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Rape forage

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Description
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Common names 

Rape forage, forage rape, rapeseed forage, canola forage [English]; colza fourrager, colza-fourrage, canola fourrager [French]; canola forrajera, colza forrajera, forraje de canola, forraje de colza [Spanish]

Description 

Rape forage (Brassica napus L. and interspecific crosses of other Brassica species including Brassica rapa L. and Brassica campestris L.) is a catch crop that can be sown from spring to autumn and produce valuable fodder for livestock. A high-quality forage, it can be grazed, cut for cut-and-carry systems, or made into hay or silage. In temperate areas, rape forage helps bridging the forage gap by the end of summer. Rape forage provides several environmental services (GNIS, 2019). Cultivars of rape developed specifically for forage production are available worldwide.

Morphology

Rape forage has very variable habit depending on the variety or the type of hybrid. The plant is taprooted and the stems are erect and many branched. The basal and lower leaves are petiolated, very variable in shape, 5-40 cm long x 2-10 cm broad. The upper leaves are sessile, lanceolate, ovate or oblong, 8 cm long x 3.5 cm broad (eFloras, 2014). In the USA, two types of forage rape have been described: a giant type that is leafy and upright and a dwarf type that is short and branched. The giant type is reported to be preferred by cattle (Lemus et al., 2014).

Uses

Rape forage can be used for pasture, silage and in cut-and-carry systems. The plant can be sown in spring or after harvest of the main crop (wheat, barley, maize, etc.) at the end of summer or during autumn so that it can produce supplementary green forage for livestock during summer or just before or after winter and provides green feed to the animals in times of scarcity. Rape forage provides several environmental services: it improves the soil, decreases the risk of N leaching and soil erosion, it fights against parasites and provides nesting for wildlife. It is a source of nectar for bees (GNIS, 2019).

Distribution 

Oilseed and forage rape are thought to have originated from Europe and is now grown worldwide. Oilseed rape is mostly cultivated in temperate areas but it is also grown in the tropics at high elevations (between 1500 and 2200 m) (Ecocrop, 2014). When it is grown for forage, oilseed rape can be sown during spring, summer or autumn. Oilseed rape is winter hardy and frost resistant: winter types can survive down to -15°C/-20°C for short periods (Ecocrop, 2014). However, rape forage cannot grow below 5°C (GNIS, 2019)

Rape forage does well under a wide range of soil conditions, provided that they are well-drained and that moisture and fertility levels are adequate (Snowdon, 2006; Duke, 1983). It grows where annual rainfall is between 300 and 2800 mm. It responds positively to N and P fertilizers and requires large amounts of sulphur (Herkes, 2014; Duke, 1983). Rape is sensitive to aluminium and manganese toxicity in acidic soils but it is relatively tolerant of soil salinity (up to 5-6 dS/m) (CCC, 2014). Rape is a fast growing plant that can yield a valuable amount of forage within 60-80 days. It does not require much work nor fertilizer and it is suitable for direct drilling (GNIS, 2019).

Forage management 

Forage rape can be sown during a long period between spring and autumn. It can be sown in order to be used very quickly  (60-80 days after sowing) and then removed by grazing/cutting or it can be let for regrowth and grazed/cut once again. It has been possible to gain multiple forage harvests when 30 cm high stems are left to recover for 30 days (Johnston, 2009). Rape can also be sown, grazed and then let to regrow during winter (vernalization) for further oilseed production (Paridaen et al., 2015).

The seeds can be drilled into stubbles just after harvest of the main crop or after grass or it can be broadcast on naked soil. Sowing density varies from 6-10 kg depending on sowing conditions and locations (direct drill or broadcast) (GNIS, 2019; Limagrain, 2019). Lower seed rate were reported in the USA (3.5-4.5 kg/ha)(Lemus et al., 2014; Johnston, 2009). When rape is sown after a cereal, the straw should be removed before sowing. The seeds should be plugged to a depth of 2-4 cm depending on soil texture and moisture (GNIS, 2019). When oilseed rape is sown at the end of spring weeding is not necessary because the plant develops readily and smoother weeds (GNIS, 2019).

Rape establishes readily and can be ready to harvest for forage between roughly 60-80 days for first cut (GNIS, 2019; Johnston, 2009). In Zacatecas, a semi-arid area of Mexico, livestock could graze rape forage sown during autumn after only 30-42 days and that the better time for making silage was 63 days after sowing (Sanchez-Gutierrez et al., 2018). The plants are reported to be ready when they develop a reddish tinge (Lemus et al., 2014).

Yields 

Forage rape is highly productive. Average yields in Europe range between 25-36 t/ha of fresh forage (4-5 t DM/ha) (GNIS, 2019; Limagrain, 2019). In a semi-arid zone of Mexico, it produced 2.5-3 t DM/ha (Sanchez-Gutierrez et al., 2018). In the high rainfall zones of Australia, it was possible to grow biennal dual-purpose (forage and seeds) types of rapeseed and have 1000–2000 sheep-grazing days in winter (2.5-4 tonnes DM/ha) with little impact on seed yields (3.5-5.0 t/ha)(Paridaen et al., 2015).

Management

Green feed

Rape forage can be grazed by all classes of livestock. However, strip-grazing is recommended for cattle while it is not necessary for sheep or goats

Strip-grazing

It is possible to have rape forage strip-grazed by livestock. This can be achieved with the use of an electric fence set on a large front and moved everyday so that animals are allowed to access long narrow strips which will reduce wastage. Animals should be introduced to the crop slowly (at least 8 to 15 days). They should preferably enter the stand in the afternoon and should have access to water and to a dry run back to keep them clean. It is recommended that dairy cows do not consume rape forage at least one hour before milking to avoid a "cabbage" taint in the milk (GNIS, 2019).

Cut-and-carry

Green rape forage can be brought to the stall and fed to livestock

Silage

It is possible to make silage from rape forage provided it is cut at optimal DM (13-14%) and sugar (25%) contents. Prewilting is recommended prior to ensiling. The forage should then be chopped to 3-4 cm pieces. It can be mixed with dried beet pulp to prevent leaching and it is possible to add beet molasses to fasten fermentation process. Unlike maize or grass silage, the pile of rape forage should not be too compacted. It is important that no soil particles are brought to the pile as it may contaminate the silage (GNIS, 2019).

Environmental impact 

Cover crop, soil improver

Rape forage is a valuable cover crop during end of summer, autumn and winter. It prevents soil erosion and N leaching. It can be used as green manure in order to improve soil structure  (GNIS, 2019).

Water saving

In semi-arid areas of Mexico, rape forage can be an alternative to traditional feeds for dairy cows (oats, barley, wheat and perennial ryegrass) as it requires 40% less water than these latter (Sanchez-Gutierrez et al., 2018).

Methane emissions

In a experiment in New Zealand, lambs fed fresh winter forage rape yielded 22–30% less CH4 than those fed perennial ryegrass and the difference persisted for 15 weeks. The lower CH4 yields from forage rape were associated with a different microbial community, a faster fermentation and a lower ruminal pH. Forage rape could be a viable CH4 mitigation tool for pastoral-based sheep production systems (Sun et al., 2015).

Nutritional aspects
Nutritional attributes 

Rape forage contains typically about 20% protein and is considered as a high-quality forage. It can be extremely variable: depending on maturity and on the leaf:stem ratio, its protein content ranges from 9% DM (Westwood et al., 2012) to more than 30% DM (Kaur et al., 2010). The fibre content is relatively low, though extreme values occur.

Potential constraints 

Bloat

Rape forage is readily degraded in the rumen. It is thus necessary to balance the ration with fibre alongside the crops, and to introduce non-hungry stock gradually (Limagrain, 2019).

Nitrate poisoning

If rape forage grows fast after rain on a soil with high N fertilizer or nitrate content, the leaves accumulate nitrates that can cause nitrate poisoning in livestock. Nitrate content was reported to be between 1.5-2% at first grazing in Australia. This condition can be detrimental to cows if they are not restricted (Fulkerson, 2008).

Sulphur induced haemolytic anemia and polioencephalomalacia

Rape forage contains high amounts of sulphur in the form of S-Methyl Cysteine Sulfoxide (SMCO). SMCO levels are higher when soil phosphate levels are low and nitrogen and sulphur levels are high. SMCO levels also increase when crops are flowering (Limagrain, 2019). The content of forage rape in sulphur is 0.5-1.3%, much higher than the recommended requirement for cattle (Johnston, 2009). The ingestion of high sulphur forage causes feed intake depression, weight loss, weakness and haemoglobinurea and risk of heamolytic anemia in cattle (Johnston). It can cause polioencephalomalacia (PEM) a condition characterized by lethargy, ataxia and blindness (hence the name "rape blindness"). (Kelly, 2013). PEM can be prevented by limiting the rape forage to 35-50% of total DM intake. In any case, flowering rape forage should not be fed to cattle.(Limagrain, 2019). In Australia, a PEM outbreak could be alleviated by intramusculary injections of thiamine (Kelly, 2013).

Goitre

Rape forage may contain elevated levels of isothiocyanate, a compound that blocks iodine uptake. Rape forage is itself low in iodine, which may increase the risk of iodine deficiency, affecting the thyroid gland and the hormones it produces (Limagrain, 2019; Johnston, 2009). Iodine deficiency induces goitre in livestock. Symptoms include growth depression, thyroid enlargement, hypothermia and tendon contractions in neonates (Johnston, 2009). To avoid those issues, it is recommended that fresh forage or silage are not fed above 35-50 % of total DM on a daily basis, with the remainder of the ration being fibrous and/or dry feeds such as straw, hay and grains (Limagrain, 2019).

Scouring

Long-term feeding of rape forage at greater than 60 % of the diet may cause scouring (Johnston, 2009).

Pesticides residues

When the rape crop was not originally intended for livestock, it is important to check grazing and feeding restrictions which may apply to crops treated or sprayed with pesticides or herbicides (Johnston, 2009).

Ruminants 

Rape forage is a valuable fodder for ruminants that provides green feed during summer, autumn and early spring when grasses are not available. Rape forage helps sparing grass hay or silage. However, due to several potential constraints, some precautions should be taken before introducing cattle to this forage. Animals should get used to eat rape forage gradually. This can be done through mixing the rape forage with other forages (Johnston, 2009). After the accustoming period, livestock should be offered sufficient dry feeds like hay or straw and free access to water (GNIS, 2019; Limagrain, 2019). Rape forage should not represent more than 35-50% of total DM intake (Limagrain, 2019).

Digestibility and degradability 

Rape forage is highly digestible. In vitro DM digestibility values reported for different varieties ranged from 87 to 91% (Pearce et al., 1991; Lancaster et al., 1990Guillard et al., 1988, Jung et al., 1988). In vivo OM digestibilities reported by different authors ranged from 73 to 90% (Dumont et al., 1978; Alibes et al., 1990; Emile et al., 1993; Sun et al., 2015). This high digestibility could result in acidosis if the ration is not adequately balanced with roughage (Meslier et al., 2014).

Cattle

In France, rape forage can be a valuable grazed resource for cattle. Strip-grazing of rape forage is recommended in order to prevent trampling. Dairy cows should be allowed to graze 20 m²/day to receive 25% to 33% of their daily ration. Grazing rape forage provides good supplement to maize silage and it can help saving 1 kg concentrate/day (Sagot, 2012). In Australia, it is recommended to supplement dairy cows with high fibre sources like grass or maize silage, kikuyu (Pennisetum clandestinum), or paspalum (Fulkerson, 2008). Dairy cows should preferably graze rape forage after the afternoon milking as the nitrate content of rape is lower and the sugar content is higher. They should never  graze rape forage less than 2 hours before milking because of the risk of milk taint (GNIS, 2019; Fulkerson, 2008). 

Milk thiocyanate content was shown to increase for dairy cows fed on about 50% rape forage. This higher thiocyanate content was shown to have goitrogenic activity on rats fed on milk only. This could be potentially an issue for newborns fed only on milk from cows grazing high-thiocyanate rape forage (Grongnet, 1982). 

Sheep

Rape forage is not very palatable to sheep because of the cabbage taint. Neither gradual introduction to rape forage nor restricted feeding (strip-grazing) are necessary provided sheep have been fed prior to entering the stand. After a while, rape forage is eaten more readily and no concentrate is required (Sagot, 2012). In Australia, in a high-rainfall zone, dual-purpose rape forage grown during winter to feed Merino growing lambs (hoggets) was eaten readily and the sheep had 210 g/day growth rate (Kirkegaard et al., 2008).

In the UK, finishing lambs grazing on rape forage gained 273 g BW/day without requiring other forage. This reduced their concentrate needs dramatically in comparison to lambs fed on concentrates (5 kg vs. 66 kg per kilogramme of meat). For better economical returns, it was recommended to feed finishing lambs and culled ewes on rape forage (AHDB, 2015). In a comparative experiment, growing lambs were fed either on rape forage or on irrigated grass pasture. Growth rates for both diets were similar during the first 6 weeks, but after that the lambs fed on grass pasture had lower weight gains. At slaughter, lambs fed on rape forage were heavier and fattier, the carcass had higher pH, the meat had significantly lighter colour but there was no significant difference in cooking loss. Overall meat quality based on objective assesssments was the same for both groups of lambs but sensorial analysis through panellists detected a stronger, less acceptable flavour from the meat of rape-fed lambs (Hopkins et al., 1995).

Rabbits 

Rape forage is frequently grazed by wild rabbits, and many authors describe rabbit as a potential rape predator (Inglis et al., 1992; Mithen, 1992; Griffiths et al., 1994). Almost all published papers indicate that the grazing pressure of rabbits in rape crops is independent of the glucosinolate content of the rape, cultivar. Grazing increases significantly the glucosinolate content of leaves (Griffiths et al., 1994; Inglis et al., 1992; McFarlane-Smith et al., 1991).

Smallholder rabbit farms have been using fresh rape forage for a long time, and they also use other Brassica species such as cabbage, turnips, radishes, white mustard or swedes (King Wilson, 1944; Nollet, 1943; Charon, 1927). When distributed ad libitum together with a mixture of grains (also ad libitum) during 6 weeks, the voluntary intake of rape forage represented 21% of the total intake of growing rabbits. It should be noticed that in the same conditions, cabbage intake represented 24% of the total intake, and live weight gain during the experimental period was 1000 and 1080 g for rabbits for the rape and cabbage groups respectively (Fedeli Avanzi et al., 1976). For experimental reasons fresh rape forage was proposed as only feed to almost adult rabbits, a feeding regime which appear able to permit at least weight maintenance on a period of 30 days minimum, without apparent health disturbance (Richter et al., 1989; Bonadonna et al., 1957). Similarly, rations mixing dried rape pellets (comparison of 2 cultivars) together with wheat straw also allowed increased liveweight, independently of the cultivar (Richter et al., 1989).

Despite the known possibility of safe use of rape forage in rabbit feeding, no experiment seems available in the international literature on the optimum conditions of introduction of this forage in balanced rabbits diets. The nutritive value was not determined, but since digestibility of dry matter or energy of 3 other Brassica fresh forages i.e. cabbage, turnips and rutabaga (swedes) are close to 100%, it can be supposed that it is the same for rape forage. Digestibility of proteins of these 3 forages was 90-97% and that of crude fibre 82 to 100% (Voris et al., 1940). Rape forage may thus be considered for rabbits as a source of energy (about 16-16.5 MJ/kg DM), of digestible proteins (20-25%), and of digestible fibre.

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 12.1 2.1 7.5 15.2 50  
Crude protein % DM 19.3 5.8 7.2 33.7 70  
Crude fibre % DM 15.8 2.8 9.8 23.8 31  
Neutral detergent fibre % DM 28.9 14.5 13.2 60.4 35  
Acid detergent fibre % DM 23.2 11.7 9 52.1 36  
Lignin % DM 4.5 1.2 3.6 6.3 5  
Ether extract % DM 3.8 1.3 1.8 5.8 17  
Ash % DM 14.7 3.7 7.9 22.9 50  
Insoluble ash % DM 10.7       1  
Gross energy MJ/kg DM 17.4       1 *
               
Fatty acids Unit Avg SD Min Max Nb  
Myristic acid C14:0 % fatty acids 1.4   1.2 1.5 3  
Palmitic acid C16:0 % fatty acids 17.4   17.2 17.7 3  
Palmitoleic acid C16:1 % fatty acids 1.8   1.3 2.6 3  
Stearic acid C18:0 % fatty acids 3.3   2.8 3.6 3  
Oleic acid C18:1 % fatty acids 1.7   1.4 2 3  
Linoleic acid C18:2 % fatty acids 16.3   16 16.9 3  
Linolenic acid C18:3 % fatty acids 58.1   56.9 59.1 3  
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 21.7 13.4 5.5 41.8 13  
Phosphorus g/kg DM 5.8 4.2 3.1 17.3 13  
Potassium g/kg DM 26.8 10.2 18.3 45.4 7  
Sodium g/kg DM 0.95   0.4 1.5 2  
Magnesium g/kg DM 2.2 0.9 1.2 4 7  
Sulfur g/kg DM 4.9       1  
Manganese mg/kg DM 39   32 49 4  
Zinc mg/kg DM 42 7 37 54 6  
Copper mg/kg DM 6 3 4 11 6  
Iron mg/kg DM 55   48 71 4  
               
In vitro digestibility and solubility Unit Avg SD Min Max Nb  
In vitro DM digestibility (pepsin) % 54       1  
In vitro OM digestibility (pepsin) % 79 8 66 93 19  
In vitro DM digestibility (pepsin-cellulase) % 80 2 79 84 5  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 79.2 4.1 72.5 89.9 28 *
Energy digestibility, ruminants % 75.8         *
DE ruminants MJ/kg DM 13.2         *
ME ruminants MJ/kg DM 10.6         *
Nitrogen digestibility, ruminants % 88.5       1  
Nitrogen degradability (effective, k=6%) % 81   71 85 2 *
Nitrogen degradability (effective, k=4%) % 85         *
a (N) % 39   34 44 2  
b (N) % 58   53 63 2  
c (N) h-1 0.16   0.06 0.26 2  
Dry matter degradability (effective, k=6%) % 82   76 86 3 *
Dry matter degradability (effective, k=4%) % 86         *
a (DM) % 49       1  
b (DM) % 49       1  
c (DM) h-1 0.129       1  

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

References

AFZ, 2017; Alibes et al., 1990; Çaçan et al., 2017; Clapham et al., 2005; Dumont et al., 1978; Emile et al., 1993; Espinoza-Canales et al., 2017; Fulkerson et al., 2008; Kaur et al., 2010; Kaur et al., 2010; Kunelius et al., 1990; Lambert et al., 1987; Luo et al., 2015; Min, 2013; Pearce et al., 1991; Salgado et al., 2013; Sun et al., 2012; Sun et al., 2015; Westwood et al., 2012

Last updated on 12/08/2019 23:17:24

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 17.2 3 14 23.2 14  
Crude protein % DM 16.4 2.9 9.6 20.4 14  
Crude fibre % DM 18.7 4.8 12.4 25.7 12  
Neutral detergent fibre % DM 29.9         *
Acid detergent fibre % DM 23.8         *
Lignin % DM 5.4   4.9 5.9 2  
Ether extract % DM 3.8          
Ash % DM 19 3.5 13.8 25.6 12  
Gross energy MJ/kg DM 16.5         *
               
In vitro digestibility and solubility Unit Avg SD Min Max Nb  
In vitro OM digestibility (pepsin) % 62 11 50 75 6  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 78.3 4.7 68.8 87.5 12 *
Energy digestibility, ruminants % 74.8         *
DE ruminants MJ/kg DM 12.4         *
ME ruminants MJ/kg DM 9.9         *
Nitrogen digestibility, ruminants % 74.9 3.8 70.1 80.8 6  
               
Rabbit nutritive values Unit Avg SD Min Max Nb  
Energy digestibility, rabbit % 50.7         *
DE rabbit MJ/kg DM 8.4         *
MEn rabbit MJ/kg DM 7.7         *
Nitrogen digestibility, rabbit % 87.1         *

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

References

Dumont et al., 1978; Emile et al., 1993; Lancaster et al., 1990

Last updated on 12/08/2019 17:42:22

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 92.1   89.3 94.5 4  
Crude protein % DM 5.7 1.7 3.4 9.3 11  
Crude fibre % DM 48.2   44.1 51.3 3  
Neutral detergent fibre % DM 74.2 5.5 64.9 81.6 6  
Acid detergent fibre % DM 58.9 2.7 56.4 62.3 6  
Lignin % DM 13   10.8 14.7 4  
Ether extract % DM 2.1 1.6 0.7 5.4 7  
Ash % DM 7 3.3 2.1 12.8 10  
Starch (polarimetry) % DM 0.3       1  
Gross energy MJ/kg DM 18.9         *
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 9.8   9 10.7 2  
Phosphorus g/kg DM 0.9   0.7 1 2  
Magnesium g/kg DM 2.6       1  
Sulfur g/kg DM 5.4       1  
Manganese mg/kg DM 30       1  
Zinc mg/kg DM 9   7 11 2  
Copper mg/kg DM 3       1  
Iron mg/kg DM 61       1  
               
In vitro digestibility and solubility Unit Avg SD Min Max Nb  
In vitro OM digestibility (pepsin) % 38       1  
In vitro OM digestibility (pepsin-cellulase) % 26       1  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 40.1       1  
Energy digestibility, ruminants % 36.5         *
DE ruminants MJ/kg DM 6.9         *
ME ruminants MJ/kg DM 5.5       1 *
Dry matter degradability (effective, k=6%) % 21   12 35 3 *
Dry matter degradability (effective, k=4%) % 24   14 36 2 *
a (DM) % 3       1  
b (DM) % 33       1  
c (DM) h-1 0.07       1  
               
Rabbit nutritive values Unit Avg SD Min Max Nb  
Energy digestibility, rabbit % 21         *
DE rabbit MJ/kg DM 4         *
MEn rabbit MJ/kg DM 3.8         *
Nitrogen digestibility, rabbit % 58.6         *

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

References

Abreu et al., 1998; Adapa et al., 2010; AFZ, 2017; Griffith et al., 2017; Nasehi et al., 2013; Naseramini et al., 2012; Orskov et al., 1992; Rasool et al., 1998; Zhao et al., 2015; Zhao et al., 2015

Last updated on 12/08/2019 22:35:28

References
References 
Datasheet citation 

Heuzé V., Tran G., Lebas F., 2019. Rape forage. Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. https://feedipedia.org/node/15683 Last updated on August 12, 2019, 23:23

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