194 M
.J. Ranilla et al. Livestock Production Science 62 2000 193 –204
mentation rates, digestibility and digesta flow kinet- of the experiment, with grass:clover ratios of
ics when the animals where kept in the same 86:11 and 85:10.
environment and received the same diet Ranilla et This study was part of a larger grazing experi-
al., 1997, 1998. Other studies have reported differ- ment. Plots were continuously grazed by non-ex-
ences between Churra and Merino sheep in voluntary perimental sheep on a ‘put and take’ basis through-
intake of forages Amor, 1994, digestibility of fresh out the experiment to control sward heights. Ex-
´ herbage Giraldez et al., 1994 and in diet selection
perimental animals were moved to the plots at the when grazing hill shrub communities Revesado et
beginning of each experimental period. Sward sur- al., 1994. However, virtually no information is
face height was measured three times each week available on rumen fermentation in Churra and
using the Hill Farming Research Organisation sward Merino sheep grazing irrigated pastures. Sheep pro-
stick Barthram, 1986. Forty measurements were duction based on grazing irrigated systems could be
taken at random in each plot. More details about an alternative, in many areas such as north-west
pasture conditions and herbage mass are given by ´
Spain, where current irrigated agricultural systems Mantecon et al. 1995. Three experimental periods
´ have led to surplus production Lavın et al., 1994.
were conducted during the grazing season: June 10 As ruminal conditions affect both the rate of fermen-
to 22 middle June, July 23 to August 4 late July tation and the rate of passage, and therefore the
and September 28 to October 10 early October. voluntary intake in grazing ruminants Van Soest,
1994, such information would be valuable for 2.2. Animals
establishing optimal grazing sheep production sys- tems. The present study was conducted to examine
Three oesophageal-cannulated Churra sheep aver- fermentation rates and ruminal parameters pH,
age initial body weight BW 48.764.01, three ammonia and volatile fatty acid concentrations of
oesophageal-cannulated Merino sheep average ini- Churra and Merino sheep grazing grass white clover
tial BW 43.73.60 kg, three rumen-cannulated Chur- irrigated pasture.
ra sheep average initial BW 42.74.73 kg and three rumen-cannulated Merino sheep average initial BW
40.11.25 kg were used. All animals were healthy
2. Material and methods and between 2 and 3 years old. Oesophageal fistula-
tion procedure was carried out two months before the 2.1. Study area, treatments and sampling periods
start of the experiment. Fistulation procedure and postoperative care, involving topical and intramuscu-
´ Grazing trials were conducted at the Estacion
lar antibiotic application for a period of 2 weeks after ´
Agrıcola Experimental of Consejo Superior de Inves- surgery, were outlined by McManus 1981. Rumen
´ ´
tigaciones Cientıficas C.S.I.C. located at Leon on fistulation was carried out by inserting a rumen
north-west Spain latitude 428 359 N; longitude 58 cannula of 35 mm diameter two months before the
439 E. The experiment was carried out over 5 start of the experiment. Throughout the experiment,
months, from middle June to early October, on a sheep were given free access to water, shade and
seven-year-old field sown with ryegrass Lolium trace mineral salts. Animals were weighed at the
perenne, tall fescue Festuca arundinacea and beginning and end of each sampling period at about
white clover Trifolium repens in a proportion of 20, 11.00 h.
15 and 1 kg per ha, respectively. The sward height imposed was 3.5 cm. The field was divided in two
2.3. Experimental procedure plots of 0.15 ha that were randomly assigned to each
of the two breeds. Every year each plot received 45 Rumen-fistulated animals of each of the breeds
kg ha of each N, P and K, and 300 kg ha of 33 were assigned randomly to one of the plots and then
NH NO . Each plot was irrigated every nine days remained on the same treatment across sampling
4 3
for 24 h throughout the experiment. Both plots periods. Sampling periods consisted on a 7-day
presented a similar botanical composition at the start adaptation phase and a 6-day collection period. On
M .J. Ranilla et al. Livestock Production Science 62 2000 193 –204
195
day 8 of each period the oesophageal-cannulated obtained from each sheep through the rumen cannula
at 11.00, 14.00, 17.00 and 23.00 h. Rumen fluid was sheep were used to collect representative forage
strained through four layers of cheese-cloth, its pH samples of the diet selected by each breed of sheep.
determined immediately and duplicate samples were Animals were fasted for 12 h overnight prior to
taken for volatile fatty acids VFA and ammonia collection of masticate samples. At about 08.00 h the
analyses. One ml of rumen fluid was added to 1 ml plug of the oesophageal-cannula was removed, plas-
of deproteinizing solution 0.10 of metaphosphoric tic bags were attached to the neck of the fistulated
acid and 0.0006 crotonic acid; w v for VFA de- animals and the sheep allowed to graze until the bags
termination. Twenty ml of rumen fluid were acidified were filled about 30 min. After collection, the
with 20 ml 0.5 M HCl for ammonia-N determination. fistulated sheep were administered salts and water,
Samples were stored at 2 208C until analyses were the plug reinserted and sheep allowed to graze
undertaken. normally in the assigned plots the remainder of the
day. Samples were examined for contamination by 2.4. Analytical procedures
regurgitated material any contaminated material was discarded and composited within breeds across
DM was determined by drying at 1008C until sheep. Saliva was eliminated by gently squeezing
constant weight. Ash was determined by ashing and a portion of the samples was immediately deep
samples in a muffle furnace for 8 h at 500–5058C. frozen 2208C and freeze-dried for dry matter
Nitrogen N was determined according to Associa- DM determination and stored for chemical analy-
tion of Official Analytical Chemists AOAC, 1990. ses. The rest of sample was used to measure its
NDF, ADF and lignin analyses were carried out rumen degradability using the nylon bag technique
according to Goering and Van Soest 1970. Ammo- Ørskov et al., 1980. The bags measured 12.5 3 10
nia-N concentration was determined using an auto- cm and had a mean pore size of 40 mm. About 30 g
analyser Kjeltec Auto 1030 Tecator as described by of sample was weighed without further manipulation
McDonald et al. 1960. VFA were determined in into nylon bags, which were incubated in the rumen
centrifuged samples 1 ml by gas chromatography, of each rumen-cannulated sheep for 3, 6, 12, 24, 48,
using a Shimadzu GC-14B gas chromatograph 72 and 96 h. One bag was incubated per time
equipped with an autosampler and a GP 60 80 interval per sheep beginning at about 11.00 h. As
Carbopack C 0.3 Carbowax 20M 0.1 H PO
3 4
soon as the bags were removed from the rumen, they column Supelco Inc., Spain.
were washed thoroughly under running cold water for 2 min and then washed in the cold rinse cycle 20
2.5. Calculations and statistical analyses min of a washing machine. A further two bags per
grazed herbage sample received this washing treat- The values for disappearance of DM from grazed
ment alone zero-time washout value. DM disap- herbage and grass hay were fitted to the exponential
2c t
pearance was estimated from the loss in weight model y 5 a 1 b 1 2 e
Ørskov and McDonald, following oven drying at 608C for 48 h. The residues
1979, whereas the values for NDF disappearance were analysed for neutral-detergent fibre NDF to
were fitted to the exponential model y 5 a 1 b 1 2
2c t2lag
estimate fibre degradation. e
Dhanoa, 1988. Data were fitted with To evaluate rumen activity over the grazing
time using the NLIN procedure of the SAS package periods, samples from grass hay crude protein CP:
SAS, 1997. 86 g, NDF: 693 g, acid-detergent fibre ADF: 345 g
Effective degradability ED was estimated in and lignin: 56 g kg DM were also incubated in situ.
each sheep by using the parameters a, b, c and lag Samples of grass hay were ground using a hammer-
and assuming a rumen particulate outflow rate k of
p 21
mill fitted with a 2 mm screen and about 5 g were 0.03 h
according to the equation proposed by weighed into nylon bags, which were incubated in
France et al. 1990: the rumen of each sheep following the same schedule
b 3 c
2k 3lag
described for grazed herbage samples.
s
p
d
]] ED 5 a 1
3 e c 1 k
p
On days 10 and 12 rumen fluid samples were
196 M
.J. Ranilla et al. Livestock Production Science 62 2000 193 –204
A lag time value of 0 was assumed for the heights were similar for Churra 3.8, 3.6 and 3.5 cm
calculation of DM effective degradability DMED. in June, July and October, respectively and Merino
In situ data were analysed by variance analysis as sheep 3.6, 3.4 and 3.5 cm in June, July and October,
a split-plot design with breed as the main-plot respectively. Animals remained healthy through the
treatment and sampling period as the subplot treat- experimental period and no variations in their BW
ment Steel and Torrie, 1980. Effects for breed, were observed. Marked changes in daily tempera-
sampling period, breed3sampling period, and sheep tures
were registered
during the
experimental within breed were included in the model. Breed
periods, with minimum and maximum temperatures effects were tested using sheep within treatment as
ranging from 6 to 248C, from 13 to 338C and from 5 the error term. The interaction breed3sampling
to 188C for June, July and October, respectively period and the main effect of sampling period were
Table 1. No rain was recorded during any of the tested using residual error. When a significant P ,
sampling periods. 0.05 breed3sampling period interaction was de-
Changes in chemical composition of grazed her- tected, data were analysed within sampling period.
bage through the experimental periods were similar Rumen pH, ammonia-N and VFA data average
for both breeds Table 2. CP content increased from values of two sampling days were analysed as a
June through October for both breeds of sheep, split–split-plot design Steel and Torrie, 1980 with
whereas NDF, ADF and lignin contents declined. sampling time and the interactions breed3sampling
Merino animals tended P ,0.10 to present a period3sampling time and breed3sampling time
lower potential degradability of both DM and NDF added to the model. When significant P ,0.05
of grass hay than Churras Table 3, but no signifi- breed3sampling period3sampling time, breed3
cant differences P .0.05 were detected for ED of sampling period and breed3sampling time interac-
DM and NDF NDFED. tions were detected, which precluded pooling pH,
As significant breed3grazing period3sampling VFA and ammonia-N data across sampling time and
time interactions P ,0.05 were detected for pH, sampling period, these variables were analysed for
ammonia-N and VFA concentrations, mean values each individual sampling period and sampling time.
for these parameters for each breed, grazing period The method of least significant difference was used
and sampling time are presented in Figs. 1–3, to separate treatment means when a significant P ,
respectively. In addition, molar proportions of the 0.05 F-test for treatment was detected. The GLM
main VFA mean values for the day are presented in procedure of SAS 1997 was used for all statistical
Table 4. analyses.
During June, Churras presented higher P ,0.05 pH values at 11.00 and 17.00 h sampling than
Merino sheep, and tended P ,0.10 to present a
3. Results greater acetate propionate Ac Pr ratio. No differ-
