The objective of this study was to evaluate nutrient digestibility, nitrogen balance, and purine derivative excretion from growing sheep fed on ryegrass silage (S) or ryegrass hay (H) cut at two maturity stages (21 and 35 d). In an in vivo trial, 32 Suffolk × Merino growing sheep (22 ± 2 kg) were used in a completely randomised design with eighth replications in a 2 × 2 factorial arrangement. Four diets were used containing 75% forage (S at 21 or 35 d and H at 21 or 35 d) and 25% concentrate. In an in vitro trial, a completely randomised design was used for gas production parameters. Contents of N and NDF were higher in H (30 and 674 g/kg DM) than in S (26 and 411 g/kg DM). Animals fed on S had higher digestibility (P <.008) of DM and OM (661 and 715 g/kg) than H at 35 d (557 and 596 g/kg). In vitro gas production was lower (P <.04) in H at 35 d. In vitro DM disappearance at 96 h was lower (P <.03) for H at 35 d. Excretion of allantoin (mmol/day) in urine was higher (P <.001) in S (7.91 and 3.95) than H (5.01 and 3.03) at 21 and 35 d respectively. Overall, compared to ryegrass hay, ryegrass silage cut at 21 d can be an advantageous feeding strategy for growing sheep without negative effects in nutrient intake, N-balance, and purine derivatives.Highlights Contents of N and NDF were higher in hay than in silage form ryegrass. Animals fed on silage had higher digestibility of DM and OM. In vitro gas production was lower in hay cut at 35 days.