Concentrations of Glucosinolates and S-Methylcysteine Sulfoxide in Ensiled Rape (Brassica napus L.)

Abstract

Cruciferous forages (Brassica sp.) contain glucosinolates and S-methylcysteine sulfoxide, compounds that are potentially toxic to livestock, but there is little information concerning the possible effects of ensiling on these constituents. This study compared concentrations of glucosinolates and S-methylcysteine sulfoxide in rape (Brassica napus L.) forage before and postensiling after 0, 4, or 25 h of field wilting. Field-grown rape was harvested 100 d after planting and immediately ensiled in laboratory scale silos or wilted for 4 or 25 h prior to ensiling. After 30 d, silages were frozen and stored at −20°C. Unensiled samples also were frozen at −20°C for an estimate of glucosinolates and S-methylcysteine sulfoxide in fresh forage. In addition to analysis for glucosinolates and S-methylcysteine sulfoxide, determinations were made of DM concentration in fresh and ensiled material and pH of the silage. Ensiling reduced glucosinolate concentration from approximately .3 to .03% of DM and wilting had little additional effect. Ensiling slightly but significantly reduced S-methylcysteine sulfoxide; wilting had no significant additional effect. Results of this study indicate that ensiling can effectively reduce the potential toxicity of rape forage. © 1987, American Dairy Science Association. All rights reserved.