Research Summaries: Canola and Peas in Livestock Diets

9. Improving the Nutritional Value of Canola Meal

Various attempts have been made to improve the nutritive value of CM by reducing its high fibre levels. Dehulling is the most obvious means of removing fibre. Hulls constitute 16 - 19% of seed weight and 30% of meal weight (Bell 1993 {1714}), and their removal can reduce crude fibre from 13.3% of meal to 6.6% (DM basis; Zuprizal et al.1992 {394}) and from 8.1% of seed to 2.6% (DM basis; Shires et al. 1981{553}). Fibre in CM is poorly digested by poultry (Campbell and Slominski 1990 {460}) and hull removal has been shown to increase protein digestibility from 70.5 to 76.7% in 6 week broilers (Zuprizal 1992 {394}), and average amino acid digestibilities from 80.8 to 85.2% in ISA Brown roosters (Zuprizal et al. 1991{431}). The ME and NE values of diets were numerically improved when dehulled CM (120 kg t^-1) was used in place of hulled CM (180 kg t^-1) in broiler diets. However, the moderate levels at which CM is used in poultry diets, combined with the modest improvement in chick performance, make the economics of dehulling questionable (Shires et al. 1983{547}).

b. Enzyme Supplementation

Enzyme supplementation is a potential means of improving the nutrient digestibility and ME of CM. Enzyme use in cereal-based diets is effective because cleavage of viscous polysaccharides logarithmically reduces their antinutritive effects. Enzyme supplementation of CM may be ineffective because the objective is to hydrolyze the NDF and resistant protein fractions of the meal, releasing their subunits for absorption by the bird. Unfortunately, the NSP component of CM consists of arabinose (33%), xylose (13%), mannose (3%), rhamnose (2%), fucose (2%), uronic acids (30%), galactose (13%) and glucose (5%) (Campbell and Slominski 1990{460}), only the last two of which are likely to be metabolized efficiently. Most feeding trials have indicated that enzyme supplementation of CM with carbohydrase and protease preparations does not produce a statistically significant improvement in broiler chick performance (Simbaya et al. 1996{315}; Alloui et al. 1994{340}; Charlton and Pugh, 1995{320}; Sosulski et al. 1990{466}), although results to the contrary exist (Ward et al. 1991{450}). Phytase supplementation of CM-based rations (500 g kg^-1) improved phosphorus and calcium retention in broilers (7-14d, P<0.05, Ward et al. 1991{450}). However, enzyme supplementation must produce a significant improvement and be cost-effective before it can be adopted by industry.

c. Genetic Selection

Genetic selection provides the best solution to reducing fibre levels in CM. It may be possible to breed new, low-fibre cultivars of brown-seeded B. napus and B. rapa; however, yellow-seeded strains of these species already contain significantly lower dietary fibre levels (34.1, 35.0 vs. 27.5, 28.5%, DM basis, respectively). Brassica juncea strains of canola quality have recently been developed, and may be adopted widely by canola producers because they are less susceptible to heat and drought stress. Some pure yellow-seeded strains have produced meal containing 27.8% dietary fibre (DM basis), combined with higher average levels of sucrose (8.7 vs. 7.5% of DM; P<0.05) and protein (44.5 vs. 42.7% of DM; P>0.05) than found in brown-seeded strains (Simbaya et al. 1995 {328}). A broiler trial indicated experimental strains of yellow-seeded B. juncea supported improved broiler performance relative to a traditional brown-seeded cultivar of B. napus (Table 5). Differences in CP and dietary fibre values between these brown and yellow-seeded meals were smaller than in samples analyzed by other authors (Simbaya et al. 1995 {328}; Slominski and Campbell 1991 {2059}); therefore, even greater improvements in performance may be possible. The agronomic and oil-production qualities of yellow-seeded strains will determine whether they are adopted wide-scale by canola producers. However, with the canola industry's record for agressively developing and adopting improved technology, there is reason to be optimistic regarding genetic improvements in CM quality.

Table 5. Composition of low glucosinolate Brassica napus, B. juncea (MM1 to MM4) and soybean (SBM) meals¹, and the growth performance and nutrient retention ¹ of broiler chicks ² consuming diets containing ³ those meals.

B. napus MM1 MM2 MM3 MM4 SBM

Crude protein 44.6 46.3 47.2 45.0 45.1 51.7

Total dietary fibre 29.47 27.90 25.55 27.76 27.68 16.76

Weight gain (g) 617^ab 589^bc 637^ab 640^ab 645^ab 654^a

Gain to feed 0.711^ab 0.720^a 0.731^a 0.731^a 0.732^a 0.719^a

AMEn (kcal/kg) 1,832^d 2,171^bc 2,382^ab 2,011^cd 2,302^ab 2,476

Ileal protein digestibility (%) 75.34^c 78.02^b 82.99^a 76.65^bc 76.39^bc 83.22^a

^a-d Means in the same row with no common superscript differ significantly (P<0.05).

¹ Dry matter basis; ² 0 - 21 days of age; ³ 40% and 20% CM inclusion in nutrient retention and performance study diets, respectively;

⁴ From (Newkirk et al. 1997 {303})

d. Copper and Iodine

Copper treatment of CM and iodine-supplementation of CM-based diets have been investigated to determine if they can reduce GL effects on livestock species. High-GL CM was soaked in a copper sulphate solution which hydrolyzed GL and aglucones to one-tenth of their original values. Copper treatment increased the heat-labile nitrile content of CM, but it was reduced from 45 to 5 mmol kg^-1 by drying the CM at 60°C. Performance of broilers consuming diets supplemented (160 g kg^-1) with copper-treated CM from high and low-GL cultivars were equivalent to the control and not improved relative to the CM diets not treated with copper or iodine (P>0.05; Schone et al. 1993{368}). A subsequent study also noted that copper pretreatment and iodine supplementation significantly reduced thyroid weight, without affecting growth (Schone et al. 1994{344}). Diet formulation only permitted substandard levels of broiler performance (1569g corn-soy control at 43d); therefore, the numerical improvements noted with iodine supplementation may have differed if birds were growing at industry rates (Schone et al. 1993{368}). Supplementation of CM-based diets with iodinated casein reduced broiler thyroid size at 25 ppm inclusion, and also body weight at 50 ppm inclusion (Nassar and Arscott 1986{537}).

It is not indicated by these studies that iodine or copper treatments are of practical benefit to broiler performance. The GL in CM produce organ hypertrophy (Schone et al. 1994 {344}; 1993 {368}), but broilers appeared able to compensate and perform equal to birds on non-CM diets. However, supplementary iodine (0.5 mg kg^-1 feed) reduced the liver weight of broilers (P<0.05) consuming diets containing CM (160 g kg^-1) (Schone et al. 1993 {368}), which may be of interest in the study of CM and fatty liver hemmorrhagic syndrome in layers. In addition, iodine supplementation may improve the hyperthyroidism and reduced hatch weight reported in chicks from hens consuming CM diets. The literature reviewed by Mawson et al. (1994{349}) indicated that thiocyanate ions may inhibit iodine transfer to the egg and that supplementary dietary iodide might overcome this effect.

e. Heat Treatment

Heat treatment, including extrusion or expansion reduces the GL content of CM but may lower protein digestibility and produce harmful aglucones. Glucosinolates decreased from 118 mmol to 55 mmol g^-1 with extrusion of high-GL CM, but broiler performance was not improved relative to the non-extruded CM control (Liang et al. 1993 {372}). Diets containing expanded canola seed-CM blends had protein digestibility values similar to untreated or heat-pelleted blends, but nitrogen retention was reduced (P<0.05), indicating that essential amino acids such as lysine were less available (Fasina et al. 1997 {304}). The damage that heat does to protein quality makes it difficult to justify using heat to degrade GL until the hydrolysis products are proven less toxic than GL themselves.

f. Ammoniation

Glucosinolate removal by ammoniation has also been ineffective at improving chick performance. Ammoniation (2% ammonia) of extruded CM did not improve broiler chick (8-21 d) performance relative to a diet containing non-ammoniated CM (175 g kg^-1 of diet), despite a reduction in GL content from 55 to 29 mmol g^-1 (Liang et al. 1993 {372}) This was confirmed by another study in which ammoniation (3 and 6%) of CM used in diets (150 to 250 g kg^-1) numerically increased GL hydrolysis products but reduced weight gain (P<0.01) and feed intake (P<0.05) (Paik 1991{439}). However, the validity of this last study is questionable as TME determination measured protein digestibility at 21.7 to 50.4% and crude fibre digestibility at 28.5 and 33.6% for 0 and 2% ammoniated samples, respectively.

g. Water Extraction

Water extraction has been used to markedly reduce GL levels in RSM (169 vs. 3 mmol g^-1 DM), and may be useful for improving the feeding value of CM. However, when extracted (residue) and unextracted RSM was included at 300 g kg^-1 in diets, liveweight and feed consumption were similar to that of the corn-soy control (Table 6)( Quinsac et al. 1994{343}). This indicated that in this instance there was no practical benefit to extracting GL from RSM, even though the level in the unextracted RSM diet (15.2 mmol g^-1) would normally be expected to reduce broiler performance.

Table 6. Feed consumption, liveweight, weight of liver, kidneys and thyroid of broilers fed, from hatching to 28d, on different rapeseed meal fractions with glucosinolate contents as indicated. ^b

Diet Glucosinolates (mmol g^-1) Feed Intake (g/bird) Liveweight^a
(g)
Liver
(g/100g LW)
Kidneys
(g/100g LW)
Thyroid
(mg/100g LW)

Control 0.0 1548 999b 2.38^a 0.82^a 10.2^a

RSM 15.2 1582 1004^b 3.12^c 0.95^b 24.0^b

RSM extract 15.2 1380 858^a 2.78^b 0.89^ab 25.9^b

RSM residue 0.6 1571 1004^b 2.47^a 0.86^ab 12.1^a

RSM residue + extract 15.8 1427 930^ab 3.08^bc 1.05^c 32.8^c

^a Liveweight = LW; ^b From (Quinsac et al. 1994 {343}).

Values followed by different letters within columns differ significantly (P<0.05).

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Table 5. Composition of low glucosinolate Brassica napus, B. juncea (MM1 to MM4) and soybean (SBM) meals¹, and the growth performance and nutrient retention ¹ of broiler chicks ² consuming diets containing ³ those meals.
	B. napus	MM1	MM2	MM3	MM4	SBM
Crude protein	44.6	46.3	47.2	45.0	45.1	51.7
Total dietary fibre	29.47	27.90	25.55	27.76	27.68	16.76
Weight gain (g)	617^ab	589^bc	637^ab	640^ab	645^ab	654^a
Gain to feed	0.711^ab	0.720^a	0.731^a	0.731^a	0.732^a	0.719^a
AMEn (kcal/kg)	1,832^d	2,171^bc	2,382^ab	2,011^cd	2,302^ab	2,476
Ileal protein digestibility (%)	75.34^c	78.02^b	82.99^a	76.65^bc	76.39^bc	83.22^a

Table 6. Feed consumption, liveweight, weight of liver, kidneys and thyroid of broilers fed, from hatching to 28d, on different rapeseed meal fractions with glucosinolate contents as indicated. ^b
Diet	Glucosinolates (mmol g^-1)	Feed Intake (g/bird)	Liveweight^a (g)	Liver (g/100g LW)	Kidneys (g/100g LW)	Thyroid (mg/100g LW)
Control	0.0	1548	999b	2.38^a	0.82^a	10.2^a
RSM	15.2	1582	1004^b	3.12^c	0.95^b	24.0^b
RSM extract	15.2	1380	858^a	2.78^b	0.89^ab	25.9^b
RSM residue	0.6	1571	1004^b	2.47^a	0.86^ab	12.1^a
RSM residue + extract	15.8	1427	930^ab	3.08^bc	1.05^c	32.8^c