Canola meal in layers: Nutritional composition, anti-nutritional factors and production performance: A comprehensive review

Introduction

The global poultry sector dependence on soyabean meal as primary protein source has become increasingly untenable, driven by volatile commodity prices, land-use concerns and supply chain disruptions. Against this backdrop, canola is now ranked the second most widely cultivated oilseed globally (FAOSTAT, 2024). Soybean meal has long served as the predominant protein source in commercials poultry diet. But its widespread use has led to economic, environmental, and sustainability problems mainly due to fluctuation in prices and overexploitation of land resources, and thus sparked the growing enthusiasm in other protein sources including canola. The use of rapeseed varieties was historically limited as feed or food due to high levels of erucic acid and glucosinolates which impair thyroid function and reduce the performance (Mawson et al., 1994) [26] . This limitation was overcome by the work of Dr. Baldur R. Stefansson at the University of Manitoba in releasing low-erucic acid rapeseed varieties, which earned him recognition as the "Father of Canola." (Dao and Moss, 2025) [13] . By definition established by the Canola Council of Canada, 2025; a variety qualifies as canada only if the extracted oil contains no more than 2% erucic acid and resulting meal carries fewer than 30 mol/g of specified aliphatic glucosinolates, applicable to B.napus, B.rapa and B.juncea varieties. Although canola supports bird growth and production, its high fiber content and antinutritional compounds deteriorate metabolizable energy (ME). Full-fat canola seed has also proven to be an effective alternative source of both energy and protein, especially when it is economically competitive with conventional feed ingredients (Emmanuel and Jeong., 1988).

Nutritional Profiling of Canola meal 2.1.1 Proximate Composition

Canola meal, a co-product of oil extraction from Canola seed, which contains around 40% oil and 17-26% Crude protein, with protein content varying based on the extraction method and degree of processing.(Uppstrom., 1995) [42] .

The full fat varieties of canola seeds increase the concentration of polyunsaturated essential fatty acids (omega-3s) in eggs which were indicated by the enhanced level of linolenic and docosahexaenoic acids in yolk. (Emmanuel and Jeong., 1988)

Protein Content and Amino Acid Profile

Canola meal contains approximately 35-40% crude protein. While lower in total protein than soybean meal (SBM), it has an excellent amino acid balance, particularly being a rich source of methionine cysteine, which are often limiting in cereal based diets (Newkirk et al., 2003; Bonnardeaux, 2007) [6, 28] and are crucial for egg production and feathering. This abundance creates a wonderful opportunity for nutritional complementarity when used along with wheat and other grains in reduced protein diets. In commercial practices, the Total Sulfur Amino Acid (TSAA) requirement is met with the addition of crystalline methionine for it being more cost effective than cysteine (Kandel et al., 2025) [22] and upon the assumption that methionine can be efficiently converted into cysteine. Under these situations, the higher cysteine content of canola meal offers an important advantage helping to restore a more balanced cysteine to methionine ratio. The standardized ileal digestibility values in laying hens were reported to ranging between 78%-84% (Rezvani et al., 2012) [34] , showing better digestibility than broilers for methionine, tryptophan and histidine (Adedokun et al., 2009) [1] . Arginine and methionine showed better digestibility compared to lysine and threonine. [28] ; Bonnardeaux, 2007 [6] The research indicates that digestibility of amino acids in canola mean is generally lower and variable when compared to SBM (Khajali and Slominski, 2012) [23] . These variations are mostly associated with the processing conditions. Excess heat during the canola seed meal production has shown to reduce the amino acid levels and their availability (Parsons et al., 1992) [33] . Solvent extraction (even though it increases the CP content), desolventization and toasting treatments has been shown to lower the lysine digestibility considerably in canola meal (Anderson-Hafermann et al., 1993) [4] , (Newkirk et al., 2003) [28] . In contrast, cold-pressed canola meals have shown retaining more digestible amino acids and energy (Agyekum and Woyengo, 2022) [3] .

Nutrient

Fiber and Carbohydrate content

In canola meal, the non-starch polysaccharides constitute roughly 53% to 80 % of the dietary fiber fraction, whereas only a small proportion (around 10% or less) is water-soluble (Lannuzel et al., 2022) [24] . These polysaccharides are minimally digested by poultry, with total tract digestibility ranging from 2.1% to 8.6% (Bryden et al., 2009) [7] . Almost 12% of the crude fiber content is mostly from the hull, consisting of carbohydrate polymers along with proteins and non-starch polysaccharides (Naczk et al., 1998) [27] . The fiber components include lignin with associated polyphenols (8%), cellulose (4-6%), and non-cellulosic polysaccharides (13-16%). The non-cellulosic polysaccharides are largely composed of pectic substances (Canola Council of Canada., 2009) [10] . The small size of canola seed and high oil concentration (42-45%) is the reason for the residual meal retaining its high fiber content. These high fiber contents is the main constraint which is limiting the wider use of canola meal in the poultry diets (Hanna et al., 2018) [17] . Other constituents include oligosaccharides (2.5%), glycoproteins (approximately 5%, e.g., arabinogalactan-proteins and cell wall proteins), phytate (3.3%), fiber-bound minerals (1%), and gum substances (4%) (Wickramasuriya et al., 2015) [43] .

Energy Value

Metabolizable energy (ME) is an important factor which directly affects diet formulation and feed cost evaluations. Compared to SBM, canola meal shows lower ME values approximately 1700-2000 kcal/kg, mostly due to canola's high fiber and lower protein concentration (Khajali and Slominski, 2012) [23] . Solvent-extracted canola meal provides approximately 2000 kcal/kg, which is around 230 kcal/kg less than non-dehulled soybean meal (Jia et al., 2012) [20] . Expeller-pressed canola meal shows higher ME values than solvent-extracted meal because of its greater residual oil concentration (Smulikowska et al., 1997) [37] Improvement of canola meals' energy profile can be achieved by dehulling, thereby lowering its fiber levels. A significant difference in digestible energy was observed between the standard (3346 kcal/kg) and dehulled fractions (4063 kcal/kg) of canola mean as a result of removal of the fibrous hull which constitutes almost 12-16% of the seed (Bell, 1993) [5] .

The energy deficits can be lowered through precise formulation strategies that help in balancing nutrient density and bird performance.

Mineral and Vitamin Profile

Canola meal also has appreciable amounts of essential minerals and vitamins supporting its role as a cost effective alternative to expensive protein sources. This is particularly relevant in layer hen diets, where its inclusion has supported high egg production (Canola Council of Canada., 2024) [11] . Canola meal supplies calcium, manganese, iron, selenium, and a variety of trace elements necessary for growth, immune function, and reproductive performance in poultry (New kirk., 2009). Canola meals have reported higher concentrations of calcium and phosphorus in comparison with SBM (Summers et al., 1989; Swick, 1999) [39,40] . Approximately 65% of phosphorus is stored as phytate and poorly available to monogastric animals. This limitation is addressed through phytase supplementation improving bioavailability while reducing the phosphorous excretion (Hanna et al., 2018) [17] . The overall contribution of calcium and phosphorus from canola meal remains greater than that of SBM (Summers et al., 1989; Swick, 1999) [39,40] . Canola meal also contains higher levels of biotin, folic acid, niacin, riboflavin, and thiamin than soybean meal (Newkirk, 2009).

Reduced-Protein Diets and Amino Acid Dynamics

By partially or completely substituting the SBM with lesser protein varieties (like canola meal) may lead to drop in the protein quality affecting the digestion. This limitation can be overcome by addition of threonine and glycine equivalents to the lesser protein substitutes. This has shown to increase the distal ileal digestibility by almost 8 % and lower the distal ileal starch: protein disappearance rate ratio, helping the digestion of energy and protein in a more balanced manner (Sonia et al., 2021)

Anti-Nutritional Factors (ANFs)

The inclusion of canola meal as a protein source in poultry is mainly limited by the presence of anti-nutritional factors which have been linked to reduced growth performance. The primary antinutritional constituents of canola meal are glucosinolates, sinapine, tannins, and phytic acid (Wickramasuriya et al., 2015) [43] . Even though modern canola varieties have been bred to contain lower glucosinolate levels than the traditional rapeseed varieties, these compounds can still affect the palatability, nutrient availability of the feed particularly at higher rates of inclusion (Khajali et al.,2012) [23] .

Glucosinolate

Concentrations in canola seeds considerably vary across regions and the extraction processes but typically range from 3.6 to 9.2 μmol/g. Although these levels are below the associated levels of acute toxicity, higher inclusions of canola meal in diet may still affect the bird negatively (Spragg and Mailer., 2007) [38] .In broilers, dietary inclusion levels of canola meal above commonly recommended (20%) has been reported to be tolerable without adverse production effects, providing that total glucosinolate concentration does not exceed 4 μmol/g feed (Khajali et al., 2012) [23] .

3.2 Sinapine is the main phenolic compound and comprises roughly 1% of canola meal. It has been associated with the development of "fishy" offflavors in eggs (Bonnardeaux., 2007) [6] . But further research revealed that this phenomenon is a result of sinapine and also a recessive gene mutation in the suspected hens, causing trimethylamine (TMA) accumulation (Ward et al., 2009). Successfully removal of this trait from commercial brown-egg layers through breeding programs, reduced the risk of TMA off-flavor (Oryschak et al., 2020) [31] . 3.3 Tannins in canola are concentrated primarily in the seed hulls. Studies have shown that rapeseed and canola hulls contain between 1.9 and 6.2g of tannins per 100g of oil free material (Naczk et al., 2000). Proanthocyanids which are responsible for the dark pigmentation of the seeds are from the fraction of insoluble tannins (Khajali et al., 2012) [23] .

3.4 Phytic acid is one of the most important ANF in canola meals. The phosphorus in canola meal is locked as monogastric animals lack sufficient endogenous phytase to facilitate their digestion (Bonnardeaux., 2007) [6] . This can be overcome by the supplementation of exogenous phytase to unlock the phosphorus and reduce the mineral waste (Hanna et al., 2018) [17] .

Physiological effect of Canola meal in Layers

Canola Meal has gained recognition as a sustainable protein ingredient for poultry diet (Dao & Moss, 2025) [13] though its inclusion warrants careful attention to glucosinolate contents and its physiological effects. However, sensory quality of Poultry Products can be affected at elevated dietary inclusion levels. Studies have reported reduction in chicken flavor intensity and an increase in offflavor incidence at higher inclusion rates, Such as at 28% in chick starter. In contrast, Moderate level around 21% in starters did not cause adverse sensory outcomes (R.E. Salmon et al., 1980) [35] suggesting balanced appropriate formulation can preserve meat quality. The concern around glucosinolates become particularly pronounced in laying hens, which appear more metabolically sensitive to these anti-nutritional factors compared to broilers. Dietary glucosinolates concentrations exceeding 1.5μmol/g have been associated with an elevated risk of hemorrhagic liver syndrome in laying hens. Research indicates that laying hens can tolerate generous inclusion level of canola meal, provided glucosinolate content kept within safe approximately 1.43μmol/g [Campbell et al., 1991]. Interestingly, while chicks fed glucosinolates did not exhibit significant liver weight changes but thyroid enlargement was observed particularly when glucosinolates were fed alongside nitrites. Notably when purified glucosinolates were added in isolation, Thyroid weight did not increase, implying that interaction between glucosinolates and other dietary components play major organ response role, underscoring the importance of using low-glucosinolate canola meal in a commercial poultry feeding system. (Slominski et., 1988).

Effects of canola meal on Egg quality

Egg quality parameters are highly sensitive to dietary protein sources and nutrient availability, making evaluation of alternative protein ingredients essential in layer nutrition (Mailer et al, 2008) [25] .

Early studies that formulated diets on a crude protein basis reported reduction in egg weight when canola meal replaced soybean meal primarily due to insufficient lysine content in canola based diet [Kaminska et al.,2003].This was further supported by [Novak et al., 2004] Inadequate lysine directly compromise egg weight. However when diets are properly balanced for amino acids, Canola meal can be included at up to 20% of diet without negatively affecting egg production, hen health, egg quality or egg fatty acid content (Oryschak & Beltranena,2013) [32] .

Regarding sensory quality, sinapine present in canola meal can be metabolized by intestinal microflora into trimethylamine [TMA], potentially causing fishy or off-odor egg in susceptible hens (Hobson-Frohock et al., 1973) [18] . Modern commercial white egg strains, however, possess sufficient hepatic TMA oxidase activity that prevent such accumulation, allowing canola meal use at recommended level without sensory impairment (Hyline international, 2010) [19] . Indirect effect of canola meal inclusion, such as enhanced fat-soluble pigment absorption, often result in improved yolk color (Costa et al., 2008) [12] . Overall, adverse effects on egg quality can be minimized through use of low glucosinolate canola meal varieties at controlled inclusion level (Khajali & Slominski, 2012) [23] .

Economic efficiency and cost effectiveness of canola meal in poultry diet

When evaluating feed ingredients in poultry production, academic research often focuses primarily on growth rates and performance metrics. In practice, the industry takes a broader view, one that weighs ingredient cost alongside productivity, animal health and survival rates to arrive at true cost per unit of gain. From this perspective, canola meal presents a compelling case. Even in situations where it may not maximize growth rates outright, its inclusion in poultry diet has been shown to meaningfully lower the overall cost of production, making it an attractive option for producers operating under tight economic margins (Canola council of Canada).

Analyses had already pointed in this direction, suggesting that canola meal could substitute for up to half of convention protein supplements in livestock rations without compromising animal performance, provided market pricing was favorable. This highlight that economic viability of canola meal is not fixed it is sensitive to market dynamics, and producers who track commodity prices closely stand to benefit the most from its strategic inclusion (Agriculture Canada. 1990) [2] . [40] . Supporting these finding, also reported a measurable reduction in diet cost as the proportion of soyabean meal replaced by canola meal increased, reinforcing that canola meal serves as economical protein alternative, the available evidence suggest that thoughtful incorporation of canola meal with attention to processing type, inclusion level and prevailing market prices can improve the economic resilience of commercial poultry operations (Moraes et al., 2015).

Conclusion

Canola meal presents a nutritionally credible and economically attractive alternative to soybean meal in layer hen diets, provided its inclusion is managed thoughtfully. Its favorable sulfur amino acid profile, micronutrient density and consistent cost advantage over soybean meal make it a legitimate candidate for partial substitution in commercial layer nutrition. The performance concerns documented in literature reduced egg weight, compromised digestibility are now largely attributable to crude protein based formulation practices rather than any fundamental deficiency of canola meal itself. Under modern digestible amino acid formulation frameworks, inclusion level of 15-20% paired with low antinutritional factor, consistently support productive performance egg quality and hen health without compromise. The performance of high producing modern laying strains under sustained canola meal inclusion, particularly in tropical production environment and heat stress, is insufficiently characterized. As canola meal breeding continues to push glucosinolates level lower and processing technologies improve energy availability, the practical ceiling for inclusion may shift upward. Until that evidence matures, a conservative but confident stand canola meal, correctly sourced and precisely formulated, is a sound, sustainable and costeffective partial replacement for soybean meal in commercial layer production.

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