

Feed is one of the important production inputs that affect the size of livestock production. Palm kernel cake is one of un-conventional feed stuff obtained from palm oil extraction which can be used as a feed for various livestock production1-3. The chemical composition of palm kernel cake varies depending on the type of the fruits palm, source of sample and method of processing oil extraction (solvent or mechanical extraction)4-7. The average chemical composition of palm kernel cake was 89.00-95.00% for dry matter8-11, 6-24.9%12 for crude fibre, Also, acid detergent fibre being 43.7%, neutral detergent fibre being 66.7% and lignin being 21.1% of palm kernel cake9,13, 0.5-3% for ether extract of solvent extracted palm kernel and 4.5-19.5% expeller pressed7 and 3.06 and 5.6% for total ash7,11,14.
Several researchers were used physical and chemical treatments to improve nutrient contents of palm kernel cake15-18. The chemical processes of palm kernel cake using alkaline (ammonium hydroxide) or acid (acetic and formic acids) solution has been suggest to enhance the palm kernel cake nutrients digestibility and nutritive values by increasing the crude protein and decreasing the crude fibre contents19. The biological treatment such as enzymes, fungi and bacteria have been used to increase the nutritional value of palm kernel cake20-23.
Many studies suggested that the animals performed satisfactorily well when fed on diets containing different levels of palm kernel cake24-26. Palm kernel cake was used as feed for fattening and dairy cattle where as it has a source of protein, energy, vitamins and minerals27-29. Digestibility coefficients for palm kernel cake were affected by adding it to animal's diets at high levels30,31. The objective of this review was carried out to investigate the effect of using palm kernel cake as a feed for animal on digestibility coefficients, daily weight gain, milk production and composition.
IDENTIFICATION AND PRODUCTION PALM KERNEL CAKE
Palm kernel cake is a gro-industrial by product which obtained from palm oil extraction in cultivated tropicalrain countries laying between 12°N and 12°S, such as Indonesia, Malaysia and Nigeria1. Indonesia and Malaysia are the largest producer and exporter of palm oil and palm oil by-products while, Nigeria, Colombia and Thailand are recorded less than 10% of the world production26.
When the palm fruits are processed. It is produced palm oil, palm kernel cake and meal according to the method of extraction. Palm kernel cake resulted from the mechanical expeller procedure contains 5-12% oil while, palm kernel meal obtained from solvent extraction technique contains 0.5-3% oil32.
Palm kernel cake has been used as a feed for various livestock production2,24-26,33. Several studies reported that the animals performed satisfactorily well when fed on diets containing levels of palm kernel cake.
Chemical composition of palm kernel cake: The chemical composition of palm kernel cake varies (crude protein, crude fiber, ether extract, ash and nitrogen free- extract) depending on the sources of the samples34,4, soil type, method of processing oil extraction (e.g., mechanical or solvent extraction), the amount of endocarp remaining5-7 and the efficiency of oil extraction from the kernel35,36.
Dry matter refers to proportion of moisture in the palm kernel cake. The dry matter content is important to determination bulk purchasing and storage of palm kernel cake. Increasing moisture content than 14% could not be stored in bulk and it is the best culture for the molds growing on it Hartley37. Dry matter of palm kernel cake was recorded a range of 89.00-95.00% by several studies8-11. Palm kernel cake is low in crude protein content compared with soybean meal and groundnut cake. Various literature have indicated that the crude protein content of palm kernel cake ranges6,38,11 between 14-20%. Protein content of palm kernel cake had poor amino acid balance, lysine followed by methionine, tryptophan, threonine and histidine contents39,34,6,40,41 being the major limiting amino acids. The crude fibre is consists mainly of cellulose, hemicellulose and lignin. Crude fibre is an index that can used to be predict the feeding value and nutrients digestibility of the feeds. There was reversed relationship between crude fibre and nutrients digestibility to the animals42,5. The composition of crude fibre content of mechanically extracted was lower compared to solvent extracted of palm kernel cake43. The crude fibre content of palm kernel cake was about12 6-24.9%. Also, acid detergent fibre being 43.7%, neutral detergent fibre being 66.7% and lignin being 21.1% of palm kernel cake9,13. The sugar content in the cell wall of palm kernel cake fibre was mainly contributed by 56.4% mannose, followed by 11.6% glucose, 3.7% xylose and 1.4% galactose44. Ether extract of solvent extracted palm kernel cake was low 0.5-3% while the expeller pressed contained between7 4.5-19.5%. The total ash content of palm kernel cake as recorded by various studies ranges7,14,11 between 3.06 and 5.6%. Palm kernel cake is relatively high in minerals content were calcium 0.276%, phosphore 0.645%, magnesium 0.158%, zinc 0.214%, sodium 0.187%, potassium 0.365%, copper 0.25%, manganese 1.3 ppm and iron, 0.75 ppm11. It was observed that the Ca:P ratio is low and most diets based on palm kernel cake need to be supplemented with calcium to cover the requirement of animals and the carotene and vitamin E (about 0.3 IU kg1).
Enhancing nutritive value of palm kernel cake: Various treatments of agro-industrial and agriculture by-products could improve their NDF, ADF and hemicellulose content15,17,18,45. Until now there is no study has been investigated on the effect of physical treatments of palm kernel cake on its nutrient contents46. But, combination of physical and chemical processes could be enhanced nutrient contents of palm kernel cake16.
The chemical treatments of palm kernel cake using alkaline (ammonium hydroxide) or acid (acetic and formic acids) solution has been suggest to enhance the palm kernel cake nutrients digestibility and nutritive values by increasing the crude protein and decreasing the crude fibre contents19. Also, chemical treatment processes using alkaline and/or acid solution acids can be used as delignification agents to decrease lignin content of palm kernel cake. The degradation of lignin could be affected by the concentration of the acid solution. There are relationship between using higher concentration of the acid used and more lignin could be removed16. While, using alkaline solution to treat palm kernel cake can be absorbed into the cell wall and thus hydrolysis the ester chemical bonds between cellulose, hemicellulose and lignin which finally make the structural fibre to swell47.
The biological treatment has been used to increase the nutritional value of palm kernel cake. High level of non-starch polysaccharides contents of the cell wall of palm kernel cake contributes to reduce digestibility of its nutrients48. However, fibre in palm kernel cake is degraded to the smaller units of sugar, mostly mannose it has been suggested that the absorption of mannose is much lower than glucose, particularly when glucose is present in the system23.
The addition of enzymes to palm kernel cake and its effect on nutrient content analysis49,50, nutrient digestibility trial51,22. However, using fibrolytic enzymes as a biological treatment for palm kernel cake diets was reduced the fibre content and the increase of the total sugar released and there was an improvement in the metabolic energy value23,49,50,52. The effect of productive performance of different classes of livestock such as pig22, layers49, fish53 and broiler chickens52 have been evaluated. While, the studies of using enzymes to palm kernel cake for ruminants was poor. The composition of NDF, ADF, cellulose and hemicellulose contents of enzyme treated palm kernel cake was significantly decreased50.
Various studies have been reported to enhance nutrients digestibility and nutritive values of palm kernel cake through solid-state fermentation either by using fungi such as Sclerotium rolfsii, Trichoderma harzianum21, Aspergillus niger20,21,54, Trichoderma longibrachiatum and Trichoderma koningii 20, Trichoderma varidae and Mucor mucedo54, Rhizopus spp.55,54,21 and bacteria such as Bacillus 7DY7 56.
Forming palm kernel cake under sold state fermentation conditions have been reported to be more proper for low purpose and there is no any waste disposal at the end because the whole product may be used directly in animal feeds. Also, solid state fermentation of palm kernel cake produces a product that contains low hemicellulose and cellulose contents and high protein concentration. The levels of saturated fatty acids decrease while unsaturated fatty acids increase as a result of solid state fermentation of palm kernel cake using fungi as culturing agents20,57.
Feed intake and digestibility: There is a linear decrease in dry matter intake was observed due to the lower palatability and higher fiber content of the palm kernel cake58,27. Neutral detergent fiber (NDF) intake by the animals showed a negative effect on nutritive value and digestibilities28. Moreover, there was increase (p<0.05) for the efficiencies of rumination of dry matter and total digestible nutrients with the inclusion palm kernel cake in diets at level 15% on dry matter but the dry matter intake was not affected29. While, replacement of soybean meal with palm kernel cake at level 16% on dry matter was influenced on feeding behavior of steers and decreased dry matter intake59. Maciel et al.60 observed that the use of palm kernel cake in the diet of dairy heifers at the highest level was 54.5% lead to decrease the intake of dry matter and neutral detergent fibre. The inclusion of by-products such as palm kernel cake and cocoa meal in diets for lactating goats, significantly increased fibre content but the feeding behavior had not changed61. Palm kernel cake expeller, rather than solvent extracted palm kernel cake is used as a source of protein, energy and fibre for dairy cattle at levels 300-500 g kg1 of total diet62. However, using palm kernel cake at level 400 g kg1 DM has been associated with reduced concentrate feed intake due to palatability problems63. While, increasing levels of solvent extracted palm kernel cake (50, 100 and 150 g kg1 DM) in a total mixed ration have been found not affect cow dry matter intake64.
Dry matter, crude protein and NDF digestibilities were lower (p<0.05) in buffalo calves fed diet contain 30% palm kernel cake than those fed other diets contain low level of palm kernel cake. The reason behind low digestibility diet 30% palm kernel cake was due to increased amount of NDF in feed65,66,28. The other reason to low digestibility for diet contain palm kernel cake may also undergo Maillard reaction (the reaction of mannose with amino groups leading to the formation of a brown complex) due to heat applied in the process before and during oil extraction and this may adversely affect the digestibility13,28. Digestibility coefficients for expeller pressed palm kernel cake were 70% for dry matter, 63% for crude protein, 53% for neutral detergent fibre (NDF), 52% for acid-detergent fibre (ADF) and 88% for gross energy were obtained using sheep30. While, the digestibility coefficients of solvent extracted palm kernel cake was determined by using cattle at 65.1% for dry matter, 72.7% for organic matter, 69.7% for crude protein and 86.7% for the nitrogen free extract component67. The digestibility of dry matter, organic matter, crude protein, total carbohydrates and non-structure carbohydrate were significantly increased with an increased percentage of palm kernel cake in a dietary supplement for dairy cows of the Holstein x Gir crossbreed at pasture31.
Effect of feeding palm kernel cake on dairy cattle: Feeds is important factors affecting on milk production and animal performance which, constitutes about 70 % of the total cost of enterprises. Therefore, using a gro-industrial by-products are very important to minimize the cost of feeds by including cheaper source of energy and protein without any adverse effect on animal productivity. Palm kernel cake plays a significant role in utilization has effectively reduced the cost of milk production as a result of replace expensive conventional feedstuffs, such as maize, cotton seed cake and soybean meal with a more economical and locally available one that also meets the nutrient requirements of livestock.
Palm kernel expeller is a low cost by-product and high fibre, it has been used extensively as a feed by the dairy cattle68 at 56%. Using palm solvent extracted kernel cake at levels (50, 100 and 150 g kg1 DM) in a concentrate feed mixture have been found not to affect cow milk yield and composition64. Moreover, milk yield and composition except milk lactose were not affected in a study in which cows grazed high quality pasture in spring season, added with two levels of palm kernel cake (200 and 400 g kg1 DM) in total mixed ration63. While, supplementation of palm kernel cake may induce a positive milk yield and composition response when the nutrient supply of a pasture based system is at sub-optimum levels69. The high neutral detergent fibre content of palm kernel cake may induce a positive milk fat content response70. Comparative between the use of expeller pressed palm kernel cake and solvent extracted palm kernel cake for fed cows on milk production, it was found out that pressed palm kernel cake gave significantly lower (4.8 kg milk/day) milk production than the solvent extracted palm kernel cake (7.9 kg milk/day). In the same trial, when Sahiwal-Friesian cow were fed on expeller pressed palm kernel cake and solvent extracted palm kernel cake lead to a low fat content71 of 7%. Other study found, there are no significant difference on daily milk yield between cow Sahiwal-Friesian cows fed on conventional concentrate feed mixture without palm kernel cake (8.4 kg milk/day) and those fed on identical amounts of solvent extracted palm kernel cake (7.7 kg milk/day)72. The milk of dairy cattle fed palm kernel cake tends to produce a firm butter and the ration containing on 2-3 kg of palm kernel cake daily is more satisfactory for adult dairy cattle73. Increased fat yield and fat corrected milk yield of dairy Jersey cows fed on 200 g palm kernel expeller/kg DM can partially replace maize in a dairy concentrate feed mixture74. Milk composition such as milk lactose and milk protein content were not affected by palm kernel expeller supplementation63,64,74,75. No change in behavior activities for dairy cows with the inclusion of palm kernel cake in diets at level 15% on dry matter29. Also, no significant difference in milk yield and fat corrected milk yield for lactating Saanen goats when, replacing maize and soybean meal with palm kernel cake in the concentrate feed mixture at level 30% on dry matter76.
Effect of feeding palm kernel cake on fattening cattle: Palm kernel cake was used as the sole feed for commercial feed lotting where it has included on more vitamins and minerals8. Also, palm kernel cake is used in mixture with other oil palm by-products (such as palmpressed fiber) for feeding growing dairy bull calves77. Various studies suggested that average daily weight gain ranged from a lower 0.39 kg/day achieved by the indigenous Kedah-Kelantan cattle fed a 100% expeller pressed palm kernel cake diet to 0.83 kg/day obtained by drought master cattle fed a mixed ration comprising 60% solvent extracted palm kernel cake and 40% palm oil sludge78,79,8. No significant difference in daily gains was found between Sahiwal-Friesian animals when fed the expeller pressed palm kernel cake/dried sago pith at 50/50 ratio group and the solvent extracted palm kernel cake/dried sago pith at 50/50 ratio group as compared to animals fed 100% Palm kernel cake without dried sago pith, this was due to the higher energy availability of diets with dried sago pith71. In the same trial, Sahiwal-Friesian cows were fed on expeller pressed palm kernel cake and solvent extracted palm kernel cake lead to a low fat content71 of 7%. Moreover, there was no significant difference in the daily gain among Sahiwal-Friesian dairy heifers fed on Napier grass plus tow kg of supplementary rations comprising palm kernel cake alone or with either cassava or molasses as a source of energy80. The growth performance of daily weight gain was not affected in buffalo calves fed palm kernel cake at level 30% against cotton seed cake in diets day28. Also, 30% palm kernel cake is a source of energy and protein in feedlot cattle and sheep62. Drough master animals were superior on Brahman bull calves in terms of a better carcass analysis and daily weight gain when, it was fed a ration of palm kernel cake with palm oil sludge in the ratio81 of 60/40. Under intensive management, an adding of palm kernel cake to grass molasses diets has improved the performance daily weight gains of growing Zebu-Holstein dairy bulls compared to those receiving either grass or grass-molasses mixture77. Daily weight gain was highest in WAD goats fed on soybean meal compared with palm kernel cake82.
In general, incorporation palm kernel cake with different levels in animal diets has positive effect on animal performance, weight gain, milk production and coefficients of digestibility. Also, it was contributed to solve some problems related to with increase in feeds prices.
This study was carried out to investigate the effect of using palm kernel cake as a feed for animal on digestibility coefficients, daily weight gain, milk production and composition. Animal performance, weight gain, milk production and coefficients of digestibility were significantly improved by using palm kernel cake with different levels in animal diets. Incorporation palm kernel cake in animal diets had no negative effect on animal health status. Using palm kernel cake was contributed to solve some problems related to with increase in feeds prices.