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Rapeseed hulls

Datasheet

Description
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Common names 

Rapeseed hulls, canola hulls [English]; coques de colza, pellicules de colza, coques de canola, pellicules de canola [French]; cascara de colza, cascara de canola [Spanish]

Related feed(s) 
Description 

Rapeseed hulls - called canola hulls in North America and other countries - are the teguments of the seeds of the oilseed rape plant (Brassica napus L. and interspecific crosses of Brassica napus with other Brassica species including Brassica rapa L. and Brassica juncea (L.) Czern), resulting from the extraction of rapeseed oil. Rapeseed hulls are a fibrous byproduct, but they also have a valuable oil and protein content and they can be used to feed ruminants and rabbits.

Description

Rapeseed hulls account for 12-20% of seed weight. As the separation between kernels and hulls is imperfect, the hull fraction contains kernel fragments. It is rich in fibre, notably lignin, but also in residual oil and protein. The complete dehulling of the seeds yields a rapeseed meal much richer in protein than the regular one (Carré et al., 2015).

Uses

When available, rapeseed hulls are mainly used in ruminant and rabbits feeding (Carré et al., 2015; Kazmi, 2011). Due to their fat content, they can be used as biofuel for drying seeds in oil mills, or they can be fermented to produce biogas. The hulls can be further extracted but the resulting oil is of poor quality (high acidity, poor storage, dark colour)(Kazmi, 2011). Rapeseeds hulls are used as substrate for mushroom production (Usubharatana et al., 2016). Rapeseeds hulls could be a source of high value added biopolymers (Asad et al., 2017).

Distribution 

Rapeseed hulls are potentially available wherever rapeseed oil is produced. However, rapeseed dehulling is not widely used in large-scale oil mills since the process is often not profitable: oil is lost in the hulls, the dehulled seeds are more difficult to process, and the market for the hulls is limited (Kazmi, 2011). Considering that the amount of rapeseeds processed worldwide was 60 million t, dehulling could virtually yield 6-12 million t assuming 12-20% hulls (FAO, 2019; Carré et al., 2015). With 10% dehulling, the amount would be about 0.6 to 1.2 million t (Kazmi, 2011).

Processes 

Rapeseed meal is relatively rich in fibre and removing the hulls results in a meal containing more protein and less fibre, thus improving its digestibility and nutritional value, particularly for monogastric animals (Skiba et al., 1999). The production of high-protein, low-fibre rapeseed meal has been extensively studied since the late 1970s and many technologies have been tested. Some consist in removing the hulls before oil extraction (cracking and air-classification, crushing seeds directly on a hard surface or in the gap between two rotating rolls) while other separate the hulls after extraction (air-classification, liquid cyclone fractionation)(Rekas et al., 2017). Dehulling of rapeseed prior to oil pressing allows to maintain the screw press temperature below 40°C, while oil extraction from dehulled rapeseeds enables recovery of most of the oil from kernel. Oil produced from dehulled seeds has better sensory characteristics (milder taste and flavour, bright yellowish colour, and lower content of waxes) (Rekas et al., 2017). However, dehulling has some important drawbacks: lower profitability, loss of oil in the hull fraction, degradation of press performance, limited market interest in the dehulled meal or in the hulls. Also, glucosinolates may concentrate in the dehulled meal. For those reasons, rapeseed dehulling is still not widely used in large-scale oil mills. For instance, a dehulling process was implemented industrially in France in the 1980s, but abandoned after a few years for technical and economic reasons (Carré et al., 2016).

Since the 2000s, the search for plant-based protein sources other than soybean has sparked renewed interest in rapeseed dehulling and new technologies are being investigated (Carré et al., 2016; Martinez-Soberanes et al., 2017; Rekas et al., 2017). A process developed in EU Feed-a-Gene project consists in applying tail-end fractionation to the meal obtained after crushing. Using a plantsifter, the meal is separated into a high-protein fraction and a low-protein fraction (Bach Knudsen, 2018).

Environmental impact 

Methane emissions

The use of crushed rapeseeds in the diet of dairy cows has yielded substantial reductions in methane emissions (Beauchemin et al., 2009).With their high oil and fibre content, rapeseed hulls could help to lower the amount of methane emitted by ruminants (Carré et al., 2015).

Nutritional aspects
Nutritional attributes 

Rapeseed hulls are a fibrous by-product containing large amounts of crude fibre (about 30% DM, ranging from 13% to almost 40%) and particularly lignin (about 20% DM, up to 30% DM). However, depending on the dehulling technology, variable quantitities of kernel fragments can be present and the rapeseed hulls are often rich in protein (about 16% DM, up to 20%) and fat (about 13% DM, up to 24%) and thus energy.

Potential constraints 

Oil rapeseeds used to have a high content of erucic acid and glucosinolates that are of concern for animal and human health, but those problems have been eliminated or largely reduced through traditional genetic selection since the 1970s (Snowdon, 2006).

Erucic acid

Erucic acid is no longer present in significant amounts in rapeseeds and canola seeds cultivar grown for food oil production. The concern about erucic acid, which was extremely serious in the 1970-1980s, has somehow diminished today, as its adverse effects on livestock other than poultry remain difficult to prove or at least to separate from those caused by other dietary components (EFSA, 2016). However, the rise of erucic-rich cultivars grown for niche industrial markets (Tonin, 2018) could result in hulls rich in this fatty acid.

Glucosinolates

Rapeseed hulls contain much less glucosinolates than the kernels: in a study based on glucosinolate-rich cultivars, hulls contained in average 10 µmol/g of glucosinolates whereas the kernels contained 10 times more. In modern cultivars containing low amounts of glucosinolates, the glucosinolate content of the hulls should be minimal (Carré et al., 2016).

Ruminants 

Rapeseed hulls can used as an energy source for ruminants, due to their composition somewhat similar to that of alfalfa in terms of crude protein content and fibre content, but with a relatively high fat content. This fat content could help reducing enteric methane emissions, which could make rapeseed hulls a promising feed for ruminants in the climate change context (Carré et al., 2015; Beauchemin et al., 2009). Few trials are available: trials with cattle were relatively positive while a sheep trial resulted in poor performance.

Degradability and digestibility

When compared to soybean hulls and beet pulp in a digestibility trial with sheep, rapeseed hulls were found to have a much lower digestibility for organic matter (60% vs 84% and 85% respectively) and crude fibre (74% vs 91 and 85%). Protein digestibility was comparable (55% vs 48 and 56%). The low OM and fibre digestibiltiy could be explained by the high lignin content of the cell layer. Rapeseed hulls degrade relatively poorly in the rumen: after 72h in nylon bag in cannulated sheep only 61% of DM had disappeared (Grenet et al., 1990). Another experiment reported low degradability values for DM and protein (< 50%) and very low degradability values for NDF and ADF (< 20%) (McKinnon et al., 1995).

Dairy cows

While no dairy cow trials with rapeseed hulls seem available in the scientific literature, it can be noted that the introduction of oil-rich expeller rapeseed meal in dairy diets results in higher milk production with more protein and less saturated fatty acids (Brunschwig et al., 2006). The oil content of rapeseed hulls could thus be beneficial.

Beef cattle

Rapeseed hulls from glucosinolate-rich cultivars could be fed at 1% LW and 1.67% LW to growing cattle weighing 100 kg and 300 kg respectively (Ahlström, 1973). In growing heifers, rapeseed hulls could represent 50% of the diet concentrate for 13 weeks without impairing feed intake. In spite of the presence of glucosinolates and erucic acid, the hulls were well accepted by the animals. Growth rate was similar to that obtained with the control diet during 11 weeks, but performance decreased in the last 2 weeks, possibly due to a change in hull composition (the latter batch contained 20% oil vs 11% in the first batch) (Ahlström et al., 1978). Feeding 9 month-old steers during 6 months with 25% rapeseed hulls (DM dietary level) replacing maize silage resulted in a lower feed efficiency but did not affect growth rate, carcass weight and carcass composition (Baudet et al., 1978).

Sheep

In lambs fed on 25 to 75% rapeseed hulls, processed (ammonia treated, solvent extracted or a combination of both processes) or not, as a partial replacement for alfalfa hay, increasing the amount of rapeseed hulls decreased feed intake and the digestibility of energy and nutrients, whatever the process. Processing did not improve DM and nutrient degradability, which was low (McKinnon et al., 1995). 

Pigs 

Information on the use of rapeseed hulls for pigs is limited. The apparent ileal digestibility of protein and amino acid was low: 26% for protein and lower than 50% for most individual amino acids (18% for lysine), which is probably due to the linkage between protein and fibre in the hulls (Grala et al., 1999). In weanling pigs, the effects of rapeseed hulls inclusion the diet during 4 weeks depended on the cultivar. Hulls from the Tower cultivar, an dark-hulled low-erucic rapeseed, resulted in performance and intake similar to those obtained with soybean hulls or a purified fibre source (respectively 400-466 g/day and 755-882 g/day). Hulls from the yellow-hulled cultivar R500, a high-erucic rapeseed, reduced average daily weight gain (273 g/day) and feed intake (481g/day). The difference could be due to the presence of glucosinolates (Mitaru et al., 1985).

Poultry 

Rapeseed hulls have a very poor nutritional value in poultry. Metabolizable energy and protein digestibility of diet decreased linearly with the inclusion of rapeseed hulls from an early 00 cultivar, being almost null for pure rapeseed hulls in cockerel diets (Lessire et al., 1991). Rapeseed hulls from an early low-erucic, dark-hulled cultivar could be included at 10% dietary level in broiler diets without impairing bird growth, feed efficiency or protein digestibility and metabolizable energy. The tannins contained in the rapeseed hulls were not detrimental to the birds (Mitaru et al., 1983).

Rabbits 

When available, rapeseed hulls can be included in the list of ingredients usable to feed rabbits (Lebas et al., 1983; Kowalska et al., 2016). The inclusion of rapeseed hulls was tested with success in balanced diets for growing rabbits as partial or almost complete replacement of alfalfa, up to 39-40% of the diet, without significant modification of growth rate (Lebas et al., 1981; Gidenne, 1987). As a consequence of the higher lipid content of rapeseed hulls compared to that of dehydrated alfalfa (2.5-3%), the feed efficiency was improved (reduction of 16% of feed conversion ratio) but without significant modification of the diets digestibility for proteins or energy, and without modification of slaughter yield (Lebas et al., 1981). With the same diets, increasing dietary rapeseed hulls induced a significant decrease in saturated fatty acids (especially palmitic acid) in kidney fat and a significant increase in mono-unsaturated fatty acids, especially oleic acid, and in polyunsaturated fatty acids. The kidney fat of rabbits fed the largest amount of rapeseed hulls (40%) was more flabby and translucent than that of the controls (Ouhayoun et al., 1981).

Despite these modifications in the lipids composition, the acceptability of rabbits meat was not altered during a tasting test, even after prolonged storage in frozen form (Ouhayoun et al., 1982). This absence of effect on meat taste is most probably related to a very moderate influence of rapeseed hulls on lipids of the longissimus dorsi, in comparison with those of kidney fat (Ouhayoun et al., 1982). Use of a diet with 20% rapeseed hulls 2 weeks before first mating of young rabbit does and during first gestation reduced mating acceptation and gestation rate in comparison with diets containing soybean meal (16%) raw or dehulled rapeseed meal (20%). The reduction of performance at first mating was associated with a lower growth rate of the young does although they received the same limited quantity of diet: 150 g/d (Lebas et al., 1982). However, for pregnant does, individual growth rate during gestation, number and weight of embryos alive at 28 days of gestation was not affected by the mother dietary treatment (Lebas et al., 1982).

As a conclusion, rapeseed hulls may be considered as safe raw material for growing rabbits feeding with an incorporation level of 20-30%. It is an atypical product with high levels of fibre and lipids, and a moderate level of proteins. The digestible energy content was estimated in vivo at 14.8 MJ/kg DM (Lebas et al., 1981). For breeding does, new information would be useful before recommending unrestricted inclusion of rapeseed hulls.

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 87.5 2.1 83.1 92.3 27  
Crude protein % DM 16.1 1.7 13.2 20.9 41  
Crude fibre % DM 27.3 7.8 12.7 38.8 40  
Neutral detergent fibre % DM 55.8 10.8 37.4 72.1 24 *
Acid detergent fibre % DM 42.2 10.8 22.9 58.1 24 *
Lignin % DM 22.7 6.3 6.1 31.4 25 *
Ether extract % DM 13.2 4.5 7.4 24.4 32  
Ash % DM 5.5 0.5 4.1 7 37  
Insoluble ash % DM 1.4       1  
Starch (polarimetry) % DM 6       1  
Total sugars % DM 2.6   2.5 2.8 2  
Gross energy MJ/kg DM 21.2 1.1 20.4 22.8 6 *
               
Amino acids Unit Avg SD Min Max Nb  
Alanine g/16g N 4.1   3.7 4.5 2  
Arginine g/16g N 4.3   3.9 4.8 3  
Aspartic acid g/16g N 7.9   7 8.8 2  
Cystine g/16g N 2.5   2.1 2.8 4  
Glutamic acid g/16g N 13   11.5 14.5 2  
Glycine g/16g N 4.4   4.1 4.7 2  
Histidine g/16g N 2.4   1.8 3.4 3  
Isoleucine g/16g N 3.4   2.8 4 3  
Leucine g/16g N 5.5   4.8 6.3 3  
Lysine g/16g N 6.2   5.3 7.1 3  
Methionine g/16g N 1.7   1.3 2 4  
Methionine+cystine g/16g N 4.2   3.8 4.8 3 *
Phenylalanine g/16g N 3.5   3.1 3.9 3  
Phenylalanine+tyrosine g/16g N 6.9       1 *
Proline g/16g N 7.1   6 8.3 2  
Serine g/16g N 4.5   4.2 4.8 2  
Threonine g/16g N 5   4.1 5.7 3  
Tryptophan g/16g N 1.1   1 1.3 2  
Tyrosine g/16g N 3.3   2.9 3.8 2  
Valine g/16g N 4.8   4.1 5.9 3  
               
Fatty acids Unit Avg SD Min Max Nb  
Myristic acid C14:0 % fatty acids 0.03          
Palmitic acid C16:0 % fatty acids 4.8       1  
Palmitoleic acid C16:1 % fatty acids 0.2          
Stearic acid C18:0 % fatty acids 1.6       1  
Oleic acid C18:1 % fatty acids 59.9       1  
Linoleic acid C18:2 % fatty acids 20.4       1  
Linolenic acid C18:3 % fatty acids 9.2       1  
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 12.9 1.3 10.7 15.1 9  
Phosphorus g/kg DM 2.6 0.8 1.8 4.2 9  
Potassium g/kg DM 9.9   8.8 11 2  
Sodium g/kg DM 0.14   0.09 0.2 2  
Magnesium g/kg DM 1.3   1.2 1.4 2  
Manganese mg/kg DM 36   32 40 2  
Zinc mg/kg DM 15   11 20 2  
Copper mg/kg DM 5   5 6 2  
Iron mg/kg DM 141   118 165 2  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 60.6         *
Energy digestibility, ruminants % 60.1         *
ME ruminants MJ/kg DM 10.2         *
Nitrogen digestibility, ruminants % 74.1         *
Nitrogen degradability (effective, k=6%) % 48   39 62 3 *
Nitrogen degradability (effective, k=4%) % 51       1 *
a (N) % 34       1  
b (N) % 32       1  
c (N) h-1 0.047       1  
Dry matter degradability (effective, k=6%) % 37         *
Dry matter degradability (effective, k=4%) % 41       1 *
a (DM) % 24   20 27 2  
b (DM) % 33   29 38 2  
c (DM) h-1 0.042   0.04 0.044 2  
               
Pig nutritive values Unit Avg SD Min Max Nb  
Energy digestibility, growing pig % 42       1 *
DE growing pig MJ/kg DM 8.9       1 *
MEn growing pig MJ/kg DM 8.4         *
NE growing pig MJ/kg DM 6.1         *
Nitrogen digestibility, growing pig % 42.9       1 *
               
Poultry nutritive values Unit Avg SD Min Max Nb  
AMEn cockerel MJ/kg DM 7          
AMEn broiler MJ/kg DM 6.4         *
               
Rabbit nutritive values Unit Avg SD Min Max Nb  
Energy digestibility, rabbit % 66       1  
DE rabbit MJ/kg DM 14       1 *
MEn rabbit MJ/kg DM 13.4         *
Nitrogen digestibility, rabbit % 70.4       1  

The asterisk * indicates that the average value was obtained by an equation.

References

AFZ, 2017; Ahlström et al., 1978; Ashes et al., 1978; Aufrère et al., 1988; Aufrère et al., 1991; Carré et al., 2016; Chapoutot et al., 1990; Grala et al., 1999; Grenet et al., 1990; Kracht et al., 2004; Lebas et al., 1981; Lebas et al., 1982; Lessire et al., 1991; McKinnon et al., 1995; Michalet-Doreau et al., 1980; Noblet, 2001; Orskov et al., 1992

Last updated on 11/09/2019 16:45:05

References
References 
Datasheet citation 

Heuzé V., Tran G., Lebas F., 2019. Rapeseed hulls. Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. https://www.feedipedia.org/node/15618 Last updated on September 2, 2019, 10:43