Abstract Four yearling male red deer ( Cervus elaphus) and four yearling male sheep were fed tropical grass ( Digitaria decumbens) hay supplemented with or without 30% dried leucaena ( Leucaena leucocephala) leaves. Voluntary feed intake (VFI), digestibility of dietary components, haematological parameters and serum thyroxine concentrations were determined. Leucaena supplementation reduced VFI of pangola grass by 8% but increased total DMI of both species by 30%. Digestibility of DM, OM and N was higher for both species when leucaena was fed but sheep digested these dietary components more efficiently than deer. Leucaena supplementation did not influence blood cell numbers or haemoglobin and thyroxine concentrations in either species. Deer had higher concentrations of red blood cells and lower concentrations of white blood cells than sheep. It was concluded that leucaena at 30% could be a suitable supplement for deer and sheep consuming sub-tropical pastures.