Palm kernel meal is mostly used to feed ruminants. In spite of a nutritional value lower than that of other meals, it remains a source of protein and energy and its cost may make it particularly attractive when compared to more expensive ingredients such as maize grain and soybean, and it can often partially replace them when economic conditions allow it.
Digestibility and energy value
The in vivo OM digestibility of palm kernel meal has been found to be extremely variable (OMD = 68.6 ± 5.3%, N = 22 from data pooled by Feedipedia). Tables have proposed diverse estimates for the in vivo OM digestibility of expeller meal, including 68% (INRA-AFZ Tables, Sauvant et al., 2004), 73% (German tables, Schiemann, 1981) and the quite high 77% (Jentsch et al., 2003). The expeller meal, possibly due to its higher oil content, is generally considered to be more digestible than the solvent-extracted meal (73 vs. 67%, Schiemann, 1981; 77 vs. 75%, Jentsch et al., 2003). Somewhat imprecise relationships between OM digestibility, NDF and ADF can be established by pooling together samples of palm kernel and copra meal (the regression coefficients are not significantly different between the two products):
- OMD = 100.6 - 0.418 NDF% DM (n = 27, R² = 0.40, RSD = 4.7)
- OMD = 94.4 - 0.510 ADF% DM (n = 26, R² = 0.59, RSD = 4.0)
These OMD values result in ME estimates of 11.6 and 10.7 MJ/kg DM for expeller and solvent-extracted palm kernel meal respectively. Compared with copra meal, corn distillers dried grains and corn gluten feed, the low energy value of some palm kernel meals could limit their inclusion in diets for high-performance ruminants (Carvalho et al., 2005).
The prediction of palm kernel meal digestibility by in vitro methods is not accurate and underestimates the in vivo digestibility (Castagna et al., 1984), even with procedures involving enzymes (gamanase) or rumen fluid (Dowman, 1993; O'Mara et al., 1999). This problem is due to the presence of galactomannans that are not readily hydrolyzed by the enzymes in the cellulase preparation. Palm kernel meal is, after guar gum, the feed ingredient that is the richest in non-starch polysaccharides (NSP) and galactomannans. This may also explain why palm kernel meal studied in sacco in the rumen has a particularly long lag phase, which can exceed 10 hours, before the onset of cell wall degradation (Sauvant et al., 1986; Hindle et al., 1995; Chapoutot et al., 2010). This fermentation pattern suggests that the effective rumen digestion of palm kernel meal is particularly sensitive to transit outflow rates. After the lag phase, cell wall degradation becomes important and palm kernel meal can be considered to be a source of highly digestible fibre, similar to copra meal, soybean hulls and maize bran (Sauvant et al., 1986; Chapoutot et al., 2010). The rumen undegradable fraction of cell wall components varied between 23 and 37% (Steg et al., 1993) but a higher value (47%) has been proposed by Chapoutot et al., 2010.
Due to its low degradation rate in the rumen, palm kernel meal is not considered to be acidogenic and its inclusion at up to 55% of DM intake had no detrimental effect on rumen conditions in goats (Chanjula et al., 2009). Moreover, the supplementation of low quality hay with palm kernel meal or copra meal improved the production of microbial protein in the rumen (Marsetyo, 2007).
Although palm kernel cake supplies both protein and energy, it is looked upon more as a source of protein. The fraction of rapidly fermentable N in the rumen is low (15-16%) (Sauvant et al., 2004; Woods et al., 2003a) and the effective degradability of the protein is low, usually in the 40-50% range (Carvalho et al., 2009; Sauvant et al., 2004; Woods et al., 2003a; Hindle et al., 1995; Umunna et al., 1994) although 34% has been reported (Promkot et al., 2007). The digestibility of by-pass protein in the intestine, which is generally lower than 80%, is not particularly high compared to other feeds (Carvalho et al., 2005; Sauvant et al., 2004; Woods et al., 2003b), though higher values (83-92%) have been proposed, and correlated to in vitro pepsin digestibility (Steg et al., 1993).
In the areas of palm oil production, a typical feed ration for dairy cattle may contain up to 50% of palm kernel meal. In Malaysia, for example, the use of palm kernel meal helps to reduce dairy production costs because it replaces more expensive imported feeds such as soybean meal or maize grain. The inclusion of solvent-extracted palm kernel meal at up to 15% of the diet decreased feed costs and increased milk protein content without affecting milk yield (Carvalho et al., 2006). Due to its specific fatty acids profile, palm kernel meal fed at 2-3 kg daily to dairy cattle tended to increase milk fat content and to produce a firm butter (Witt, 1953).
Palm kernel meal is widely used for feeding growing cattle and a ration of 2-5 kg per day has been found satisfactory for adult animals. It is considered as a reasonably profitable feed for cattle, both for fattening and supplementary feeding. In Malaysia, feedlot cattle are normally fed up to 80% palm kernel meal in the diet DM. However, based on chewing activities and rumen digestion indicators, ingredients such as tomato pomace, dried brewers' grains and soybean hulls may be better sources of fibre than palm kernel meal in total mixed rations (Chumpawadee et al., 2009).
Supplementation with up to 30% palm kernel meal in sheep fed koronivia grass (Brachiaria humidicola) did not induce any physiological or nutritional damage and increased ADF digestibility (Costa et al., 2010). The partial substitution of maize grain and soybean meal with palm kernel meal was found satisfactory in sheep fed ammoniated elephant grass silage (Pennisetum purpureum) (Silva et al., 2007). In growing sheep fed native hay, increasing the inclusion rate of palm kernel meal in the supplement up to 90% did not significantly affect performance and decreased the feed cost, making the substitution of maize grain and oil meals by palm kernel meal economically attractive (Umunna et al., 1994). In grazing hair ewes, including up to 30% palm kernel meal in the supplement in partial substitution of maize grain did not alter reproductive performance (Luna Palomera et al., 2010). Supplementation with zinc and phytase prevented chronic copper toxicity in West African Dwarf sheep fed palm kernel meal (Akpan et al., 2005).
Palm kernel meal as the sole component of the supplement was an adequate protein source for West African Dwarf goats (Aina et al., 2002). The performance of West African Dwarf goats fed wilted Guinea grass (Megathyrsus maximus) and palm kernel meal was better than that of goats supplemented with brewer's grains, similar to the performance of goats fed cottonseed meal and lower than that of goats supplemented with soybean meal (Arigbede et al., 2006). Partial substitution of maize grain and soybean meal with palm kernel meal in diets of lactating goats did not affect significantly dairy performance when palm kernel meal was included at up to 30% in the supplement (corresponding to 18% of the diet DM) (Silva et al., 2005).