1. Nutritional Assessment of Peas
1.1 Amino Acid and Protein Digestibility of Peas
In the past decade swine nutrition has undergone significant evolution. Focus has shifted from total content of protein to availability of individual amino acids at the ileal level. These changes have allowed for more accurate diet formulation resulting in less waste and better animal performance. As with most natural unprocessed ingredients pea composition varies. Typical compositional values can be found in Table N-1.
In peas, protein is laid down early in seed development (Daveby et al. 1993 {1325}) and the amino acid composition is dependent upon the proportion of the three major soluble protein fractions (legumins, vicilins and albumins) found in the seed. Pea protein solubility is very dependent upon pH, in comparison to wheat, soyabean meal (SBM), meat and bone meal or sunflower meal. With peas, 80% of the protein is solubilized at pH 9 and less than 30% at pH 3. At pH 4.5, pea albumins resist precipitation (Le Guen et al. 1993 {1340}). Vicilin even unheated is sufficiently degraded by pepsin in the stomach to allow effective breakdown by trypsin and chymotrypsin in the intestine (Neilsen et al. 1988 {1424}. This indicates that when peas comprise the major dietary protein, they are not effectively solubilized by gastric juices containing pepsin. As the protein moves towards the small intestine, pH rises and more proteins are degraded (Cone 1993 {1349}).
Peas are characterized by high ileal digestibility
of lysine and methionine and a comparatively low digestibility
of cysteine and tryptophan (Table 1) (Leterme et al. 1990
{1389}). The availability of lysine in peas (Australian cultivar
Early Dunn ; 20-45kg pigs) was 0.93 as determined using a slope
ratio assay on lean ham tissue, while for SBM the value was only
0.89 (Batterham et al. 1984 {1457}). Ileal amino acid
digestibilities (35 kg pigs) of several Canadian varieties (Titan,
Stegholdt, Tipu, Miranda, Princess and Victoria; produced in Alberta)
indicated significantly different digestibilities of amino acids
with lysine and arginine being consistently high and cysteine,
threonine and glycine relatively low (Fan and Sauer 1994 {1292}).
| Table 1 Apparent ileal digestibilities (%) of dry matter, protein and amino acids of peas | |||||||||||||||
| PeaVariety | Solara f | Solara | Radley J | Radley | Radley | Solara | H 61 g | Laser h | Frijaune i | ||||||
| Methodology | IRAa | T-Cb | T-Cb | T-Cb | T-Cb | ||||||||||
| Dirc | Difd | Rege | |||||||||||||
| Pig weight (kg) | 50 | 50 | 35 | 35 | 35 | 40-60 | 40-60 | 40-60 | 40-60 | ||||||
| Apparent Digestibilities | |||||||||||||||
| Dry matter | |||||||||||||||
| Protein | 69.9 | 73.6 | 75.91.2 | 75.11.2 | 80.2 | 69.6 | 60.9 | 62.0 | |||||||
| Indispensable amino acids | |||||||||||||||
| Arginine | 82.0 | 84.6 | 89.80.81 | 90.90.57 | 89.40.67 | ||||||||||
| Histidine | 74.9 | 78.4 | 80.11.08 | 81.31.12 | |||||||||||
| Isoleucine | 72.7 | 74.4 | 75.21.05 | 76.92.13 | 74.91.36 | ||||||||||
| Leucine | 72.4 | 74.9 | 74.91.38 | 77.01.68 | 74.81.27 | ||||||||||
| Lysine | 75.6 | 79.5 | 83.51.20 | 83.80.70 | 82.50.85 | 82.8 | 76.3 | 66.5 | 65.9 | ||||||
| Methionine | 70.9 | 78.1 | 66.31.43 | 65.31.58 | 64.91.67 | 80.7 | 75.2 | 69.6 | 68.4 | ||||||
| Phenylalanine | 72.6 | 75.6 | 76.11.55 | 78.51.23 | 76.21.04 | ||||||||||
| Threonine | 60.6 | 65.5 | 68.01.8 | 69.81.54 | 76.5 | 68.7 | 60.2 | 60.0 | |||||||
| Tryptophan | 65.2 | 58.3 | 69.7 | 62.5 | 46.6 | 50.1 | |||||||||
| Valine | 69.1 | 71.2 | 72.81.29 | 74.51.82 | |||||||||||
| Methionine + Cysteine | 76.3 | 68.7 | 62.0 | 60.5 | |||||||||||
| Dispensable amino acids | |||||||||||||||
| Alanine | 63.3 | 67.9 | 71.01.45 | 70.51.88 | |||||||||||
| Asparic acid | 72.0 | 72.8 | 78.10.85 | 79.61.45 | 77.61.25 | ||||||||||
| Cysteine | 61.7 | 63.6 | 57.31.27 | 56.31.91 | 56.51.39 | ||||||||||
| Glutamic acid | 76.0 | 79.0 | 84.10.88 | 88.41.23 | 83.90.83 | ||||||||||
| Glycine | 61.9 | 55.4 | 67.41.67 | 64.73.28 | |||||||||||
| Proline | 59.9 | 69.5 | |||||||||||||
| Serine | 66.5 | 70.2 | 72.71.21 | 72.10.65 | 71.91.00 | ||||||||||
| Tyrosine | 73.5 | 75.6 | 69.51.91 | 70.21.50 | 69.01.35 | ||||||||||
| Reference | {1389} | {1389} | {1275} | {1275} | {1275} | {1353} | {1353} | {1353} | {1353} | ||||||
| Table | 3 | 3 | 6 | 6 | 6 | 3 | 3 | 3 | 3 | ||||||
a Ileo-rectal Anastomosis;
b Simple T-Cannula; c Direct; d
Difference; e Regression ;
f Spring variety
most commonly grown in France; g Winter variety with
a low TIA; h Winter variety medium TIA;
iWinter variety most
commonly grown in France; J Spring variety grown
in Canada
| Table 1 (continued) Apparent ileal digestibilities (%) of dry matter, protein and amino acids of peas | ||||||||
| Variety | Dundale K | Dundale | Titan J | Stegholdt J | Tipu J | Miranda J | Princess J | Victoria J |
| Methodology | IRA | T-C | T-C | T-C | T-C | T-C | T-C | T-C |
| Pig weight (kg) | 45 | 45 | 35 | 35 | 35 | 35 | 35 | 35 |
| Dry matter | 81 | 74 | ||||||
| Protein | 66 | 60 | 75.6 | 70.1 | 70.9 | 74.8 | 74.4 | 75.9 |
| Indispensable amino acids | ||||||||
| Arginine | 75 | 79 | 89.0 | 82.2 | 81.3 | 84.8 | 85.3 | 85.6 |
| Histidine | 71 | 69 | 74.7 | 72.5 | 69.6 | 74.7 | 74.1 | 74.8 |
| Isoleucine | 70 | 62 | 77.0 | 73.9 | 73.3 | 77.7 | 76.8 | 77.9 |
| Leucine | 67 | 55 | 77.4 | 75.8 | 74.0 | 78.7 | 77.8 | 78.6 |
| Lysine | 76 | 75 | 83.8 | 81.0 | 80.3 | 82.9 | 83.4 | 84.0 |
| Methionine | 72.3 | 67.8 | 72.6 | 75.1 | 72.6 | 71.9 | ||
| Phenylalanine | 72 | 68 | 73.3 | 70.6 | 68.0 | 73.9 | 74.6 | 73.0 |
| Threonine | 64 | 43 | 65.2 | 59.6 | 61.1 | 67.4 | 65.8 | 66.3 |
| Tryptophan | ||||||||
| Valine | 67 | 57 | 73.3 | 69.0 | 67.8 | 72.7 | 73.1 | 73.5 |
| Cystine | 62.2 | 58.5 | 60.8 | 65.5 | 62.9 | 65.9 | ||
| Tyrosine | 69 | 59 | 74.6 | 66.1 | 66.2 | 66.8 | 71.4 | 71.0 |
| Methionine + Cysteine | 66.3 | 62.1 | 65.5 | 69.4 | 66.9 | 67.5 | ||
| Dispensable amino acids | ||||||||
| Alanine | 66 | .51 | 72.4 | 66.9 | 68.1 | 72.4 | 71.4 | 71.9 |
| Asparic acid | 71 | .68 | 79.9 | 76.6 | 73.9 | 78.1 | 79.4 | 79.5 |
| Cysteine | ||||||||
| Glutamic acid | 75 | .75 | 82.7 | 80.5 | 77.7 | 82.3 | 82.9 | 82.8 |
| Glycine | 38 | .40 | 61.6 | 59.8 | 57.8 | 66.8 | 64.6 | 65.4 |
| Proline | 48 | .35 | ||||||
| Serine | 66 | .55 | 72.9 | 69.4 | 68.7 | 73.4 | 72.6 | 74.5 |
| Tyrosine | ||||||||
| Reference | 1313 | 1313 | 1292 | 1292 | 1292 | 1292 | 1292 | 1292 |
| Table | 7 | 6 | 4 | 4 | 4 | 4 | 4 | 4 |
a Ileo-rectal Anastomosis; b Simple T-Cannula; c Direct; d Difference; e Regression ;
f Spring variety most commonly grown in France; g Winter variety with a low TIA; h Winter variety medium TIA;
i Winter variety
most commonly grown in France; J Spring variety grown
in Canada; k variety grown in Australia
There was a tendency to increased true ileal digestibility with increasing protein content in peas (Buraczewska et al. 1989 {1413}). In very young pigs (7.5 - 8.5 kg), true ileal digestibility was very high (0.951 and 0.929) indicating that the protein of raw peas was almost completely digested in the small intestine (Huisman et al. 1992 {1365}). Others, (Le Guen et al. 1995 {1286}) found that with piglets (10-15 kg body weight) fed diets containing raw peas, 20-30% of the amino acids present in the ileal digesta originated from undigested pea proteins, most probably the albumin fraction. This resulted in low apparent ileal digestibilities for tryptophan, cysteine and methionine which are concentrated in albumins. Leterme et al. (1990 {1389}) concluded that the low content of these amino acids in pea proteins, in conjunction with lower digestibility, may explain the response variability observed during a great number of trials when the rations were based on only amino acid composition emphasizing the importance of balancing diets on an ileal digestibility basis. True ileal digestibility values are found in Table 2.
Implications of the high ileal digestibility of peas are that total crude protein content of the diet can be lowered when using peas with the addition of supplemental amino acids, resulting in lower nitrogen excretion - less pollution - less metabolic cost while maintaining pig growth performance (Gatel and Grosjean 1992 {1354}).
| Table 2 True ileal digestibilities (%) of dry matter, protein and amino acids of peas | ||||||||
| Variety | . | . | Winter | |||||
| Belinda 1 d | Kaliski d | Mige d | Belinda 2d | Opal d | Matmal e | Solara c | Solara c | |
| Methodology | T-Cb | T-Cb | T-Cb | T-Cb | T-Cb | T-Cb | IRAa | T-Cb |
| Pig weight (kg) | 40 | 40 | 40 | 40 | 40 | 40 | 50 | 50 |
| Dry matter | ||||||||
| Protein | 83 | 81 | 76 | 73 | 72 | 66 | 78 | 80 |
| Indispensable amino acids | ||||||||
| Arginine | 85.8 | 87.9 | ||||||
| Histidine | 81.1 | 83.3 | ||||||
| Isoleucine | 78.4 | 79.2 | ||||||
| Leucine | 85 | 81 | 74 | 74 | 73 | 78 | 78.7 | 80.0 |
| Lysine | 85 | 86 | 79 | 76 | 76 | 72 | 80.2 | 83.6 |
| Methionine | 79 | 80 | 72 | 65 | 59 | 58 | 77.8 | 83.3 |
| Phenylalanine | 78.1 | 80.4 | ||||||
| Threonine | 84 | 83 | 74 | 73 | 69 | 65 | 73.0 | 76.1 |
| Tryptophan | 77 | 78 | 68 | 67 | 57 | 58 | 77.9 | 68.9 |
| Valine | 76.6 | 77.7 | ||||||
| Cysteine | 68 | 69 | 59 | 61 | 44 | 48 | ||
| Tyrosine | ||||||||
| Methionine + Cysteine | ||||||||
| Dispensable amino acids | ||||||||
| Alanine | 72.4 | 75.3 | ||||||
| Asparic acid | 77.5 | 77.4 | ||||||
| Cysteine | 66.7 | 67.9 | ||||||
| Glutamic acid | 80.4 | 82.5 | ||||||
| Glycine | 75.5 | 76.1 | ||||||
| Proline | 70.5 | 76.9 | ||||||
| Serine | 74.4 | 76.7 | ||||||
| Tyrosine | 77.8 | 79.0 | ||||||
| Reference | 1413 | 1413 | 1413 | 1413 | 1413 | 1413 | 1389 | 1389 |
| Table | 3 | 3 | 3 | 3 | 3 | 3 | 5 | 5 |
a Ileo-rectal Anastomosis; b Simple T-Cannula;
c Spring variety
most commonly grown in France; d white flowered
Polish variety; e colored flower Polish variety
Explanations for the lower digestibility of certain amino acids have included enzyme specificity during hydrolysis where lysine and arginine are released first and threonine last or endogenous secretions which tend to have high concentrations of threonine and glycine (Fan and Sauer 1994 {1292}). Buraczewska et al. (1989 {1413}) found that the higher tannin contents in dark as compared to white flowered peas (7.1 versus 1.6mg g-1 dry matter (DM) respectively) negatively affect nitrogen digestion. Significantly different ileal digestibilities of crude protein and amino acids found between cultivars (Buraczewska et al. 1989 {1413}; Jondreville et al. 1992 {1353}; Fan et al. 1994 {1292}); were attributed to possible to fluctuations in trypsin inhibitor activity (TIA), variation in fibre levels, varying starch - protein matrices which offer greater resistance to digestive enzymes and/or environmental influences.
Fibre has been shown to increase pancreatic secretions, the number of goblet cells and mucus secretion in the small intestine. Leterme et al. (1996 {1269}) suggested that the high water holding capacity of the pea inner fibres increased ileal flow of both endogenous and bacterial N compounds, thus reducing retention time of the digesta. Endogenous secretions may be trapped in the viscous components preventing reabsorption. Leterme et al. (1990 {1389}) speculated that alpha galactosides (approximately 5%) and pea cell walls comprised of pectins reduced ileal digestibility of protein. Attempts to substantiate these hypothesis by adding total pea carbohydrates including starch, -galactosides and hulls back to a pea protein isolate did not affect nitrogen apparent ileal digestibility. It is possible that in the process of isolating the major pea fractions, enzyme accessibility to proteins or carbohydrates may actually have been improved by disrupting the physical structure of the cells or bonding between constituents. This has been found for chickens and the same explanation may hold true for piglets (Huisman et al. 1990 as cited by Le Guen et al. 1993 {1340})
Excessive heating has deleterious effects on protein availability. Native (unheated) vicilin was extremely susceptible to trypsin digestion yet in vitro digestibility of vicilin slowed to half previously observed after heating (99oC, 15 minutes). A high degree of structural integrity was maintained indicating strong hydrophobic interactions in stabilizing the protein structures which reduces susceptibility to digestion (Deshpande and Damodaran 1989 {1418}). A series of four papers examined the effects of heat treatment of peas on lysine digestibility, availability and utilization. As heating increased from 110oC to 165oC (15 minutes) there was little change in lysine apparent ileal digestibility over raw peas (0.79-0.56) (Barneveld and Batterham 1994 {1313}). However lysine availability declined from 0.96 to 0.47, resulting in poorer growth performance. The implication was that although the amino acid was absorbed it was poorly utilized after heat treatment (Barneveld and Batterham 1994 {1315}; Barneveld and Batterham 1994 {1314}). A large proportion of non-utilizable amino acids in heated field peas may be excreted from the pig via the urine in the form of a protein. Differences in pea cultivars were noted suggesting that some cultivars were more susceptible to heat damage than others (Barneveld and Batterham 1995 {1291}). (Heating for fifteen minutes is far longer than most practical feed applications- Editor's note.)
Extruding pea protein appears more favourable. Extruding
starter diets (150oC, 15 seconds) containing either
45% winter or spring peas, significantly improved apparent ileal
digestibility of dry matter and nitrogen for the winter peas,
with no effect on spring varieties. The same was true for nitrogen
retention which was significantly higher for spring than winter
peas, with extrusion significantly improving winter peas and no
effect on spring peas. It is suggested that the destruction of
antinutritional factors (ANF) by extrusion was responsible for
the significant improvements (Freire et al. 1991 {1377}).