A series of experiments was conducted in which summer- and fall-grown Brassica species were evaluated for production of dry matter and nutritive value. Species that possessed edible roots produced the highest yields of dry matter and estimated digestible energy in either season. Summer totals were higher than fall totals. Turnip (Brassica rapa L.) root yields were greater and contributed more to total dry matter yields than either swede (Brassica napus L.) or a Brassica hybrid, Tyfon [Brassica rapa L. × Brassica pekinensis (Lour.) Rupr.]. In all species, dry matter content of herbage was low (65–175 g kg−1), while digestibility values were high (> 840 g kg−1). Concentrations of neutral-detergent and acid-detergent fiber, acid-detergent lignin, and hemicellulose were generally higher in summer-grown species than in fall-grown species. Based on fiber values, digestible energy content of the foliage and roots was estimated and the values of all species were 12 MJ kg−1 or greater. Seasonal differences in herbage constituents were particularly evident for rape (Brassica napus L.) and kale (Brassica oleracea L. var. acephala DC). Under fall conditions, species differences were less than differences over summer conditions. Higher light intensities and temperatures over summer-growing conditions appear to promote greater production of dry matter and structural components in these crops compared to similar growth periods over fall conditions. Brassica spp. can be used as supplemental or alternate forage crops.Key words: Brassica spp., yield, digestibility, fiber, energy
