Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol81.Issue3-4.Oct1999:
Animal Feed Science and Technology
81 (1999) 221±235
Rumen and blood variables in steers fed grass
silage or whole-crop fodder beet silage
A.P. Moloney*, P. O'Kiely
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland
Received 19 November 1998; received in revised form 12 May 1999; accepted 15 June 1999
Abstract
The objectives of this study were (i) to examine the effects on rumen and blood variables when grass
silage (GS) was replaced with whole crop fodder beet silage (FBS) in the diet of beef cattle, and (ii) an
abrupt change from GS to FBS. Six rumen-fistulated Friesian steers (initial bodyweight (BW) 416 kg,
SD 43) were offered GS ad libitum for four weeks. The dry matter (DM) consumed daily by each animal
in that period (14.3 g/kg BW) was used as the daily allowance for that animal for three consecutive twoweek periods, during which the animals were offered diets consisting of increasing proportions (420,
880 and 1000 g/kg) of FBS DM in the total DM. FBS was then offered ad libitum for 14 days. Cattle were
then offered GS ad libitum for 14 days, after which GS was substituted with FBS for 14 days. The DM
content (g/kg) and contents (g/kg DM) of organic matter, crude protein and total volatile fatty acids
(VFA) were 220 and 174, 905 and 749, 153 and 115, and 26 and 75 for GS and FBS, respectively.
Animals fed the diets of 0, 420, 880 and 1000 g FBS DM/kg DM had rumen pH, concentrations of
ammonia (mg/l), l-lactic acid (mmol/l), d-lactic acid (mmol/l) and VFA (mmol/l) of 6.44, 6.18, 6.61 and
6.75 (linear p < 0.001, quadratic p < 0.001), 149, 104, 65 and 50 (linear p < 0.001), 0.76, 1.69, 1.15 and
3.98 (linear p < 0.01, cubic p < 0.01), 1.65, 2.67, 2.83 and 5.93 (linear p < 0.001, cubic p < 0.001) and
82.7, 81.8, 72.8 and 73.7 (linear p < 0.01), respectively. The corresponding plasma concentrations of
urea (mmol/l) were 3.74, 2.32, 1.95 and 1.51 (linear p < 0.001), glucose (mmol/l) were 3.81, 3.51, 3.70
and 3.70 (quadratic p < 0.05) and insulin (mIU/ml) were 19.2, 31.0, 17.4 and 20.4 (quadratic; p < 0.05).
Animals offered unsupplemented FBS ad libitum had no obvious symptoms of ill-health and rumen
fermentation was qualitatively similar to when offered at a restricted level. When animals were abruptly
offered FBS, they had adapted in terms of feed consumption and rumen pH after six days. It is concluded
that (i) GS and FBS had different patterns of fermentation in the silo and in the rumen, and (ii) cattle
adapted quickly to an abrupt change from GS to FBS. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Cattle; Silage; Fodder beet; Rumen fermentation; Blood metabolites
*
Corresponding author. Tel.: +353-46-25214; fax: +353-46-26154
E-mail address: amoloney@grange.teagasc.ie (A.P. Moloney)
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 9 3 - 0
222
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
1. Introduction
Fodder beet (beta vulgaris) when grown under suitable conditions, can produce almost
20 t dry matter (DM)/ha (DAF, 1998) compared with 13±15 t DM/ha from four harvests
of grass. Approximately 75% of fodder beet DM is in the root component (DAF, 1998).
The roots are a high energy, low crude protein (CP) feedstuff (in vitro digestible organic
matter in DM value of 850 g/kg; Givens, 1990). They are usually stored in large clamps,
and may be subsequently washed or dry cleaned on a batch basis prior to chopping or
slicing and feeding. The leaf portion of beet, together with the upper part of the root, can
have a high CP concentration (Givens, 1990). Beet leaves are normally wilted prior to
feeding to avoid the reported toxicity, attributed to oxalic acid and/or saponins (Clarke
and Clarke, 1975), if they are consumed fresh. Leaves may then be left in the field to be
grazed in situ, used as a green manure, harvested and zero-grazed or harvested and
ensiled for subsequent feeding.
Both sugar beet pulp (Courtin and Spoelstra, 1989) and tops (leaves + crown; Thomas,
1989) have each been successfully ensiled. Moreover, the fact that 6 kg of ensiled
unwilted sugarbeet leaves were consumed by dairy cows without an adverse reaction
(Engling and Rohr, 1988) suggests that ensiling also decreases the risk of toxicity from
beet leaves. Ensiling the whole-crop of fodder beet provides the opportunity to streamline
the harvesting and storage of both the root and leaf components of the crop to produce a
feedstuff that can be incorporated into cattle diets without further processing.
Furthermore, the relatively high CP concentration in the leaf component of the crop
can partially compensate for the relatively low CP concentration in the roots. Thus, high
growth rates were recorded in finishing beef cattle offered whole crop fodder beet silage
(FBS) (1.12±1.05 kg/day) relative to an ad libitum concentrate ration (1.26 kg/day), and
no response was observed to supplementary CP in addition to that supplied by barley
(O'Kiely and Moloney, 1999).
Little information is available on the end-products of digestion of FBS or the ruminal
consequences of consumption of large amounts of FBS. The objectives of this study were
to examine the impact on rumen fermentation in steers of (i) an increase in the ratio of
FBS to grass silage in the diet, (ii) offering unsupplemented FBS ad libitum, and (iii) an
abrupt change from grass silage to FBS.
2. Materials and methods
2.1. Silage/animals
Whole-crop fodder beet (cv. Magnum) was harvested adjacent to Oak Park, Carlow,
Ireland, between October 4 and 11. A prototype harvester was used (Suicre Eireann,
Carlow, Ireland) that separated the leaf plus stem component from the roots, vibrated
adhering soil from the roots before crushing them and then mixing them back with the
leaves plus stems. The crop was transported (2 h) to Grange Research Centre and ensiled
without an additive in a horizontal, concrete, walled silo that allowed effluent release.
223
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
The ensiled crop was sealed with two layers of black 0.125 mm polythene which were
then covered with tyres. The silo was opened and feeding commenced after 315 days
ensilage. The grass silage used was a primary growth of perennial ryegrass. It was cut
with a rotary mower and harvested within 15±30 min with a precision-chop harvester.
Grass was ensiled with 2.3 l sulphuric acid (450 g/kg)/tonne in a horizontal walled silo
and sealed as described above. This silo was opened and feeding commenced after 150
days ensilage.
Six Friesian steers (liveweight 416 (SD 43) kg), each fitted with a permanent rumen
cannula (internal diameter 32 mm), were used. The animals were individually tethered in
concrete-slatted pens with free access to fresh water.
2.2. Experimental procedures
2.2.1. Phase 1
Animals were offered unsupplemented grass silage (Table 1) ad libitum for 28 days and
their daily DM consumption was monitored for the final 21 days. In the remainder of this
phase, each animal was offered this amount of DM daily. The animals were then offered
for three consecutive 14-day periods, a diet consisting of increasing proportions (420, 880
and 1000 g/kg) of FBS DM in the total DM. The remainder of the diet was the grass
silage used in the introductory period. The appropriate daily allowance of FBS and grass
silage was weighed into each individual feed box and manually mixed. The daily
allowance was offered at 0800 h.
Table 1
Chemical compositiona of grass and whole crop fodder beet silage (FBS)
Dry matter (g/kg)
pH
Crude proteinb
In vitro dry matter digestibility (g/kg)
In vitro organic matter digestibility (g/kg)
Ammonia (g/kg N)
Ashb
Organic matterb
Neutral detergent fibreb
Acid detergent fibreb
Lactic acidb
Ethanolb
Acetic acidb
Propionic acidb
Butyric acidb
Total volatile acidsb
Water soluble carbohydrateb
a
b
Mean (SD), n = 8.
In g/kg DM.
Grass silage
FBS
220 (21.6)
3.68 (0.075)
153 (4.4)
718 (18.9)
702(16.6)
73 (17.2)
95 (8.2)
905 (8.2)
480 (15.1)
290 (7.4)
141 (17.1)
10 (1.1)
22 (5.8)
1.6 (1.51)
2.6 (1.60)
26 (8.4)
27 (14.2)
174 (6.9)
3.67 (0.076)
115 (3.8)
700 (26.6)
731(22.7)
59 (15.5)
251 (20.1)
749 (20.1)
264 (4.0)
171 (8.1)
170 (18.7)
59 (8.9)
67 (6.0)
4.0 (1.8)
3.6 (0.58)
75 (7.8)
54 (5.2)
224
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
On days 27 and 28 of the introductory period and on days 13 and 14 of each subsequent
period, rumen fluid samples were withdrawn immediately before, and 1, 2, 4, 8 and 12 h
after, offering fresh silage, as previously described (Moloney et al., 1996). The pH was
measured immediately following collection and a 20 ml sub-sample acidified with 0.5 ml
9 M sulphuric acid and stored at ÿ208C. A blood sample was obtained by jugular
venipuncture from each animal prior to offering fresh silage on Day 28 of the
introductory period and prior to feeding on Day 14 of each subsequent period. Sodium
ethylenediamine tetra-acetic acid was used as anti-coagulant. Further blood samples were
collected 2 and 4 h thereafter. Blood samples were centrifuged at 2000 g for 20 min
and plasma stored at ÿ208C. Animals were weighed at the end of the introductory period
and at the end of Phase 1.
2.2.2. Phase 2
Following completion of Phase 1, all animals were offered unsupplemented FBS ad
libitum at 0800 h for 30 days. Daily DM consumption was monitored. Rumen fluid
samples were collected on days 13 and 14 and blood samples on Day 14 of this phase as
described above (in vivo digestibility of FBS was measured between Day 18 and Day 30
of this phase and is reported by O'Kiely and Moloney (1999)). Animals were weighed at
the end of this phase.
2.2.3. Phase 3
Following completion of Phase 2, all animals were offered ad libitum the same grass
silage as used in Phase 1, at 0800 h, for 14 days. Daily DM consumption was monitored
and rumen fluid samples were collected on days 13 and 14 of this phase as described
above.
2.2.4. Phase 4
Following completion of Phase 3, FBS was offered ad libitum at 0800 h to four
fistulated steers. Rumen fluid samples were collected as described above on days 2, 5, 6,
10 and 15 of FBS feeding. Only the pH of rumen fluid was measured in this phase. Daily
DM consumption was monitored.
Throughout the experiment, daily silage samples were collected and stored at ÿ208C.
Upon thawing, samples were composited and sub-sampled on a weekly basis prior to
chemical analysis.
2.3. Chemical analyses
The DM concentration of silage was determined by drying at 408C (48 h) in an oven
with forced air circulation. Other chemical analyses of silage (Table 1) were carried out
as described by O'Kiely and Moloney (1995). Neutral detergent and acid detergent fibre
concentrations were analysed as described by Van Soest et al. (1991) and Van Soest
(1973), respectively. Rumen fluid samples were centrifuged at 2500 g for 20 min and
supernatants pooled within time across both days within each period for each animal.
Samples taken immediately before, and 2 and 8 h after feeding were analysed for
ammonia and volatile fatty acid (VFA) concentrations. These samples, together with
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
225
samples taken at 1 h after feeding, were also analysed for d- and l-lactic acid
concentrations. The concentration of VFA was determined by gas chromatography
(Shimadzu gas chromatography GC-8A) as described by Supelco Inc. (1975) and of
ammonia and lactic acid (both d and l-isomers) using a Ciba Corning Diagnostics
530 express clinical chemistry analyzer with appropriate reagent kits. Plasma
concentrations of urea and glucose were determined using the above analyser with
appropriate reagents kits. Plasma insulin concentration was determined by radioimmunoassay as described by Chikhou et al. (1991) using bovine insulin (Novobiolabs,
Bagsvaerd, Denmark) as reference standard, guinea-pig antiporcine insulin antisera as
first antibody (1 : 30 000 working dilution; Scottish Antibody Production Unit,
Lanarkshire, Scotland) and cellulose coated antibody (SacCell, Wellcome Ireland,
Dublin) as second antibody.
2.4. Statistical analyses
Data were subjected to analysis of variance. The experimental design was a
randomised block (animals) with repeated measures. For Phase 1 metabolite data, the
model used had animals and diet in the main plot and sampling time within a diet and the
time by diet interaction in the sub-plot. For ruminal fluid pH data, the mean of both
sampling days within FBS level for each sampling time for each animal was used. Feed
intake data were analysed using a model that had animal and diet as main effects. The
linear, quadratic and cubic effects of inclusion of FBS in the diet were partitioned using
orthogonal polynomials. Similar models were used for Phase 2 and Phase 3 data. For
Phase 4, ruminal fluid pH data were analysed using a model that had animal and day in
the main plot, and sampling time within a day and time by day interaction in the sub-plot.
Feed intake was analysed similarly but with the effect of time omitted.
3. Results
Unless otherwise stated, only significant (p < 0.05 or greater) treatment effects and
interactions are presented.
3.1. Silage composition
The chemical composition of grass silage and FBS is summarised in Table 1.
Both silages were well preserved. Silage made from whole crop fodder beet underwent
an extensive lactic acid-dominant fermentation, and was characterised by lower
CP and organic matter concentrations, but higher organic matter digestibility than
grass silage.
While not measured, the particle size distribution of the grass silage appeared similar
to that previously observed (O'Kiely and Flynn, 1991), i.e. most particles were 0.05) kg/animal. Mean rumen fluid pH
was 6.56, 6.22, 6.81, 6.65, 6.75 and 6.66 (SED 0.134; (p < 0.05) for animals offered grass
silage ad libitum, and on day 2, 3, 6, 10 and 15 after the grass silage was substituted with
FBS. Daily pH profiles are shown in Fig. 4. There was a day-of-sampling by sampling
time interaction such that rumen fluid pH tended to be lowest at all times on the second
day after the introduction to FBS ad libitum.
230
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
Table 3
Feed intake and mean rumen fluid and plasma variables in steers fed either grass silage or whole crop fodder
beet silage (FBS) ad libitum in Phase 2
Grass silage
FBS
14.3
13.0
2.2
15.9
11.9
1.9
0.63
0.48
0.08
6.44
0.71
1.60
8.8
82.7
628
238
105
30
1
2.70
6.97
1.43
2.75
2.4
68.3
647
187
102
32
34
3.48
0.06
0.19
0.29
0.66
5.8
10.0
4.5
3.0
2.0
4.0
0.12
3.81
3.73
19.2
3.95
1.30
17.1
Feed intake (g/kg bodyweight)
Dry matter
Organic matter
Crude protein
Rumen fluid
pH
l-Lactic acid (mmol/l)
d-Lactic acid (mmol/l)
Ammonia (mmol/l)
Volatile fatty acids (mmol/l)
Acetateb
Propionateb
Butyrateb
Valerateb
Caproateb
Acetate: propionate
Plasma
Glucose (mmol/l)
Urea (mmol/l)
Insulin (mIU/ml)
a
b
SED
0.149
0.351
3.93
Significance
*
+a
*
***
*
*
***
+a
+a
***
NS
NS
***
**
NS
***
NS
p < 0.1.
In mmol/mol.
Table 4
Dry matter intake and rumen fluid variables in steers fed grass silage ad libitum at the beginning of the study and
between Week 11 and Week 13 thereafter, in Phase 3
Week
Dry matter intake (g/kg bodyweight)
Rumen fluid
pH
l-Lactic acid (mmol/l)
d-Lactic acid (mmol/l)
Ammonia (mmol/ml)
Volatile fatty acids (mmol/l)
Acetatea
Propionatea
Butyratea
Valeratea
Acetate : propionate
a
In mmol/mol.
SED
Significance
ÿ3 to 0
11±13
14.3
13.4
0.59
NS
6.44
0.71
1.60
8.8
82.7
628
238
105
30
2.70
6.67
0.84
1.33
6.4
85.7
622
236
104
31
2.71
0.066
0.361
0.315
0.56
2.51
3.8
3.1
4.5
1.7
0.045
*
NS
NS
**
NS
NS
NS
NS
NS
NS
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
231
Fig. 4. Rumen fluid pH (sampling time diet SED 0.19) in cattle fed grass silage (^) or on Day 2 (&), Day 3
(~), Day 6 (X), Day 10 (&) and Day 15 (*) after feeding unsupplemented fodder beet silage ad libitum.
4. Discussion
4.1. Methodology
The primary objective of this study was to define rumen fermentation in steers fed
whole crop FBS. There was no a priori information on the effect of feeding FBS per se on
rumen physiology. However, O'Kiely and Moloney (1999) reported that, in the
preparatory phase of their study, cattle abruptly offered FBS ad libitum vomited the
silage. Because of this and because of the time likely to be required for pre-measurement
adaptation to high levels of FBS, a sequential design was employed rather than a Latin
square/changeover design. The effect of FBS on permanent rumen function was tested by
offering the original grass silage ad libitum upon completion of the ad libitum FBS phase.
The general similarity in feed intake and rumen fermentation before, and after, FBS
feeding indicates that the animals were not deleteriously affected by FBS. Moreover, it
gives confidence that the procedures for sample collection and analysis used throughout
the study were consistent. The difference in rumen ammonia concentration before, and
after, FBS feeding most likely reflected the small variability in CP concentration in the
grass silage (155 g/kg DM during the early phase and 145 g/kg DM during the later
phases) and the non-significant difference in DM intake than any physiological
consequence of FBS consumption in the interval between these phases.
4.2. Influence of FBS inclusion in the diet of steers
The grass silage used was of good quality with respect to in vitro digestibility and
preservation as indicated by the pH and concentration of ammonia (Haigh and Parker,
1985). In general, when compared to other studies where animals were offered unwilted,
unsupplemented grass silage, pH and concentrations of metabolites in rumen fluid were
within the range previously reported (Moloney and O'Kiely, 1994; McKee et al., 1996;
Thiago et al., 1992). In Phase 1, to ensure complete consumption by all animals and to
reduce variation, the initial intention was to offer animals an allowance of DM on an
232
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
individual animal basis equal to that consumed when grass silage was offered ad libitum.
The linear decrease in DM intake was due to the lower DM concentration of FBS as fed
compared to that measured at the outset of the study. Nevertheless, the difference was
only 5%. Despite the higher DM intake for FBS compared to grass silage when both were
offered ad libitum, organic matter intake was lower. This reflected the high ash
concentration of FBS. Of the total ash concentration, there were 138 g acid insoluble ash/
kg DM (O'Kiely and Moloney, 1999), indicative of considerable soil contamination
during harvesting. Decreases in organic matter and CP consumption, when FBS was
offered as a proportion of the diet or ad libitum, were reflected in decreases in VFA and
ammonia concentrations in ruminal fluid (particularly 8 h after feeding), respectively.
The decrease in CP intake was also reflected in a decrease in plasma urea concentration
which was more pronounced 4 h after feeding. The mean rumen ammonia concentration
in animals offered the grass silage, 420 g FBS or 880 g FBS/kg DM diets exceeded the
minimum level of 2.9 mmol/l recommended to maintain maximum microbial protein
synthesis (Satter and Slyter, 1974), and was close to this value in the rumen of animals
receiving the 1000 g FBS/kg DM diet. Reports on the ammonia concentration necessary
for optimum ruminal cellulose digestion are, however, inconsistent. Hoover (1986)
concluded that when the CP concentration of the diet was 60 g/kg, the ruminal
ammonia concentration required for optimum microbial growth and digestion was
12.6 mmol/l. When the CP concentration of the diet was >60 g/kg, an ammonia
concentration of 4.7 mmol/l was necessary. It is clear, however, that for several hours
during the day, rumen ammonia concentration may have been below that required
for optimum cellulose digestion and microbial protein synthesis in the 880 g, 1000 g
FBS/kg DM diets and when FBS was offered ad libitum. The lack of any symptoms
of illness in animals offered FBS ad libitum indicates that no additional roughage was
required.
The pattern of pH decline post-feeding in animals fed grass silage is similar to that
observed previously (Moloney and O'Kiely, 1999). In contrast, the pH pattern in animals
offered FBS, on a restricted basis, had a more rapid initial pH fall. This may reflect the
higher concentrations of water soluble carbohydrate (WSC) and lactic acid in FBS than
grass silage. It may also be influenced by the pattern of intake, i.e. animals offered FBS
may have had a greater first meal when offered the fresh diet. That the minimum pH is
lower for animals fed 420 g FBS/kg DM than 880 g or 1000 g FBS/kg DM most likely
reflects total digestibile organic matter intake. Since cellulolytic activity is impaired
when pH falls below pH 6.2±6.3 (Stewart, 1977), it is possible that fibre digestion was
impaired for at least a portion of the day in animals fed these diets. The similarity in the
pattern of pH between animals offered FBS and grass silage ad libitum may again reflect
the meal pattern of the animals, and was never
81 (1999) 221±235
Rumen and blood variables in steers fed grass
silage or whole-crop fodder beet silage
A.P. Moloney*, P. O'Kiely
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland
Received 19 November 1998; received in revised form 12 May 1999; accepted 15 June 1999
Abstract
The objectives of this study were (i) to examine the effects on rumen and blood variables when grass
silage (GS) was replaced with whole crop fodder beet silage (FBS) in the diet of beef cattle, and (ii) an
abrupt change from GS to FBS. Six rumen-fistulated Friesian steers (initial bodyweight (BW) 416 kg,
SD 43) were offered GS ad libitum for four weeks. The dry matter (DM) consumed daily by each animal
in that period (14.3 g/kg BW) was used as the daily allowance for that animal for three consecutive twoweek periods, during which the animals were offered diets consisting of increasing proportions (420,
880 and 1000 g/kg) of FBS DM in the total DM. FBS was then offered ad libitum for 14 days. Cattle were
then offered GS ad libitum for 14 days, after which GS was substituted with FBS for 14 days. The DM
content (g/kg) and contents (g/kg DM) of organic matter, crude protein and total volatile fatty acids
(VFA) were 220 and 174, 905 and 749, 153 and 115, and 26 and 75 for GS and FBS, respectively.
Animals fed the diets of 0, 420, 880 and 1000 g FBS DM/kg DM had rumen pH, concentrations of
ammonia (mg/l), l-lactic acid (mmol/l), d-lactic acid (mmol/l) and VFA (mmol/l) of 6.44, 6.18, 6.61 and
6.75 (linear p < 0.001, quadratic p < 0.001), 149, 104, 65 and 50 (linear p < 0.001), 0.76, 1.69, 1.15 and
3.98 (linear p < 0.01, cubic p < 0.01), 1.65, 2.67, 2.83 and 5.93 (linear p < 0.001, cubic p < 0.001) and
82.7, 81.8, 72.8 and 73.7 (linear p < 0.01), respectively. The corresponding plasma concentrations of
urea (mmol/l) were 3.74, 2.32, 1.95 and 1.51 (linear p < 0.001), glucose (mmol/l) were 3.81, 3.51, 3.70
and 3.70 (quadratic p < 0.05) and insulin (mIU/ml) were 19.2, 31.0, 17.4 and 20.4 (quadratic; p < 0.05).
Animals offered unsupplemented FBS ad libitum had no obvious symptoms of ill-health and rumen
fermentation was qualitatively similar to when offered at a restricted level. When animals were abruptly
offered FBS, they had adapted in terms of feed consumption and rumen pH after six days. It is concluded
that (i) GS and FBS had different patterns of fermentation in the silo and in the rumen, and (ii) cattle
adapted quickly to an abrupt change from GS to FBS. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Cattle; Silage; Fodder beet; Rumen fermentation; Blood metabolites
*
Corresponding author. Tel.: +353-46-25214; fax: +353-46-26154
E-mail address: amoloney@grange.teagasc.ie (A.P. Moloney)
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 9 3 - 0
222
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
1. Introduction
Fodder beet (beta vulgaris) when grown under suitable conditions, can produce almost
20 t dry matter (DM)/ha (DAF, 1998) compared with 13±15 t DM/ha from four harvests
of grass. Approximately 75% of fodder beet DM is in the root component (DAF, 1998).
The roots are a high energy, low crude protein (CP) feedstuff (in vitro digestible organic
matter in DM value of 850 g/kg; Givens, 1990). They are usually stored in large clamps,
and may be subsequently washed or dry cleaned on a batch basis prior to chopping or
slicing and feeding. The leaf portion of beet, together with the upper part of the root, can
have a high CP concentration (Givens, 1990). Beet leaves are normally wilted prior to
feeding to avoid the reported toxicity, attributed to oxalic acid and/or saponins (Clarke
and Clarke, 1975), if they are consumed fresh. Leaves may then be left in the field to be
grazed in situ, used as a green manure, harvested and zero-grazed or harvested and
ensiled for subsequent feeding.
Both sugar beet pulp (Courtin and Spoelstra, 1989) and tops (leaves + crown; Thomas,
1989) have each been successfully ensiled. Moreover, the fact that 6 kg of ensiled
unwilted sugarbeet leaves were consumed by dairy cows without an adverse reaction
(Engling and Rohr, 1988) suggests that ensiling also decreases the risk of toxicity from
beet leaves. Ensiling the whole-crop of fodder beet provides the opportunity to streamline
the harvesting and storage of both the root and leaf components of the crop to produce a
feedstuff that can be incorporated into cattle diets without further processing.
Furthermore, the relatively high CP concentration in the leaf component of the crop
can partially compensate for the relatively low CP concentration in the roots. Thus, high
growth rates were recorded in finishing beef cattle offered whole crop fodder beet silage
(FBS) (1.12±1.05 kg/day) relative to an ad libitum concentrate ration (1.26 kg/day), and
no response was observed to supplementary CP in addition to that supplied by barley
(O'Kiely and Moloney, 1999).
Little information is available on the end-products of digestion of FBS or the ruminal
consequences of consumption of large amounts of FBS. The objectives of this study were
to examine the impact on rumen fermentation in steers of (i) an increase in the ratio of
FBS to grass silage in the diet, (ii) offering unsupplemented FBS ad libitum, and (iii) an
abrupt change from grass silage to FBS.
2. Materials and methods
2.1. Silage/animals
Whole-crop fodder beet (cv. Magnum) was harvested adjacent to Oak Park, Carlow,
Ireland, between October 4 and 11. A prototype harvester was used (Suicre Eireann,
Carlow, Ireland) that separated the leaf plus stem component from the roots, vibrated
adhering soil from the roots before crushing them and then mixing them back with the
leaves plus stems. The crop was transported (2 h) to Grange Research Centre and ensiled
without an additive in a horizontal, concrete, walled silo that allowed effluent release.
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The ensiled crop was sealed with two layers of black 0.125 mm polythene which were
then covered with tyres. The silo was opened and feeding commenced after 315 days
ensilage. The grass silage used was a primary growth of perennial ryegrass. It was cut
with a rotary mower and harvested within 15±30 min with a precision-chop harvester.
Grass was ensiled with 2.3 l sulphuric acid (450 g/kg)/tonne in a horizontal walled silo
and sealed as described above. This silo was opened and feeding commenced after 150
days ensilage.
Six Friesian steers (liveweight 416 (SD 43) kg), each fitted with a permanent rumen
cannula (internal diameter 32 mm), were used. The animals were individually tethered in
concrete-slatted pens with free access to fresh water.
2.2. Experimental procedures
2.2.1. Phase 1
Animals were offered unsupplemented grass silage (Table 1) ad libitum for 28 days and
their daily DM consumption was monitored for the final 21 days. In the remainder of this
phase, each animal was offered this amount of DM daily. The animals were then offered
for three consecutive 14-day periods, a diet consisting of increasing proportions (420, 880
and 1000 g/kg) of FBS DM in the total DM. The remainder of the diet was the grass
silage used in the introductory period. The appropriate daily allowance of FBS and grass
silage was weighed into each individual feed box and manually mixed. The daily
allowance was offered at 0800 h.
Table 1
Chemical compositiona of grass and whole crop fodder beet silage (FBS)
Dry matter (g/kg)
pH
Crude proteinb
In vitro dry matter digestibility (g/kg)
In vitro organic matter digestibility (g/kg)
Ammonia (g/kg N)
Ashb
Organic matterb
Neutral detergent fibreb
Acid detergent fibreb
Lactic acidb
Ethanolb
Acetic acidb
Propionic acidb
Butyric acidb
Total volatile acidsb
Water soluble carbohydrateb
a
b
Mean (SD), n = 8.
In g/kg DM.
Grass silage
FBS
220 (21.6)
3.68 (0.075)
153 (4.4)
718 (18.9)
702(16.6)
73 (17.2)
95 (8.2)
905 (8.2)
480 (15.1)
290 (7.4)
141 (17.1)
10 (1.1)
22 (5.8)
1.6 (1.51)
2.6 (1.60)
26 (8.4)
27 (14.2)
174 (6.9)
3.67 (0.076)
115 (3.8)
700 (26.6)
731(22.7)
59 (15.5)
251 (20.1)
749 (20.1)
264 (4.0)
171 (8.1)
170 (18.7)
59 (8.9)
67 (6.0)
4.0 (1.8)
3.6 (0.58)
75 (7.8)
54 (5.2)
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On days 27 and 28 of the introductory period and on days 13 and 14 of each subsequent
period, rumen fluid samples were withdrawn immediately before, and 1, 2, 4, 8 and 12 h
after, offering fresh silage, as previously described (Moloney et al., 1996). The pH was
measured immediately following collection and a 20 ml sub-sample acidified with 0.5 ml
9 M sulphuric acid and stored at ÿ208C. A blood sample was obtained by jugular
venipuncture from each animal prior to offering fresh silage on Day 28 of the
introductory period and prior to feeding on Day 14 of each subsequent period. Sodium
ethylenediamine tetra-acetic acid was used as anti-coagulant. Further blood samples were
collected 2 and 4 h thereafter. Blood samples were centrifuged at 2000 g for 20 min
and plasma stored at ÿ208C. Animals were weighed at the end of the introductory period
and at the end of Phase 1.
2.2.2. Phase 2
Following completion of Phase 1, all animals were offered unsupplemented FBS ad
libitum at 0800 h for 30 days. Daily DM consumption was monitored. Rumen fluid
samples were collected on days 13 and 14 and blood samples on Day 14 of this phase as
described above (in vivo digestibility of FBS was measured between Day 18 and Day 30
of this phase and is reported by O'Kiely and Moloney (1999)). Animals were weighed at
the end of this phase.
2.2.3. Phase 3
Following completion of Phase 2, all animals were offered ad libitum the same grass
silage as used in Phase 1, at 0800 h, for 14 days. Daily DM consumption was monitored
and rumen fluid samples were collected on days 13 and 14 of this phase as described
above.
2.2.4. Phase 4
Following completion of Phase 3, FBS was offered ad libitum at 0800 h to four
fistulated steers. Rumen fluid samples were collected as described above on days 2, 5, 6,
10 and 15 of FBS feeding. Only the pH of rumen fluid was measured in this phase. Daily
DM consumption was monitored.
Throughout the experiment, daily silage samples were collected and stored at ÿ208C.
Upon thawing, samples were composited and sub-sampled on a weekly basis prior to
chemical analysis.
2.3. Chemical analyses
The DM concentration of silage was determined by drying at 408C (48 h) in an oven
with forced air circulation. Other chemical analyses of silage (Table 1) were carried out
as described by O'Kiely and Moloney (1995). Neutral detergent and acid detergent fibre
concentrations were analysed as described by Van Soest et al. (1991) and Van Soest
(1973), respectively. Rumen fluid samples were centrifuged at 2500 g for 20 min and
supernatants pooled within time across both days within each period for each animal.
Samples taken immediately before, and 2 and 8 h after feeding were analysed for
ammonia and volatile fatty acid (VFA) concentrations. These samples, together with
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
225
samples taken at 1 h after feeding, were also analysed for d- and l-lactic acid
concentrations. The concentration of VFA was determined by gas chromatography
(Shimadzu gas chromatography GC-8A) as described by Supelco Inc. (1975) and of
ammonia and lactic acid (both d and l-isomers) using a Ciba Corning Diagnostics
530 express clinical chemistry analyzer with appropriate reagent kits. Plasma
concentrations of urea and glucose were determined using the above analyser with
appropriate reagents kits. Plasma insulin concentration was determined by radioimmunoassay as described by Chikhou et al. (1991) using bovine insulin (Novobiolabs,
Bagsvaerd, Denmark) as reference standard, guinea-pig antiporcine insulin antisera as
first antibody (1 : 30 000 working dilution; Scottish Antibody Production Unit,
Lanarkshire, Scotland) and cellulose coated antibody (SacCell, Wellcome Ireland,
Dublin) as second antibody.
2.4. Statistical analyses
Data were subjected to analysis of variance. The experimental design was a
randomised block (animals) with repeated measures. For Phase 1 metabolite data, the
model used had animals and diet in the main plot and sampling time within a diet and the
time by diet interaction in the sub-plot. For ruminal fluid pH data, the mean of both
sampling days within FBS level for each sampling time for each animal was used. Feed
intake data were analysed using a model that had animal and diet as main effects. The
linear, quadratic and cubic effects of inclusion of FBS in the diet were partitioned using
orthogonal polynomials. Similar models were used for Phase 2 and Phase 3 data. For
Phase 4, ruminal fluid pH data were analysed using a model that had animal and day in
the main plot, and sampling time within a day and time by day interaction in the sub-plot.
Feed intake was analysed similarly but with the effect of time omitted.
3. Results
Unless otherwise stated, only significant (p < 0.05 or greater) treatment effects and
interactions are presented.
3.1. Silage composition
The chemical composition of grass silage and FBS is summarised in Table 1.
Both silages were well preserved. Silage made from whole crop fodder beet underwent
an extensive lactic acid-dominant fermentation, and was characterised by lower
CP and organic matter concentrations, but higher organic matter digestibility than
grass silage.
While not measured, the particle size distribution of the grass silage appeared similar
to that previously observed (O'Kiely and Flynn, 1991), i.e. most particles were 0.05) kg/animal. Mean rumen fluid pH
was 6.56, 6.22, 6.81, 6.65, 6.75 and 6.66 (SED 0.134; (p < 0.05) for animals offered grass
silage ad libitum, and on day 2, 3, 6, 10 and 15 after the grass silage was substituted with
FBS. Daily pH profiles are shown in Fig. 4. There was a day-of-sampling by sampling
time interaction such that rumen fluid pH tended to be lowest at all times on the second
day after the introduction to FBS ad libitum.
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Table 3
Feed intake and mean rumen fluid and plasma variables in steers fed either grass silage or whole crop fodder
beet silage (FBS) ad libitum in Phase 2
Grass silage
FBS
14.3
13.0
2.2
15.9
11.9
1.9
0.63
0.48
0.08
6.44
0.71
1.60
8.8
82.7
628
238
105
30
1
2.70
6.97
1.43
2.75
2.4
68.3
647
187
102
32
34
3.48
0.06
0.19
0.29
0.66
5.8
10.0
4.5
3.0
2.0
4.0
0.12
3.81
3.73
19.2
3.95
1.30
17.1
Feed intake (g/kg bodyweight)
Dry matter
Organic matter
Crude protein
Rumen fluid
pH
l-Lactic acid (mmol/l)
d-Lactic acid (mmol/l)
Ammonia (mmol/l)
Volatile fatty acids (mmol/l)
Acetateb
Propionateb
Butyrateb
Valerateb
Caproateb
Acetate: propionate
Plasma
Glucose (mmol/l)
Urea (mmol/l)
Insulin (mIU/ml)
a
b
SED
0.149
0.351
3.93
Significance
*
+a
*
***
*
*
***
+a
+a
***
NS
NS
***
**
NS
***
NS
p < 0.1.
In mmol/mol.
Table 4
Dry matter intake and rumen fluid variables in steers fed grass silage ad libitum at the beginning of the study and
between Week 11 and Week 13 thereafter, in Phase 3
Week
Dry matter intake (g/kg bodyweight)
Rumen fluid
pH
l-Lactic acid (mmol/l)
d-Lactic acid (mmol/l)
Ammonia (mmol/ml)
Volatile fatty acids (mmol/l)
Acetatea
Propionatea
Butyratea
Valeratea
Acetate : propionate
a
In mmol/mol.
SED
Significance
ÿ3 to 0
11±13
14.3
13.4
0.59
NS
6.44
0.71
1.60
8.8
82.7
628
238
105
30
2.70
6.67
0.84
1.33
6.4
85.7
622
236
104
31
2.71
0.066
0.361
0.315
0.56
2.51
3.8
3.1
4.5
1.7
0.045
*
NS
NS
**
NS
NS
NS
NS
NS
NS
A.P. Moloney, P. O'Kiely / Animal Feed Science and Technology 81 (1999) 221±235
231
Fig. 4. Rumen fluid pH (sampling time diet SED 0.19) in cattle fed grass silage (^) or on Day 2 (&), Day 3
(~), Day 6 (X), Day 10 (&) and Day 15 (*) after feeding unsupplemented fodder beet silage ad libitum.
4. Discussion
4.1. Methodology
The primary objective of this study was to define rumen fermentation in steers fed
whole crop FBS. There was no a priori information on the effect of feeding FBS per se on
rumen physiology. However, O'Kiely and Moloney (1999) reported that, in the
preparatory phase of their study, cattle abruptly offered FBS ad libitum vomited the
silage. Because of this and because of the time likely to be required for pre-measurement
adaptation to high levels of FBS, a sequential design was employed rather than a Latin
square/changeover design. The effect of FBS on permanent rumen function was tested by
offering the original grass silage ad libitum upon completion of the ad libitum FBS phase.
The general similarity in feed intake and rumen fermentation before, and after, FBS
feeding indicates that the animals were not deleteriously affected by FBS. Moreover, it
gives confidence that the procedures for sample collection and analysis used throughout
the study were consistent. The difference in rumen ammonia concentration before, and
after, FBS feeding most likely reflected the small variability in CP concentration in the
grass silage (155 g/kg DM during the early phase and 145 g/kg DM during the later
phases) and the non-significant difference in DM intake than any physiological
consequence of FBS consumption in the interval between these phases.
4.2. Influence of FBS inclusion in the diet of steers
The grass silage used was of good quality with respect to in vitro digestibility and
preservation as indicated by the pH and concentration of ammonia (Haigh and Parker,
1985). In general, when compared to other studies where animals were offered unwilted,
unsupplemented grass silage, pH and concentrations of metabolites in rumen fluid were
within the range previously reported (Moloney and O'Kiely, 1994; McKee et al., 1996;
Thiago et al., 1992). In Phase 1, to ensure complete consumption by all animals and to
reduce variation, the initial intention was to offer animals an allowance of DM on an
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individual animal basis equal to that consumed when grass silage was offered ad libitum.
The linear decrease in DM intake was due to the lower DM concentration of FBS as fed
compared to that measured at the outset of the study. Nevertheless, the difference was
only 5%. Despite the higher DM intake for FBS compared to grass silage when both were
offered ad libitum, organic matter intake was lower. This reflected the high ash
concentration of FBS. Of the total ash concentration, there were 138 g acid insoluble ash/
kg DM (O'Kiely and Moloney, 1999), indicative of considerable soil contamination
during harvesting. Decreases in organic matter and CP consumption, when FBS was
offered as a proportion of the diet or ad libitum, were reflected in decreases in VFA and
ammonia concentrations in ruminal fluid (particularly 8 h after feeding), respectively.
The decrease in CP intake was also reflected in a decrease in plasma urea concentration
which was more pronounced 4 h after feeding. The mean rumen ammonia concentration
in animals offered the grass silage, 420 g FBS or 880 g FBS/kg DM diets exceeded the
minimum level of 2.9 mmol/l recommended to maintain maximum microbial protein
synthesis (Satter and Slyter, 1974), and was close to this value in the rumen of animals
receiving the 1000 g FBS/kg DM diet. Reports on the ammonia concentration necessary
for optimum ruminal cellulose digestion are, however, inconsistent. Hoover (1986)
concluded that when the CP concentration of the diet was 60 g/kg, the ruminal
ammonia concentration required for optimum microbial growth and digestion was
12.6 mmol/l. When the CP concentration of the diet was >60 g/kg, an ammonia
concentration of 4.7 mmol/l was necessary. It is clear, however, that for several hours
during the day, rumen ammonia concentration may have been below that required
for optimum cellulose digestion and microbial protein synthesis in the 880 g, 1000 g
FBS/kg DM diets and when FBS was offered ad libitum. The lack of any symptoms
of illness in animals offered FBS ad libitum indicates that no additional roughage was
required.
The pattern of pH decline post-feeding in animals fed grass silage is similar to that
observed previously (Moloney and O'Kiely, 1999). In contrast, the pH pattern in animals
offered FBS, on a restricted basis, had a more rapid initial pH fall. This may reflect the
higher concentrations of water soluble carbohydrate (WSC) and lactic acid in FBS than
grass silage. It may also be influenced by the pattern of intake, i.e. animals offered FBS
may have had a greater first meal when offered the fresh diet. That the minimum pH is
lower for animals fed 420 g FBS/kg DM than 880 g or 1000 g FBS/kg DM most likely
reflects total digestibile organic matter intake. Since cellulolytic activity is impaired
when pH falls below pH 6.2±6.3 (Stewart, 1977), it is possible that fibre digestion was
impaired for at least a portion of the day in animals fed these diets. The similarity in the
pattern of pH between animals offered FBS and grass silage ad libitum may again reflect
the meal pattern of the animals, and was never