Context Brassica forages are used in times of seasonal shortage to fulfil nutritional requirements of beef cattle, dairy cows, sheep or pigs. Although brassicas have been reported with high concentrations of readily fermentable carbohydrate, details have not been fully described and there is little information about the non-structural carbohydrate (NSC) profiles of Brassica forages. Aim The study was designed to evaluate nutrient concentrations, as well as NSC levels and constituents, of the main Brassica forages and to determine differences among varieties. Methods Five varieties of each of the four main forage brassicas (summer turnip, forage rape, kale and swede) were grown in plots and harvested for chemical analysis of the nutrient concentrations and NSC profiles of leaf and bulb (turnip and swede) and leaf and stem (rape and kale) components. Key results Brassica species differed in the amounts and types of NSC; swede had the highest concentration of NSC, mainly comprising sugars (glucose and fructose), followed by kale (with similar proportions of glucose, sucrose and fructose), turnip (with similar concentrations of glucose and starch and slightly lower fructose), and forage rape (in which starch was the main NSC). Forage chemical composition and NSC profile of plant organs varied among varieties of individual Brassica forages; for example, there were significant differences among swede varieties for concentrations of starch and sugar (total and profile) in bulbs. Conclusions Brassica forages differed with respect to quantities and types of NSC; swede had higher concentrations, mainly composed of glucose and fructose, followed by kale with similar proportions of glucose, sucrose and fructose, and turnip with NSC represented by glucose, starch and slightly lower fructose; and finally, forage rape, in which starch was the main NSC. Chemical composition, as well as NSC profile of plant organs (leaves, bulbs or stems), varied among varieties of Brassica species. Implications The approach described here has implications for ration formulation and is useful when considering the nutritional and dietary requirements of the animals of interest, because the type of Brassica, the variety and the proportion of plant organs can affect animal performance.

Simple SummaryWinter brassica crops such as kales and swedes are used to supply feed in times of seasonal shortage. However, to the best of our knowledge, there is little information about the fermentation characteristics of these forages in the rumen. This study assessed the nutrient concentration, in vitro fermentation and in situ rumen degradation characteristics of Brassica oleracea (L.) ssp. acephala (kales) and Brassica napus (L.) ssp. napobrassica (swedes). The kales and swedes both showed different nutrient concentrations and fermented fast and extensively in the rumen. However, in vitro fermentation of swedes resulted in lower acetate and greater proportions of butyrate and propionate. Varieties of swedes showed more differences in terms of degradation and fermentation in the rumen compared to kale varieties.AbstractThe aim of the present study was to evaluate the nutritional value, the rumen in vitro fermentation, and the in situ degradation of Brassica oleracea (L.) ssp. acephala (kales) and Brassica napus (L.) ssp. napobrassica (swedes) for winter use. Five varieties of each brassica were used in three field replicates and were randomized in a complete block nested design. All forage varieties were harvested at 210 days post-sowing to analyze the chemical composition, in vitro gas production, volatile fatty acid (VFA) production and in situ dry matter (DM) and crude protein (CP) degradability. Kales presented higher DM and neutral detergent fiber (NDF) content (p < 0.01), whereas swedes showed higher CP, metabolizable energy (ME), glucose, fructose, total sugars, NFC, and nonstructural carbohydrate (NSC) content (p < 0.01). The kale and swede varieties differed in their CP and sugar concentrations, whereas the kale varieties differed in their DM and raffinose content. The rates of gas production were higher for swedes than for kales (p < 0.01). No differences between the brassica species (p > 0.05) were observed in the total VFA production, whereas kales had a higher proportion of acetate and swedes had higher proportions of butyrate (p < 0.05). Only the swede varieties showed differences in VFA production (p < 0.05). The soluble fraction “a”, potential and effective in situ DM degradability were higher in swedes (p < 0.01), but kales presented greater DM and CP degradation rates. Differences were observed between brassica species in the chemical composition, degradation kinetics, and ruminal fermentation products, whereas differences among varieties within species were less frequent but need to be considered.