-supplemented group spent more time eating (325 vs. 242 min/d, P = 0.009), however ruminating time was similar between treatments. Whole diet digestibility was not affected by the inclusion of corn or barley, but the inclusion of soyhulls increased NDF digestibility from 0.66 to 0.76 (P = 0.005). Ruminal pH was lower for the supplemented groups (6.47 vs. 6.82, supplemented vs. non-supplemented, respectively; P < 0.001). Supplementation with soyhulls led to the highest daily mean total VFAs concentration (P < 0.001) and insulin concentrations were higher in animals supplemented with starchy concentrates (P = 0.011). Supplementation did not affect microbial N supply, nor its efficiency. Overall, our results indicate that the supplementation of temperate pasture silage with energy concentrates at low levels once a day to supplement improved energy related parameters but not microbial N supply. Under these feeding conditions, the effect of using soyhulls, corn or barley was similar, despite their differences in composition and fermentation characteristics.