L. S. Ellwood M.Sc.
The nutritional value of peas (Pisum
spp.) in human diets has been known for many years. In contrast,
there is a lack of nutrition information regarding the nutritional
value of feeding peas to livestock, particularly ruminants. Peas
contain a moderate amount of high quality protein and a high level
of starch. This makes peas a unique dual purpose feed, rich in
both energy and protein. Pea protein is rapidly degraded in the
rumen and the starch is slowly degraded. Therefore, the value
of peas differs depending on diet formulation, age of the animal
and processing (Marquardt and Bell 1988 {2053}). The purpose
of this section is to review the factors influencing the nutritional
value of peas in ruminant diets.
Pea Composition Relative to Ruminants
Pea seeds consist of a high quality protein with an average crude protein content between 20-25% DM (Lalles 1993 {580}, Monti 1983 {685}). Reichert and MacKenzie (1982 {690}) reported a considerable range (14-28.5% DM in Pisum sativum L. cv. Trapper) in protein in feed peas and reported that starch accounted for most of the difference in protein content while the remainder of variation was due to lipid, NDF, soluble sugars and ash. Composition of five pea varieties (table 2) was reported by Christensen et al. (1998). The wide variation in protein and starch was mainly due to the different varieties. Peas are characterized by a low ADF and NDF nitrogen content compared to other feed stuffs. Pea protein is highly soluble at over 70% of CP (Christensen et al. 1998; Mustafa et al. 1998; Kossen et al 1994 {572}; Walhain et al. 1992 {585}). Pea protein is characterized by a high rumen degradability and a low bypass protein value (22% NRC 1989; Mustafa et al. 1998).
The amino acid composition of peas is characterized by a high lysine and arginine content and a low methionine, cystine and tryptophan content (Leterme et al. 1990 {603}, Lalles 1993 {580}). In young growing preruminant calves, in which the limiting amino acids are the sulfur amino acids lysine, threonine and isoleucine (van Weerden and Huisman 1985 as cited by Lalles 1993 {580}) it was concluded with the addition of methionine calf requirements would be met.
Feed peas have a relatively variable high starch content (27-50% DM) making them a rich energy source for animals (Table 1) (Christensen et al. 1998). Starch is the main constituent in dehulled peas (Daveby et al. 1993 {576}). Synthesis of amylose and amylopectin, the two major components of starch, increase rapidly after the first third of seed dry matter is produced (Haeder 1989 as cited by Daveby et al. 1993, {576}). Wrinkled peas have greater amounts of amylose (60-90%) in comparison to smooth peas (30-45%) (Otto et al. 1997). Flatus-producing sugars are common in grain legumes but are least troublesome in peas (Bond and Smith 1988 {634}). The oligosaccharides (% dry matter) present in dry peas include raffinose (0.6%), stachyose (1.9%) and verbascose (2.2%) (Saini 1989 {632}).
| Table 1. Energy values of pea seeds (Pisum spp.) for cattle | |
|---|---|
| Energy Values | Dairy |
| TDN % | 87 |
| DE (Mcal/kg) | 3.84 |
| ME (Mcal/kg) | 3.42 |
| NEM (Mcal/kg) | 2.16 |
| NEG (Mcal/kg) | 1.48 |
| NEL (Mcal/kg) | 2.01 |
| Reference | NRC, Dairy Nutrient Requirements (1989) |
The neutral detergent fiber content of peas, which approximates the sum of hemicellulose, cellulose, and lignin present in the cell wall, was negatively correlated with the content of pea protein (Reichert and MacKenzie 1982 {690}). Because the majority of fiber exists in the form of hemicellulose and cellulose with very little lignin, the fiber content is considered highly digestible (Racz 1997 Feed Industry Guide).
| Table 2. Protein and carbohydrate composition of peas (DM)z | |||||
|---|---|---|---|---|---|
| Pea variety | |||||
| Scout | Express | Marrowfat | Polo M19 | Radley | |
| Ash % | 3.68 | 3.01 | 3.02 | 3.74 | 3.18 |
| Ether extract % | 1.97 | 1.12 | 1.30 | 2.09 | 1.04 |
| Crude protein % | 27.23 | 22.86 | 23.38 | 25.14 | 27.38 |
| SCP (% of CP) | 79.05 | 84.97 | 85.52 | 76.91 | 89.01 |
| NPN (% of SCP) | 12.88 | 7.40 | 18.49 | 9.77 | 19.24 |
| NDICP % (% of CP) | 0.51 | 2.41 | 2.19 | 0.63 | 1.51 |
| ADICP % (% of CP) | 0.40 | 0.57 | 0.36 | 0.63 | 0.25 |
| ADF % | 10.88 | 8.42 | 7.61 | 11.48 | 8.85 |
| NDF % | 19.44 | 17.95 | 15.50 | 20.35 | 16.17 |
| ADL (% of NDF) | 1.65 | 1.63 | 3.41 | 1.41 | 2.56 |
| Starch % | 27.21 | 49.62 | 46.40 | 32.21 | 43.60 |
| NSC % | 47.83 | 55.61 | 57.30 | 48.84 | 52.65 |
| Starch (% of NSC) | 56.89 | 89.23 | 80.98 | 65.95 | 82.81 |
zChristensen
et al. 1998. SCP=soluble crude protein, NPN=non-protien nitrogen,
NDICP=neutral detergent insoluble crude protein, ADICP=acid detergent
insoluble crude protein, ADF=acid detergent fiber, NDF=neutral
detergent fiber, ADL=acid detergent lignin, NSC=non-structual
carboydrates