Research Summaries: Canola and Peas in Livestock Diets

1. 0 Nutritional Assessment of Canola Meal

1.1 Amino Acid and Protein Digestibility

In general, amino acid digestibilities (Table 1) of canola meal are lower than SBM but rarely significantly (Sauer and Thacker, 1986 {1880}); (Imbeah and Sauer, 1991 {1804}). Older pigs, in particular utilize canola meal well (Moon et al. 1994 {1671}). Schone et al. (1992 {1713}) reported that ileal digestibility of protein in RSM diets was decreased due to fibre but that pigs responded to the additional fecal N excretion by lowering urinary N excretion, thus achieving the N balance of the animals fed on SBM.

Table 1 Apparent ileal digestibilities (%) of dry matter, protein and amino acids of canola meal
	CM Diet a	CM Diet	RSM	RSM	CM	RSM	CM	CM	CM	RSM 1b	RSM 2c
Methodology	T-Ce	T-C	IRAf	MNBTg	T-C	T-C	T-C	T-C	T-C	ICAd	ICA
							DIRh	DIih	REGj
Pig weight (kg)		38	35	35	25	25	40	40	40	40	40
Dry matter	65.6	66.4								82.6	80.9
Protein	66.5	66.0	66.8	65.8	62.9	52.7	66	62.5	64.3	66.2	70.7
Indispensable amino acids
Arginine	82.8	80.3	75.5	80.8	90.5	90.7	80.8	79.4	79.5	74.8	79.8
Histidine	81.7	77.4	76.1	84.8	43.5	43.8	80.0	77.4	78.7	77.6	76.6
Isoleucine	71.4	69.4	72.2	74.3	69.9	55.8	69.3	65.3		72.8	81.0
Leucine	73.6	72.3	75.5	74.5	72.3	62.2	70.8	67.7		76.7	77.1
Lysine	72.8	71.0	68.3	75.6	70.4	63.2	73.7	70.7	71.8	58.3	73.9
Methionine		79.8	81.9	87.7	89.3	81.5				77.5	83.4
Phenylalanine	73.8	68.4	86.4	84.3	50.3	73.6	70.8	37.9		72.8	65.9
Threonine	62.1	59.7	68.2	73.3	65.6	49.4	63.1	60.7		69.1	72.8
Tryptophan		63.1
Valine	69	67.0	69.1	73.0	71.9	53.1	67.5	63.8		69.5	76.4
Dispensable amino acids
Alanine	70.9	71.8	68.0	72.3	64.7	51.9	68.9	65.2	66.6	68.8	68.6
Asparic acid	66.4	65.6	67.9	72.5	68.6	70.3	64.1	61.2		68.7	75.6
Cysteine		62.8
Glutamic acid	81.4	81.1	81.6	79.9	76.2	76.1	80.3	75.8	79.6	82.5	84.6
Glycine	63.1	60.7	69.1	74.4	68.4	59.7	63.4	63.7	62.0	67.6	73.9
Proline		61.7	68.8	71.2	55.1	26.8				63.6	67.7
Serine	69.1	73.0	70.7	73.0	65.6	61.8	65.0	62.0		78.2	76.2
Tyrosine	69.6	71.9	80.0	82.3	62.1	70.4	66.0	64.5	64.5	55.9	69.0
Reference {}	1804	1829	1622	1622	1671	1671	1621	1621	1621	1694	1694
Table	3	4	5	5	5	5	9	9	9	4	4

^a corn starch based diet ^b Screw pressed RSM ^c Screw pressed RSM NH3;

^d Ileal caecal anastomosis; ^e Simple T-cannula; ^fIleo-rectal anastomosis; ^gMobile nylon nag technique

^h Direct; ⁱ Difference; ^j Regression

Many explanations for the lower digestibility of CM (canola meal) compared to SBM have been proposed, centering on fibre, unpalatable tannins, lignins, pectins, cellulose (de Lange et al. 1990 {1829}) and glucosinolates. Fibre alone induces a faster passage rate which reduces the opportunity for digestion to some degree (Imbeah and Sauer 1991 {1804}). Lignin occuring mostly in the hulls may decrease protein digestibility by hydrophobic binding of amino acids. RSM (rapeseed meal) hulls contain significant non-lignin non-extractable polyphenyls (tannin type) that may also interfere with digestion. Pectins, by forming a gel matrix, may restrict proteolytic access. Fibre may also increase endogenous N loss through abrasive effects or binding endogenous protein (Mitaru et al. 1984 {1904}; Sauer and Thacker 1986 {1880}; de Lange et al. 1990 {1829}; Imbeah and Sauer 1991 {1804}). Grala et al. (1997 {1266}) found low apparent and true ileal digestibilites resulted from a high flow of both endogenous N (nitrogen) and undigested dietary N in young pigs (12-25kg) fed RSM.

Various methodologies (mobile nylon bag, ileocaecal re-entrant cannulae, ileal rectal anastomosis) appear to have little effect on CM digestibility values (Yin et al. 1993 {1697}). Digestibility values were similar when determined using direct, difference and regression methods in 40-56kg pigs (Fan and Sauer 1995 {1621}). Using the ¹⁵N-isotope dilution technique, Lange et al. (1990 {1829}) were able to differentiate actual endogenous protein from non-digested dietary protein, thus real protein digestibilities could be determined directly(Table 2). Only slight differences were detected between this method and true ileal digestibilities which support with findings that endogenous loss as pancreatic protein or proteolytic secretions did not differ significantly between CM or other ingredients. Similarly, Sauer et al. (1983 {1921}), Imbeah et al. (1988 {1866}) and Pohland et al. (1993 {1704}) reported daily secretion of pancreatic juice, pH, total and precipatable N and enzymes were not significantly affected (P>0.05) whether the diet contained 445g kg^-1 canola meal, 355g kg^-1 SBM or 939g kg^-1 wheat or barley. They did find that most amino acid concentrations in the pancreatic secretion were lowest when canola meal was fed. In another study, although enzyme volume remained similar, slight differences were found comparing rapeseed and casein digestibility in vitro. Total nitrogen and amino acid digestion was not significantly different after 24 hours, yet canola meal digestion was significantly slower during the first 12 hours. This was attributed to the possibility of more complex and compact structure of canola meal globulins, which resist water penetration and digestion (Valette et al. 1993 {1722}). Interestingly, Valette et al. (1992 {1756}) found in 15 kg pigs that the activities of trypsin, chymotrypsin and carboxypeptidase secreted in pancreatic juice were increased on the rapeseed diet during the post prandial periods but that elastase and carboxypeptidase A were decreased during the nocturnal period in this diet relative to pigs fed casein. All in all it is concluded that the ileal digestibility of CM is hindered by inherent factors rather than excess endogenous secretions.

Table 2 True and real ileal digestibilities of canola meal
	CM	RSM	CM Diet	CM Diet
Methodology	Simple T-Cannula	Simple T-Cannula	True	Real
	25 kg	25 kg	38 kg	38 kg
Dry matter
Protein	88.7	88.3	73.5	84.1
Indispensable amino acids
Arginine	90.5	96.0	84.4	90.2
Histidine	58.5	56.3	81.3	86.7
Isoleucine	82.0	77.9	75.0	82.9
Leucine	80.0	79.1	77.4	84.5
Lysine	65.2	56.2	76.4	84.0
Methionine	92.0	88.8	84.8	91.8
Phenylalanine	84.7	88.8	74.9	83.9
Threonine	79.9	76.3	71.1	87.2
Tryptophan			68.8	76.9
Valine	79.5	77.9	74.1	84.1
Dispensable amino acids
Alanine	72.7	73.9	80.3	92.3
Asparic acid	80.2	84.7	73.8	85.3
Cysteine			71.4	83.5
Glutamic acid	85.9	89.1	85.2	91.0
Glycine	80.2	80.7	70.8	85.0
Proline	78.8	73.4	68.4	77.9
Serine	79.4	82.7	81.1	92.3
Tyrosine	82.4	79.4	83.4	99.7
Reference	{1671}	{1671}	{1829}	{1829}
Table	5	5	6	7

As with other ingredients, digestibilities of canola meal determined in single ingredient experiments are considered to accurately predict apparent ileal digestible amino acid supply within the diet (Sauer et al. 1983 {1921}; Fan et al. 1993 {1739}). Exceptions to this were found by Bell and Keith (1989 {1837}), where crude protein digestibility of CM was lower when paired with hulless barley (82%) as compared to wheat (89 %) (which may reflect interference by the high -glucans found in early hulless barley varieties - editor's note). As CM level was increased in the diet (0, 150 or 300g kg^-1) CP digestibility increased, whether the basal diet was barley, wheat or hulless barley. Apparent ileal digestibility of both lysine and leucine was higher than calculated in typical barley-canola meal diets of western Canada. The difference was interpreted as a possible associative effect, yet despite statistical significance (P<0.05), the effect is considered inconsequential in terms of practical importance (Imbeah et al. 1988 {1866}). Nonetheless the relationship of any one amino acid to lysine remains relatively constant when canola meal was included in the diet, supporting the position that CM provides an excellent complementary source of amino acids (Hansen 1992 {1769}).

Recent data indicated that the digestibility of canola meal may be reduced by overprocessing during oil extraction (Siljander-Rasi et al. 1996 {1612}). Grala et al. (1994 {1662}) found as processing temperature increased from 90-100^oC total lysine declined by 20% while available lysine decreased by 43% in double low glucosinolate rapeseed. Ileal digestibility of lysine declined to the largest extent, (66.8 to 49.6%), with other amino acids affected to a lesser degree. Heat damage may have rendered lysine undetectable during the assay procedure, or alternatively, the lysine may have been bound in a Maillard reaction preventing liberation during digestion. Interestingly in a second plant toasting rapeseed meal to 120^oC resulted in meal similar to that toasted to only 90^oC in the first plant. The difference was the addition of moisture prior to processing in the first plant, which exacerbates Maillard reactions. Moisture and duration of heat may modify the effect of temperature and influence the protein quality resulting in both decreased amino acid content and digestibility. These effects are important in canola due to its comparatively high level of free sugars (Campbell and Slominski 1991 {2060}). Another factor found to negatively affect canola meal quality is the quantity of screenings or dockage contained in the meal. Protein and energy digestibility of canola meal were depressed with the addition of screenings significantly by the time 80g kg^-1 screenings were included (Bell and Shires 1980 {1935}).