Rapeseed napin and cruciferin are readily digested by poultry
Rapeseed co‐products are of considerable interest as a protein source in animal feeds due to a high content of protein with a greater content of sulphur‐rich amino acids (cysteine, methionine) compared to a standard soya bean meal (Wickramasuriya et al., 2015). During rapeseed oil production, whole seeds are de‐fatted by hexane extraction producing a rapeseed meal (RSM), or by cold pressing producing a rapeseed cake (RSC) (Untersmayr and Jensen‐Jarolim, 2008). The crude protein content of the co‐products may range from 329 to 437 g/kg dry matter (DM) (Seneviratne et al., 2011a,b; Maison and Stein, 2014). However, protein content and individual amino acid levels will vary depending on rapeseed variety and oil extraction method used (Kasprzak et al., 2016). Several studies have shown that rapeseed protein is less digestible (by an absolute decrease of 14–16%) than soya bean protein or casein protein in standard diets (Savoie et al., 1988; Adedokun et al., 2008). This difference in nutritional value of protein is not only attributed to variation in chemical composition between the co‐products, but also to the compact structure and relatively high content of disulphide bonds in rapeseed protein. When in vitro models were used, napin was reported to be extremely resistant to pepsin digestion and denaturation caused by heat and low pH (Murtagh et al., 2003; Abeysekara and Wanasundara, 2009; Wanasundara, 2011).
To the best of our knowledge, there is no in vivo study focusing on digestibility of napin and cruciferin in the gastrointestinal tract of non‐ruminants when examining rapeseed proteins. The aim of the current study was to identify proteins in de‐fatted rapeseed co‐products, and the corresponding ileal digesta from broilers fed rapeseed diets.