Canola meal contains one of the highest levels of biotin found in typical North American ingredients. Biotin aids in the utilization of polyunsaturated fatty acids as substrates for energy metabolism, improving both feed conversion and weight gain. Total biotin in canola meal ranges between 1152 g/kg DM and 1231 g/kg with bioavailability at 70.9% (Misir and Blair 1988 {1845}). Others found ileal digestibility of biotin to be a meagre 3.9% in CM, compared with 55.4% in SBM (Sauer et al.1988 {1862}). Biotin addition to grower finisher diets significantly improved FC and ADG. The addition of biotin and 2% rapeseed oil resulted in still greater improvement (0.1- 0.2 improvement in FC and 30-40g/day gain) over biotin addition alone (Paschma et al. 1992 {1777}).
Matte and Girard (1994 {1679}) found the concentration of pteroglutamic (folic) acid in rapeseed meal (as measured by total pteroylglutamates) to be 0.88 mg(milligram)/kg, which was significantly lower than previously reported by NRC or Clandinin et al. 1981 (2.30 mg/kg in 1981). Differences in assay techniques, ingredient sources and reporting procedures account for the discrepancy.
Glucosinolates are the major antinutritional factor found in canola meal and mainly, if not entirely, located in the embryo. The principal glucosinolates of canola meal are gluconapin, glucobrassicanapin, progoitrin, napoleiferin, 4-hydroxyglucobrassicin, goitrin, epiprogoitrin, glucoerucin, glucoberteroin, glucoraphanin, glucoalyssin, gluconasturtiin, neoglucobrassicin, glucobrassicin, glucoverteroin and 4 methoxyglucobrassicin (Busato et al. 1991, {1788}). The glucosinolates that constitute the <30 moles/g in canola meal are of the aliphatic type. The Canadian canola designation does not take into account the tryptophan based indole types of glucosinolates (glucobrassicin (3-indolylmethyl) and 4-hydroxy-glucobrassicin (4-hydroxy-3-indolylmethyl)) which now constitute one third to 60% of the total glucosinolates in canola. (Bell 1993 {1714}). Presently the European Union is considering adoption of 20 mole/g total glucosinolate maximum for double low rapeseed that includes both indolyl and aliphatic types.
Glucosinolates per se are not considered toxic, however, their hydrolysis byproducts have established goitrogenic and hepatoxic effects. They also tend to be bitter tasting, thus potentially affecting feed intake (Sarwar et al. 1981 {1933}; Bell and Shires 1982 {1929}; Bourdon and Aumaitre 1990 {1819}). These byproducts are responsible for the decreased performance that affect utilization or absorption of DE and other nutrients (Yin et al. 1993 {1694}). Of the different glucosinolates identified in rapeseed, the most important are progoitrin, gluconapin and glucobrassicanapin producing mainly isothiocyanates, thiocyanates and nitriles after hydrolysis (Etienne and Dourmad 1994 {1666}). Hydrolysis occurs when the glucosinolates are exposed to the enzyme myrosinase, found within the canola seed but also produced by intestinal microflora (Smithard 1993 {1719}. Maskell and Smithard (1994 {1651}) determined that the caecum was the major site of GL degradation. During in vitro caecal incubation 78.8% of total GL were degraded as compared to 14.7% during in vitro peptic or 15.8% during in vitro small intestine incubations. In support, Lawrence et al. (1995 {1630}) determined that CHB (1-cyano-2hydroxy-3-butene), (a nitrile produced by the hydrolysis of progoitrin) was most likely produced in the foregut, as it was not detected in fecal but was found in ileal digesta.
The glucosinolate daughter compounds exert their deleterious effect by two mechanisms. First iodine transfer to the thyroid may be limited by competition from thiocyanates. Second, although there may be increased iodine transfer, synthesis and release of triiodotyronine (T3) and thyroxine (T4) may be inhibited. This action is specific to goitrin (an isothyocyanate derived from progoitrin) (Speigal et al. 1993 {1729}; Etienne and Dourmad 1994 {1666}). The resulting goitrogenic and hepatoxic effects include thyroid, liver and kidney enlargement, with the extent of hypertrophy positively correlated with the quantity of glucosinolates ingested (Bourdon and Aumaitre 1990 {1819}). In contrast, Schone and Paetzelt (1985 {1891}) found urinary thiocyanate excretion increased linearly with increasing intakes of RSM. This did not correlate with the severity of the goitrogenic reaction (Schone and Paetzelt 1988 {1851}).
Major decomposition of indole GL occurs during desolventization process of the canola crush due, to a combination of moisture (~13%) and temperature (~105C). Only minor decomposition occurs prior to this stage or later during drying (Campbell and Slominski 1990 {1815}). Desolventizing toasting at 80-120C destroys up to 2/3 of the GL present, inactivates the myrosinase and thus prevents the hydrolysis of GL into harmful end products (Siljander-Rasi et al.1996 {1612}). Glucosinolate content is not dependent on toasting temperature (Grala et al. 1994 {1662}) although ammonia and steam are effective in removing approximately one-half of the glucosinolates with methoxyindolyl being most affected (Keith and Bell 1982 {1930}). Additionally enhanced seed cleaning prior to the canola crush would reduce GL levels as total GL in RSM screenings ranged from half to double the GL level of RSM (Bell and Shires 1980 {1935}).
Although glucosinolates may have negative effects
on utilization of energy or other nutrients, the effect of GL
at current levels in Canadian canola meal (<30 moles/g) is
considered less than that of fibre (Yin et al. 1993 {1694}).
Also reduction of the GL levels to < 5mol g-1 results
in only marginal improvement in nutrient digestibility or pig
performance (Siljander-Rasi et al.1996 {1612}).
Sinapine, the major phenolic constituent of CM is bitter tasting (Blair and Reichert 1984 {1903}) and mainly a constituent of the embryo (Bell and Shires 1982 {1929})). Although rarely identified as a detriment for pigs, sinapine may be removed via hydrolysis with ammonia and steam (Bell and Keith 1982 {1930}). Removal via breeding is a possible area for improvement of canola meal since its competitor SBM contains no sinapines (Blair and Reichert 1984 {1903}).
Tannins were detected in the cotyledons but only
at very low levels (Blair and Reichert 1984 {1903}). Canola,
rapeseed and soybean hull tannins are not capable of inhibiting
-amylase (Mitaru et al. 1982 {1931}).