Carob pods contain large amounts of sugars, which makes them a good source of energy and very palatable. Carob bean meal has been used as a substitute for grain in the diets of ruminants. Carob pods may be beneficial as a supplement for ruminants under critical feeding conditions (Hall et al., 1977). However, protein supplementation is required when high amounts of carob pods are included into ruminant diets. While tannins can have positive effects on ruminant diets because they increase the bypass protein content (Aharoni et al., 1998), carob tannins are known to be detrimental to growth in ruminants.
Estimations of the digestibility of carob pods vary widely between references. The CIHEAM tables report an OM digestibility value of 59% (Alibes et al., 1990) while the INRA-AFZ tables give 70% (Sauvant et al., 2004). Carob trials tend to report the digestibility of mixed diets rather than the digestibility of carob pods alone: from one of these experiments, it is possible to calculate an OMD value of 74% (Obeidat et al., 2011). Values of 74-75% estimated by the gas production method have been reported for both the whole pods and kibbles (Karabulut et al., 2006). The OM digestibility (%) of carob pods can also be predicted from crude fibre (CF, % DM):
OM digestibility = 78.1 - 1,73 CF (n=7, R²=48%, RSD=9.3)
Based on this equation, the mean crude fibre content of 9.0% DM corresponds to an OMD of 63% (close to the CIHEAM value) and to an ME content of 9.6 MJ/kg DM. Carob pod meal is less digestible than other feeds with a similar crude fibre, which may be explained by the detrimental effect of carob tannins on digestibility. High OM digestibility values such as the one reported in the INRA-AFZ tables are probably overestimated.
Growing sheep and goats
Inclusion levels in the 20-25% range seem to be appropriate for growing sheep and goats. The replacement of barley grain by carob pods up to 25% in fattening Awassi lambs did not affect feed intake, growth performance, carcass characteristics and meat quality. Diet digestibility was only slightly affected by increasing the inclusion rate of carob pods from 12.5% to 25% (Obeidat et al., 2011). However, condensed tannins from carob pulp can be detrimental to feed digestibility and growth performance (Priolo et al., 2000). In Comisana lambs, feeding a diet containing 20% carob pulp in replacement of barley did not affect live weight and most meat quality parameters but resulted in a higher feed intake and a depressed feed conversion ratio (Priolo et al., 1998). Anglo-Nubian kids fed 52% carob pods performed very poorly, with reduced growth rates (-40%) and poor conversion ratios (Silanikove et al., 2006).
Treatment with PEG (polyethylene glycol) has been proved as an effective mean to counteract the negative effects of tannins. For example the inclusion of 4% PEG in a diet containing 56% of carob pod meal resulted in performance and meat quality similar to the one obtained with the maize-based control diet (Priolo et al., 2000). Similar results have been observed on kids (3.3% PEG, 52% carob meal, Silanikove et al., 2006). Lambs and kids fed high-tannin diets containing carob pulp have a lighter longissimus muscle colour, an effect that is again corrected by PEG supplementation. This effect could be linked with a reduced myoglobin synthesis although iron absorption seemed not to be affected by condensed tannins in sheep (Priolo et al., 2004).
Supplementation with carob pulp (45% as fed) can also alter the composition in minor intramuscular fatty acids in lambs, resulting notably in a lower percentage of conjugated linoleic acid (Vasta et al., 2007; Priolo et al., 2007).
Carob kibbles can be associated with ammoniated straw (45% and 40% of diet DM respectively) as supplementary sources of N for the rumen ecosystem (Milad et al., 2010).
Ewes and lactating goats
It was estimated that carob pods contain sufficient crude protein and energy to meet the maintenance and lactation requirements of ewes in semi-arid rangelands (El-Shatnawi et al., 2001). In dairy goats, a non-forage diet containing an adequate amount of structured fibre, contributed by carob pods (26%) and beet pulp (27%), could replace a ration based on poor quality forage (Rapetti et al., 2005).
There is little information available on the use of carob seeds for ruminants. It was estimated that carob pods contain sufficient crude protein and energy to meet the maintenance and lactation requirements of ewes in semi-arid rangelands (El-Shatnawi et al., 2001). Gas production of carob seeds was found to be significantly lower than that of carob pods and kibbles, while the estimated OMD (79%) and ME value (11.6 MJ/kg DM) of carob seeds were significantly higher. However, the authors caution that the higher crude protein content of the seeds may have resulted in overestimation of OMD and ME (Karabulut et al., 2006).
In Ethiopia, carob foliage compared to 40 other tropical browse species was found to have a very low protein solubility, low DM and rumen degradable protein, coupled with very low values of DM and N disappearance in the intestine (Kaitho et al., 1998). Fibre digestibility significantly decreased in ewes fed carob leaves that contained high concentrations of tannins (Silanikove et al., 1996).