Pea forages are generally rich in protein though less so than other temperate forage legumes such as alfalfa and clover. These forages are also highly variable: forage type, variety, age at harvest and mode of preservation all have a great influence and it is important to assess the protein content of the forage before feeding it to livestock (Leclerc, 2003). One drawback of pea crops is that its protein is highly degradable in the rumen (Mustafa et al., 2000; Wilkins et al., 2000).
Cattle and other ruminants can graze pea stands, provided that the usual practices concerning the grazing of pure legume pastures are followed. Animals should not graze peas permanently and for too long each day (maximum 2.5 to 3 hours). Besides, their previous diet should be rich in energy or at least poor in protein. Crude protein in peas is highest at flowering (Brunschwig, 2003b). Pea pasture can be grazed by fattening lambs when the crop has completed its growth and dried out (Göhl, 1982).
Whole-crop pea hay contains 15-20% DM protein, 38-56% DM NDF, 32-39% ADF and about 5% ADL, depending on the stage of maturity. Observed OM digestibility is in the 60-65% range (Neumark, 1970; Hadjipanayiotou et al., 1987; Hayashi et al., 2007). Starch content is extremely variable (5-25% DM), depending on seed maturity (Borreani et al., 2007). Pea hay protein is highly degradable, with an effective degradability that decreases between the bud stage (96%) and the pod formation stage (88%) (Iliev et al., 2002).
There is scarce information about the use of pea hay in ruminants. In an experiment with buffaloes in Nepal, pea hay offered at 1% BW as a supplement to a commercial concentrate, up to a 5:3 hay:concentrate ratio, increased body weight, daily gain, DM intake, milk production and milk fat yield (Hayashi et al., 2007).
Pea silage is considered to be an excellent feed for ruminants, though it has a strong odour (Göhl, 1982). Its nutritive value depends firstly on the pea variety: semi-leafless, short, stiff-stemmed varieties, low in condensed tannins and rich in protein are recommended (Rondahl, 2004). The nutritive value also depends on the stage of maturity of the pea (Cavallarin et al., 2006). At the end of flowering, pea silage has a low starch content (5% DM) and a high OM digestibility (74%) (Børsting et al., 2002). Soluble protein content of pea silage is higher than that of soybean silage, but it is the reverse for neutral (NDICP) and acid (ADICP) detergent insoluble protein levels. Pea silage and soybean silage have a similar rumen degradability of DM (average 69%), crude protein (83%) and NDF (average 35%) (Mustafa et al., 2003).
Pea silage has been used as a feed for dairy cows with variable results. In cows fed rations containing 50:50 forage:concentrate, pea silage, barley silage and alfalfa silage gave similar dry matter intakes and milk yields. Milk composition was similar for cows fed pea or barley silage. Cows fed pea silage produced milk with a higher fat and a lower protein percentage than those fed alfalfa silage. It was concluded that pea silage can replace barley or alfalfa silage as a forage source for dairy cows in early lactation (Mustafa et al., 2000). When high or low tannin forage pea silages replaced approximately 1.1 kg/d of soybean meal in the diet of mid-late lactation dairy cows, animal performance was unaffected, but N efficiency for milk production was decreased (Sinclair et al., 2009). Less positive results were found when feeding pea silage (67% of diet DM) harvested with immature seeds to dairy cows in mid-lactation: this led to a lower DM intake, milk yield and milk protein yield in comparison to perennial ryegrass silage made with a comparable crude protein content (Børsting et al., 2002).
There is scarce data about the use of pea silage for sheep. In one experiment, lambs offered forage pea silage had extremely low live-weight gains during the first 3 weeks, and the trial had to be cancelled. This problem may have been due to mould contamination of the original crop (Marley et al., 2007).
Pea-grass silage may offer a more efficient nutrient utilization due to a possible synchronization of the supply of readily fermentable energy and nitrogen in the rumen (Salawu et al., 2002). Bi-crop silages are ingested at higher levels than grass silages and can save part of the concentrate. They increase N retention and microbial protein synthesis (Adesogan et al., 2004; Rondahl et al., 2007; Sinclair et al., 2009).
Pea straw is the most common type of pea forage. Its protein content is variable: values in the 5-10% DM range (Leclerc, 2003) and in the 10-15% DM range have been reported. The NDF content is about 53-63% DM (Borreani et al., 2007). It is also rich in minerals (7-12% DM), notably calcium (1.5-2%) (Leclerc, 2003). With a higher protein content and less fibre, pea straw has a higher nutritive value than that of cereal straws. Its quality is intermediate between a cereal straw and a good grass hay (Leclerc, 2003; Ellwood, 2004; Mould et al., 2001).
The palatability of pea straw is good but depends on the harvesting and storage conditions (Leclerc, 2003). In particular, it should be harvested when dry to prevent moulding, which has a detrimental effect on its digestibility and acceptance (Ellwood, 2004). Harvesting should occur immediately after threshing to avoid the accumulation of dirt (Leclerc, 2003). Pea straw is ingested at higher levels (expressed on a body weight basis) by small ruminants (sheep and goats) than by large ones (cattle and buffaloes) (Bachchu et al., 1994).
In temperate regions, pea straw is suitable for livestock that have low nutritional requirements, such as suckling cows and animals with a moderate growth. Lactating ewes can be given 0.5-1 kg/d, lambs 0.5 kg/d and goats 1-2 kg/d. For cattle, it is roughly equivalent to a low quality grass hay (Leclerc, 2003). In France, 12-17 month old heifers fed pea straw ad libitum in addition to a concentrate had a daily growth of 600 g/d, allowing them to reach the ideal weight at calving (Brunschwig, 2003a). In Egypt, pea straw replaced berseem hay (Trifolium alexandrinum) in the complete diets of weaned lambs. Nutrient digestibility and feed conversion were similar for both forages (Abdel-Magid et al., 2008).
Fungal treatment can increase N content and decrease cell wall contents, thereby increasing the nutritive value of pea straws (Neijat et al., 1997). Urea treatment was not satisfactory for pea straw, as the increase in N content was counterbalanced by a decrease in nutrient digestibility and straw intake because of the large increase in water intake (Sabbioni et al., 1992).
Green pea haulms can be given either fresh or ensiled to ruminants. With pea haulms containing 12% DM of crude protein, OM digestibility in ewes were 74 and 63% for the fresh and ensiled haulms respectively (Gasa et al., 1989).