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2.1 Physical characteristics

Crude olive cake contains the olive kernel shell crushed into fragments, the skin and the crushed pulp, about 25 percent water and a remaining quantity of oil making them subject to rapid spoilage.

Exhausted olive cake differs from crude olive cake mainly by lower oil content and a smaller water content because it has been dehydrated during the extraction process.

Partly destoned exhausted olive cake consists mainly of pulp (mesocarp) and still contains a small proportion of shell which cannot be completely separated by the screening or ventilation methods employed.

Figure 4 gives the yields of different types of olive cake from treated olives and their respective physical composition.

2.2 Conditions of olive cake preservation

The main problem in preserving crude olive cake is its relatively high water content and the still large quantity of oil it retains. When exposed to air this type of olive cake quickly becomes rancid and unfit for animal consumption.

It has been estimated that crude olive cake obtained by centrifugation, being wetter, deteriorates after 4–5 days, whereas olive cake obtained by pressure deteriorates after about 15 days; dehydrated, the same olive cake probably could not be stored longer than 45 days. On the other hand, exhausted olive cake which has also been dehydrated during the extraction process could be stored for over a year.

At present dehydration is a costly process in view of the high cost of the energy required. Furthermore, in the case of crude olive cake which still has a high oil content, its effectiveness as a preservation method appears to be very scarce. The few small-scale silage storage tests made suggest a possibility of simpler, more economic and more efficient preservation using the stack-silo method which allows storage of quantities varying widely from a few to several hundred tons.

Considering the fact that crude olive cake only keeps for a very short time, it should be distributed quickly to animals or ensiled as soon as possible so that it does not spoil.

However, it should be mentioned that it is usually more economically profitable to extract the oil from the olive cake beforehand, but that when for certain reasons the oil has not been extracted the crude olive cake can be stored for distribution to animals later on.

2.3 Chemical characteristics

2.3.1 Chemical composition of olives

For easier understanding of the variations in the chemical composition of different types of olive cake it may be useful to review (Table 4) the chemical composition of the various components in olives.

Table 4: Chemical composition of ripe olive components
PartCrude ProteinEther extractCrude FibreAshNitrogen-free extract
(stone and     

Source: Maymone et al, 1961

Obviously the part with the highest oil content is the mesocarp (or pulp) and that which the highest crude fibre content is the endocarp (or stone).

2.3.2 Chemical composition of olive cake

Unlike other oil cakes, crude olive cake has a low crude protein and high crude fibre content. It retains a relatively high fat content. Exhaustion by solvent extraction decreases its fat content and relatively increases its other contents. Partial destoning by screening or ventilation lowers its crude fibre content. (Table 5).

Because the kernel is totally separated before pressure extraction, the pulp has the lowest crude fibre content.

Table 5: Indicative chemical composition of different olive cake types
  % of dry matter
TypeDry matterAshCrude ProteinCrude FibreEther Extract
Crude olive cake75–803–55–1035–508–15
Partly destoned olive cake80–956–79–1220–3015–30
Exhausted olive cake85–907–108–1035–404–6
Partly destoned exhausted     
olive cake85–906–89–1415–354–6
Fatty pulp35–405–89–1316–2526–33

Sources: many authors.

The values given above vary widely, mainly for crude olive cake and partly destoned fatty olive cake, and can only be considered indicative.

It should be mentioned that these different cakes are obtained from olives of various origins and have been subjected to different treatments which accounts for the heterogeneity of some results.

  1. Crude fibre

    As mentioned above, the crude fibre content in destoned olive cake is high. Partial destoning decreases the content considerably but even pure pulp contains about 20 percent crude fibre.

    Analysis of fibres by the Van Soest (1975) method shows that olive cake has high cell wall constituents (NDF) and ligno-cellulose (ADF) and lignin (ADL) contents (Table 6).

    Table 6: Characteristics of olive cake cell wall constituents
     Exhausted olive cakePartly destoned exhausted olive cake
     (Tunisia)(1)Tunisia (1)Spain (2)Greece (3)

    Sources: (1) Nefzaoui, 1979
    (2) Alibes and Berge, 1983, results not published
    (3) Ohlde and Becker, 1982

    Paradoxically, screening therefore mainly decreases cellulose content while minimally reducing lignin content. This composition of olive cake cell wall constituents can be compared to that of cereal straws having an apparently high degree of lignification.

  2. Crude protein

    The content varies according to the type of olive cake (see Table 5) but remains relatively small. True protein nitrogen constitutes more than 95 percent of all nitrogen and has particularly low solubility (1.5 of total nitrogen according to Zelter, 1968, cited by Theriez and Boule 1970, and Gomez-Cabrera, 1983, (personal communication); 3 percent according to Nefzaoui, 1983). In addition, a large proportion of the proteins (80 to 90 percent) is linked to the ligno-cellulose fraction (ADF - N) (Nefzaoui, 1983).

  3. Fats

    Olive cake fat is high in unsaturated C16 and C18 fatty acids which constitute 96 percent of total fatty acids. Olive cake is highly vulnerable to air oxygen which is the main cause of spoilage of its organoleptic properties. However, Theriez and Boule (1970) observed that rancid olive cake oil does not seem to be the cause of the decrease in digestibility they observed in vitro, since the results obtained with olive cake accumulated during more than a year were the same as those of fresh olive cake.

    The fat content of crude olive cake can be a major source of energy, but its contribution to the energy supply in exhausted olive cake is small.

2.4 Factors capable of affecting digestive utilization of olive cake

Many experiences have shown “poor digestive utilization” of olive cake. This may be caused by decreased activity of the rumen microflora which (measured by gas release) may decrease by 40 percent after ingestion of crude olive cake (Theriez and Boule, 1970). The ammonia production of sheep rumen liquor receiving olive cake also confirms decreased activity of the rumen microflora (Balti, 1974, Nefzaoui and Abdouli, 1979, Nefzaoui et al 1982).

Three hypotheses may be advanced to explain this:

2.4.1 Influence of fat content (especially for non-exhausted olive cake)

High concentrations of free fatty acids in the rumen can alter digestion and appetite. Fat can act through one or all of the following factors:

2.4.2 Inhibiting factors

These could be simple phenol type compounds which would inhibit fermentation, or more complex ones of a tannin type which would insolubilize the proteins in the diet or in the olive cake itself (Theriez and Boule 1970).

Nevertheless in general the results cited in the bibliography refer to the fruits before the oil is extracted, whereas this operation eliminates large quantities of polyphenols and tannins in the vegetation waters.

Analyses of olive cake by Nefzaoui (1978) showed that tannin rates below 1 percent, were not sufficient to act as a depressant on rumen microflora and on the digestibility of protein; and polyphenol levels between 0.15 and 0.75 percent of dry matter are not sufficient to inhibit fermentation.

2.4.3 Influence of lignin

Olive cake is particularly rich in lignin and poor in cell content. It seems there is the same phenomenon of “protection” of carbohydrates related to lignin as occurs with straw. In fact, when olive cake was treated with alkalis its in vitro digestibility was almost four times higher (Nefzaoui, 1983).

2.5 Nutritive value of olive cake

2.5.1 Digestibility

First, it should be recalled that in case studies of certain by-products of the olive cake type, a number of researchers (Michalet-Doreau, 1981, Orskov, 1977, and Preston et al, 1981) showed the importance of the degree of participation of this feed in the total diet, type of associated feeds (fodders, concentrates), level of animal feeding, and, lastly, method of calculating or estimating digestibility.

There are few studies on olive cake digestibility and the results are very heterogeneous. Table 7 gives the main results of in vivo digestibility obtained with different types of olive cake.

Table 7: Main results of in vivo digestibility of different types of olive cake
Type of olive cakeMethod of determinationDry matterOrganic matterCrude proteinEther extractCrude fibreSource
Fatty pulpOn sheep, by difference--21.685.60Maymone et al, 1962
On sheep, by difference (24% of the diet) 43.713.4--Theriez, Boule, 1970
On sheep, by difference (15% of the diet) 57.466.890.0-Theriez, Boule, 1970
Exhausted pulpOn sheep, by difference (21% of the diet)-69.428.0--Theriez, Boule, 1970
Crude olive cakeIn vivo on sheep-30,86,665,528,4Kellner, 1924
In vivo on sheep---860Meade, Guilbert, 1927
In vivo by difference on sheep32.935.424.557.729.6Boza, Varela, 1960
-- et al, 1970
-- et al, 1970
In vivo by difference on sheep-45.723.675.2-Theriez, Boule, 1970
Partly destoned fatty olive cakeOn sheep, by regression41.949.932.591.522.2 
      Ben Hamouda, 1975
On sheep, direct-37.219.484.133.6Maymone, Carusi, 1935
On sheep, by difference-21.615.585.512.8Maymone, Battaglini, 1962
Exhausted partly destoned olive cakeOn sheep, by difference--10.167.911.1Maymone et al, 1961
On sheep, by difference--14.060.917.9Maymone et al, 1961
On sheep, by difference--, Carusi, 1935
On sheep, by regression43.054.435.9-36.4Nefzaoui, 1978
On sheep, direct48., Abdouili, 1978
On sheep, direct30.532.238.881.822.5Nefzaoui, 1980
On sheep, direct36.439.629.077.439.1Nefzaoui et al, 1982
- et al, 1978
-- et al, 1978
On sheep, by difference19.1-25.488.927.0Valamotis, 1983
-36.736.715.874.1-Accardi et al, 1979
-50.551.99.988.057.0Duranti et al, 1978
 57.457.611.090.566.4Duranti et al, 1978

It is sometimes difficult to classify accurately the type of olive cake concerned according to reports of experiments since experimental conditions are not always clearly defined, and they also correspond to different years, products of different origins, etc. Consequently it is often difficult to interpret the results presented in such reports.

Generally, however, we can conclude that:

2.5.2 Intake

The available results are scarce and refer mainly to partly destoned exhausted or non-exhausted olive cake, (Nefzaoui, 1983, Boza et al, 1970, Eraso et al, 1978). Olive cake as such is not very palatable and is not widely consumed. Most of the tests described included an addition of 8 to 10 percent of molasses (sometimes 30 percent). In these conditions rations containing a smaller or larger proportion (20 to 83 percent) of olive cake are satisfactorily ingested.

- 85 to 130 g dry matter/day/P0.75 or 1.4 to 2.2 kg of DM/day for sheep

2.5.3 Degradability

According to Nefzaoui (1983), since olive cake is rich in ligno-cellulose, it has a low degradability in the rumen and the maximum values reached are low (in the case of exhausted screened olive cake 32 percent of dry matter was degraded after remaining 72 hours in the rumen). Protein degradability is also very low, which may be due to the fact that 75 to 90 percent of the nitrogen is linked to the ligno-cellulose fraction, thereby resulting in low nitrogen solubility, which is only 2.3 percent (soluble N % total N) in the case of crude olive cake and about 0.2 to 0.4 percent in that of screened olive cake.

2.5.4 Biochemical characteristics in the rumen

The few existing data come from studies made in Tunisia by Nefzaoui (1979) and Nefzaoui et al (1982) on exhausted screened olive cake.

2.5.5 Feeding behaviour

In its physical appearance exhausted screened olive cake (1 to 4 mm pellets) does not directly resemble rough fodders (straw, hay). However this type of olive cake provides perfectly normal rumination and intake identical with that of chopped hay (Table 8). This positive aspect of olive cake is due to its abundance of structural elements (high cell wall constituent and especially ligno-cellulose contents).

Table 8: Feeding behaviour of Texel breed sheep receiving exhausted screened olive cake (Nefzaoui et al, 1982)
 Chopped hay (1)Hay pellets (1)Olive cake (2)Olive cake pellets (3)4 %soda olive cake pellets (4)3% NH3 olive cake (5)
Intake duration, %20.4014.8019.
Rumination duration, %32.906.1036.430.428.832.1
Number of rumination balls,      
Duration of ball (seconds)--
UID, min/g DMi/P0.75--
URD, min/g DMi/P0.75--
Rumination unit ball      
(nbr/g DMi/P0.75--8.514.33.66.5

(1) According to Ruckebusch and Marquet, 1963
(2) Olive cake with 8% molasses and 100 g ground barley, consumption ad libitum (6 sheep,recording period, 12 days)
(3) Olive cake with 8% molasses and 1.5% urea then made into pellets. Distributed separ-ately, consumption ad libitum - Idem 2
(4) Olive cake previously treated with 40 g NaOH/kg - Idem 2
(5) Olive cake previously treated with 3 % ammonia - Idem 2.UID= Unitary intake durationURD= Unitary rumination duration

2.6 Possibilities of improving nutritive value of olive cake

As in the case of straw, alkali treatments have received the most study.

2.6.1 Soda treatment

Small quantities of soda less than 4 percent, have only slight effect on in vitro digestibility of dry matter. The latter increases progressively, reaching levels of 50 to 70 percent for 6 to 8 percent quantities of soda, (Abdouli, 1979; Nefzaoui, 1979). Washing and filtering of olive cake to eliminate excessive soda decrease digestibility.

Treatment of fatty olive cake with soda can cause formation of soap by saponification. This phenomenon was also pointed out by Karalazos (1979). Therefore only exhausted olive cake must be treated or else alkalis (Na2CO3, NH4OH), which do not provoke saponification reactions, must be used.

  1. Influence of treatment on chemical composition

    Besides the predictable increase of ash content, the treatment modifies mainly the cell wall constituents (Table 9) and protein fraction contents linked to ADF.

    Table 9: Average cell wall constituents of exhausted screened olive cake untreated or treated with 4 percent soda (6 percent of DM) (Nefzaoui, 1979)
     UntreatedTreated (6% NaOH/DM)
    Corrected ADL26.817.5
    Total ADF-N/N, %94.974.6
  2. Influence on digestive utilization:

    Degradability of proteins and dry matter improved. In vivo digestibility of dry matter, especially proteins and crude fibres increased. (Table 10).

    Table 10: Influence of soda treatment (industrial processing) on in vivo digestibility of exhausted screened olive cake
    Distribution methodTreatmentApparent digestibility coefficient
    Distributed separately, Thibar black rams(1)Untreated48503247     
    Treated 4% NaOH52524355     
    With molasses, as pellets distributed with 100 g hay and 1.5% urea, Texel sheep (2)Untreated313239232418144926
    Treated 4% NaOH353646333326236229
    40% olive cake, 49% barley, 8% molasses and 3% mineral concentrates, Thibar black rams (3)Untreated68705949     
    Treated 4% NaOH74756561     
    Treated 4% NaOH         
    + 1.5% urea71747058     

    (1) Exhausted screened olive cake with 26 percent CF, Nefzaoui A., and Abdouli, H., 1979.
    (2) Exhausted screened olive cake with 14 percent CF, Nefzaoui, A., Marchand, S. and Vanbelle, M.1982.
    (3) Exhausted screened olive cake with 26 percent CF, Nefzaoui, A., and Abdouli, H., 1979.

    The already large intake did not increase. On the other hand, the animal's water consumption was more than doubled and urine excretion more than tripled.

2.6.2 Ensilage with alkalis

Micro-silo (1.5 1) studies showed considerable in situ improvement of digestibility with large doses of soda (8%) which was higher than that obtained with ammonia (Table 11).

Table 11: In situ digestibility of alkali-treated exhausted screened olive cake silage (Nefzaoui, A. et al, 1982)
Apparent digestibility coefficientDMOMADFCP
Ammonia 2%60.2561.5345.8881.34
Ammonia 4%58.3260.3638.8983.80
Ammonia 6%63.0463.8648.1886.90
Ammonia 8%64.2865.3449.8789.54
Soda 4%62.8662.0046.6372.84
Soda 6%62.4660.5547.1773.93
Soda 8%78.5177.6762.0479.35

2.6.3 Ammonia treatment

Exhausted screened olive cake with molasses added previously was stored in plastic bags with an injection of NH3 (3%). The result was a considerable improvement of nutritive value (Table 12) especially through:

Table 12: Digestibility, intake and protein balance of exhausted screened olive cake ensiled with ammonia * (Nefzaoui, A. et al, 1983)
 Untreated olive cakeTreated 3% NH3
Digestibility (%)  
Intake g DM/d/P0.759998
Protein balance: g N/d/P0.75  
Ingested1.903 (100%)3.610 (100%)
Faecal1.353 (71%)1.632 (45%)
Urinary0.240 (13%)1.147 (32%)
Retained0.310 (16%)0.831 (23%)

* Factorial cross-over experiment with Texel breed lambs receiving olive cake freely 100 gbarley per day.

2.6.4 Ensilage of screened olive cake with poultry manure

Trials made by Nefzaoui and Deswysen (1982) showed that silages containing 70 percent of manure accumulated during less than 21 days and 30 percent exhausted screened olive cake were excellently preserved (according to the FLIEG's evaluation criteria).

2.6.5 Treatment with Na2 CO3

Vaccarino et al (1982) compared treatments with different doses of NaOH and Na2CO3 on partly destoned olive cake at 70° C during 150 minutes before adding solvent. Both methods improved digestibility in vitro considerably; however, soda proved the most effective (Table 13).

Table 13: Effects of treatment of partly destoned olive cake with NaOH or Na2CO3 on in vitro digestibility (Vaccarino et al, 1982)
 ControlNaOH, %Na2 CO3, %
Digestibility of       
Org. Mat.15.820.732.350.826.940.647.9
Digestibility of       
dry matter9.78.827.

2.6.6 Mechanical treatment

The only practical mechanical treatment consists of partly separating the shell of the kernel by screening or ventilation. This has the effect of markedly reducing the crude fibre (see Table 5) and true cellulose contents but, paradoxically, the lignin content (see Table 6) is reduced very little.

If we refer to Table 7, the effect of partial destoning on digestibility of non-exhausted olive cake is not clear; the results are so few and heterogeneous that no specific conclusions can be drawn from them.

However recent studies (Nefzaoui et al, 1983, unpublished results) comparing exhausted olive cake, unscreened, screened, or treated with different alkalis (Figure 5), showed that by itself screening improved:

Therefore screening seems to be a very effective treatment for improvement of the nutritive value of exhausted olive cake.

2.6.7 Biological treatment

Very few experiments have been conducted in this field. However Karapinar (1977) and Worgan (1978) reported that the tissues contained in olive cake are resistant to microbial degradation. Fungi cultures on the olive cake have not noticeably decreased fibre content even after alkali treatment. Sporotriclum pulverulentum culture on screened olive cake increased crude protein content but did not significantly decrease that of crude fibre (Table 14

Figure 5: Effect of screening exhausted olive cake compared to various alkali treatments (Nefzaoui et al, 1983)

Figure 5

ESOC: Exhausted screened olive cake
EUOC: Exhausted unscreened olive cake

Table 14: Action of fungi (S. pulverulentium) on olive cake
TreatmentYield: g/100 g by-productComposition
Dry matterCPCPCrude fibre
Olive cake1007.37.342
Crushed olive cake screened514.89.421
Fungi culture43.56.314.520.7
Fungi + alkaline treatment348.52515

Sources: Karapinar (1977); Worgan (1978)
Cited by Zoiopoulos, 1983 a,b,c,d

2.7 Use of olive cake in animal feeding

Olive cake in its different forms is traditionally used in most producer countries. Curiously, few thorough studies have been conducted to evaluate the effect of including it in varying degrees in animal diets.

2.7.1 Crude olive cake

This is used in Tunisia mixed with bran or even cactus to feed dromedaries most of the year or sheep during difficult seasons. But very few tests have been made with this type of olive cake.

2.7.2 Partly destoned fatty olive cake

  1. on sheep: Bloemeyer (1977), distributing a concentrate containing 0 to 40% olive cake with urea-molasses obtained weight gains of 125 to 101 g/d with grazing sheep receiving 500 g of hay and the concentrate according to liveweight (20–30 g/kg liveweight).

    Ben Hamouda (1975) replacing 0 to 30 percent barley by olive cake in sheep diets obtained growths that were about the same, although slightly decreasing (274 g/d to 226 g/d) but with a higher conversion rate.

    Accardi et al (1979) replacing 30 percent of Sulla hay by 30 percent of olive cake in a lamb ration including 38 percent maize and 30 percent soya cake obtained slightly lower growths (191 g/d compared to 209 g/d) and a higher conversion rate (4.91 compared to 4.24).

    In Sardinia, Piccarolo and Paschino (1978), Paschino and Piccarolo (1980), Dattilo (1980), and Dattilo and Congiu (1979) introduced screened olive cake (about 20 percent) in pellets containing various other by-products and reported ewe milk outputs comparable to those obtained with grazing.

    Giouzelgiannis et al (1978) introducing 15 to 25 percent of olive cake (Kourgi method) in the lamb ration discovered no significant differences in terms of weight gain, intake or carcass quality; only the conversion rate was at a 25 percent higher level with olive cake.

  2. on cattle: Experiments conducted in Italy (Piccinnini, 1906; Gugnoni, 1920; Maymone and Guistozzi, 1935 a and b) seem to show a positive effect of olive cake on the fat content of cow's milk with practically equal milk production (at 4% fat) when the cows receive 1.8 to 4 kg of olive cake/day.

    In Greece Belibasakis (1982) feeding dairy cows with proportions between 10 and 20 percent of olive cake in the concentrate found no significant differences in milk production and composition.

    Maymone and Giustozzi (1935), using heifers weighing 295 kg fed during 60 days with hay and lucerne silage, adding maize or olive cake meal (with 8 percent fat), obtained respective weight gains of 630 g/d (with 922 g/d of maize consumed) and 370 g/d (with 775 g/d of olive cake consumed).

2.7.3 Partly destoned exhausted olive cake

  1. On sheep

    This olive cake was used in “shortage periods” rations in Tunisia by Nefzaoui and Ksaier (1981), who incorporated 0–35 or 70 percent of it in concentrate distributed with 300 g/d of straw to ewes which were first pregnant and then nursing (Table 15), during a period of 17 weeks. The performances of the ewes receiving 35 percent of olive cake were comparable to those of the control animals. Those receiving 70 percent had a 20 percent weight loss; weight of lambs at birth was lower and mortality was much higher (61 percent compared to 29 percent). However it must be mentioned that this ration not only enabled the mother ewes to survive but also made it possible to save a considerable number of lambs during a period of more than four months.

    Table 15: Maintenance of pregnant ewes from mating to parturition in central Tunisia (Ousseltia) with rations based on exhausted screened olive cake (Nefzaoui, A., Ksaier, H., 1981)
     Control animal35% olive cake70% olive cake
    Composition of rations (%)   
    Olive cake0.0035.0070.00
    Number of animals202020
    Initial weight, kg52.3552.1552.45
    Final weight, kg57.3057.3342.77
    Weight of lambs at birth3.503.302.60
    Intake g DM/d/P0.7576.00105.0085.00

    (1) Ewes belonging to the Barbarine breed, average age 6 years.
    (2) The animals receive 300 g/d of straw and rations ad libitum.

  2. On cattle

    With young growing cattle, replacement of oat-vetch hay of poor quality by 0-20-40-60 percent of exhausted screened olive cake led to a steady decrease of weight gains which were 536-260-190-39 g/day respectively, (Bougalech, 1980). In this case too as high a proportion as 60 percent of this type of olive cake in the ration was able to ensure maintenance of the animals.

    In Lybia, O'Donovan (1983), using 32 Holstein heifers weighing 284 kg receiving straw ad libitum (5.7 kg/d) and 2.7 kg of a concentrate containing 0-15-30-45 percent of partly destoned olive cake obtained no difference in weight gains, which were 688-706-695 and 698 g/d respectively. In another experiment 12 Holstein heifers and 12 Holstein bull calves weighing 130 kg and receiving a minimum of straw (0.6 kg/d) and 3.3 kg of a concentrate containing 0-15-30 percent of olive cake had respective increases of 1 029, 975 and 813 g/d.

2.7.4 Alkali-treated partly destoned exhausted olive cake

Treatment of exhausted screened olive cake with soda can improve digestibility (see paragraph 2.5.1).

Table 16: Fattening of Barbarine breed sheep with screened olive cake untreated or treated with soda (Nefzaoui, A. and Abdouli, H., 1979)
 Control40% untreated olive cake40% olive cake treated with 4% NaOH40% olive cake treated with 4% NaOH+ urea
Composition of rations    
Untreated olive cake-40.00--
Olive cake treated with 4% NaOH--40.0040.00
Minerals + vitamins3.
Initial weight, kg41.9437.4937.6436.78
Final weight, kg54.1849.3152.0951.04
ADG, g/day175.00169.00206.00203.00
Intake, g DM/d/P0.7589.00109.00108.00110.00
Consumption index kg DM/kg gain9.2910.949.049.24

(1) Each lot consisted of 10 male sheep aged 15 to 16 months.
(2) The animals received 200 g of Oat-vetch hay per day and concentrates ad libitum.
(3) The duration of the trial was 90 days.

Although replacement of 40 percent untreated olive cake in the concentrate distributed ad libitum to sheep also receiving 200 g/d of hay did not change their growth, the 4 percent soda treatment allowed increased weight gains and improvement of the conversion rate. This result was unchanged for the addition of urea (Table 16). However the differences were not striking. This may be because the proportion of olive cake remained low,_i.e., 40 percent of the ration; the rest of the ration was very rich (about 50 percent barley and 8 percent molasses), and the proportion of soda-only 4 percent-was probably too low (see para. 2.6.2). In present economic circumstances it is unlikely that this soda treatment could become profitable by such a slight improvement of performance.

2.7.5 Other prospects

The plans for treatment of olive cake for furfural production in Tunisia, and probably in other countries, should lead to an increase in the proportion of partly destoned exhausted olive cake. It would be possible (and desirable) to carry out such destoning in the extraction plants rather than in the furfural plants. This would lower transport costs and keep the olive cake nearer the stock-raising areas, thereby making it more readily available to stock-raisers.

2.8 Conclusions

  1. Olive cake is a rough ligno-cellulose feed because of:

  2. Olive cake probably contains no toxic or inhibiting substances. Its poor digestive and metabolic utilization is probably due mainly to its high degree of lignification and to the tech nological process for oil extraction in which it is frequently subjected to high heat.

  3. Distributed alone:

  4. The tegument and shells have low digestibility. Screening, which eliminates part or all of the stones, improves the nutritive value of olive cake. Intensive screening, leaving only a very light product consisting mainly of the tegument would have the opposite effect. The screening operation should retain fragments of the crushed kernel which are especially rich in proteins and have high digestibility.

  5. Its use without any previous treatment can ensure:

  6. Treatment can improve the nutritive value of olive cake:

    1. Development of industrial treatment with soda in spite of some improvement is still limited since the investments involved are high.

    2. Treatment with 6 to 8 percent doses of soda through ensilage would be effective but also too costly.

    3. Ammonia treatment (ensilage) would be more promising, since it would improve digestibility and provide an additional protein supply.

  7. Supplementing olive cake by a good quality and low cost protein source would undoubtedly be profitable. Initial trials with poultry manure seem promising.

  8. Table 17 sums up the possibilities of using olive cake in animal feeding. From the present state of information it seems that all types of olive cake can be used ad libitum without risk for survival operations, but none of them can provide for an intensive type of production.

    Table 17: Possibilities of using different types of olive cake in animal feeding.
    Type of ProductionSurvivalMaintenanceModerate production levelIntensive production
    Type of olive cake
    Exhausted olive cakead lib+   
    fodder +…---
    Crude olive cakead lib+ad lib+  
    fodder + …fodder + …--
    Fatty screened olive cakead lib+< 30%< 30%-
    fodder + …   
    Exhausted screened olive cakead lib+ad lib+  
    fodder + …fodder + …< 40–50%-
    Pulpidem screened fatty olive cake
  9. One can find practically no experiments on pigs except that of Maymone and Durante (1945) who replaced 50 percent of maize in a concentrated ration containing 70 percent maize and obtained respective weight gains of 940 g/d with 70 percent maize and 770 g/d with 50% of partly destoned fatty olive cake (20 percent EE) and 20 percent maize during a period of 64 days with pigs weighing about 16 kg at the start. However these results have not been confirmed subsequently by other experiments and are hard to interpret in view of the lignocellulose content of olive cake.

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