Canola is a crop well suited for the
use in ruminant diets. This paper reviews the literature published
since 1980 pertaining to the use of canola products in ruminant
diets. Canola is a very important part in the feeding of ruminants
and there are many different canola products available. Supplementing
ruminant diets with canola may result in improved human nutrition
as well. The following sections discuss how inclusion rates, digestibility
(rumen and total tract) and feeding innovations can be used to
enhance nutritional value of canola in ruminant rations. Emphasis
has been placed on Canadian and North American studies, although
results from around the world have also been included.
Chemical composition of Canola Meal
Canola is the common name used to identify two plants species, Brassica napus and B. campestris, that have developed by Canadian plant breeders from its predecessor rapeseed. Rapeseed meal (RSM), unlike canola meal (CM) usually contains high glucosinolate (50-100 mol/kg) and erucic acid (25-45% of rape oil) concentrations. Canola meal (CM) is obtained from the whole seed after removing oil by a direct solvent or prepress solvent extraction process. Canola oil contains less than 2% erucic acid. Canola meal must contain a minimum of 35% crude protein (CP), a maximum of 12% crude fiber (CF), and a maximum of 30 mol GL/gram (AAFCO 1992 as cited by Price et al. 1993 {918}). The removal of oil from canola seed concentrates the remaining ingredients, namely fiber and protein. Canola meal has been reported to contain 38.3% CP, 21.5% neutral detergent fiber (NDF), 17.5% acid detergent fiber (ADF), 12% CF, 3.6% ether extract (EE), 0.6% Ca, 1.0% P and 0.9% sulfur (S) (Bell 1993 {907}; Bell and Keith 1991 {972}) (table N-1). The estimated gross energy (GE) values for CM and soybean meal (SBM) were 18.64 and 20.07 MJ/kg. A typical metabolizable energy (ME) value used in cattle diets is 12.1 MJ/kg DM. In comparison to SBM, CM contains less GE, less protein and over three times as much fiber. However, CM is richer in most B-vitamins and essential minerals (Table N-5, N-6) (Bell 1993 {907}). Canola meal is higher in the sulfur amino acids (AA) and SBM is higher in lysine (Parker 1992; Bell and Keith 1991 {972}) (table N-2).
Protein is the main nutrient in CM (table 1). A
comparison of protein fractions of common protein supplements
are shown in table 1. Composition of CM is similar to SBM however,
true protein (73%) of CM consists of rapid (15.3%), intermediate
(79.2%) and slowly degradable (5.5%) protein fractions and SBM
contains less rapid and slowly degradable protein (0.5 and 3.5%,
respectively) and more intermediately degradable protein 86.0%
(Van Soest and Fox 1992). Because CM and SBM both contain small
amounts of slowly degradable protein most of the protein will
be degraded in the rumen.
| Table 1. Protein fractions of common protein supplements. | |||||
|---|---|---|---|---|---|
| CM | SBM | CSM | Sunflower meal | Brewers grains | |
| CP (CP) | 42.3 | 49.0 | 45.6 | 25.9 | 26.0 |
| Non-protein nitrogenz | 21.0 | 11.0 | 8.0 | 11.0 | 3.0 |
| Available true proteinz | 73.0 | 87.0 | 84.0 | 81.0 | 83.0 |
| Unavailable Proteinz | 6.0 | 2.0 | 8.0 | 5.0 | 12.0 |
z% of CP.
Van Soest and Fox (1992).
Canola meal protein is more soluble than SBM (table
2). The variation in CM and SBM protein solubility was measured
by Christensen et al. (1998) on 11 separate CM purchases and 4
SBM purchases. The CP solubility ranged from 14.6 to 29% for
CM and 7.8 to 21.3% for SBM. Fiems et al. (1985 {1193}) compared
five batches of RSM and SBM and the average protein solubility
was 40.7% and 18.9%, respectively. The amount of protein associated
with NDF and ADF is higher in CM than SBM (table 2). This is
due to the seed hulls (30% of the oil-free meal) remaining with
the canola meal after processing. Levels of neutral detergent
insoluble CP ranged from 8.4-16.8% and levels of acid detergent
insoluble CP ranged from 5.1-6.7% (Moshtaghi Nia and Ingalls 1992
{937}, McAllister et al. 1993 {928}, McKinnon et al. 1995 as cited
by Mustafa (1996); Mustafa et al. 1996 {2061}).
| Table 2. Protein fractions of canola and soybean meal. | ||
|---|---|---|
| Protein Fraction | CM | SBM |
| CP (%) | 42.3 | 49.0 |
| Soluble CP (% CP) | 32.0 | 20.0 |
| Non-protein nitrogen (% CP) | 21.0 | 11.0 |
| Neutral detergent insoluble CP (% CP) | 11.0 | 5.0 |
| Acid detergent insoluble CP (% CP) | 6.0 | 2.0 |
Van Soest and Fox (1992).
The first limiting factor in CM inclusion in diets
is energy availability (Bell 1993 {907}). The low DE and ME values
of CM are due to the high fiber levels caused by the hull remaining
with the meal (30% of oil free meal). Canola meal has three times
more crude fiber (12.1%) compared to SBM (3.4%) (Bell 1993 {907}).
Canola meal contains 13.1% crude fiber, 23.4% NDF and 19.1% ADF
(Bell and Keith 1991 {972}). Another study by Khorasani et al.
(1994 {858}) reported that CM contained 30.3% NDF, 20.9% ADF,
8.3% acid detergent lignin (ADL) and 12.6% cellulose. Fiber values
for CM are higher than soybean and solvent extracted linseed meal.
The NDF, ADF, and ADL values for soybean and linseed meal were
8.5, 4.6, and 0.2% and 25.9, 14.6 and 5.8%, respectively (Khorasani
et al. 1994 {858}).
As previously mentioned, the relatively low energy
value of CM is associated with the high fiber levels and is considered
the limiting factor in CM usage (Bell 1993 {1232}). However,
fiber digestion is less of a problem for ruminants than monogastrics
and the available energy from CM is usually higher for ruminants.
Gross energy (GE) of CM averages 4.4 0.2 Mcal/kg (Bell and Keith
1991 {972}) or ranges from 13.39 to 17.57 MJ/kg DM (Bell 1984
{1232}; NRC 1989; Zinn {884}). Zinn (1993 {884}) reported a DE
of 4.12 Mcal/kg for CM and 4.57 Mcal/kg for SBM. Variation in
GE content of CM is due to differences in lipid, protein and fiber
contents (Bell 1984 {1232}).
Canola meal quality has increased with the development
of low GL varieties (Bell 1993 {907}). The GL content is much
lower in CM than RSM, 30 vs. 90 to 140 mol/g (Fiems et al. 1985
{1193}; Lardy and Kerley 1994 {851}) and is no longer the main
limiting factor in CM usage. Canola meal contains less GL than
whole canola seed (WCS) due to the thermal degradation during
processing. Bell and Keith (1991 {972}) reported a wide variation
in GL destruction, 15 to 77% among different crushing plants resulting
in GL values of 6.8 to 33.7 mol/g. Cattle have a higher tolerance
to GL products in comparison to monogastric animals (Subuh et
al. 1995 {843}). Heifers fed 300g/kg of HG (60.7 mmol/g) or LG
(29.0 mmol/g) RSM reported that the rumen was the principal site
of GL breakdown and that the liver was mildly damaged by hydrolyzed
products, mainly isothiocyanates (SCN). Glucosinolates are broken
down into SCN, thiocyanates and nitriles (VanEtten and Tookey
1983 as cited by Lardy and Kerley 1994 {851}). When GL are hydrolyzed
the thiocyanate ion is released, this prevents iodination and
activation of thyroid hormones leading to hypothyroidism (Guyton
1986 as cited by Lardy and Kerley 1994 {851}; Bell 1984 {1232}).
Thyroid activity of fast growing, young calves may be affected
by smaller amounts of goitrogenic chemicals than adult cattle
(Claypool et al 1985 {1181}). Glucosinolates have a pungent flavor
(Fenwick et al. 1983 as cited by Lardy and Kerley 1994 {851})
and reduce palatability (Hill 1991 {996}). Some studies confirm
an increase in calf feed intake (FI) with the use of low GL varieties
(Stedman and Hill 1987 {1139}; Mawson et al. 1993 {922}).
Processes that Reduce the Glucosinolate Content
Many methods have been used to reduce GL content
of increasing RSM value (Stedman and Hill 1987 {1139}; Lardy and
Kerley 1994 {851}; Fenwick et al. 1986 as cited by Rhee 1993 {887}).
These include heat + ammonia, steam, steam + ammonia, calcium
hydroxide + ammonia and ammonia + extrusion. Most of these processes
significantly reduced the GL content of RSM. Extrusion reduced
the GL content by 75% (from 118 to 28 mol/g), but only steam alone
reported a significant increase in FI in calves (Stedman and Hill
1987 {1139}; Lardy and Kerley 1994 {851}; Liang et al. 1993 {906}).
Palatability was not increased (except with steam alone) with
the reduction in GL. The lack of response was attributed to the
remaining GL or their degradation products, nitriles, thiocyanates
and isothiocyanates (Lardy and Kerley 1994 {851}). Slominski
and Campell (1987 as cited by Stedman and Hill 1987 {1139}) demonstrated
that there is little decomposition of GL with a dry heat (100
C), but decomposition occurs with a moist heat. Moist heat treatment
at 127 C for 15 min reduced total GL concentration from 19.07
to 0.78 mol/g DM. Moist heat treatment decreased total and individual
GL content increasing grass silage intake in Finnish Ayrshire
bulls (Aronen and Vanhatalo 1992 {948}). The decrease was due
to the thermal decomposition of the GL.