Rapeseed/canola meal is a high-quality, high-protein feed ingredient. The amino acid profile of rapeseed/canola meal is comparable to soybean meal: its methionine content is higher than that of soybean, while its lysine content is lower and reported to be limiting for pigs (Bell, 1993). Moreover, amino acids would be less available in rapeseed/canola meal than in soybean meal (Aherne et al., 1985; Thacker, 1990). Because of its high fibre content (> 110 g/kg), rapeseed/canola meal contains less digestible energy (13.2 MJ/kg) than soybean meal (16.8 MJ/kg) (Feedipedia, 2012; Thacker, 1990).
Rapeseed/canola seeds (and thus meal) are better sources of calcium, selenium and zinc than soybean meal, but are poorer sources of potassium and copper. However, high phytic acid and fibre contents reduce the availability of many mineral elements (Blair, 2007). Rapeseed/canola meal is a good source of vitamins (choline, niacin, riboflavin and biotin) (Blair, 2007).
Glucosinolates limited the use of canola meal in pig diets in the past as they had a goitrogene effect and deleterious effects on liver and reproduction (Blair, 2007). An estimate of the tolerable level of glucosinolates in the total diet of pigs is 2.4–2.5 μmol/g (Schöne et al., 1997a, Schöne et al., 1997b; Bell, 1990).
Modern varieties of canola and rapeseed contain much lower levels of glucosinolates, however, cold pressed canola/rapeseed meals and expeller rapeseed/canola meal may still contain small amounts of glucosinolates. These glucosinolates become deleterious after being hydrolysed by myrosinase, a heat sensitive enzyme. In solvent extracted rapeseed/canola meal, myrosinase is desactivated by heat but in expeller and cold pressed meals, myrosinase may remain active.
Palatability of rapeseed/canola meal was referred to as a limiting factor for applications in pigs (Frederick et al., 2014; Bell, 1993).
Technological treatments such as toasting, extrusion or dehulling have been assessed to enhance energy or protein digestibility of rapeseed/canola meal. Dehulling could be used to increase the digestible energy content. It is also possible to process rapeseed/canola meal in order to optimize the utilization of the protein.
It is important to notice that modern varieties of rapeseeds and canola with low glucosinolate, low erucic acid and low tannins have considerably enhanced and increased the use of rapeseed/canola meal in pig diets. Most recommendations which dealt with very low levels or rapeseed/canola meal such as 5% in starter diets, 10% in sows and finishers, and 15% in growing pigs were provided in the 80-90's (Lewis et al., 2001); they are underestimated if modern varieties of rapeseed/canola are used.
Solvent-extracted rapeseed/canola meal
The response of pigs of all ages to rapeseed/canola meal inclusion in diets is generally favourable. Early recommendations were that rapeseed/canola meal could be included in grower diets to supply up to 50% of the supplementary protein required. Recent research proved that it was possible to use 100% rapeseed/canola meal as the protein source of growing pig diets (Roth-Maier et al., 2004).
In piglets, recent experiments showed that rapeseed/canola meal could be included in the diet at up to 15-20% of the diet (DM basis) without compromising growth performance, organ weights, bone ash or blood parameters (Peñuela Sierra et al., 2015; Parr et al., 2015; Royer et al., 2011).
Using rapeseed meal (8.3 µmol/kg glucosinolates), as the sole protein source had no effect on feed intake, or growth performances of growing pigs (Roth-Maier et al., 2004).
When pig diets (either for growers or finishing pigs) were formulated in order to get the same amount of digestible lysine from rapeseed meal as from soybean meal, growth performance and carcass quality were similar (Raj et al., 2000; Siljander-Rasi et al., 1996).
Fattening pigs and sows
In fattening pigs, rapeseed/canola meal could be used to completely replace soybean meal without considerable changes in growth performance, visceral mass, carcass characteristics, fresh meat quality, or carcass cutability, provided that diets were formulated to contain similar quantities of standardized ileal digestible amino acids (Little et al., 2015; Rojo-Gomez et al., 2001). In France it was shown that fattening pigs could be fed up to 18% rapeseed/canola meal and 40% peas as protein sources in order to totally replace soybean meal (Royer et al., 2005).
In sows, it is important to limit the level of glucosinolates in order to prevent reproduction diseases. Sow diets could contain up to 10% rapeseed/canola meal during lactation and gestation without having deleterious effect on animal health, reproductive performance of sows (including hyper prolific sows) or on piglet growth (Quiniou et al., 2014; King et al., 2001; Jost, 1996; Thacker, 1990; Aherne et al., 1985; Flipot et al., 1977). It was reported that rapeseed meal inclusion had positive effect on sows' feed intake during lactation (King et al., 2001). Heat treatment (103°C) of rapeseed meal improved palatability and increased feed intake compared with untreated rapeseed meal (Jost, 1996).
Other rapeseed/canola meals
Expeller and cold-pressed rapeseed/canola meals result from mechanical extraction of oil. Thus, they have higher residual oil and are considered valuable sources of energy in pig diets (Blair, 2007). However, as they are not submitted to heat, glucosinolates remain high (11.9 µmol/g) in expeller meal and in cold-pressed meal (5.96 µmol/g), above the level recommended for optimal pig growth (level for optimum growth performance of growing pigs: 2.0–2.4 µmol/g). Besides, the myrosinases involved in glucosinolate degradation are not deactivated and may result in health problems (Grageola et al., 2013).
However, the low temperature of the meal produced by expeller-pressing and cold-pressing limited heat damage during processing, and lysine availability in both expeller meal and cold-presed indicated limited lysine damage (Grageola et al., 2013).
Expeller rapeseed/canola meal
Expeller rapeseed/canola meal results from the mechanical extraction of oil. It has higher residual oil and may thus be a valuable source of energy in pig diets. It was referred to be 10 points higher in energy than solvent extracted rapeseed/canola meal (Skiba et al., 1999). However, it was reported to result in lower feed intake, lower average daily gain and a 3 days delay in reaching slaughter weight when offered during 90 days to growing/fattening pigs (Seneviratne et al., 2010). It was suggested to limit expeller rapeseed/canola meal to 22,5% during the first 50 days of the growing period and to 18% during the next 40-day period (Seneviratne et al., 2010). In 6-7 kg weaned piglets, including increasing levels of expeller rapeseed/canola meal linearly decreased the total tract digestibility of energy, DM and CP. It was suggested to limit expeller rapeseed/canola meal at 20% in their diet (Landero et al., 2012; Seneviratne et al., 2011).
Cold-pressed rapeseed/canola meal
Cold-pressed rapeseed/canola meal has higher content of oil and thus higher digestible energy than expeller (+10 points) and solvent-extracted rapeseed/canola meal (+20 points) (Skiba et al., 1999). The DE (MJ/kg, air-dry basis) was 16.57, compared with 14.23 in expeller rapeseed/canola meal and 12.41 in solvent-extracted meal. Total amino acid levels appeared to be relatively unaffected by the process or degree of heat treatment. However, in the absence of heat treatment glucosinolates or their degradation products remain high in the meal.
A cold-pressed canola meal (96 g oil and 10.5 μmol total glucosinolates per kg (oil-free DM basis)) was increasingly included in diets for growing-finishing pigs at up to 200 g/kg to replace sweet lupin seed. Beyond 150 g/kg, rapeseed meal reduced the performance of growing-finishing pigs and thyroid hypertrophy was evident (Mullan et al., 2000). These results suggest that cold-pressing does not inactivate myrosinase sufficiently to allow the extracted meal to be incorporated into pig diets at maximum levels. It is thus recommended to do more frequent analysis of expeller canola meal for oil and protein contents and to set more conservative limits on the levels of expeller canola meal used in pig diets (Blair, 2007).