216 E
.M. Alcaide et al. Livestock Production Science 64 2000 215 –223
between goats and sheep concerning the digestive forages than sheep, they were able to maintain a
´ physiology were made Isac et al., 1994; Garcıa et
larger rumen fill without increasing ruminal disten- al., 1994, 1995; Molina Alcaide et al., 1997 when
sion. This fact would contribute to increased vol- low to medium quality diets were offered. Partially
untary intakes with respect to sheep. However, our this home information refers to non-producing ani-
results are opposite to the information reported by mals fed at maintenance level and confined in
AFRC 1997 as far as kinetics outflow is concerned metabolic crates Isac et al., 1994 and, therefore,
as they indicate shorter mean retention times of the minimizing differences in selective behaviour be-
digesta in the rumen of the goats in comparison with tween animals which might account for unequal
sheep. They are also contradictory concerning the digestive efficiencies. In these experiments we failed
rumen fermentation pattern, although observed dif- to find interspecies differences in digestibility and
ferences were of minor importance. The evidence in degradation rate when medium quality forages were
this aspect is inconclusive. offered. However, most of the data from our labora-
With this background and given the dearth of tory were obtained in non-producing animals grazing
comparative digestion studies with sheep and goats low to medium quality pastures in semi-arid lands of
fed on good quality forages under conditions which ´
the South of Spain Garcıa et al., 1994, 1995; Molina prevent selective intake AFRC, 1997, the aim of
Alcaide et al., 1997. In these trials some contro- the present work was to widen the range of observa-
versial results were observed concerning interspecies tions from medium to high quality diets for which
differences for in vitro digestibility: when grasses the hypothesis of a similar digestion capacity was
were the main component 78 of the pasture stated, implying a unique energy value for both goats
consumed and differences in chemical composition and sheep.
between the material selected were negligible, the in vitro digestibility of dry matter DM and organic
matter OM of the material ingested by sheep was
2. Material and methods
on average 3.5 percentage units higher than that observed for the pasture selected by goats. However,
2.1. In vivo digestibility experiments when shrubs and tree leaves accounted for the most
part of the diet ingested 80 the in vitro Four
dry non-pregnant
Granadina goats
digestibility of the forage grazed by goats was on 40.661.07
kg body
weight BW
and four
˜ average 7 percentage units higher than that observed
Segurena wethers 60.661.04 kg BW were used to in sheep. The diet consumed by the sheep showed
determine the nutrients digestibility of three different higher fibre content and degree of lignification than
diets Table 1: Alfalfa hay AH, alfalfa hay plus the material selected by the goats. These findings
sugar beet pulp in the ratio 4:1 AH SB and alfalfa emphasise that differences in selective behaviour
hay plus sugar beet pulp and oat grain in the ratio between animal species could account for unequal
3:1:1 AH SB OG. Two wethers and two goats had digestive efficiencies. Results of the studies carried
permanent ruminal cannulae. After completion of the out with grazing animals were clear to demonstrate
digestibility trials cannulated animals were used to that goats had higher energy intakes than sheep
determine sequentially the rate of degradation of the which could be explained by a faster rate of passage
digesta in the rumen, the fermentation pattern and of particles out of the rumen and a systematic
the fractional rate of passage of particles out of the ´
tendency Garcıa et al., 1995; Molina Alcaide et al., rumen.
1997 for a higher rate of degradation of the material The animals were kept in individual crates and had
when placed in bags suspended in the rumen. Also free access to water. In three consecutive trials, they
the size of the rumen content g dry matter was were fed at maintenance level diets AH, AH SB and
found to be larger in goats than in sheep. So, in AH SB OG in two meals of equal sizes at 09:00 and
agreement with relevant information reviewed by 16:00 h along with a vitamin–mineral mixture and
AFRC 1997, we concluded that while goats seem daily feed intakes were individually recorded. The
to have a similar capacity to digest medium quality intake of metabolisable energy for maintenance
E .M. Alcaide et al. Livestock Production Science 64 2000 215 –223
217 Table 1
pore size was 36 m. The bags were incubated during,
Ingredients g kg fresh matter and chemical composition g kg
4, 8, 16, 24, 48 and 72 h in the rumen of the
dry matter of the experimental diets
cannulated animals fed one of the experimental diets
Experimental diet AH
AH SB AH SB OG
containing the ingredient to be tested. Three con-
Ingredients
secutive trials were performed in which the animals
Alfalfa hay 1000
800 600
received diets AH, AH SB and AH SB OG, respec-
Sugar beet pulp –
200 200
tively, at maintenance level. After incubation, the
Oat grain –
– 200
bags were washed in a washing machine during 20 min, then stomached during 5 min and, finally, dried
Chemical composition Dry matter, g kg fresh matter
899 903
906
at 608C. Aliquots of the remainder dry matter were
Organic matter 869
872 891
used for organic matter OM and nitrogen N
Crude protein 181
166 153
analyses. The profiles of degradation were calculated
Neutral detergent fibre 390
402 410
by the non-linear least square approach, using the
Acid detergent fibre 294
284 259
exponential model
described by
Ørskov and
Acid detergent lignin 65.5
59.4 50.8
N-ADF, g 100 g total N 6.05
6.96 10.5
McDonald 1979. The effective degradability Ed
Gross energy, MJ kg DM 18.4
16.5 17.9
in the rumen was calculated as Ed 5 a 1 [bc c 1 k] were a is the soluble fraction, b the potentially
degradable insoluble fraction, c the degradation rate
0.75
MEm was taken to be 374 and 421 kJ kg BW constant and k is the passage rate of the digesta from
for wethers and goats, respectively Aguilera et al., the rumen.
1986, 1991. The ME content was estimated to be 9 MJ kg dry matter DM for diets AH and AH SB
2.3. Composition of the rumen liquor and 10.5 MJ kg DM for diet AH SB OG, irre-
spective of the animal species to be fed. Therefore, Samples of rumen content from the goats and
air-dry matter intake of diets AH and AH SB was on wethers fitted with ruminal cannulae were taken once
0.75
average 46 and 52 g kg BW for wethers and
at day, 2 h after feeding, during two consecutive
0.75
goats, respectively, and 40 and 45 g kg BW days at the end of the experiments described in
when diet AH SB OG was assayed. Each trial Section 2.2. They were strained through a layer of
included a 15-day adaptation period and a 10-day cheesecloth and the pH of the filtrate was immedi-
collection period. Daily total faeces, urine and feeds ately determined. An average composite sample of
refusal were individually collected and then, weighed the squeezed liquor per sampling day and animal
and 10, 20 and 30 of daily collection, respectively, species was built up. Aliquots of the composite
were stored at 2 208C. Samples of the ingredients samples were used for the determination of ammonia
were also daily collected, pooled and kept at 2 208C nitrogen NH –N and total volatile fatty acids
3
for analysis. The coefficients of digestibility of VFA and their individual concentrations were also
nutrients and the energy values of the experimental measured. The remainders of these filtrates were
diets were obtained from measurements of nutrients freeze dried to determine DM, OM and total nitrogen
and gross energy intake and losses in faeces and TN contents.
urine, when appropriate. Energy losses as methane were calculated as described by Aguilera and Prieto
2.4. Fractional passage rate 1991.
After 20 days of consumption of each experimen- 2.2. Rumen degradation
tal diet AH, AH SB and AH SB OG, 25 g of chromium mordanted fibre Uden et al., 1980 of the
Bulked samples of alfalfa hay, sugar beet pulp or corresponding experimental diet were directly placed
oat grain were mill ground through a 2 mm screen in the rumen of each animal immediately before
and aliquots of approximately 2 g were placed in feeding. Faeces were individually taken by rectal
nylon bags which measured 7 3 10 cm and whose grab sampling at 6, 9, 12, 24, 28, 32, 48, 53, 72 and
218 E
.M. Alcaide et al. Livestock Production Science 64 2000 215 –223
79 h after dosage of the mordanted material and formed with animal species as main effect. For
stored at 2208C until analysed. The fractional rate degradability profile two replicates of four combina-
of passage from the rumen k was calculated as the tions of treatments incubated feed diet offered
slope of the regression of the logarithm of chromium within animal species were used. Differences be-
concentration in faeces with time post dosing. The tween means were tested by the Bonferroni test. A
equation log Y 5 log A 2 kt was used, where log one-way ANOVA was also made to determine the
e e
e
Y and log A are the natural logarithms of chromium statistical significance of dietary treatment AH vs.
e
concentration in faeces and t is the time after the AH SB when alfalfa hay was incubated in the
administration of the marker. rumen of the animals.
2.5. Analytical procedures
3. Results
