Dry matter yield, percent dry weight, in vitro digestible dry matter, in vitro digestible organic matter, neutral detergent fiber, acid detergent fiber, ash and hemicellulose contents were determined for spring- and fall-sown common wheat, barley, rye and triticale and spring-sown durum wheat and oats for the period from late boot to maturity. Differences among cultivars and stages of maturity were significant for all parameters. These differences were accompanied by stage of maturity interactions. Consideration of the interrelationships among these parameters revealed that level of in vitro digestible dry matter was reflected in measures of acid detergent fiber and ash or percent dry weight. Further analyses indicated that differences in digestibility due to stage of maturity were primarily reflected by changes in ash or percent dry weight, while differences in digestibility among cultivars were mainly attributable to differences in acid detergent fiber.