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Palm kernel meal is an important feed ingredient and the by-product of the oil palm ( Elaeis guineensis Jacq.). This palm tree is cultivated for its oils rich in highly saturated vegetable fats: the palm oil, extracted from the fruit flesh; and the palm kernel oil, extracted from the fruit kernel. Palm oil is both a major staple oil (a "poor man’s cooking oil", common in South-East Asia and tropical Africa) and an indispensable ingredient for the food industry ( Prabhakaran Nair, 2010 ). It has also numerous non-food applications, including as a feedstock for biodiesel. Palm kernel oil, which is semi-solid at room temperature, is economically less important. The demand for palm oil, fueled by the growth of the Chinese and Indian economies, has been growing rapidly since the 1990s. Palm oil production doubled between 1996 and 2005 and increased yearly by 10% during the 2000s. Palm oil overtook soybean oil in 2004 to be the world’s leading vegetable oil (45 million t in 2010). The production of palm kernel oil, while less important (5.6 million t in 2010) overtook that of groundnut oil in 2007 ( FAO, 2012).
The oil palm tree The oil palm is an evergreen monoecious tree, 18 to 30 m tall ( Ecocrop, 2011 ; Ataga et al., 2007). Though the tree can live up to 200 years, its productive life is about 25-35 years as older trees are too tall and impractical to harvest ( Ecocrop, 2011 ). The tree has a stout trunk, up to 75 cm in diameter, a crown made of 40-100 fronds (leaves) spirally arranged at the top, and an adventitious root system ( Rossin, 2009 ; Ataga et al., 2007). The compound leaves are up to 8 m long with 250-350 leaflets irregularly inserted on the rachis ( Ataga et al., 2007). Inflorescences are borne at the leaf axil. After pollination, female inflorescences develop into large and heavy fruit bunches bearing about 200-500 fruits ( Ecocrop, 2011 ; Ataga et al., 2007). A tree may bear between 2 and 6 bunches a year. The fruit is a fibrous, ovoid drupe, 2-5 cm long and about 2 cm broad, usually orange when ripe. The fruit has a thin epicarp, a fleshy and oily mesocarp and a hard endocarp that contains an oil-rich endosperm (kernel) ( Vaughan et al., 2009 ). Fruit bunches can be harvested 3 to 4 years after planting and the largest amount of fresh fruit bunches is obtained after 8 to 10 years ( Poonam Singh Nigam et al., 2009 ). The fruit bunches are cut off or knocked down carefully when the fruit is ripe ( Ecocrop, 2011 ).
80% of palm oil originates from Indonesia and Malaysia. Indonesia is the largest producer and exporter of palm oil and palm oil by-products. In 2010, this country produced 21.5 million t of palm oil (48% of world production) and 2.3 million t of palm kernel oil. Malaysia produced 17 million t of palm oil (38%) and 2 million t of palm kernel oil. The other 5 main producers (Nigeria, Thailand, Colombia, Papua New Guinea, Ecuador) represent less than 10% of the world production (FAO, 2012).
Palm kernel meal is an important feed commodity internationally traded with 90% of the production (5 million t) being exported, 50% of it to the European Union (FAO, 2012; USDA, 2013).
Oil palm is a high yielding crop, though productivity is variable, from 0.3 t/ha in Nigeria to 4.2 t/ha in Indonesia (Ataga et al., 2007). In optimal conditions, the fruit yield can be as high as 30 t/ha/year, which corresponds to 7 t/ha of palm oil, or 3 times the oil productivity of coconut and 7 times that of rapeseed. Palm kernel oil productivity is much lower and about 0.8 t/ha (Ecocrop, 2011; FAO, 2012).
In Malaysia and Indonesia, palm oil is generally produced in large plantations owned by private companies, though smallholders account for as much as 33% of the output. Elsewhere, as in West African countries, smallholders produce up to 90% of the annual harvest (Vermeulen et al., 2006). Oil palm can be included in integrated farming systems where it is grown with companion crops such as legumes and grass grazed by livestock. In Malaysia, more than 60,000 cattle are raised in oil palm plantations (Khusahry et al., 2003).
Palm kernel meal is a common feed ingredient, particularly in ruminant feeding. It is the less nutritionally valuable of the major oil meals due to its low protein content (14-20% DM, lower than copra meal) and its large quantities of cell wall constituents (crude fibre 14-28%; NDF 60-80%; ADF 35-50%; lignin 10-18% DM). The proportion of lignin in the cell walls of palm kernel meal (18% of NDF) is higher than in copra meal (13% of NDF). For these reasons, its nutritive value is inferior to that of the main oil meals, notably soybean meal, groundnut meal and cottonseed meal. Unlike those products, palm kernel meal is often obtained from mechanical extraction (expeller meal) and its oil content is quite high (6-15% DM). The less common solvent-extracted palm kernel meal contains less oil (about 3% DM) and slightly more protein (19% vs.17% on average) than the expeller meal, but the cell wall constituents and minerals are only slightly affected by the extraction process.
Palm kernel meal is dry and gritty and is not readily accepted by ruminants and pigs. However, as it is mainly used in compound feeds, its lack of palatability is of less importance (Göhl, 1982).
The following significant relationships between NDF, ADF and crude fibre content have been established (the slopes are identical for palm kernel meal and copra meal but the intercepts are different as palm kernel is significantly richer in cell walls):
NDF = 63.3 + 0.49 x CF (N = 150, RSD = 6.1% DM)
ADF = 31.9 + 0.65 x CF (N = 138, RSD = 4.8% DM)
|Dry matter||% as fed||91.2||1.4||87.2||95.0||1268|
|Crude protein||% DM||16.7||0.9||13.5||19.4||1114|
|Crude fibre||% DM||19.8||2.5||14.0||27.7||1097|
|Ether extract||% DM||9.2||1.5||6.2||15.4||983|
|Total sugars||% DM||2.4||0.5||1.7||3.1||12|
|Gross energy||MJ/kg DM||20.1||1.5||18.3||23.8||30||*|
|Aspartic acid||% protein||7.7||1.4||4.5||9.2||16|
|Glutamic acid||% protein||18.6||1.5||15.7||21.3||16|
|Tannins (eq. tannic acid)||g/kg DM||4.5||4.0||5.0||2|
|Ruminant nutritive values||Unit||Avg||SD||Min||Max||Nb|
|OM digestibility, ruminants||%||71.6||7.9||62.2||78.6||5||*|
|Energy digestibility, ruminants||%||71.2||7.3||62.6||78.3||5||*|
|DE ruminants||MJ/kg DM||14.3||1.2||12.9||15.5||5||*|
|ME ruminants||MJ/kg DM||11.6||1.1||10.5||13.0||5||*|
|Nitrogen digestibility, ruminants||%||73.3||5.1||70.3||84.9||6||*|
|Nitrogen degradability (effective, k=6%)||%||40||9||27||59||11|
|Pig nutritive values||Unit||Avg||SD||Min||Max||Nb|
|Energy digestibility, growing pig||%||42.0||3.3||42.0||67.3||3||*|
|DE growing pig||MJ/kg DM||8.4||2.0||8.4||14.1||4||*|
|MEn growing pig||MJ/kg DM||7.8||0.8||7.8||13.5||3||*|
|NE growing pig||MJ/kg DM||5.4||*|
|Nitrogen digestibility, growing pig||%||63.1||6.4||48.0||63.1||3||*|
|Poultry nutritive values||Unit||Avg||SD||Min||Max||Nb|
|AMEn broiler||MJ/kg DM||11.1||10.9||11.3||2|
The asterisk * indicates that the average value was obtained by an equation.