226 T
. Gidenne et al. Livestock Production Science 64 2000 225 –237 Table 1
measurements of parameters cited previously in a set
Ingredients and composition of the experimental diets
of experiments using a single and a simplified dietary
Diets A20
A16 A12
model. A reduced fibre intake is known to increase the
Ingredients
incidence of digestive disturbances in the growing
Wheat 12.0
32.0 50.0
Soya bean meal 9.7
13.7 17.5
rabbit Lebas et al., 1998. Digestive consequences
Wheat bran 22.0
9.8 –
of fibre are determined as well by the quantity of
Dehydrated lucerne meal 24.0
17.0 9.0
dietary fibre consumed as by the degradability of cell
Dehydrated beet pulp 25.0
19.5 15.0
wall components in relation to their physico-chemi-
Wheat straw 6.0
6.0 6.0
a
cal structure, such as particle size Gidenne et al.,
Minerals and vitamins 1.3
2.0 2.5
1991a. However, very few studies separated the
Chemical analysis g kg air dry basis
effect of the DF content from that of the nature of
Organic matter 858
861 864
the cell wall, because complex dietary models were
Crude protein Nx6.25 153
161 170
b
often used. Thus in the present study, we studied
Lysine 8.2
8.1 8.3
b
only the effect of a fibre level reduction, without
Sulphur amino acids 6.8
6.9 7.0
Starch 104
213 295
variations in the proportions of the different fibre
Neutral-detergent fibre NDF 393
313 238
fractions cellulose, lignin, etc., and using an origi-
Acid-detergent fibre ADF 202
155 117
nal comprehensive approach of rabbit digestion.
Acid-detergent lignin ADL 36
28 21
b
Water insoluble pectins 88
71 57
c
NNCC 312
387 456
ADF starch ratio 1.9
0.7 0.4
2. Materials and methods
a
Sodium chloride, calcium carbonate, dibasic calcium phos- phate, DL methionine, L-lysine, premix 0.5.
2.1. Experimental design and diets
b
Calculated from tabulated data on ingredients IO7, 1993.
c
NNCC: Non nitrogenous cellular content5OM2CP2NDF.
A set of four experiments was designed to test the impact of dietary fibre level on several parameters of
rabbit digestion and on health, feed intake and deficient levels of fibre. In parallel, the level of
growth. In the first, digestibility, ileal flow and starch increased from 10 to 30, so the ratio ADF
bacterial fibrolytic activity BFA were measured in starch reduced four times. In addition, the ratio
adult animals New Zealand White 3 Californian digestible crude protein digestible energy was con-
fitted with an ileal cannula. Using the same animals, trolled to obtain a similar digestible protein supply
the rate of passage between ileum and rectum was among diets in agreement with recommendations.
measured in the second experiment. Two further Diets were given in pelleted form, ad libitum
experiments were made on growing rabbits from throughout the experiments.
weaning to slaughter, one to measure intake, growth and health status, and the other to evaluate starch
2.2. Total tract and ileal digestibility, and digestion in the ileum and caecal fermentative activi-
fibrolytic activity in the caecum ty.
Three experimental diets were formulated Table Ileal flow was measured in 12 adult female rabbits
1 to obtain a linear reduction of the different fibre live weight 2.8–3.2 kg surgically fitted with a glass
fraction hemicelluloses, cellulose, lignins, corre- cannula at the terminal ileum Gidenne et al., 1988.
sponding to a 20 to 12 ADF reduction respective- After a three week recovery period animals were
ly A20, A16, A12. Therefore, the proportions of the divided into two groups GI and GII of six animals.
different type of cell wall polysaccharides remained Animals of GI were successively fed with diets
unchanged. The dietary ADF level of 20 corres- containing 20–16–12 of ADF over three periods,
ponded to current recommendations Maertens, while animals of GII received the diets in the inverse
1992; De Blas and Mateos, 1998, while 16 and 12 order. Within each period, total digestive tract appar-
were respectively corresponding to intermediate and ent
digestibility was
measured according
to
T . Gidenne et al. Livestock Production Science 64 2000 225 –237
227
E.G.R.A.N. 1995, using total and individual faecal retention time of digest without a delay in the mixing
collection over 4 days. Ileal flow was then measured compartments, and so represents the rate of passage
using diets labelled with mordanted chromium cell in the tubular segment of the tract, i.e. mainly in the
wall. Six samples of ileal digesta were collected 30 distal colon Gidenne, 1994.
min duration at 12 or 16 h interval from the cannula, over a 3 day period, such that they covered
2.4. Health status, growth and caecal fermentation a 24 h period Gidenne, 1992. The calculation of
activity ileal digestibility coefficients Gidenne and Ruc-
kebusch, 1989 implies for rabbit a measurement of From weaning day 28 to slaughter day 70 the
the intake of feed plus soft faeces. The composition three diets were given ad libitum to three groups of
of soft faeces and its production were evaluated on 48 rabbits New Zealand3Californian housed in-
rabbits wearing a collar to prevent caecotrophy dividually in cages, and submitted to a 12 h light 12
Gidenne and Lebas, 1987 for two periods of 24 h h dark schedule. Health status was individually
separated by an interval of 24 h. recorded three times a week from weaning to
The enzymatic fibrolytic activity of caecal bacteria slaughter: all clinical signs of sickness transitory
was determined on soft faeces since it give a similar diarrhoea, presence of mucus in excreta, abnormal
result compared to sample of caecal content Jehl et behaviour, etc. were registered. In addition, feed
al., 1996. Immediately after excretion a sample of intake and live weight were measured weekly and
soft faces was collected in precooled 48C tubes allowed us to detect any growth disturbances. Mor-
containing an anaerobic buffer, and then stored at bidity was defined as animals having abnormally low
2 808C until further processing. intake or growth ,mean22.2 sd or clinical signs
of sickness, and they were not included in growth 2.3. Rate of passage of solid phase in the caeco-
performances analyses Table 3. colic segment of the tract
To evaluate caecal fermentative activity and starch level in the ileum segment of 20 cm prior to the
The rate of passage between ileum and rectum was ileo-caecal junction, samples of digesta were ob-
measured on the two groups of 6 ileo-cannulated tained from animals slaughtered between 11:30 and
adult rabbits, following the same design previously 12:30 at 42 days and 70 days of age 10 samples per
described. Caecotrophy was not prevented. Digesta diet and per age. The caecal VFA pool was calcu-
mean retention time of solid phase was obtained by lated by multiplying the caecal content g digesta
following the rate of faecal excretion of a dose of and the caecal VFA level.
141
Ce-labelled fibre particles Gidenne, 1994, intro- duced in the ileum via the cannula. The faecal
2.5. Analytical methods excretion was fractionated in 36 samples during 96 h
by means of an automatic faecal sampler API, Organic matter OM was determined by ashing
Castanet, France adapted for use in the rabbit samples at 5508C for 5 h. Measurements of fibre
metabolism cages. After drying, faeces were directly fractions neutral detergent fibre: NDF, acid de-
analysed for their marker content in a gamma tergent fibre: ADF, acid detergent lignin: ADL were
spectrometer Packard Instrument, model 5530, made according to the sequential Van Soest pro-
Downergrove, IL, USA. The digesta mean retention cedure Van Soest et al., 1991 using an amylolytic
MRT was calculated by numerical integration of pre-treatment with a thermostable amylase. Nitrogen
the quantity of marker excreted in faeces: MRT 5 o
was determined by DUMAS combustion method M .t
o M , were t is the time that has elapsed using Leco apparatus model FP-428, Leco Corp., St
i i
i i
between marker administration and the ith defecation Joseph, MI, USA, and converted to crude protein
and M is the quantity of marker excreted. MRT CP using the factor 6.25. Gross energy was mea-
i
includes transit time TT, which is the time that has sured by an adiabatic calorimeter PARR Instrument;
elapsed between marker administration and the first Moline, IL. Starch was hydrolysed enzymically and
appearance of marker in the faeces. TT reflects the the resultant glucose was measured by using the
228 T
. Gidenne et al. Livestock Production Science 64 2000 225 –237
hexokinase EC 2.7.1.1-glucose-6-phosphate dehy- were subjected to a statistical analysis in three steps.
¨ drogenase NAD EC1.1.1.49 system Boehringer
First, the effect of the animal group I vs. II was Mannheim.
Non-nitrogenous cellular
content controlled using data from the two groups fed
NNCC was calculated as follows: NNCC5OM2 simultaneously period 2 the same feed inter-
NDF1CP. This fraction corresponds mainly to mediate ADF level. The second step consisted of a
starch but also pectin substances, plus free sugars, two factorial variance analysis period and diet. As
oligosaccharides, and lipids. Particle size distribution no significant effect of group and no interaction
of feeds were analysed on pellets by wet sieving P .0.2 were observed between period and diet
Table 2. effect we presented only the results concerning the
Volatile fatty acids VFA were analysed on caecal diet effect Tables 4–6. Means comparison was
digesta samples by gas liquid chromatography performed using the Scheffe test.
CP9000, Chrompack, Middelburg, The Netherlands on a semi-capillary column Bellier, 1994.
After sonication of caecal content, fibrolytic en- 3. Results
zymes were extracted from bacteria according to Jehl et al. 1996. Cellulolytic, xylanolytic and pec-
According to dietary formulation constraints, the tinolytic activities were assayed respectively on the
ratio ADF starch effectively decreased from 1.9 to following substrates: carboxymethylcellulose, wood
0.4, and the proportions in of total dietary fibre xylan and citrus pectin Jehl et al., 1996. The
of the different type of cell wall polysaccharides amount of reducing sugars released after incubation
remained unchanged as determined with Van-Soest with enzyme preparation was then measured and
criteria Table 1. We expressed, however, the fibre expressed as mmol of reducing sugars released per h
level using only the ADF level, for simplicity and and per g of digesta.
because this unit is presently used to define recom- mendations. Besides, the particle size distribution
2.6. Statistical analysis remained unchanged among the diets Table 2,
except a slight increase in very fine particles ,0.1 Data on growth and BFA were examined by one-
mm. way analysis of variance using the GLM procedure
of SAS Statistical Analysis System, 1988. Catmod 3.1. Regulation of feed intake, growth, and health
procedure SAS was utilised for data of morbidity status
and mortality. Data from unhealthy animals or animals having a reversed VFA pattern propionate
With the reduction of the dietary fibre level from butyrate ratio over 2 were not included in the
A20 to A12, the voluntary intake of animals was statistical analysis of VFA. Results were subjected to
significantly reduced by 25 during the two weeks a two factorial age and diet analysis of variance
postweaning Table 3 and by 18 during the according to general linear model GLM procedure.
finishing fattening period 42–70 days. In adult Data on digestibility coefficients and rate of passage
rabbits the intake was reduced by only 8 39.2 vs. 35.9 g kg LW when fed the A12 diet instead of
A20 Table 7. The growth was also significantly lower 29, significant linear effect with the
Table 2
21
Class of particle size g.kg DM in the experimental diets
lowest fibre supply diet A12 during the postwean- ing period Table 3. Feed conversion was lowered
Diets A20
A16 A12
by 20 over the complete period of growth 28–70
Particle size
days, mainly because of the reduction of the feed
x .1 mm 236
242 224
intake.
1 mm.x .0.5 mm 151
159 133
0.5 mm.x .0.315 mm 85
84 84
Intake variations combined with differences in the
0.315 mm.x .0.1 mm 158
137 152
dietary chemical composition produced exaggerated
x ,0.1 mm 370
378 407
differences in nutrient intake. For instance the reduc-
T . Gidenne et al. Livestock Production Science 64 2000 225 –237
229 Table 3
a
Feed intake and growth according to dietary fibre level, in growing rabbits from weaning 28 days old to slaughter 70 days old
b
Diets A20
A16 A12
SEM P level
Weaning–42 days old Daily feed intake g
84.8a 73.3b
64.1c 0.73
,0.001 Daily weight gain g
43.3a 41.2ab
39.5b 0.49
0.010 Feed conversion ratio
1.97c 1.77b
1.65a 0.016
,0.001 42–70 days old
Daily feed intake g 139.1a
126.3b 112.8c
1.44 ,0.001
Daily weight gain g 39.4
43.6 41.5
0.82 0.119
Feed conversion ratio 3.42c
2.88b 2.59a
0.020 ,0.001
Weaning–70 day old Daily feed intake g
121.6a 108.3b
96.2c 1.18
,0.001 Daily weight gain g
41.0 42.6
39.6 0.58
NS Feed conversion ratio
2.89c 2.52b
2.28a 0.032
,0.001
a
Means having a common letter did not differ significantly at level P 50.05. Number of animals per diet5number of animal at weaning n 548 minus morbidity and mortality.
b
SEM: Standard error of the mean; NS5P .0.15
tion of dietary ADF 20 vs. 12 led to a higher 3.2. Digestion in the whole tract and partition
reduction in ADF intake 253 for growing rabbits between small intestine and caeco-colic segment
over the 28–70 day period, inversely the starch intake increased from 13 to 28 g d.
The expected differences of digestibility for OM Over the complete growth period, the mortality
and energy in the whole digestive tract TTAD, rate remained relatively low ,10 and was not
Table 5 were observed according to fibre level significantly affected by dietary treatment Table 4,
21.6 point per ADF. In parallel, crude protein although the sanitary risk mortality1morbidity
digestibility increased by 10 P ,0.001 as ex- tended to increase P 50.11. Nevertheless from 42
pected from feed formulation substitution of protein to 70 days old there was a linear increase P 50.02
from alfalfa by those of soya and wheat, and of morbidity when the dietary fibre level was re-
growing rabbits thus consumed a similar quantity of duced. No mortality or morbidity was observed in
digestible protein 13 g d among diets. Starch was any adult rabbits.
almost completely digested mean 99.5, although a slight increase was obtained with reduction of the
Table 4
ratio ADF starch. No significant change in fibre
Morbidity and mortality between weaning day 28 and slaughter
digestibility was registered according to the dietary
day 70, according to dietary fibre level
fibre level. The soft faeces production corresponded
Diets A20
A16 A12
P level
to almost 12 of the feed intake with the highest
Weaning to day 42
supply in fibre A20 and was significantly reduced
Morbidity n 7
6 5
NS
225 with the lowest supply of fibre A12.
Mortality n 1
NE
For a dietary ADF reduction from 20 to 12, the ileal digestibility between mouth and ileal cannula
Day 42 to slaughter
Morbidity n 5a
9ab 16b
0.02
of OM increased from 38 to 61 Table 6, while it
Mortality n 2
1 1
NE
decreased from 27 to 17 in the caeco-colic segment between ileum and rectum. Crude protein ileal
Weaning to slaughter
digestibility improved by 10 units 57 vs. 67 with
Morbidity n 12
15 21
0.12
fibre reduction, whereas caeco-rectal digestibility
Mortality n 2
1 2
NE Total
14 16
23 0.11
remained at a low level ,14 and was similar among the diets. The mean ileal recovery ileal
n: Number of rabbits initial number per diet548; a,b: See Table 3; NS5P .0.15; NE: Non estimable.
flow total intake of ADF was 87, while that of
230 T
. Gidenne et al. Livestock Production Science 64 2000 225 –237 Table 5
a
Total tract apparent digestibility TTAD and soft faeces production in adult rabbits, according to dietary fibre level Diets
A20 A16
A12 SEM
P level n 512
n 511 n 512
TTAD coefficients Organic matter
64.7a 72.7b
78.2b 0.5
,0.001 Crude protein N36.25
70.9a 76.6b
78.5b 0.8
,0.001 NNCC
92.5a 95.8b
97.4b 0.4
,0.001 Starch
99.2b 99.5a
99.7a 0.09
,0.01 Energy
63.3a 71.4b
76.8c 0.5
,0.001 NDF
41.8 43.8
42.9 0.9
NS ADF
34.2 33.8
32.5 1.2
NS Soft faeces g DM d
14.5a 13.4a
10.8b 0.78
0.005
a
SEM: Standard error of the mean; n: Number of rabbits; a,b,c: See Table 3; NNCC: Non nitrogenous cellular content5OM2CP2NDF.
Table 6
a
Ileal and caeco-rectal digestibility in adult rabbits, according to dietary fibre level Diets
A20 A16
A12 SEM
P level n 59
n 59 n 58
Ileal digestibility coefficients Organic matter
37.6c 46.3b
61.1a 1.6
,0.001 Crude protein N36.25
57.0b 62.4ab
66.5a 2.2
,0.001 Starch
98.7a 97.1a
93.0b 0.7
,0.001 NNCC
49.2a 64.6b
75.1c 1.9
,0.001 NDF
22.9 19.1
28.6 2.9
NS ADF
16.8 7.9
18.4 3.2
NS Caeco-rectal digestibility coefficients
Organic matter 26.8a
25.8a 17.0b
1.6 ,0.001
Crude protein N36.25 13.1
13.4 11.7
2.5 NS
Starch 0.5b
2.4b 6.7a
1.4 0.011
NNCC 43.2a
31.2b 22.3c
2.2 ,0.001
NDF 18.7
23.6 14.3
3.0 NS
ADF 17.2
24.7 14.9
3.5 NS
a
SEM, a,b,c: See Table 3.
NDF was lower 78.5, and no significant varia- with the increase in dietary starch level corre-
tions in ileal or caecal fibre digestibility NDF or sponding to fibre level reduction. Similarly, in
ADF were observed. growing rabbits, ileal starch concentration rose from
Ileal digestibility of starch was lowered by almost 0.9 to 2.6 with dietary starch level Table 8. No
6 units with the reduction of the ADF starch ratio in significant differences in ileal starch concentration
the diet inverse trend for faecal digestibility, but were noticed at 6 or 10 weeks of age among diets.
remained at a very high level .93. Starch However, a significantly lower starch level 1.9 vs.
concentration at the ileum was very low in adults 2.9 was found for adult .16 wk old compared
mean 1.3 DM, and less than 0.4 in faeces, but to 10 wk old rabbits, for the diet with the higher
significantly increased from 0.7 to 1.9 P ,0.05 starch content A12.
T . Gidenne et al. Livestock Production Science 64 2000 225 –237
231
3.3. Rate of passage in caeco-colic segment and The bacterial fibrolytic activity BFA in soft
bacterial fibrolytic activity in adult rabbit faeces of adult rabbits was significantly reduced with
the feed having the lowest fibre level Fig. 1. The Although feed intake of adult rabbits was only
pectinolytic activity was more particularly affected slightly reduced with the reduction of the fibre level
250. 28, Table 7, there was a sharp increase in mean
retention time MRT between ileum and rectum 3.4. Caecal fermentation pattern in the growing
138, reaching 19 h for the lowest fibre level rabbits
A12. Besides, the ileo-rectal minimal transit time TTm was not affected by dietary treatments. There-
A significant interaction P ,0.05 between the fore, we estimated the retention in the caecum and
effect of the age 6 vs. 10 weeks old and the effect proximal colon difference between MRT and TTm
of the diets was detected for the caecal VFA that was 10.4 and 15.2 h respectively for diets A20
concentration, therefore we present our results ac- and A12.
Table 7 Ileo-rectal rate of passage in adult rabbits, according to dietary fibre level reduction
a
Diets A20
A16 A12
SEM P level
n 59 n 510
n 59
b
Feed intake g d kg LW 39.2a
39.0a 35.9b
1.0 0.050
Ileo-rectal rate of passage Mean retention time MRT, h
13.7a 15.0ab
19.0b 1.3
0.014 Minimal transit time TTm, h
3.3 3.1
3.8 0.05
NS
a
SEM, a,b: see Table 3.
b
Intake during measurements 4 days.
Fig. 1. Bacterial fibrolytic activity mean6sd of the caecal flora of adult rabbit n 58 diet according to dietary fibre level 20 vs. 12 ADF.
232 T
. Gidenne et al. Livestock Production Science 64 2000 225 –237
Fig. 2. Caecal total VFA concentration mmol l, mean6sd, according to age and dietary fibre level.
cording to age and fibre level in Fig. 2. In 6 weeks with a change in the VFA molar proportion: increase
old rabbits 2 wk after weaning, the VFA level in butyrate compensated by a decrease in acetate.
decreased linearly and significantly P ,0.01 from A20 to A12. For instance, VFA level reached 72
mM l for rabbits fed A20, compared to only 52
4. Discussion
