The effect of stage of maturity on the ensiling properties of whole crop maize was studied under laboratory conditions. Maize (Zea mays L.) was harvested at four maturity stages being, early dent (ED), one-third milkline (ML), two-thirds ML and blackline (BL). The chopped forages were ensiled in 1.5-1 anaerobic jars. Three jars per treatment were sampled on days 2, 4, 8, 15, and 90. After 90 days of ensiling, the silages were subjected to an aerobic stability test lasting 5 days, in which CO2 production was measured, as well as chemical and microbiological parameters. In addition, fibre content and in situ rumen degradability were analysed at the four stages of maturity. Water-soluble carbohydrates decreased in the silages with maturity. The silages from the ED stage had more lactic acid, ethanol, weight loss, yeast, and moulds than at one-third ML, two-thirds ML and BL stages. The silages from the ED stage produced more CO2 than the one-third ML, two-thirds ML and BL stages (P < 0.05). Silages from the ED stage were not judged to be stable under aerobic conditions. The fibre contents decreased in one-third ML, two-thirds ML and BL stage as compared with the ED stage (P < 0.05). The neutral detergent fibre (NDF) content of silages decreased from 527 to 421 g/kg dry matter (DM) (P < 0.05). The hemicellulose content did not change consistently throughout the growth period of the maize, but the crude protein (CP) content decreased in the BL stage as compared with the ED and one-third ML stages (P < 0.05). The CP content decreased from 80 to 58 g/kg DM (P < 0.05). The highest in situ rumen DM and organic matters degradabilities, and degradable yields, were obtained at two-thirds NIL stage. The highest NDF degradability was at the ED stage, but yields of degradable NDF were highest at two-thirds ML stage. Optimum whole crop maize harvest is at two-thirds ML stage to maximize yield of fermentable nutrients per hectare. (C) 2004 Elsevier B.V. All rights reserved.