The objective of this experiment was to study the effects of interactions between grass silage (GS) dominated by orchardgrass (Dactylis glomerata L.) and maize silage (MS) (Zea mays L.) on ad libitum intake, digestibility and nitrogen retention in wether sheep. The GS in this experiment reflected the quality of GS produced on family farms in Croatia, while the MS used is frequently produced in seasons unfavourable for high quality MS production. The study consisted of four feeding treatments involving GS and MS alone, and GS and MS mixtures in ratios of 67 : 33 or 33 : 67 (DM basis), fed twice daily. Mean DM contents of GS and MS were 396 and 264 g/kg fresh weight, respectively. MS was much lower (P < 0.001) in crude protein (CP) (62 g/kg DM) than the GS (120 g/kg DM). GS contained larger (P < 0.001) quantities of neutral detergent fibre (NDF) and acid detergent fibre (ADF) than MS. In contrast, MS contained more (P < 0.001) non-structural carbohydrate than GS, as starch, which comprised 211 g/kg DM. Inclusion of MS in the diet (33% v. 67%) had positive linear effects on fresh matter voluntary intake (P < 0.05), CP and starch digestibility (P < 0.05), and N balance (P < 0.05). A positive associative effect of GS and MS was observed for DM, organic matter intake (quadratic, P < 0.05), N intake and N balance (quadratic, P < 0.01), while it was negative for ADF digestibility (quadratic, P < 0.05). It was concluded that positive interactions of GS and MS were due to a better balance of available energy and protein when the two forages were fed together. No positive associative responses were recorded for digestibility, probably due to higher passage rates of digesta with MS supplementation i.e. lower MS quality in terms of maize plant maturity at harvest.