Rapeseeds are sources of protein and energy for ruminants. It can be useful to grind rapeseeds for cattle in order to increase their digestibility. This operation is not necessary for sheep and goats because they naturally grind the seeds with their teeth (Poncet et al., 2003). Though rapeseeds are naturally rich in α-tocopherol that acts as an anti-oxidant, ground full-fat rapeseeds are prone to oxidation. This oxidation results in undesirable odours and flavours if the seeds are stored for too long, and it is thus advised to grind only small amounts of rapeseed at any one time (Blair, 2011).
Digestibility and energy content
Due to their high oil and relatively low fibre contents, rapeseeds are one of the richest plant components in terms of energy. The metabolizable energy value given by the INRA-AFZ Tables is 20.3 MJ/kg DM, which is higher than for other oilseeds (sunflower seeds and linseeds 17.9 MJ/kg, soybeans 16.4 MJ/kg DM) and much higher than the other concentrate feeds (about 12-15 MJ/kg DM) (Sauvant et al., 2004). This high value is similar to those proposed in other feed tables such as the NRC tables (NRC, 2001).
Protein value
As for most untreated oilseeds, the rumen nitrogen degradability of rapeseeds is fairly high. The INRA-AFZ Tables suggested an effective in sacco nitrogen degradability of 79% for rapeseeds, 78% for linseeds, 89% for sunflower seeds and 71% for cottonseeds. Since processing can largely reduce this degradability, values of 52% and 40% were proposed for extruded and rumen-protected rapeseed (Sauvant et al., 2004). Protein and energy utilization of rapeseed in the rumen can be changed by various physical and thermal processings (micronization, grinding, crushing and extrusion). In particular, heat processing of rapeseeds may increase milk ouput in dairy cattle (Kim et al., 2001). It has been shown that heating canola seeds reduced their in sacco nitrogen degradability (Mesgaranm et al., 2005). Micronization, which reduced rumen degradability of protein and disappearance of total and essential amino acids from canola seeds, may be efficient for improving amino acid utilization in ruminants. Grinding increased the proportion of protein digested in the intestine (Wang et al., 1997; Wang et al., 1999). The cooking-extrusion of 60:40 and 80:20 blends of peas and rapeseeds increased their metabolisable protein content and thus the delivery of amino acids to the intestine, though it decreased the proportion of lysine and methionine (in the protein) available in the intestine. Extrusion also increased the proportion of C18:1, C18:2 and C18:3 in the milk fat. These results emphasize the interest in incorporating these feeds, often at high levels, in the diets of dairy ruminants (Chapoutot et al., 1997). Treatment with 3% glucose decreased the nitrogen degradability of canola meal but not that of canola seed (Koksal et al., 2011).
In Australia, with grazing steers fed rapeseeds, a comparison of processing methods (scarification, grinding, rolling, roasting and steaming) concluded that grinding produced the most rumen degraded N/kg of organic matter digested in the rumen. Grinding was thus considered as the most efficient method for optimizing the use of rapeseeds as a supplement for grazing steers (Gunter et al., 2014). In Colombia, condensed tannins used to treat rapeseeds decreased the rumen degradability of DM and N, while autoclaving, or tannins combined with autoclaving increased the degradability of those fractions (Santos et al., 2014).
Influence of rapeseed on methane production
Rapeseed is an appropriate source of lipids for reducing enteric CH4 production. In growing sheep, rapeseed reduced methane production by 19%, less than sunflower seeds (27%) but more than linseeds (10%) (Machmuller et al., 2000). Crushed sunflower seeds, linseeds, and canola seeds fed to lactating dairy cows all decreased methane production (g/d) by an average of 13% compared with a commercial source of calcium salts. Inclusion of crushed canola seeds offered a means of mitigating methane production without negatively affecting diet digestibility, and hence, milk production (Beauchemin et al., 2009). A comparison of different rapeseed products (rapeseed meal, rapeseed cake, cracked rapeseeds and rapeseed oil) showed that the physical form of rapeseed fat did not influence its CH4-reducing effect and this could be obtained without affecting neutral detergent fiber digestion or milk production. It was concluded that crushed rapeseed could be used to reduce methane emissions in ruminants (Brask et al., 2013).
Dairy cattle
Rapeseeds can be used in dairy cattle feeding to increase the energy supply and to alter the milk fatty acid composition. The effect of rapeseeds on the milk fatty acids profile can be observed in the gut: rapeseeds altered rumen biohydrogenation of fatty acids, which was reflected in simultaneous changes in the duodenal flow of fatty acids and in the milk fatty acid profile (Mutsvangwa et al., 2012). Compared with an unsupplemented ration, unprotected canola seeds increased the C18:0 concentration in the milk while 4.8% formaldehyde-protected seeds increased the C18:2 and C18:3 contents, and reduced the C18:0 to C18:1c9 ratio (Delbecchi et al., 2001).
Feeding extruded canola seeds to low-producing cows had a positive effect on milk production and significant effects on milk composition (Kim et al., 2011). Feeding canola seeds to lactating dairy cows resulted in milk fat with higher proportions of desirable fatty acids without affecting digestion, milk yield or composition of milk (Chichlowski et al., 2005). Supplementing the diet with either ground canola seeds, extruded soybeans or whole cottonseeds increased the desirable poly- and mono- unsaturated fatty acids, and decreased the medium chain fatty acid and saturated fatty acid content of milk fat without negative effects on rumen fermentation and lactation yield (Chen et al., 2008). Feeding extruded canola seeds increased milk fat concentration of trans-11 18:1 (Neves et al., 2009). However, rapeseed does not always affect milk fatty acids, as shown in a trial where feeding dairy cows with a concentrate containing 1.2 kg/d of rapeseeds failed to affect the milk fatty profile for cis-9, trans-11, trans-10, cis-12 and cis-10 isomers of conjugated linoleic acid (Avilez Ruiz et al., 2013). Feeding high levels of rapeseeds (up to 1.15 kg oil/d) could be used as a nutritional strategy to lower the saturated fatty acids of milk without inducing adverse effects on DM intake and milk yield and composition (Kliem et al., 2011). In another trial, canola and sunflower seeds increased conjugated linoleic acid content in the milk fat of lactating cows without negatively affecting milk yield and milk fat concentration (Schroeder et al., 2013).
Growing cattle
There are few experiments reported in the literature on the effect of rapeseed on growing cattle. In Holstein steers, canola seed processing (ground vs. whole) enhanced its in situ degradation but had almost no effect on rumen or total tract digestibility of low-quality forage-based diets (Leupp et al., 2006).
Sheep
There are few reports of feeding trials on sheep offered rapeseeds. In lactating ewes, supplementation with canola seeds, sunflower seeds and linseeds had no effect on DM intake or nutrient utilization (Zhang et al., 2007). In growing lambs, partial replacement of barley starch with beet pulp, a soluble fibre, and canola seeds had positive effects on performance, nutrient digestibility and rumen pH (Asadollahi et al., 2014).
