The nutritive value of date palm crop residues has been extensively studied due to their widespread availability in the countries where date production is important. Both the energy and protein values of these by-products are low, generally comparable to that of cereal straw (Arbouche et al., 2008). Moreover, the crude fibre is not very digestible (45-50%; Chehma et al., 2001), which explains the generally low DM and OM digestibilities of these by-products.
Date palm leaves
Date palm leaves, like cereal straw, can be treated with ammonia to improve their protein value and DM digestibility (Hassan, 2006; Arbouche et al., 2008). In vivo DM digestibility of date fronds is low, values reported are between 38 and 55% (Chehma et al., 2001; Al-Yousef et al., 1993; Pascual et al., 2000), the lower values being for dry fronds (Chehma et al., 2001). In vitro gas production of dried palm leaves is lower than that of barley straw, with a longer latency time, indicating a low DM degradability (high fibre and low protein) (Medjekal et al., 2011). However, some authors have noted that there is a discrepancy between the low gas production values (less than 20% has been reported; Genin et al., 2004) and in vitro DM digestibility, and the higher in sacco DM degradability, similar to that of a good forage such as vetch-oat hay. This difference may be due to the high levels of phenols and condensed tannins that may affect gas production and in vitro analysis but not in sacco measurements (Arhab et al., 2006).
In lactating dairy cows fed on high-concentrate diets, date palm leaves can be used instead of cereal straw as a buffer to prevent acidosis. The replacement of barley straw by date palm leaves (4 kg DM/d) has no effect on milk yield (15 kg/d) and total daily DM intake (16.8 kg DM) (Bahman et al., 1997). When 4 kg of senescent date palm leaves were offered daily to dairy cows during a 196-day study, voluntary intake of the leaves ranged from 2 to 3 kg DM according to season (Bahman et al., 1993). Less positive results have been reported. Feeding lactating dairy cows with NaOH-treated and ensiled date palm leaves at 30 or 40% of the diet (based on wheat offals, poultry manure and a concentrate) resulted in lower milk yields than when the cows were fed alfalfa hay and concentrate. But date palm leaves could be a viable alternative economically because of their low price and widespread availability, though the costs of the other supplements may outweigh the benefit of palm leaves (Narendran et al., 1986a; Narendran et al., 1986b).
In sheep, voluntary DM intake and in vivo DM digestibility of dried date palm leaves given as the sole feed were 44g DM/kg W0.75/d and 38% respectively (Chehma et al., 2001). Like straw, palm leaves can be treated with urea to improve their nutritive value. However, urea-treated ensiled date palm fronds, supplemented by a concentrate made of local by-products, was shown to support only the maintenance requirements of growing sheep and very low weight gain over 120 days (Mahgoub et al., 2007). Apparent in vivo DM, NDF and ADF digestibilities of this diet were only 39, 33 and 25%, respectively, explaining the low animal performance.
In goats, the voluntary intake of date palm leaflets was higher than that of the whole frond (leaflets + rachis) (70 vs. 53 g/kg W0.75/d), though there was no significant difference in DM digestibility or digestible energy (Pascual et al., 2000). A diet containing 20% date leaves, 20% date pits, 49.5% barley and 10% dried fish fed young kids resulted in a similar or slightly higher voluntary DM intake, in vivo DM digestibility and weight gain when compared to a diet based on cereal grain and soybean meal (El-Hag et al., 1992).
Date palm pedicels
Date pedicels are similar to straw and should be used in the same way in ruminants (Arbouche et al., 2008). Pedicels are more or less comparable to fronds, but actual results depend probably on the precise nature of the materials offered to (and eaten by) the animals. It has been observed that sheep do not eat the racemes whole but select the less tough pedicels. Sheep fed date pedicels ate less DM (26 g/kg W0.75/d) than those fed palm leaves but in vivo DM digestibility of the date pedicels was higher (48%) than for palm leaves. Crude fibre digestibility (49%) was similar to that of the leaves (Chehma et al., 2001). In goats, the voluntary intake of pedicels was similar to that of whole leaves but lower than that of leaflets (52 vs.70g/kg W 0.75/d) and their DM digestibility was lower (44% vs. 54%) (Pascual et al., 2000).