3. Feeding Canola Meal to Breeding Birds
Nutrient-diluted diets are ideal for use with broiler breeders because the greater quantity of food presented reduces competition and thereby improves flock uniformity. Canola meal would be suited to use in such diets because of its high fibre level. Subsequent reproductive effects were not seen in broiler-type birds fed full-fat canola seed at a level which supplied 0.72 and 0.90 mMol/g GL in diets from 0-4 and 4-7 weeks, respectively (Swierczewska et al.1995 {327}). Canola meal is also suitable for use in the grower diets of laying strain breeders. A recent study involving White Leghorn breeders indicated that up to 100 g kg-1 CM in rations fed to 18 weeks of age did not effect subsequent reproductive performance (P>0.05) (Kiiskinen 1989{487}).
Canola meal should be used with caution in adult
breeder rations. Reduction in egg weight due to CM inclusion
in diets has been documented (Summers et al. 1988{506}),
and chicks from hens consuming 50 to 100 g kg-1 dietary
CM showed a trend toward reduced hatch weight and thyroid hypertrophy
(Kiiskinen 1989{487}). A review that includes earlier and international
works supports these observations (Mawson et al.1994{349}).
Reports of increased fatty liver hemorrhagic syndrome in laying
hens consuming CM-supplemented diets (Wight et al. 1987
{534}) suggest that CM may not be suitable for use in the diets
of adult broiler breeders - birds which are already prone to this
metabolic disorder.
4. Feeding Canola Meal to Laying Hens
The rations of white-egg layers have moderate energy and CP requirements and are therefore well-suited to the use of CM. Canola meal is also an excellent ingredient for the diets of growing flocks, and at up to 100 g kg-1 of diet did not affect health or performance parameters during subsequent lay (Kiiskinen 1989{487}). European studies have measured CM AMEn in laying hens at 1800 kcal kg-1 DM (Askbrant and Håkansson 1984{543}) and 2080 kcal kg-1 DM (Askbrant 1988{519}), indicating a wide range in values exists. The former value was associated with a high NDF level (302 g kg-1 DM). As discussed later (Section 8), sinapines limit the level of CM that can be used in rations for brown-shelled in-lay hens.
Liver hemorrhage has been documented for in-lay hens fed high dietary levels of rapeseed meal (RSM) (Wight et al. 1987{534}) or diets using CM or VLCM as the sole protein source. However, liver hemorrhage was not discernible from SBM controls in diets that contained total GL levels of up to 1.43 mmol g-1, which would be equivalent to 100 g kg-1 dietary CM inclusion (Campbell and Slominski 1992{2060}).
Egg size has been reduced in diets containing over
100 g kg-1 CM (Summers et al. 1988{506}), although
this effect was not consistant (Kiiskinen 1989{487}). Smaller
average egg size resulted from a shift to small and medium sized
eggs from large and extra large grades, an effect that increased
with dietary GL level (Campbell and Slominski 1991{2060}). Feeding
strategies to compensate for this could include reducing CM levels
in early laying rations, and increasing CM in later rations when
egg size is less of a concern. The studies quoted did not formulate
rations on an available amino acid basis, and this may have contributed
to the reduction in egg size.
5. Feeding Canola Meal to Geese
Canola meal has been recommended for use in the diets
of 3- to 8-weeks-old geese. Body weights and feed intake were
numerically superior on the CM-based ration, an effect partially
attributed to the improved dietary methionine-cystine levels (Wiliczkiewicz
et al. 1992{411}). The elevated digestibility of CM NDF
and cellulose fractions for this species (50.5 and 34.2%, respectively)
also enhances the feeding value of CM (Jamroz et al. 1992{410}).
The high fibre content of CM is now recognized as the primary obstacle to its use in poultry diets that require elevated protein and energy levels. An industry survey measured NDF, ADF and crude fibre in CM from seven crushing plants in western Canada (23, 19 and 13%, respectively, DM basis) (Bell and Keith 1991 {421}). The NSP fraction of CM is poorly digested by poultry (Slominski and Campbell 1990{460}) and would dilute available protein, amino acids and ME in the meal. Dietary fibre levels recently determined in meals from brown-seeded canola cultivars (34% DM) (Simbaya et al. 1995{328}), indicated an even higher estimate of the CM fraction likely to be unavailable to poultry. Several methods of reducing fibre in CM are discussed later in this chapter (Section 9).
The fibre in CM consists of hull and endospermal
cell wall fractions. Other than a nutrient dilution effect, canola
hulls appear innocuous and have not been shown to affect performance
at dietary inclusion levels of 100 g kg-1 in broiler
starter rations (Mitaru et al. 1983 {546}) or 64 g kg-1
in mice diets (Sarwar et al. 1981{552}). Endospermal cell
wall and hull fractions from canola each reduced apparent availability
of copper, iron, calcium, phosphorus and protein in rats when
included at 120 g kg-1 in a semi-purified diet (Ward
and Reichert 1986 {539}); however, dietary fibre levels were much
higher than would typically be encountered with CM use in industry.
7. Glucosinolates and Poultry Rations
Glucosinolates have historically been the main barrier to the use of CM in poultry diets. However, canola breeding programs have been so successful that it must be questioned what practical effect, if any, the remaining GL levels have on poultry performance.
Brassica napus and B. rapa canola species contain two main groups of GL - the aliphatic and the indolyl - each of which contains several unique GL known by a variety of scientific and trivial names. Aliphatic GL have been the main target for reduction by plant breeders (Bell 1993 {1714}) and the proportion of indole GL has therefore increased to about a third of the total. Intact GL are relatively innocuous to poultry (Sarwar et al. 1981{552}) compared to their hydrolysis products, "aglucones". Known aglucones include isothiocyanates, thiocyanates, nitriles and oxazolidinethiones (Shahidi et al.1997{301}). The effects that each of these hydrolysis products has on poultry is currently impossible to interpret because more are believed to exist (Campbell and Slominski 1990{460}) and may be confounding results from feeding trials. A few studies have been performed on rats using isolated GL hydrolysis products (Bjerg et al.1988{504}), however, the effects on poultry still are not known because toxicity has been shown to differ between rats and chickens (Nugon-Baudon et al. 1988{526}; 1990{463}). In addition, GL hydrolysis products vary with CM processing conditions (Campbell and Slominski 1990 {460}) and are produced from CM in the alimentary tract of poultry (Campbell 1988 {507}; Campbell and Slominski 1989{490}).
Therefore, it is perhaps most useful to view GL effects in the following terms summarized by Daun and Adolphe ({296, 1997). Oxazolidinethiones formed from the hydrolysis of aliphatic GL are primarily responsible for the goitrogenic effect of CM because they irreversibly block uptake of iodine by the thyroid gland. Isothiocyanates may have goitrogenic or other metabolic effects. Thiocyanates which may be formed from the hydrolysis of indolyl GL also affect uptake of iodine by the thyroid gland, but this effect can be reversed by supplemental dietary iodide. Nitriles have high toxicity and may be produced from indole GL under acidic conditions (Bell 1993 {1714}).
Indirect evidence of negative GL effects on poultry
comes from feeding studies involving VLGL CM in broiler and layer
trials. The growth rate of broilers (0-43d) declined with increased
conventional CM inclusion (0 to 300 g kg-1 diet; P<0.05),
but remained equal to the control at equivalent levels of VLCM
(Classen et al. 1991 {440}). Laying hens consuming VLCM
(240 g kg-1 diet) maintained egg production similar
to a wheat-soy control, but had reduced feed intake and egg weight
(P<0.05). Conventional CM (250 g kg-1 diet) reduced
both egg size and number (P<0.05) at a feed intake level similar
to that of the control (Campbell and Slominski 1991{2060}). However,
the trials quoted would not have been able to distinguish whether
improved performance on the VLCM diets was due solely to reduced
GL toxicity, or whether genetic selection against GL may have
improved other meal characteristics like ME or amino acid availability.
8. Tannins, Sinapines and Oligosaccharides
Tannins are antinutritional factors (ANF) of concern because they reduce protein utilization in monogastrics by inhibiting digestive enzymes. Measurements of Canadian CM indicated extractable tannin in canola hulls averaged 0.13% DM (Mitaru et al. 1983 {546}: 1982{551}) and 0.25% DM in canola cotyledons (Blair and Reichert 1984 {541}). However, the canola tannins had no effect on a-amylase activity, in contrast to sorghum tannins which constituted 2.2% DM of the grain and inhibited a-amylase activity by 79%. Broiler feeding trials indicated that inclusion of tannin-containing CM hulls did not affect performance differently from inclusion of tannin-free soybean hulls (Mitaru et al. 1983 {546}). Broiler performance was not improved by polyethylene glycol supplementation of diets containing up to 29.8% CM. Polyethylene glycol had increased protein digestibility when included in high-tannin sorghum diets; therefore, it was assumed that CM tannins did not affect bird performance (Karunajeewa et al. 1990 {458}).
Sinapine is a compound in CM which produces a "fishy" flavor in the eggs of certain brown-shelled laying strains. Egg taint occurs when sinapine levels exceed 1g kg-1 diet, and German analysis of whole seeds indicated that sinapine levels in CM were approximately 6 to 12 g kg-1. The biochemical mechanism of egg taint has been reviewed by various authors ( Pokorny and Reblova 1995 {331}; Bell 1993{1714}).
The oligosaccharide level of CM is between 2.0 and
3.3% DM (Simbaya et al.1995{328}.). Opinions vary
in the literature regarding the potential antinutritional effects
of oligosaccharides; however, ethanol-extraction of oligosaccharides
from CM reduced the true metabolizable energy (TMEn) value for
adult roosters (Slominski et al. 1994{346}). It is also
doubtful whether any measurable effects would be seen at practical
dietary CM inclusion levels.