Nutritional evaluation of cardoon
(
Cynara cardunculus
) seed for ruminants
C. Cajarville
1, J. GonzaÂlez
*, J.L. Repetto
1,
M.R. Alvir, C.A. RodrõÂguez
Departamento de ProduccioÂn Animal, Escuela TeÂcnica Superior de Ingenieros AgroÂnomos, Universidad PoliteÂcnica de Madrid, Ciudad Universitaria, 28040 Madrid, Spain
Received 9 September 1999; received in revised form 8 June 2000; accepted 3 August 2000
Abstract
Chemical composition, rumen degradability, and digestibility coef®cients of whole cardoon (Cynara cardunculus L.) seed were studied on two different samples. Ruminal degradability of whole seed was determined by using the nylon bag technique in three rumen ®stulated wethers. Four wethers were used to perform digestibility studies on a basal diet (0.5 hay and 0.5 concentrate) and three diets more where cardoon seed was included at rates of 0.1, 0.2, and 0.3 at the expense of the basal diet in a 44 Latin-square design. Additionally, the effects of three substitution rates (0, 0.1, and 0.25) on rumen fermentation patterns and ®brolytic activity, measured by the in sacco degradation of the lucerne hay included in the diets, were established using a 33 Latin-square design with three rumen ®stulated wethers. Crude protein (CP), ether extract (EE) and neutral detergent ®bre (NDF) contents of whole cardoon seed were 225, 250, and 338 g kgÿ1DM, respectively, the last being highly ligni®ed (acid detergent lignin ADF 104 g kgÿ1DM) as consequence of its high hull proportion (45%). Rumen DM degradability of whole seed was 56.8%, while CP degradability was 82.9%. Diet digestibility coef®cients were maximum for 0.1 substitution rate, except for EE, that showed a linear and quadratic increase through all diets. The estimates of seed digestibility obtained by the substitution and extrapolation methods were only similar for the 0.3 substitution rate. Digestibility coef®cients (%) obtained by substitution at this level were 83.8 for CP, 82.8 for EE, 20.3 for NDF, 56.1 for OM, and 59.2 for energy. Seed inclusion in diets up to a 25% had not effect on rumen fermentation patterns or on ruminal ®brolytic activity, in spite of the high content of fat rich in unsaturated fatty acids (85.5% of total fatty acids) of this seed.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Cynara cardunculus; Whole seed; Nutritive value; Rumen degradability 87 (2000) 203±213
*Corresponding author. Tel.:34-91-5493069; fax:34-91-5499763. E-mail address: jgonzalez@pan.etsia.upm.es (J. GonzaÂlez).
1Departamento de NutricioÂn Animal, Facultad de Veterinaria, Universidad de la RepuÂblica Oriental del Uruguay, Lasplaces 1550, 11600 Montevideo, Uruguay.
1. Introduction
The cardoon (Cynara cardunculusL.) is a kind of thistle that belongs to theasteraceae family. This perennial herbaceous species grows naturally in Mediterranean countries, where the petioles of its lowest leaves have been traditionally used as human food. The vegetative cycle of this plant, that can persist during 8 years, includes the development of leaves in autumn and winter, the elongation of the stalk in spring, and, in early summer, the formation of the capitules that contain the seeds. During summer the aerial part of the plant becomes dry, leaving underground buds in a latent state. Because of its strong root system, this plant is well adapted to semiarid conditions with high biomass production per ha, which includes 2±3 t haÿ1of seeds with high protein and lipid contents (FernaÂndez and Manzanares, 1990). As a consequence, different industrial possibilities for this crop are in study, as the use of the biomass for energy production or for pulp paper manufacture, and the oil extraction from its seeds (FernaÂndez and Manzanares, 1990; FernaÂndez et al., 1996). In addition, it is interesting to consider the potential of the different foods derived from this crop for animal nutrition. Although there is some information about the nutritive value of green forage and crop by-products of cardoon (FernaÂndez and Manzanares, 1990; Romero et al., 1997; Cajarville et al., 1999), the data concerning the nutritive value of cardoon seed is limited to some data of chemical composition (FernaÂndez and Manzanares, 1990). Therefore, the aim of the present work was to evaluate its potential use for feeding ruminants, studying its chemical composition, its rumen degradability and its digestibility.
2. Material and methods
2.1. Trial feeds
The cardoon seeds were harvested respectively in 1994 (S1) and 1995 (S2). Sample S1 was used for chemical composition determinations (including amino acids and fatty acids analysis) and for rumen degradability studies. A portion of this sample was manually dehulled to establish the proportion of hull and kernel fractions, which were also analysed for chemical composition. Sample S2 was employed in feeding trials to assess the apparent digestibility and the effects of increasing the dietary inclusion of this seed on the ruminal ®brolytic capacity. The chemical composition of both seeds is given in Table 1.
2.2. Ruminal degradability
Three wethers (2±3-year old) provided with a rumen cannula were used in the experiment. The wethers were fed a mixed (2:1 on DM) forage to concentrate diet containing 121 g CP kgÿ1DM and 354 g NDF kgÿ1DM. The diet was distributed at an intake level of 40 g DM kgÿ1BW0.75, in two equal-weight meals at 9.00 and 17.00 h.
The nylon bag technique was used to measure rumen degradability of DM and CP. The nylon-bags (Blutex nylon 120T, pore size 46mm, Tissages Tissues Techniques, Paris, France) were made by heat-sealing and measured 6.5 cm10:5 cm (inner dimensions).
The sample S1was ground to pass through a 2 mm sieve and approximately 3 g (air dry basis) was incubated in the rumen of each animal for intervals of 2, 4, 8, 16, 24, 48 and 72 h. Two series of incubation were conducted in different days in order to have two bags per animal and per incubation time. All bags of each incubation series were inserted simultaneously at the morning feeding time. After removing from the rumen, the bags were washed thoroughly under tap water and frozen (ÿ208C). Once defrosted for analysis, the bags were washed three times for 5 min in a turbine washing machine, dried at 808C for 48 h and analysed for DM and N. Three additional bags were reserved for zero incubation that involved the washing procedure without prior rumen incubation. The percentages of DM and N disappearance from the nylon bags at each incubation time were calculated from their respective amounts remaining after incubation in the rumen. Microbial contamination of the bags was not estimated. Disappearance data of DM and CP were ®tted for each sheep to the exponential model of érskov and McDonald (1979), and effective degradability (ED) values were estimated from the respective kinetic parameters and the rumen particulate out¯ow rate (kp) of this seed.
Values ofkpwere determined by supplying to the animals, immediately before the ®rst daily meal, a pulse dose (40 g) of 2 mm ground seed S1 previously washed with a commercial detergent in an automatic washing machine to eliminate the soluble components, and labelled with ytterbium. Labelling was done by the immersion method, as described by GonzaÂlez et al. (1998), at a rate of 5 mg Yb per g DM. Then, a total of 19 faecal grab samples were collected from the rectum of each animal, the ®rst before supplying the marker and the rest at intervals of 4, 6, 8 and 12 h in the periods of 16±36, 36±60, 60±84 and 84±144 h postdosage, respectively. The samples were dried, ground and analysed for Yb. The pattern of Yb concentrations in faeces with time was described by ®tting the model proposed by Dhanoa et al. (1985), and the rate constants derived from the decreasing phase of concentrations were used askpvalues.
Table 1
Chemical composition (g kgÿ1DM) ofCynara cardunculusseed and of basal diet ingredientsa
Item Cynara cardunculusseed Basal diet
S1 Hullb Kernelb S2 Hay Concentrate
DM (g kgÿ1) 948 943 955 922 883 892
OM 959 969 951 953 891 956
CP 213 54.9 317 237 177 165
EE 250 41.3c 418 250 25.8 31.7
NDF 388 812 45.5 388 448 311
ADF 306 667 14.7 304 348 104
ADL 102 220c 7.2 106 81.9 31.8
GE (MJ kgÿ1DM) 23.25 17.96 18.55
NDIN (g kgÿ1N) 137 872 26.6 ADIN (g kgÿ1N) 100 835 10.6
aDM: dry matter; OM: organic matter; CP: crude protein; EE: ether extract; NDF: neutral detergent ®bre; ADF: acid detergent ®bre; ADL: acid detergent lignin; NDIN: neutral detergent insoluble nitrogen; ADIN: acid detergent insoluble nitrogen.
bFractions obtained from S 1sample.
2.3. Feeding trials
Two trials were carried out by substituting a basal diet with ground seed S2at increased substitution rates. As basal diet was employed a mixed diet (1:1 on DM) of chopped lucerne hay and concentrate meal (0.65 barley grain, 0.2 wheat bran, and 0.15 sun¯ower meal). The chemical composition of the basal diet ingredients is given in Table 1. All diets (basal and substituted) were offered in both trials at a restricted level of 70 g DM kgÿ1BW0.75in two equal-weight meals at 9 and 17 h. In addition, animals had free access to a mineral block.
In trial 1, four wethers (59:34:15 kg BW) were used in a 44 Latin-square design
to determine the apparent digestibility of four experimental diets with substitution rates of 0, 0.1, 0.2, and 0.3. After a 15 days adaptation period to each diet, digestibility coef®cients of organic matter (OM), crude protein (CPN6:25), ether
extract (EE), neutral detergent ®bre (NDF), acid detergent ®bre (ADF), and energy were determined by collection of faeces through 7 days. The respective digestibility coef®cients for cardoon seed were determined from the digestible components of each diet by the substitution method and by extrapolation for the components which showed a linear ®tting.
In trial 2, the ruminal degradation of the lucerne hay of basal diet was determined to establish the effects of seed substitution rate on the rumen ®brolytic capacity. In this trial three substitution rates (0, 0.1, and 0.25) were studied, using a 33 Latin-square design and three rumen cannulated wethers. Each experimental period of this trial consisted in a 15 days adaptation period followed by the determination of the ruminal degradation kinetics of DM and NDF of the lucerne hay, using the in sacco methodology above described. Degradation kinetics were also described by the model of érskov and McDonald (1979). Nevertheless, the soluble fraction (a) for NDF was assumed to be zero, as zero incubation results do not show any bag disappearance. Finally, samples of rumen ¯uid were collected hourly in the interval between meals to determine rumen pH and ammonia and volatile fatty acids (VFA) concentrations.
2.4. Analytical methods
Samples of feeds and faeces were ground to pass through a 1 mm sieve before analysis. DM, ash, EE and CP were determined following the AOAC (1990) methods. The contents of NDF, ADF, and ADL were determined as described by Robertson and Van Soest (1981). Insoluble N in neutral detergent (NDIN) and in acid detergent (ADIN) solutions was determined by Kjeldahl analysis of the NDF and ADF residues, respectively. Gross energy and digestible energy contents were obtained measuring heat production from the offered feeds and faeces in an adiabatic calorimeter bomb. Proportions of fatty acids in seed were determined in a Perkin-Elmer 8500 gas chromatograph (Perkin-Elmer Co., Beacons®eld, UK), provided with a ¯ame ionisation detector. Amino acids were determined for the whole seed by high pressure liquid chromatography in reverse phase after previous derivatization, following the technique of Jones et al. (1981), but using a ¯uorescence detector only. Proline, cystine and tryptophan were not determined due to technical limitations.
Samples of faeces collected for transit studies were incinerated at 5508C and then digested by boiling with a solution of 1.5 M nitric acid and potassium chloride (3.81 g lÿ1). The resultant solutions were analysed for Yb by atomic absorption spectrometry (Smith-Hieftje 22. Thermo Jarrell Ash, MA, USA), using predosed samples of faeces to prepare common matrix standards.
Ammonia in rumen ¯uid was analysed by distillation with a solution of sodium tetraborate (2.5% w/v), collected on boric acid solution (1% w/v) and titrated with hydrochloric acid (0.02 M). Rumen ¯uid VFA concentration was determined in a Hewlett-Packard 5710 A (Hewlett-Packard, Palo Alto, CA, USA) gas chromatograph with a ¯ame ionisation detector.
2.5. Statistical analysis
The transit and degradation kinetics were ®tted by non-linear regression. The differences between DM and N degradation values were compared by the pairedt-test. Data of feeding trials were examined by analysis of variance, and linear and quadratic effects of diet were established in trial 1 by orthogonal polynomials. When linear effects at P<0:05 were observed for the content of digestible components, response curves
were ®tted to estimate seed digestibility by extrapolation. Standard errors of the substitution and the extrapolation values of cardoon seed digestibility were determined as indicated by Villamide (1996). All statistical analyses were performed with the Statistical Analysis System for windows software, version 6.12 (SAS, 1990).
3. Results
3.1. Chemical composition of cardoon seed
The proportions of hull in whole cardoon seed was 45% (sample S1). This seed presents high contents in EE and CP (concentrated in the kernel), but also high levels of ®bre and lignin (mainly located in the hull, which concentrates also the main part of the ®bre bound nitrogen) (Table 1). Proportions of lipid fatty acids in the whole seed were 56.8% polyunsaturated (C18:256:7%; C18:30:11%), 28.7% monounsaturated
( C 1 6 : 10:11%; C 1 8 : 128:4%; C 2 0 : 10:13%) a n d 1 4 . 5 % s a t u r a t e d
(C16:010:6%; C18:03:56%; C20:00:37%). The amino acid content
(g kgÿ1DM) in the whole seed were: 11.7 arginine, 3.2 histidine, 6.1 isoleucine, 10.2 leucine, 6.1 lysine, 1.2 methionine, 8.3 phenylalanine, 6.4 threonine, 7.8 valine, 8.0 alanine, 16.9 aspartic acid, 30.7 glutamic acid, 8.9 glycine, 11.8 serine, and 5.9 tyrosine. Essential amino acids represent 46.9% of total analysed amino acids.
3.2. Ruminal cardoon seed degradability
Degradation extent (ab) and fractional degradation rate for seed S1 were much higher for CP than for DM, though the difference for degradation rate was not signi®cant, as consequence of the high variability observed (Table 2). Mean value of the rumen
particulate out¯ow rate (kp) of cardoon seed was 3.44% hÿ1and the resultant values of ED were higher (P<0:001) for N (82.9%) than for DM (56.8%).
3.3. Feeding trials and seed digestibility
Diet digestibility coef®cients (Table 3) showed the highest values for the substitution rate of 0.1, except for EE, which showed a linear and quadratic increase through all levels of the substitution rate. Linear and quadratic effects were also observed for the remainder factors, except for ADF, that was only linear, and for CP, that was only quadratic.
Whole seed apparent digestibility coef®cients obtained by the substitution method and their associated S.E. values decreased with the increase of the substitution rate; those obtained with the 0.3 substitution rate were similar to digestibility values obtained by extrapolation (Table 4). Energy digestibility was not determined by extrapolation, because its dietary digestible content (12.5, 13.1, 13.1, and 12.9 MJ kgÿ1DM for 0, 0.1, 0.2, and 0.3 substitution rate, respectively) did not show a linear effect and varied only in quadratic form (P0:012). Considering only the observation sets obtained at 0.3
Table 2
Rumen degradation kinetics and effective degradability of dry matter (DM) and crude protein (CP) of whole Cynara cardunculusseed
Item DM CP S.E.D.b Pc
Soluble fraction (a, %) 33.3 49.5 0.33 <0.001
Potentially degradable fraction (b, %) 27.4 36.3 1.04 0.014 Undegradable fractiona(u, %) 39.3 14.2 1.10 0.002 Fractional degradation rate (kd, % hÿ1) 20.6 50.8 14.3 0.170 Effective degradability (ED, %) 56.8 82.9 0.54 <0.001
aCalculated as 100ÿ ab.
bS.E.D.: standard error of the difference. cP: signi®cance level of the pairedt-test.
Table 3
Effect of increasing substitution rates ofCynara cardunculusseed on digestibility coef®cients (%) of dietsa
Item Substitution rate S.E.b Lc Qd
0 0.1 0.2 0.3
DM 68.4 69.4 67.6 64.4 0.74 0.004 0.026
OM 71.1 72.0 69.8 66.5 0.68 <0.001 0.015
CP 77.6 81.0 80.3 79.9 0.62 0.081 0.026
EE 48.5 71.5 75.6 75.7 2.46 <0.001 0.003
NDF 48.5 49.2 45.7 39.9 1.22 <0.001 0.025
ADF 43.1 43.6 39.8 35.0 1.44 0.002 0.094
Energy 68.5 69.9 68.2 65.2 0.72 0.007 0.015
aFor abbreviations see Table 1. bS.E.: mean standard error.
cL: signi®cance of linear effect of substitution rate. dQ: signi®cance of quadratic effect of substitution rate.
substitution rate, digestibility values were high (83%) for CP and EE and very low (20± 21%) for NDF and ADF. Therefore, the digestibilities of OM and energy were intermediate.
Seed inclusion until levels of 25% of the diet does not show any effect (P>0:05) on
the rumen degradation kinetics of NDF or DM of the lucerne hay included in the diets (Table 5), although the 0.1 substitution rate diet shows, in relation to the basal diet, an important increase of the fractional degradation rate for NDF (41.6%) as well as for DM (25.8%). No effects were also observed on ruminal fermentation parameters (pH, ammonia, VFA, Table 6). The variations of these parameters were small, though the cardoon seed inclusion decreased total VFA concentrations, especially for the diet at 0.25 substitution rate, and increased ammonia concentrations.
Table 4
Mean digestibility values (%) ofCynara cardunculusseed obtained by the substitution and the extrapolation methodsa
Item Substitution rate Extrapolation value
0.1 0.2 0.3
DM 78.611.9b 64.36.5 55.03.9 55.73.8
OM 79.88.6 64.74.6 56.13.1 56.63.1
CP 103.111.6 88.26.0 83.84.1 83.63.5
EE 95.06.9 87.74.9 82.81.9 83.22.3
NDF 54.913.5 34.916.0 20.38.7 21.48.6
ADF 46.524.2 30.011.7 20.86.5 21.36.3
Energy 79.728.8 67.314.5 59.28.9
aFor abbreviations see Table 1. bStandard error.
Table 5
Effect of increasing substitution rates ofCynara cardunculusseed on rumen degradation kinetics of dry matter and neutral detergent ®bre of the dietary lucerne haya
Item Substitution rate S.E.b
0 0.10 0.25
Dry matter
a(%) 30.4 30.1 29.9 0.31
b(%) 38.8 38.8 39.3 0.23
u(%) 30.8 31.1 30.8 0.21
kd(% hÿ1) 10.1 12.7 9.33 1.98
Neutral detergent ®bre
b(%) 43.2 42.7 43.4 0.15
kd(% hÿ1) 4.40 6.23 4.61 0.70
aa,bandurepresent soluble, non-soluble degradable, and undegradable fractions, respectively.kd, fractional degradation rate of fractionb.
bS.E.: mean standard error.
4. Discussion
4.1. Chemical composition
The nutritive value of cardoon seed is mainly conditioned on its high hull proportion (45%), that is higher than in other oil seeds as rape seed (15±20%) or sun¯ower seed (until 30%) (Bell, 1984; Thibault et al., 1989). As this hull shows very high levels of ®bre and lignin (similar to those of sun¯ower hulls), the concentration of these constituents in the whole seed is much higher than in the indicated seeds. Values of chemical composition (Table 1) of seeds harvested in different years show a great repeatability and were similar to those reported by FernaÂndez and Manzanares (1990), except for the CP content (169 g kgÿ1DM). The fatty acid pro®le of cardoon seed, characterised for a high insaturation degree (85.5%) and for the predominance of the linoleic and oleic acids (56.7 and 28.4%, respectively), is similar to the most common oil seeds (rape, soybean, cotton, sun¯ower). WholeC. cardunculus seed contains an acceptable proportion of essential amino acids. These values are in agreement with results showed by FernaÂndez and Manzanares (1990), except for methionine, that was 12 times higher than ours, however, that value is dif®culty explained from a biological point of view.
4.2. Ruminal degradability
The whole cardoon seed presents both high soluble and undegradable fractions and high degradation patterns rates for DM and CP. The undegradable fraction should be composed basically of residual hulls because of their very high contents in ®bre, lignin and ®bre bound nitrogen. The microscopically observation of incubation residues at 72 h supports this hypothesis. On the contrary, the others fractions (soluble and insoluble but fast degraded) should be composed mainly by the kernel, which has a great percentage of Table 6
Effect of increasing substitution rates ofCynara cardunculusseed on mean rumen pH, ammonia N and volatile fatty acids
Item Substitution rate S.E.a
0 0.10 0.25
pH 6.40 6.26 6.30 0.10
NH3-N (mg N lÿ1) 232 265 264 16.3
Total VFA (mmol lÿ1) 95.6 95.0 88.6 5.65
Individual VFA (molar % of total)
Acetic acid 62.5 60.9 61.2 0.21
Propionic acid 16.3 17.1 17.8 0.69
Butyric acid 15.3 15.8 14.9 0.48
Isobutyric acid 1.33 1.31 1.34 0.03
Valeric acid 2.90 3.10 3.08 0.07
Isovaleric acid 1.61 1.76 1.80 0.05
aS.E.: mean standard error.
cellular contents and very low values of N-®bre bound (especially ADIN). In this manner, degradation of whole seed will be the resultant of the very different patterns of degradation of their both components: the kernel highly degradable and the hulls shortly degradable.
The high CP degradability of this seed together with the increase of the dietary CP digestible content with increased substitution rates are in agreement with the apparent variation of the rumen ammonia concentration (Table 6). High values of CP degradation were also observed for other untreated seeds (Sauvant and Doreau, 1990; van Kempen and Jansman, 1994). Considering that the rumen undegradable protein fraction should also be indigestible in the small intestine (except its associated microbial contamination), the high N degradability value (82.9%) of cardoon seed indicates that undegraded feed CP, that is also digestible in the small intestine, is very limited (<3%). Therefore, available N to animals from this seed should be basically derived from the microbial protein synthesised in the rumen.
4.3. Seed digestibility and feeding possibilities
The concentration of some fractions was higher in seed S2 than in the basal diet (Table 1), so, each 0.1 increase of the substitution rate was associated with increments (g kgÿ1DM) of 22.1, 7.8, 6.6, and 4.9 for EE, ADF, CP and ADL, respectively. On the contrary, concentrations of OM and NDF were nearly constant for all diets. The change in diet digestibility values (Table 3) evidenced associative effects for low substitution rates. So, digestibility coef®cients, except for EE, raised their maximum values for 0.1 substitution rate. The linear and quadratic increase observed through all diets for apparent digestibility of EE agrees with observations of Palmquist and Jenkins (1980) and Palmquist (1991), who justify this effect by the reduction of the proportion of endogenous faecal fat with increasing fat intake and also by the substitution of forage by seed, as forage EE is abundant in non-digestible components as chlorophyll or waxes. The increase of both fat content and fat digestibility with substitution rate allows maintaining high dietary energy digestible contents despite the high inclusion of low digestible ®bre associated.
The addition of lipids to ruminant diets can reduce rumen digestibility of structural carbohydrates (Jenkins, 1993) as consequence of the anti-microbial effect of non esteri®ed fatty acids, mainly when they are unsaturated (Palmquist and Jenkins, 1980; Chalupa et al., 1984). Nevertheless, the degradation kinetics of lucerne hay (Table 5) supported that seed inclusion up to a level of 25% of the diet had no depressive effect on the rumen ®brolytic activity, in spite of the high content in unsaturated fat of this seed. More likely, the decrease in the ®bre digestibility of the diets is due to the progressive substitution of ®bre in the basal diet by that from seed hull, which is markedly ligni®ed and of low degradability. Calculations of NDF and ADF digestibilities for the 0.3 substitution rate from composition and digestibility of the basal diet (Tables 1 and 3) and seed S2 (Tables 1 and 4) yield identical values to those obtained experimentally, con®rming this hypothesis and indicating no associative effects. On the other hand, in sacco results showed an important increase (41.6%) between the 0 and 10% seed levels in the NDF fractional degradation rate (kd) of lucerne hay. This difference, although not
signi®cant, could explain the associative effects observed for digestibility values of the diet with 10% seed, through a higher degradative activity of ruminal ®brolytic microorganisms at moderate seed inclusion levels. As feed particles and microbial cells compete for adsorption of fatty acids in the rumen (Harfoot et al., 1974), a high adsorption on indigestible feed particles from the hulls may reduce the negative effects of fatty acids (Jenkins, 1993). Microbial colonisation of highly ligni®ed particles is limited (Cheng et al., 1984; Akin, 1989). Thus, the effect of fatty acids on the rumen ®brolytic activity should be small or even positive if the above mentioned preferential adsorption of fatty acids on hull particles leads to microbial colonisation of other less ligni®ed particles. Digestibility values ofC. cardunculusseed calculated by the substitution method for low substitution rates (0.1 or 0.2) are overvalued because of the associative effects. However, at a 0.3 substitution rate this method yielded similar estimates to those calculated by the extrapolation method, which are in agreement with obtained results of DM or CP rumen degradability. Digestibility values re¯ect the morphological composition of this seed. As a result, these values are high for CP and EE that are concentrated in the kernel and very low in the ®brous hull; therefore, digestibility of OM and energy raises a medium value.
5. Conclusions
The most suitable inclusion level of this seed in ruminant diets seem to be moderate (around 10%) to take advantage of its digestive effects. However, in animals with medium productivity this feed might be employed at higher levels (up to 30%) to add digestible fat. Long term feeding studies will be needed to verify this. On the contrary, inclusion levels higher than 10% should be avoided in highly productive ruminants, as the high content of ligni®ed ®bre of this seed would limit intake and its very low content of undegraded protein will limit productivity.
Acknowledgements
This work has been supported by the European Union funded Project AIR3-CT93 1089 (Cynara cardunculus Network). The authors thank to Ana Barroeta (Facultad de Veterinaria, Universidad AutoÂnoma de Barcelona) for making the analysis of fatty acids of cardoon seed.
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