Predicting the nutritive value of the olive leaf
(
Olea europaea
): digestibility and chemical
composition and in vitro studies
Manuel Delgado-PertõÂnÄez
a,*,
Augusto GoÂmez-Cabrera
b, Ana Garrido
baDpto. Ciencias Agroforestales, Universidad de Sevilla, Ctra. Utrera Km. 1, 41013 Sevilla, Spain
bDpto. ProduccioÂn Animal, Universidad de CoÂrdoba, Apdo. 3048, 14080 CoÂrdoba, Spain
Received 17 November 1998; received in revised form 11 August 1999; accepted 10 August 2000
Abstract
Eight tests of olive leaf digestibility were carried out with sheep. The olive leaves were collected using different procedures (four samples of leaves from dried branches and another four of leaves removed from chopped branches and dried) and stored for varying times. Marked differences in OMD were observed between the two types of procedures and between different times of storage. The greatest loss of nutritive value was in the chopped samples. In the leaves from dried branches, with storage periods longer than 9 months, the digestible organic matter content ranged between 431 and 448 g kgÿ1OM,
while in the chopped samples, the value ranged between 360 g kgÿ1OM (in a sample stored for only 1 month) and 177 g kgÿ1OM (in a sample with obvious signs of fermentation).
The sample set was used together with another, evaluated prior to this work, to study the prediction of in vivo digestibility (OMD, DMD and CPD) from chemical and biological (dry matter disappearance after in vitro incubation with rumen liquor±pepsin or pepsin±cellulase solutions) parameters. In the case of OMD, the best predictions were obtained with the pepsin±cellulase method (r0:91, RSD4:6) and NDF (r ÿ0:91, RSD4:6).#2000 Elsevier Science B.V. All rights reserved.
Keywords:Olive leaves; Nutritive value; Sheep; In vitro studies; Predicting in vivo digestibility
1. Introduction
In Mediterranean grassland ruminant production systems, the nutritive input from natural grazing is much reduced. In Syria, the supply was estimated as between 14 and
Animal Feed Science and Technology 87 (2000) 187±201
*Corresponding autor. Tel.:34-423-3669; fax:34-423-2644.
E-mail address: pertinez@cica.es (M. Delgado-PertõÂnÄez).
35%, depending on the characteristics of the year (Treacher et al., 1993). Various management strategies are used to complement the supply. They include long-range (trashumance) and short-range ¯ock migration, but above all, the use of crop residues, in particular those of cereals (Flamant, 1992).
Apart from cereals, an important crop in the Mediterranean basin is the olive, with the region producing 98% of the world total (approximately 11 million tons) (FAO, 1995). The use of by-products of this crop (leaf and olive pressings) has been part of the farming tradition of the region (Sansoucy et al., 1985). However, the specialization in production that has led to monocultivation of the olive in wide areas has also meant the absence of animals that could directly consume the plentiful prunings. The prunings must therefore be moved away from where they are produced, involving operations to increase their density to make their transport and storage easier (Delgado-PertõÂnÄez et al., 1994).
Various reviews of work on the use of the olive leaf (Sansoucy et al., 1985; Nefzaoui and Zidani, 1987) demonstrate a wide range in its nutritive value. It is therefore essential to identify the factors responsible for such diversity and to obtain equations for the determination of nutritive value, so that each batch can be assigned a correct value.
Previous work (GoÂmez-Cabrera et al., 1992) has shown a minor effect of variety, season and year in the nutritive value, but a greater importance of conservation by drying the leaves, mainly when they were not attached to the branches. The main aim of this work was to predict the nutritive value of the olive leaf from various chemical and biological parameters. As there is no standard system of collection and manipulation, emphasis has been placed on obtaining very different materials. Therefore we included leaves dried on the branches or obtained after chopping the branches, to con®rm our previous results (GoÂmez-Cabrera et al., 1992) and sometimes by increasing storage time.
2. Materials and methods
2.1. Effects of different drying methods on nutritive value of olive leaf
2.1.1. Collection and storage of olive leaves
Mature branches were collected during routine pruning of Picual and Hojiblanca cultivars of olive trees (Olea europaeaL.).
A set of eight samples of olive leaves were evaluated (Table 1).
2.1.1.1. Dried branches
2.1.1.1.1. Leaves from air-dried branches. Leaves dried on pruned branches in the air and under cover for 3 months. The branches were then crushed with a tractor and the leaf was coarsely separated by hand and stored for 21 months (sample B24) and 39 months (sample B42) piled on the ground. Prior to the digestibility tests, the leaf was mechanically separated from residual wood (of which some 15±20% remained at the end of the process).
Table 1
Olive leaves obtained after different methods of drying
Treatment Item Short description of treatment Storage time
Fresh leaves FLa Leaves from the branches 2±5 days
Dried branches (oven-dried) ODa/ODba,b Branches oven dried at 60±658C 16 h
Dried branches (air-dried) BOut3a Branches air-dried outdoors 3 months
B3a/B3ba,b Branches air-dried under cover 3 months
B24 Leaves from B3b were separated and stored for another 21 months 321 months
B42 Leaves from B3b were separated and stored for another 39 months 339 months
Dried branches (bales) BB9 Branches baled 7 days after pruning and stored under cover 7 days9 months
BB10 Branches baled 17 days after pruning and stored under cover 17 days9 months
Chopped branches BCa Branches chopped and leaves stored in piles outside, without rain 5±10 days
BC2a Material BC stored in evacuated airtight plastic bags for a further month 5±10 days1 month
BC24 Branches chopped and leaves stored in piles under cover 24 months
BC42 Branches chopped and leaves stored in piles under cover 42 months
BC1 Branches chopped and leaves stored in piles outside, without rain 10±15 days
BC12-F Branches chopped and wetted leaves stored in piles inside (slight fermentation) 12 months
aMaterial evaluated previously by our team (GoÂmez-Cabrera et al., 1992 and unpublished data). bTwo samples obtained in 2 years.
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2.1.1.1.2. Leaves from baled branches. Branches of less than 3 cm in diameter at the base were baled into high-pressure bales (0:6 m0:4 m0:3 m) using a LERDA machine. Some samples were baled 7 days (sample BB9) or 17 days (sample BB10) after pruning and stored under cover for 9 months. The leaves were then separated from the branches by hand. Both samples were wetted by rain before they were baled and placed under cover with sample BB9 receiving somewhat more rain.
2.1.1.2. Partially wetted chopped branches. Pruned olive branches were chopped while fresh with a DORCH chopper (Kapinka) and stored in piles under cover for 24 (BC24) and 42 (BC42) months, respectively. Some olive branches were also chopped in the same way and stored under cover for 12 months. Occurrence of fermentation was evident in this sample (BC12-F), which had been wetted by rain during chopping in the field and by infiltration at the storage site. Olive branches were chopped 10±15 days after pruning and the product was piled outside (without rainfall) a further 10±15 days (BC1). In all these samples, at the end of storage, the leaf was mechanically separated from wood (10±15% of residual wood). The mechanical separation of leaf and wood prior to the digestibility tests was carried out using a winnowing machine (prototype of the Departamento de MecanizacioÂn Agraria, University of CoÂrdoba).
2.1.2. In vivo digestibility determination and chemical composition
The digestibility of the eight samples of olive leaves after various conditions of storage was measured using four or ®ve adult Segure~naMerino sheep as described by GoÂmez-Cabrera et al. (1992). The amount of olive leaf offered to the sheep was 70 g DM kgÿ1 LW0.75 with 150 g of dehulled sun¯ower seed meal mixed with the leaf as a protein supplement. The diet was fed twice a day (9 a.m. and 6 p.m.) at an intake level close to maintenance. The adaptation period was 20 days (only 10 when two consecutive tests were made) followed by 10 days of faeces collection. The animals were offered 20 g of a mineral±vitamin corrector, STAY-DRY (18% Ca, 8% P, 10% Mg, 1.5% NaCl, 200 mg kgÿ1 Co, 400 mg kgÿ1I, 3000 mg kgÿ1Fe, 6000 mg kgÿ1Mn, 4000 mg kgÿ1Zn, 15 mg kgÿ1Se, 300 UI kgÿ1Vitamin A, 60 UI kgÿ1Vitamin D3, 800 UI kgÿ1Vitamin E).
In the leaf samples, gross energy (GE) content was measured in an adiabatic calorimeter (Parr), dry matter (DM), ash and crude protein (CP) were measured according to AOAC (1984) procedures and neutral detergent ®bre (NDF), acid detergent ®bre (ADF) and acid detergent lignin (ADL) were determined by the method of Robertson and Van Soest (1981). DM, ash and CP were determined for feed residues and faeces. Dry matter digestibility (DMD), organic matter digestibility (OMD) and crude protein digestibility (CPD) of the olive leaves were calculated by difference, taking into account the following values already obtained for sun¯ower meal (g kgÿ1): DM 650, OM 700 and CP 870 (GoÂmez-Cabrera et al., 1992).
2.2. Prediction of digestibility from chemical composition and in vitro studies
2.2.1. Collection and storage of olive leaves
Together with the formerly described eight samples of olive leaves, another eight samples were analyzed (Table 1). Their digestibility and chemical parameters had been
determined earlier by our team. These samples had been kept initially in the laboratory in airtight plastic bottles. Later, they were moved to a refrigerated room, where they were stored at 108C for 4±6 years. Of these eight samples, six were analyzed by GoÂmez-Cabrera et al. (1992). Fresh leaves (sample FL), leaves oven dried at 60±658C for 16 h (two samples obtained in 2 years, samples ODa and ODb), leaves dried on the branches for 3 months under cover (two samples obtained in 2 years, samples B3a and B3b) and leaves dried on the branches for 3 months outdoors (BOut3), exposed to rain and sun. The other two samples (unpublished results) were from machine-chopped (DORCH) branches. These were piled outside for 5±10 days. Wood material was separated out using a 1 cm mesh sieve and a fan. Digestibility was determined in one half of the material immediately (BC) and in the rest after this had been kept in evacuated airtight plastic bags for a further month (BC2).
2.2.2. Chemical composition
Contents in ash, CP, NDF, ADF, ADL and GE were determined in all the olive leaf samples of the set (16 in all).
2.2.3. In vitro studies
Two in vitro techniques were used, the rumen liquor±pepsin procedure of Tilley and Terry (1963) and the modi®ed (HCl 0.1 N) pepsin±cellulase method (AufreÁre and Michalet-Doreau, 1988). In both techniques, all samples were milled through a 1 mm screen and DM solubilities were determined in triplicate or duplicate. Rumen liquor was obtained from two mature cannulated ewes kept on alfalfa and the cellulase used was extracted from Trichoderma viridae (cellulase Onozuka R10, Medicine Department Yakult Honsha Co., Ltd.).
From in vivo and in vitro digestibility data and chemical composition of samples, Pearson's correlation coef®cients and corresponding regression equations between in vivo digestibilities and the other parameters were obtained. Analysis of variance was performed using the SAS software package (SAS, 1982) with the following treatments. PROC MEANS (to calculate means, standard deviation and ranks), PROC CORR (to calculate correlations between variables), PROC GLM (to calculate variances and regression) and MEANS/TUKEY (to calculate signi®cant differences between means).
3. Results and discussion
3.1. Effects of different drying methods on nutritive value of olive leaf
Chemical composition and in vivo digestibility values of the different leaves studied are shown in Table 2.
The variations observed in the dry material are a re¯ection of the different degrees of drying of the material and of the variation in atmospheric relative humidity during the year. Ash content is affected and increased by both wood content (Alibes et al., 1982) and soil contamination (Delgado-PertõÂnÄez, 1994). As there are only small differences in wood content in the materials used, the differences in ash might have
Table 2
Chemical composition and in vivo digestibility values of olive leaf samples dried under different conditions
Treatmenta Chemical compositionb Digestibility (%)b
DM
bFM, fresh matter; DM, dry matter; OM, organic matter; CP, crude protein; NDF, neutral detergent ®bre; ADF, acid detergent ®bre; ADL, acid detergent lignin; GE,
been the result of contamination with dust/soil. Thus, the baled samples (without residual wood) showed a higher ash content. This could also explain its lower content in gross energy.
The CP level ranged between 9.5 and 12.9%, accords with previous results (GoÂmez-Cabrera et al., 1992), although, considering the residual wood content, it is somewhat higher compared with other studies (GoÂmez-Cabrera et al., 1982; Alibes et al., 1982). According to FernaÂndez Escobar (unpublished data), the CP content can be as high as 9.5% in leaves, but only 4.4% in stems. The same author observed variations close to 2% units in leaf CP content with season, leaf age and foliar fertilization.
There was a wide variation in the content of NDF (39.9±62.6%), ADF (25.5±53.7%) and ADL (16.3±30.5%), which was greater than in the sample set studied by GoÂmez-Cabrera et al. (1992). This may have been due in part to the residual wood content, which was practically zero in the samples used by those authors. The proportion of ®bre increased with storage time, as was clearly seen in the chopped samples. NDF and ADF values in the chopped samples far exceeded those in the leaf from dried branches (air-dried and baled branches). GoÂmez-Cabrera et al. (1992) obtained a higher ADF content and a lower digestibility in leaves dried separately than in leaves dried on the branches. The most signi®cant factor for ADL seemed to be temperature. The fermented leaves, BC12-F, showed the highest value (30.5%), although a high level was also reached in leaves from chopped branches stored for more than 24 months.
DM and OM digestibility decreased signi®cantly with increasing storage time, both for leaves from dried branches and for leaves from chopped branches (Fig. 1). So, the material dried on the branches lost approximately 20% of its initial value during the ®rst 2 years of storage, even when dry and sheltered from the rain. Such effect could be due to changes in moisture content of the product resulting from seasonal changes in relative humidity. In winter, water may condense on the stored product, possibly causing fungal activity.
The loss of digestibility was particularly marked in the case of CP, whose value fell to around 10% in leaves from dried branches and was zero in leaves from chopped branches (Fig. 2). It can be seen that in all cases, the leaves from chopped branches had negative values, indicating true digestibilities close to zero. This loss of digestibility was also observed by GoÂmez-Cabrera et al. (1992). Delgado-PertõÂnÄez et al. (1998) studying a part of the material used in this study, observed high levels of the seco-iridoid glycoside oleuropein in materials freeze-dried or vacuum oven dried, disappearing during storage, with a simultaneous reduction in CP digestibility. Probably the protein from stored leaves remained complexed with the phenolic material because both increased their proportion into the water or acetone±water insoluble residues.
Considerable differences in the digestibility were found between leaves from dried branches and leaves from chopped branches. The fact that the branches were chopped partially wetted and piled immediately would create a humid atmosphere between individual leaves, leading to microbial or fungal activity and heating, particularly in the centre of the pile. The darker coloring of these materials supports this hypothesis. It is noteworthy that the leaves from chopped branches with obvious signs of fermentation (BC12-F), caused by rainwater, presented the lowest digestibility value (DMD15:7). However, the chopped samples used in the digestibility test almost immediately after
being obtained (BC) or kept in evacuated airtight plastic bags (BC2) presented values close to lowest quality leaves obtained from dried branches (DMD38:3 for BC, 37 for BC2).
3.2. Prediction of digestibility from chemical composition and in vitro studies
3.2.1. In vitro studies
Mean values of DM disappearance measured by pepsin±cellulase and rumen liquor± pepsin, together with their standard errors are given in Table 3. When the results of Fig. 1. In vivo organic matter digestibility (OMD) of olive leaf samples dried under different conditions (Treatment codes, see Table 1).
digestibility in vitro were compared with those obtained in vivo, it was observed that with the 16 samples used, the in vitro values far exceed the corresponding in vivo value.
A possible cause of the high in vitro value is the presence of substances having a toxic or inhibitory effect on microbiological activity, such as phenolic compounds. A greater dilution in the test tubes than in the rumen liquor could reduce the negative effect as suggested by Maeng et al. (1971) and Ololade and Mowa (1975) in the case of cereal straw treated with NaOH.
Hydrolyzable or condensed tannins have not been detected in olive leaves and have been ruled out as a possible antinutritional factor (Delgado-PertõÂnÄez et al., 1998). Fig. 2. In vivo crude protein digestibility (CPD) of olive leaf samples dried under different conditions (Treatment codes, see Table 1).
Similarly, though olive leaves are characterized by a high concentration of oleuropein (a seco-iridoid glycoside which gives the fruit its bitter taste, Kubo et al., 1995), there is no suggestion that oleuropein might be toxic to the rumen micro¯ora and the highest digestibilities were recorded for the samples with the greatest oleuropein content (Delgado-PertõÂnÄez et al., 1998).
The differences were generally smaller in the samples whose in vivo digestibility had been determined in the earlier tests (by GoÂmez-Cabrera et al., 1992), so that the sample used to determine in vitro digestibility had been stored for a long time. This could indicate that such samples do not remain stable at these storage times under the given conditions. A speci®c case is that of the fresh leaf sample (FL). For the determination of in vitro digestibility, this leaf was not in its original state, but had been subjected to drying, as was the oven-dried leaf of the same year (ODa). In fact, the in vitro digestibility values obtained with the two methods were similar for the two types of sample (48.3% for IVDMD and 57.8% for CELDMD in FL, versus 47.2% for IVDMD and 57.3% for CELDMD in ODa).
It was observed that the pepsin±cellulase technique gave higher values than the rumen liquor method with the samples of highest in vivo digestibility and lower values with Table 3
Dry matter in vitro Tilley and Terry (IVDMD), pepsin±cellulase (CELDMD) and in vivo (DMD) digestibilities (%) of olive leaf samples dried under different conditions
Treatmenta IVDMDb CELDMc DMD
Fresh leaves
bMean and standard error of means of triplicate determinations. cMean and standard error of means of duplicate determinations.
those of lowest digestibility. This is in accord with the results of Jones and Hayward (1973) and of McQueen and Van Soest (1975) indicating that in samples of low digestibility the enzymatic preparations do not solubilize as much organic matter as do rumen micro-organisms.
3.2.2. Prediction of in vivo digestibility
In vivo digestibility of olive leaves studied was related to various chemical parameters or in vitro disappearance by correlation (Table 4) and linear regression analysis.
Gross energy content did not reach signi®cant levels of correlation (P>0:05) with any of the chemical parameters and could not be predicted with suf®cient precision from these chemical analyses.
In contrast, the digestibility values presented signi®cant correlations with certain of the parameters analyzed. In the case of DM, both in vitro and in vivo and of OM, highly signi®cant negative correlations were obtained with NDF, ADF and ADL, while the correlation with ash or CP was not signi®cant. All the digestibilities were highly inter-correlated. There was greater precision in the estimation of in vivo digestibility with the pepsin±cellulase technique (RSD4:48 and 4.63 for DMD and OMD respectively) than with the rumen liquor method (RSD7:66 and 7.85 for DMD and OMD, respectively). This is in agreement with the results of Jones and Hayward (1975) and of AufreÁre and Michalet-Doreau (1988), but contradict the results found by others (Clark and Beard, 1977; Terry et al., 1978; Mcleod and Minson, 1978; Carlier et al., 1979; Gasa et al., 1989). Such differences could be due, as indicated by Van der Koelen and Van Es (1973) and by Aerts et al. (1977), to variability in the activity of the rumen liquor.
In all cases, the highest correlation with chemical parameters was given by NDF (r ÿ0:91 and RSD4:34 for DMD,r ÿ0:91 and RSD4:60 for OMD), with the same degree of precision as obtained for in vitro digestibility with cellulase (r0:90 for DMD and 0.91 for OMD). However, Jarrige and Thivend (1969), Van der Koelen and Van Es (1973), and Aerts et al. (1977), studying a wide range of grasses and legumes, and Gasa et al. (1989), working with a set of by-products from the canning industry, show that OMD can be more accurately predicted by biological methods (the two-stage fermentation procedure of Tilley and Terry, the pepsin±cellulase solubility bioassay or the in situ nylon bag technique).
The in vivo digestibility of CP was also correlated with these chemical parameters, although with lower precision, both NDF (r0:68) and in vitro digestibility with cellulase (r0:78). The inherent problem in the estimation of true digestibility of CP could partly explain this lower precision.
It seems clear that the material used was non-uniform under the conditions in which it is stored prior to analysis, affecting the relationship between the values of in vivo digestibility and the analytical results. This is seen in the values of in vitro digestibility obtained in many cases after years of sample storage (as were those obtained by GoÂmez-Cabrera et al., 1992). It is considered preferable in this type of estimation (and speci®cally that performed with rumen liquor) to analyze all in a single series because of the variability in conditions between different series (Van Es and Van der Meer, 1980). More important is the fact that in vitro digestibility method not allow to distinguish the
Table 4
Pearson's correlation coef®cients between different parametersaof olive leaf samples dried under various conditions
DM ASH CP NDF ADF ADL GE IVDMD CELDMD DMD OMD
ASH 0.66**
CP 0.18 0.27
NDF ÿ0.12 ÿ1.11 ÿ0.14
ADF ÿ0.19 ÿ0.17 ÿ0.05 0.97***
ADL ÿ0.09 ÿ0.06 0.08 0.87*** 0.93***
GE ÿ0.34 ÿ0.42 0.44 0.16 0.33 0.47
IVDMD 0.42 0.35 ÿ0.04 ÿ0.81*** ÿ0.87*** ÿ0.83** ÿ0.52*
CELDMD 0.23 0.16 0.11 ÿ0.94*** ÿ0.96*** ÿ0.91*** ÿ1.27 0.87***
DMD ÿ0.11 ÿ0.13 0.16 ÿ0.91*** ÿ0.89*** ÿ0.86*** ÿ1.06 0.69** 0.90***
OMD ÿ0.11 ÿ0.14 0.10 ÿ0.91*** ÿ0.89*** ÿ0.87*** ÿ1.08 0.71** 0.91*** 0.99***
CPD 0.08 0.23 0.52* ÿ0.68** ÿ0.65** ÿ0.61* ÿ1.02 0.60* 0.78*** 0.78*** 0.77***
aDM, dry matter; CP, crude protein; NDF, neutral detergent ®bre; ADF, acid detergent ®bre; ADL, acid detergent lignin; GE, gross energy; IVDMD, dry matter in
vitro Tilley and Terry digestibility; CELDMD, dry matter pepsin±cellulase digestibility; DMD, dry matter in vivo digestibility; OMD, organic matter in vivo digestibility; CPD, crude protein in vivo digestibility.
***P<0:001;P<0:01;P<0:05.
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effect of drying for the analysis, since the fresh leaves (FL) consumed by the sheep are dried prior to in vitro analysis. As a result, the latter leaf was similar to that which was oven-dried before being fed to the sheep.
Reducing the data set by (a) excluding the fresh leaf sample (n15) and (b) using only the eight samples evaluated in vivo in this work, the precision of the estima-tion increased (Table 5). This was especially signi®cant in the case of in vitro OM digestibility of Tilley and Terry (RSD6:9, with 15 samples and RSD4:4 with eight samples).
When a multiple regression was performed among the OMD or DMD and the chemical or biological parameters, the variables included in the model were digestibility with cellulase and ash. However, the introduction of a second parameter did not improve signi®cantly the accuracy of the prediction.
4. Conclusions
1. There were marked differences in nutritive value between leaves from dried branches and leaves dried off the branch, prior to being chopped. In the latter, the loss of nutritive value during drying was signi®cantly greater.
2. Storage of dry leaf in piles, sheltered from the rain but exposed to light and air, did not stop processes that reduce the nutritive value of the leaves.
3. Storage of the samples under laboratory conditions, in systems not protected from air and/or light, also resulted in reduced in vitro digestibility.
4. Neutral detergent ®bre was the best procedure, at a practical laboratory level, for predicting in vivo digestibility. It explains 83% of variability in organic matter, although only 46% of that in protein. The equations obtained with NDF and with the set of 15 samples (all except the sample of fresh leaf) were
DMD98:21ÿ1:31 NDF %=DMr0:92;RSD3:97
OMD105:65ÿ1:39 NDF %=DMr0:91;RSD4:32 Table 5
Correlation coef®cients (R) and standard error of regression (RSD) between in vivo digestibility of dry matter (DMD) or organic matter (OMD) and different chemical parameters or in vitro dry matter disappearance
Itema All the samples except fresh leaf (n15) Sample set evaluated in vivo in this work (n8)
DMD OMD DMD OMD
R RSD R RSD R RSD R RSD
NDF 0.92 3.97 0.91 4.32 0.93 3.73 0.95 3.65
ADF 0.91 4.23 0.91 4.50 0.93 3.84 0.94 3.73
ADL 0.87 4.83 0.88 5.08 0.89 4.66 0.90 4.83
IVDMD 0.74 6.70 0.76 6.90 0.91 4.30 0.92 4.37
CELDMD 0.92 3.84 0.92 4.05 0.93 3.73 0.95 3.62
aNDF, neutral detergent ®bre; ADF, acid detergent ®bre; ADL, acid detergent lignin; IVDMD, dry matter in
vitro Tilley and Terry digestibility; CELDMD, dry matter pepsin±cellulase digestibility.
Acknowledgements
The authors thank the ComisioÂn Interministerial de Ciencia y TecnologõÂa for the provision of funding (Project GAN 89-0289), the Centro de InvestigacioÂn y FormacioÂn Agraria de CoÂrdoba for the samples, and Jaime PelaÂez for his assistance in preparing the manuscript.
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