The Feeding Value of Peas as Forage, Silage, Straw and Screenings
Pea seeds generally provide more useful cattle feed than whole-plant silage. Whole plants of peas cv. Consort were harvested when DM content was 28.1%. At this time over 50% of the silage was seeds. Silage composition was 159 g crude protein, 200 g crude fiber and 566 g nitrogen free extract/kg (DM). The ensilability of whole-plant peas was only moderate because of high acetic acid and ethanol levels. The organic matter digestibility was 75% compared to 89% for the seeds. Energy values were 6.3 MJ net energy for lactation and 6.4 MJ net energy for growth/kg DM for the silage and 8.0 and 8.8 MJ, respectively, for seeds. The energy value and absorbable protein content of whole plant pea silage is comparable to a medium quality maize silage (Daccord and Arrigo 1994 {571}).
Pea forage or silage, industrial pea by-products and crop residues can be used in place of the more conventional protein supplements for ruminants and have been successfully fed to ruminants (Devyatkin and Kovalev 1987 {647}; Erdinc et al. 1985 {671}). Using peas alone or in combination with other grains or forages gives farmers an alternative to alfalfa and corn silage (Jaster et al. 1985 {667}). Pea silage alone or in combination with barley and oats was examined for its nutritive value for dairy heifers. Holstein heifers offered pea silage had greater DM consumption (2.6% of body weight) and higher DM digestibility (64.8%) compared to other silages. Other studies have reported higher voluntary intake by dairy cows for whole-crop silages made from peas compared to barley silage. These findings were confirmed by liveweight gains and milk yields, which were highest when peas were included in the silage (Skovborg et al. 1987 {655}). In contrast a barley/pea silage led to a slightly lower DM intake, lower milk protein, lower fat content and reduced weight gain compared to the control. The negative performance was attributed to a high rumen solubility of pea protein resulting in low intestinal protein absorption (Jans 1993 {582}).
A mixture of field peas at the flowering stage (Pisum sativum L.) (67%) and triticale (33% on a DM basis) was harvested as silage and fed to midlactation Holstein cows for a 64-d lactation trial. Diets were formulated to contain 65% forage:35% concentrate (DM basis). The control ration contained 33.6% alfalfa silage, 33.0% corn silage, 16.6% ground corn, 6.2% soybean meal, 9.3% dried distillers grains, minerals and vitamins. The pea/triticale silage contained approximately three times the amount of acetic acid compared to typical alfalfa silage (Messman et al. 1992 {584}). Dry matter intake (22.6 kg/d) and milk yield (25.2 kg/d) for the pea/triticale silage did not differ from the control. Cows fed pea/triticale silage produced higher levels of fat corrected milk (27.3 vs. 22.1 kg/d; P < 0.03) because the milk fat percentage was substantially higher (4.59 vs. 3.35%; P < 0.01) (Messman et al. 1992 {584}). Energy use by both sets of cows was equivalent, but the partitioning of energy between body stores (13 vs. 6% for control and pea/triticale treatment, respectively) and milk production (53 vs. 63% for the control and pea/triticale treatments, respectively) was different. Cows fed the control diet gained more (P < 0.01) body weight than cows fed the pea/triticale silage. Cows consuming the pea/triticale diet may have been able to divert more energy into milk fat and less into body fat because the end products of digestion were more lipogenic than glycogenic (Messman et al. 1992 {584}).
A pea oat silage, fed to Sychevka bulls, ensiled at 70-80% moisture contained 13.6% protein, 4.4% and 30.5% fiber, 41.6 N-free extract (DM) and 20g/kg of digestible protein. When pea oat silage was substituted for maize silage the average daily gain, feed/gain ration and feed intake were similar (Epifanov et al. 1986 {662}). Pea-barley silage and pea haylage were compare to maize silage when fed to 14 months old Red Steppe bulls weighing 300 kg. Average daily gain, digestibility of DM, protein, fat, fiber, N-free extract and dressing percentage were similar between roughages (Devyatkin and Kovalev 1987 {647}).
Forages generally contribute 40 to 50% of the DM in dairy rations (Jaster et al. 1985 {667}; Messman et al. 1992 {584}) and crude protein is usually the main criteria used to judge forage (Hafley et al. 1987 {}). Stage of maturity at harvest is the most important factor influencing the composition and nutritive value of forage (McDonald et al. 1981 as cited by Jaster et al. 1985 {667}). The cell wall and crude protein concentrations of cool season forages including barley/pea, pea and oat/pea silages were reversed when harvest was delayed by 14 days (Jaster et al. 1985 {667}). Oat/pea forage DM increased by 21.1% and crude protein decreased from 20.0% to 13.0%. Winter pea (Pisum arevense, cv. Austrian) crude protein decreased 31.1% between March 29 and May 5 and an additional 28.4% decrease occurred between May and June due to advancing maturity (Hafley et al. 1987 {}). The barley/pea forage acid detergent fiber content increased by 9.4% and acid detergent lignin doubled. As a plant grows, the need for structural tissue increases. Consequently, acid detergent fiber, neutral detergent fiber and acid detergent lignin will increase with a 14-d harvest delay (Jaster et al. 1985 {667}). Pea haylage was found to have a higher feed value than oat haylage (Yarmots 1986 {656}).
Pea meal developed from the whole plant had a crude fiber content of 23.9% and a neutral detergent fiber value of 51.5% (DM). The digestibility of crude fiber was 26% and neutral detergent fiber was 44% in a diet fed to feeder cattle weighing 250 kg. Hemicellulose was significantly more digestible than either cellulose or lignin (Lipiec et al. 1988 {637}).
An alternative approach to increasing the use of structural carbohydrates is supplementing with microbial additives that digest high fiber residue feeds such as pea/bean hay (Mpofu and Ndlovu 1994 {573}). Rumen fungi have cellulolytic and hemicellulolytic activities and white rot fungi have the ability to decompose lignin or lignocellulose with a minimum amount of hemicellulose degradation (Mpofu and Ndlovu 1994 {573}). Zadrazil (1976 as cited by Mpofu and Ndlovu 1994 {573}) discovered that yeasts act as secondary lignin and lignocellulosic degraders and use the simple metabolic products that are produced. An in vitro study reported that supplementing pea/bean hay with Saccharomyces cerevisiae (yeast) and Armillaria heimii (white rot fungi) increased (P < 0.05) neutral detergent fiber degradability of pea/bean hay by 50% (Mpofu and Ndlovu 1994 {573}).
Pea straw is a good feed alternative in beef diets and has a higher feed value than wheat straw. Pea straw was reported to contain 69.5% NDF, 1.4% NDF Ash, 54.1% ADF, 15.4% hemicellulose, 42.4% cellulose, 11.6% lignin and 5.0% ash (Lee and Pearce 1984 {677}). Pea straw contained the highest proportion of lignin compared to barley, oat straw, ryegrass and lucerne hay after grinding and had the largest particle size (Lee and Pearce 1984 {677}). Pea straw was reported to contain 6.4% protein. 44-46.0% TDN, 0.60% Ca and 0.19% P (Vern Racz, Prairie Feed Resource Centre). Pea straw contains more protein and TDN than wheat straw. As long as there is no mold present the digestibility and acceptance of pea straw is high (Vern Racz, Prairie Feed Resource Centre).
Although scientific research has been
limited pea screenings are said to contain 20.0% protein, 75.5%
TDN, 0.11% Ca and 0.42% P, are highly digestible and palatable
and can compete with protein supplements in ruminant rations (Vern
Racz, Prairie Feed Resource Center).
Peas provide an array of diverse feeds
that can be used in ruminant diets. Peas are palatable, highly
digestible and can provide the sole protein source for most ruminants.
For highly productive animals the diet needs to balanced for
bypass protein. Extrusion increases the nutritional value of
peas by increasing ruminal bypass protein and gelatinizing the
starch. Much research is warranted to establish the protein and
starch degradability of raw and extruded peas, and to relate these
findings to production parameters.
Mustafa, A. F. 1998. unpublished results.
Christensen et al. 1988. Presentation at the Western Nutrition Conference 1988
Conference. Saskatoon, SK.
Racz, V. 1988. Industry report.