Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol81.Issue1-2.Sep1999:
Animal Feed Science and Technology
81 (1999) 57±68
The effects of level of fish oil inclusion in the diet
on rumen digestion and fermentation parameters
in cattle offered grass silage based diets
T.W.J. Keadya,*, C.S. Maynea,b
a
Agricultural Research Institute of Northern Ireland, Hillsborough, Co. Down BT26 6DR, UK
b
Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK
Received 7 December 1998; received in revised form 26 April 1999; accepted 19 May 1999
Abstract
A partially balanced changeover design experiment was undertaken to evaluate the effects of
level of fish oil inclusion in the diet on rumen fermentation parameters and digestion with 10 beef
cattle offered grass silage ad libitum as the basal forage supplemented with 5 kg concentrates
headÿ1 dayÿ1. Concentrates were prepared to provide either 0 (T0), 150 (T150), 300 (T300) or
450 g (T450) fish oil (Fish Industries, Killybegs, Co. Donegal, Ireland) or 300 g (T300B) fish oil
premix (J. Bibby Agriculture) per head per day. The concentrates were formulated to have similar
concentrations of crude protein, effective rumen degradable protein, digestible undegradable
protein and starch. The dry matter (DM), pH and ammonia nitrogen (N) concentrations of the silage
were 194 g kgÿ1, 3.98 and 94 g kgÿ1 N, respectively. Level or source of fish oil did not alter
(P > 0.05) the disappearance of DM, neutral detergent fibre or acid detergent fibre after 12 or 24 h
rumen incubation intervals. Increasing the level of fish oil increased rumen ammonia concentration
(P < 0.001) but did not alter (P > 0.05) rumen pH or the molar concentrations of the volatile fatty
acids. The fish oil premix decreased rumen ammonia concentration (P < 0.001), the molar
concentrations of acetate (P < 0.05), the acetate : propionate (P < 0.05), acetate + butyrate/
propionate (P < 0.01) and non-glucogenic (P < 0.05) ratios and increased the molar concentration
of propionate (P < 0.01). It is concluded that changes in rumen fermentation parameters do not
account for the depressions in milk butterfat content with fish oil inclusion observed in a concurrent
production study in which lactating dairy cows were offered similar diets to those used in the
present study. Furthermore, the changes in rumen fermentation parameters with inclusion of a fish
oil premix are probably associated with the carrier or the source of fish oil used in that product.
# 1999 Elsevier Science B.V. All rights reserved.
Keywords: Cattle; Fish oil; Rumen; Fermentation; Digestibility
*
Corresponding author. Tel.: +44-1846-682484; fax: +44-1846-689594
E-mail address: [email protected] (T.W.J. Keady)
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 7 3 - 5
58
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
1. Introduction
Given the current constraints on milk fat production within the European Union (EC),
there is considerable interest in developing strategies to reduce milk butterfat content
whilst maintaining milk output. It is generally accepted that inclusion of fish oil in the
diet depresses butterfat content of milk when animals are offered hay (Beitz and Davis,
1964; Nicholson and Sutton, 1971; Brumby et al., 1972) or maize silage (Chilliard and
Doreau, 1997) as the basal forage. More recently, Keady et al. (1999a) concluded that
increasing the level of fish oil in the diet decreased milk fat content of dairy cows offered
grass silage as the basal diet, regardless of the level of concentrate supplementation.
Possible reasons for the decreased milk fat content with fish oil supplementation include
inhibition of de-novo fatty acid synthesis and mammary gland uptake of plasma fatty
acids (Brumby et al., 1972), inhibition of lipoprotein lipase activity (Storry et al., 1969) or
mammary acetyl-CoA carboxylase (Moore and Steele, 1968), or as a result of trans fatty
acid production. It is also possible that fish oil inclusion in the diet may alter the rumen
environment, consequently decreasing fibre digestion and the ratio of lipogenic : glucogenic fatty acids. Several previous studies have shown that fish oil supplementation of
cows offered hay (Nicholson and Sutton, 1971; Brumby et al., 1972; Storry et al., 1974)
or maize silage (Chilliard and Doreau, 1997) as the basal forage, resulted in a reduction in
the ratio of lipogenic to glucogenic fatty acids in the rumen. However, in these studies the
fish oil was offered in one feed and samples of rumen fluid were collected on a few
occasions, within a maximum period of 10 h post feeding.
Given the paucity of experimental data on the effects of fish oil supplementation on
rumen digestion and fermentation patterns of cattle offered grass silage based diets the
present study was initiated to determine if the effects of fish oil inclusion on milk fat
concentration in the concurrent study (Keady et al., 1999a) were mediated through
changes in rumen fermentation parameters. The effects of fish oil inclusion on the
disappearance of dry matter (DM), neutral detergent fibre (NDF) and acid detergent fibre
(ADF) in the rumen were also examined.
2. Material and methods
2.1. Silage
Grass silage was produced from herbage harvested from the primary growth of
predominantly perennial ryegrass swards which had received 7.6 m3 cattle slurry and 127,
17.5 and 35 kg haÿ1 of nitrogen (N), P2O5 and K2O, respectively. It was mown between 4
and 7 June using a mower fitted with a V-spoke grass conditioner (Taarup, Model 307)
and harvested after a wilting period of 24 h using a precision chop forage harvester
(Reco-Mengele, Model SH40N). At ensiling the herbage was treated with an inoculant
(Ecosyl, Zeneca Bio Products) which was applied through a pump applicator and
discharged into the auger chamber of the harvester at the rate of 2.98 l tÿ1 herbage.
During filling, the silo was consolidated between loads by rolling with an industrial
loader and for a further 60 min after filling was completed. Following consolidation, two
59
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 1
Ingredient composition of concentrates (g kgÿ1 fresh weight)
Concentrate
Ingredients
Barley
Wheat
Maize gluten
Molassed sugar beet pulp
Soyabean
SoyPass
Rapeseed
Fish oil
Fish oil premix
Minerals and vitamins
Molasses
Urea
a
b
Control
FOa
FOPb
135
310
140
100
110
80
55
0
0
40
30
0
25
397
35
95
138
90
60
90
0
40
30
0
30
400
20
100
85
115
55
0
120
40
30
5
FO = fish oil included.
FOP = fish oil premix included.
polythene sheets were used to seal the silo. The entire surface was then weighed down
with a layer of tyres.
During the feeding period, silage was removed from the silos with a shear grab in
blocks containing approximately 0.5 m3.
2.2. Concentrate
Five concentrates were formulated containing different levels and sources of fish oil.
Initially three concentrates were prepared containing no fish oil (Control) and fish oil
(FO) (Fish Industries, Killybegs, Co. Donegal, Ireland) at 90 kg tÿ1 or a commercial fish
oil premix (FOP) (J. Bibby Agriculture) at 120 kg tÿ1. Two further concentrates were
prepared by mixing the control and FO concentrates in different proportions. The
concentrates were formulated to supply either 0 (T0), 150 (T150), 300 (T300) or 450 g
(T450) fish oil animalÿ1 dayÿ1 or 300 g (T300B) animalÿ1 dayÿ1 of the alternative
commercial fish oil premix, when offered at 5 kg headÿ1 dayÿ1. The concentrates were
formulated to have similar concentrations of crude protein (CP), effective rumen
degradable protein (ERDP) and digestible undegradable protein (DUP) using AFRC
(1993) published values for individual feed ingredients and starch. Concentrate
formulations are presented in Table 1. Cereals and pelleted ingredients were ground
through a 3 mm screen before mixing and pelleting through a 12 mm die.
2.3. Animals and management
The diets were offered to 10 mature steers fitted with rumen fistulae in a partially
balanced, changeover design experiment consisting of three 4-week periods giving a total
of six animals per treatment. During changeover, the concentrate treatments were
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T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
gradually introduced during a 3-day period. Silage was offered once daily at 09:00 in
sufficient quantities to allow a refusal of 50 to 100 g kgÿ1 intake. The concentrates
were offered in two equal feeds at 05:00 and 16:00 h. The animals were housed in
individual tie-up stalls. Individual intakes of silage and concentrates were recorded daily
for the duration of the study, with the last week of each period being the main recording
interval.
2.4. Measurements
Samples of offered and refused silage were retained daily for oven DM (858C)
analysis. The dried samples of offered silage were bulked weekly and analysed for ADF,
NDF, ash and acid detergent insoluble nitrogen (ADIN) concentrations. Fresh samples of
offered silage were obtained twice weekly for the determination of pH, buffering capacity
and concentrations of toluene DM, CP, ammonia N, ethanol, propanol, acetate,
propionate, valerate, butyrate and lactate.
A sample of each concentrate type was retained weekly for the determination of oven
DM (1008C), CP, ash, ether extract (EE), NDF, water soluble carbohydrates (WSC), gross
energy, starch, NDF cellulose digestibility and ADIN.
2.5. Rumen digestion study
The effects of fish oil supplementation on rumen digestion of hay were determined by
the polyester bag method as described by Mehrez and érskov (1977). Eight polyester
bags (pore size = 1600 mm2) containing the equivalent of 5 g DM of fresh chopped hay
(ADF and NDF concentrations of 420 and 722 g kgÿ1 DM, respectively) were suspended
in the rumen of the steers fitted with rumen fistulae on day 26 of each sampling period.
Four polyester bags were removed after the 12 and 24 h incubation periods, respectively.
2.6. Rumen fermentation study
On day 28 of each period samples of rumen liquor were collected via the fistulae at
05:00, 06:00, 07:00, 09:00, 10:00, 13:00, 16:00, 17:00, 19:00, 22:00 and 05:00 h
representing 0, 1, 2, 4, 5, 8, 11, 12, 14, 17 and 24 h after the morning feed, respectively.
The samples of rumen liquor were obtained as described by Keady and Steen (1996) and
were analysed for pH, ammonia N, acetate, propionate, butyrate and valerate as described
by Keady et al. (1994). Other methods of chemical analysis of the silages and
concentrates were as described by Keady et al. (1998).
2.7. Statistical analysis
Data on food intake, rumen digestion and fermentation parameters were analysed as
partially balanced changeover design experiment using the residual maximum likelihood
(REML) directive in the GENSTAT 5 statistical software package. For food intake and
rumen digestion data, the effect of oil was investigated using the REML, while for the
rumen fermentation data, REML was used to investigate the effects of oil, time and the
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
61
Table 2
Chemical composition of the silage at feeding
Dry matter (alcohol corrected toluene) (g kgÿ1)
pH
Buffering capacity (mEquiv kgÿ1 DM)
Composition of DM (g kgÿ1)
Crude protein
Ammonia nitrogen (g kgÿ1 total N)
Ethanol
Propanol
Acetate
Propionate
Butyrate
Valerate
Lactate
ADF
NDF
ADIN
Ash
194
3.98
1045
135
94
9.2
1.2
25
0.2
0.4
0.5
75
403
664
4.4
74
interaction between oil and time. Linear and quadratic contrasts were calculated for the
four levels of fish oil. Differences between treatments were tested using the student t-test.
3. Results
3.1. Chemical composition of the silages and concentrates
The chemical composition of the silage as fed is presented in Table 2. The silage was
well preserved as measured by its pH and low concentrations of ammonia N and butyrate.
The chemical composition of the concentrates at feeding is presented in Table 3. The
concentrates had similar concentrations of DM, CP and starch. Increasing the level of fish
oil in the concentrate decreased the concentrations of WSC and ash, and increased the
concentrations of ADIN, EE and gross energy. Relative to T300, T300B had lower
concentrations of WSC and gross energy and higher concentrations of ADIN and ash.
The fatty acid profiles of the fish oil, fish oil premix and the concentrates at feeding are
presented in Table 4. Increasing the level of fish oil inclusion in the concentrates
increased the concentrations of C12:0, C14:0, C18:0, C20:0, C20:4w3, C20:4w6, C22.0, C22:1,
C20:5w3, C24:0, C24:1w9 and C22:6w3 and decreased the concentrations of C18:2, and C18:3 in
total fat. Relative to T300, T300B increased the concentrations of C18:2 and C20:5w3 and
decreased the concentrations of C14:0, C20:0 and C22:6w3.
3.2. Food intake
The effects of fish oil treatment on silage and total DM intake are presented in Table 5.
Increasing the level of fish oil supplementation tended (P > 0.05) to decrease silage and
total DM intakes. There were no significant (P > 0.05) linear or quadratic contrasts across
62
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 3
Chemical composition of the concentrates at feeding
Concentrate
Chemical composition
Dry matter (g kgÿ1)
Composition of dry matter (g kgÿ1)
Crude protein
Water soluble carbohydrate
Neutral detergent fibre
Starch
NDF cellulose digestibility
Acid detergent insoluble nitrogen
Ash
Ether extract
Gross energy (MJ kgÿ1 DM)
T0
T150
T300
T450
T300B
861
864
867
870
862
219
101
308
307
824
2.94
84
28
17.87
217
98.7
307
301
811
3.13
83.3
54
18.33
215
96.3
305
296
797
3.32
82.6
79
18.80
213
94
304
290
784
3.52
82
105
19.26
218
90
332
303
777
4.54
86
81
18.52
Table 4
Fatty acid profile of the fish oils and of the concentrates at feeding
Fatty acid
(g kgÿ1 fat)
C12:0
C14:0
C14:1
C15:0
C16:0
C16:1
C17:0
C17:1
C18:0
C18:1
C18:2
C18:3
C20:0
C20:1
C20:2
C21:0
C20:3w6
C20:3w3
C20:4w6
C22:0
C22:1
C20:5w3
C24:0
C24:1w9
C22:6w3
Fish oil
0.8
58
0.5
5.2
136
41
3.5
3.2
26
158
22
22
59
79
5.0
4.5
2.3
9.3
3.8
12.2
123
81
12.2
28.8
108
Fish oil
premix
10.0
9.9
1.9
5.2
200
2.0
1.7
1.7
44
206
15.7
6.6
54
11.7
4.7
2.1
3.8
20
16.7
8.6
13.7
190
8.8
9.8
7.7
Treatment
T0
T150
T300
T450
T300B
0.0
2.4
0.0
1.1
164
3.2
1.0
0.0
16.3
184
558
66
1.6
3.7
1.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
5.3
0.0
1.2
165
3.1
1.0
0.0
17.2
184
541
64
3.1
3.9
1.1
0.1
0.1
0.6
0.5
0.3
0.4
5.7
0.3
0.3
2.3
0.6
8.2
0.1
1.4
166
3.1
1.0
0.1
18.0
185
525
62
4.7
4.1
1.2
0.1
0.2
1.2
1.0
0.5
0.8
11.4
0.5
0.6
4.6
0.9
11.1
0.2
1.5
167
3.1
1.1
0.2
18.8
186
509
60
6.3
4.4
1.3
0.2
0.3
1.8
1.5
0.8
1.2
17.1
0.8
0.9
7.0
1.2
14
0.2
1.6
168
3.0
1.1
0.2
19.6
186
490
58
7.9
4.6
1.4
0.3
0.5
2.4
2.0
1.0
1.6
22.8
1.1
1.2
9.3
63
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 5
Effect of fish oil treatment on food intake and rumen fermentation parameters
Treatment
T0
T150
s.e.m.
T300
T450
Significance
Treatmenta Time Treatment
time
T300B
Food intake (kg DM dayÿ1)
Silage
7.50 6.80 7.21 6.76
Total
12.14 11.47 11.88 11.45
6.95
11.59
0.251
0.249
NS
NS
Rumen fermentation
pH
Ammonia (m mol lÿ1)
Ethanol (m mol lÿ1)
Propanol (m mol lÿ1)
Total VFA (m mol lÿ1)
6.14
8.46bc
0.69
0.04
110
6.21
8.97c
0.82
0.00
105
0.035
0.364
0.152
0.021
3.4
NS
***
NS
NS
NS
***
***
***
***
***
NS
**
NS
NS
NS
Molar concentrations of VFAs (mmol/mol total VFAs)
Acetate (Ac)
667b 662ab 672b 652ab
Propionate (Pr)
184a 185a 182a 195ab
Butyrate (But)
124
127
123
126
Valerate (Va)
24
26
24
27
Ac/Pr
3.76b 3.75b 3.86b 3.46ab
Ac + But/Pr
4.45b 4.45b 4.55b 4.12ab
Non-glucogenic ratio
4.64bc 4.62bc 4.72c 4.25ab
641a
203b
126
30
3.24a
3.87a
4.07a
7.8
5.8
4.7
3.2
0.169
0.183
0.159
*
**
NS
NS
*
**
***
***
***
***
*
***
***
***
NS
NS
NS
NS
NS
NS
NS
6.17
6.82a
0.51
0.00
114
6.11
7.72ab
0.61
0.06
110
6.14
7.22a
0.67
0.00
109
a
Other than for the linear effect of ammonia (P < 0.05), there were no significant (P > 0.05) linear or quadratic
contrasts across the four levels of fish oil.
the four levels of fish oil. Source of fish oil did not alter (P > 0.05) either silage or total
DM intakes.
3.3. Rumen fermentation parameters
The effects of fish oil treatment on rumen fermentation parameters are presented in
Table 5. Relative to T0 and T300, T450 increased (P < 0.05) the concentrations of rumen
ammonia. T450 decreased (P < 0.05) the non-glucogenic ratio relative to T300. Other
than for the linear effect of ammonia (P < 0.05) there were no significant (P > 0.05)
linear or quadratic contrasts across the four levels of fish oil. Level of fish oil did not
significantly (P > 0.05) alter rumen pH, the concentrations of ammonia, total volatile
fatty acids (VFA), ethanol or propanol, or the molar concentrations of acetate, butyrate,
propionate or valerate. Relative to T300, T300B increased the concentrations of ammonia
(P < 0.001) and the molar proportion of propionate (P < 0.01) and decreased the molar
proportions of acetate (P < 0.01) and the acetate + butyrate/propionate (P < 0.01) acetate/
propionate (P < 0.01) and the non-glucogenic ratios (P < 0.01).
All the rumen fermentation variables determined in the present study were significantly
(P < 0.05 or greater) altered by time of sampling.
There was a significant fish oil treatment by sampling time interaction (P < 0.01) for
the concentration of rumen ammonia (Fig. 1). Treatment T300B significantly increased
the concentrations of ammonia at 1 and 2 h relative to the other treatments and at 4 h
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T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Fig. 1. The effects of fish oil treatment on rumen ammonia concentration (Control ±&± 150 g fish oil/cow/day
±^± 300 g fish oil/cow/day ±~± 450 g fish oil/cow/day ±$± 300 g fish oil/cow/day from premix ±*±).
relative to the control. At 8 h T150 increased ammonia concentrations relative to T300.
Relative to the control, rumen ammonia concentration was increased for T300B at 12 h
and for T450 at 12 and 14 h after the morning concentrate feed. Treatment had no effect
(P > 0.05) on rumen ammonia concentrations at 0, 5, 11, 17 or 24 h post feeding. There
were no treatment by time interactions (P > 0.05) for rumen pH, the molar concentrations
of acetate, propionate, butyrate, the ratios of acetate : propionate, acetate + butyrate/
propionate and non-glucogenic ratios or the concentrations of ethanol or propanol.
The effects of fish oil treatment on the disappearance of DM, ADF and NDF of hay
incubated in the rumen for 12 and 24 h are presented in Table 6. Fish oil treatment did not
alter (P > 0.05) the disappearance of DM, ADF or NDF following 12 and 24 h incubation
periods, respectively. There were no significant (P > 0.05) linear or quadratic contrasts
across the four levels of fish oil.
Table 6
The effects of fish oil treatment on the proportion of hay disappearance in the rumena
Dry matter
Acid detergent fibre
Neutral detergent fibre
a
Incubation
period (h)
Treatment
T0
T150
T300
T450
T300B
12
24
12
24
12
24
0.189
0.380
0.067
0.259
0.048
0.240
0.180
0.363
0.073
0.258
0.041
0.227
0.180
0.366
0.071
0.255
0.030
0.222
0.186
0.385
0.082
0.278
0.056
0.257
0.192
0.375
0.098
0.274
0.053
0.247
s.e.m.
Significance
0.0102
0.0185
0.0183
0.0241
0.0112
0.0229
NS
NS
NS
NS
NS
NS
There were no significant (P > 0.05) linear or quadratic contrasts across the four levels of fish oil.
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
65
4. Discussion
In a concurrent study (Keady et al., 1999a) inclusion of 450 g fish oil cowÿ1 dayÿ1 in
the diet of lactating dairy cattle altered milk composition by decreasing the
concentrations of fat and protein by 15 and 3.86 g kgÿ1, respectively. The present study
was undertaken to elucidate if the mode of action of fish oil was occurring in the rumen,
due to changes either in fermentation parameters or digestibility. In the present study
concentrates accounted for approximately 0.60 of the total diet which is similar to the
mean of the two concentrate treatments offered in the concurrent study (Keady et al.,
1999a) in which there were no fish oil by concentrate feed level interactions for milk
composition. As in the concurrent study the concentrates were formulated to contain
similar concentrations of CP, starch, ERDP, DUP, WSC and sugars. The ERDP and DUP
concentrations were based on AFRC (1993) published values.
4.1. Effects of fish oil on silage intake
Although fish oil treatment did not significantly decrease silage intake, fish oil
inclusion resulted in similar proportional decreases in intake as occurred at the higher
level of concentrate supplementation in the concurrent study (Keady et al., 1999a). Also
Wonsil et al. (1994), Chilliard and Doreau (1997) and Cant et al. (1997) reported
reductions in food intake due to fish oil inclusion in the diet. Furthermore, the absence
of an effect of fish oil type on silage DM intake in the present study is similar to the
results obtained by Keady et al. (1999a). The decrease in silage intake recorded in the
present study with fish oil supplementation may be due to a metabolic control mechanism
related to the effect of some fatty acids of fish oil on biohydrogenation in the rumen as
suggested by Doreau and Chilliard (1997) rather than to a negative effect on rumen
function, as fish oil inclusion did not affect rumen fermentation patterns or digestion of
fibre fractions, which have been identified as major factors affecting silage intake (Steen
et al., 1998).
4.2. Effects of fish oil on rumen digestion
Previous studies (Devendra and Lewis, 1974; Kowalczyk et al., 1977; Knight et al.,
1978) have shown that free oil supplementation reduced the apparent digestion of organic
matter due primarily to a reduction in fibre digestibility. Also more recently Ikwuegbu
and Sutton (1982) concluded that inclusion of free oil shifted the site of digestion of
digestible ADF to the intestines. Lipid supply generally causes no variation in retention
time of particles in the rumen (Ferlay et al., 1992). The absence of an effect of fish oil
treatment on the disappearance of DM after 12 or 24 h rumen incubation periods, is
similar to the results of Doreau (1992) and Wonsil et al. (1994). Similarly, the lack of
effect of fish oil treatment on ADF disappearance is in line with the observations of
Sutton et al. (1975) and Wonsil et al. (1994). The absence of any detrimental effects of
fish oil treatment on DM and fibre disappearance from the dacron bags in the present
study, or total diet digestibility in the concurrent study (Keady et al., 1999a), which
involved lactating dairy cows offered two level of concentrates, clearly illustrate that the
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T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
levels and type of fish oil supplementation had little effect on bacteria or protozoa growth.
Dong et al. (1994) observed no effect of including cod liver oil at levels up to 0.10 of total
DM on total or cellulolytic bacterial numbers in an artificial fermenter containing forage
or grain based diets.
4.3. Effects of fish oil on rumen fermentation
Fish oil inclusion had no effect on the composition of fatty acid in the rumen liquor in
accord with the results of Beitz and Davis (1964); Doreau (1992) and Wonsil et al.
(1994). However Nicholson and Sutton (1971), Brumby et al. (1972), Sutton et al. (1975)
and Doreau and Chilliard (1997) concluded that inclusion of fish oil in the diet decreased
the molar concentration of acetate and increased the molar concentration of propionate.
The absence of any effect of fish oil on rumen volatile fatty acid concentrations may be
associated with the sampling procedure employed in the present study, i.e., 11 samples
being taken during the 24 h sampling period. In previous studies, (Beitz and Davis, 1964;
Brumby et al., 1972; Nicholson and Sutton, 1971; Storry et al., 1974; Sutton et al., 1975;
Doreau, 1992; Wonsil et al., 1994; Doreau and Chilliard, 1997) normally only 1 to 3
samples of rumen liquor were obtained within the first 10 h after feeding. In the present
study increasing the level of fish oil tended to increase propionate concentrations at 1, 5
and 14 h after feeding but had no effect on propionate concentrations at the other
sampling times. Secondly in the present study the fish oil was offered in two equal feeds
per day, reducing total oil intake at any one period and consequently reducing potential
changes in rumen fermentation pattern. For example, Doreau and Chilliard (1997) offered
fish oil in one feed daily and concluded that the inclusion of 200 g fish oil had no effect
on rumen fermentation patterns whereas inclusion of 400 g fish oil in one feed reduced
the molar proportions of acetate and increased the proportions of propionate. In the
present study the maximum level of fish oil offered at any one time was 225 g. Finally
grass silage formed the basal forage in the present study whereas in previous studies the
basal diet consisted of either hay (Beitz and Davis, 1964; Brumby et al., 1972; Nicholson
and Sutton, 1971; Storry et al., 1974; Sutton et al., 1975) or maize silage (Doreau, 1992;
Wonsil et al., 1994; Doreau and Chilliard, 1997). Grass silage has a major impact on
rumen fermentation parameters. Keady et al. (1999b) offered three grass silages
supplemented with concentrates varying in starch content from 17 to 304 g kgÿ1 DM to
dairy cows and concluded that relative to concentrate type, silage type had a greater
impact on rumen fermentation patterns. Furthermore the rumen fermentation pattern
measured at a particular time depends not only on silage composition but also on rate of
eating (Offer and Percival, 1998). Although feeding behaviour was not measured in the
present study, in the concurrent study Keady et al. (1999a) concluded that as the level of
fish oil increased silage intake decreased from 6 to 24 h after the a.m. feed.
It is interesting to note that in the present study the fish oil premix significantly
decreased the molar proportions of acetate and increased the proportions of propionate
relative to the other fish oil source. These changes in rumen VFA concentrations are
possibly associated with the carrier used in this product, namely palm kernel, and/or its
fatty acid profile. The fish oil premix had a greater proportion of the longer chain fatty
acids (i.e. C20:0 and greater) which may have resulted in a modification of the ruminal
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
67
microbial ecosystem. Also the fish oil premix resulted in higher intakes of unsaturated oil
which are prone to cause changes in the rumen environment.
It is concluded that increasing the level of fish oil up to 450 g per day did not alter rate
of rumen digestion or fermentation parameters. However, the fish oil premix decreased
the ratio of lipogenic to glucogenic precursors. Consequently the depression in milk
butterfat content obtained in the concurrent study cannot be attributed to changes in
rumen fermentation parameters (Keady et al., 1999a). The depression in milk fat recorded
in the concurrent study (Keady et al., 1999a) was probably due firstly to the inhibition of
de-novo fatty acid synthesis and mammary uptake of plasma fatty acids which may have
occurred given the presence of C20 to C22 polyunsaturated acids in fish oil and, secondly,
to the production of trans fatty acids, particularly trans C18:1, which has been shown to
depress de-novo fatty acid synthesis.
Acknowledgements
The authors wish to thank Mr W. Clews and the staff of the dairy unit and Mr M. Porter
and the laboratory staff for their assistance.
References
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Cant, J.P., Fredeen, A.H., MacIntyre, T., Gunn, J., Croma, N., 1997. Effect of fish oil and monensin on milk
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Chilliard, Y., Doreau, M., 1997. Influence of supplementary fish oil and rumen-protected methionine on raw
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Devendra, C., Lewis, D., 1974. The interaction between dietary lipids and fibre in the sheep IV. Duodenal
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Century: Priorities and Research Needs, University of Saskatchewan, Saskatoon, SK, pp. 314
Doreau, M., 1992. Effects of supplementation with hydrogenated fish fat on digestion in dairy cows. Ann. Zoo.
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Doreau, M., Chilliard, Y., 1997. Effects of ruminal or postruminal fish oil supplementation on intake and
digestion in dairy cows. Reprod. Nut. Dev. 37, 113±124.
Ferlay, A., Legay, F., Bauchart, D., Poncet, C., Doreau, M., 1992. Effect of a supply of raw or extruded rapeseeds
on digestion in dairy cows. J. Anim. Sci. 70, 915±923.
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feeding on silage intake, digestibility, degradability and rumen volatile fatty acid concentrations in growing
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Keady, T.W.J., Mayne, C.S., Marsden, M., 1998. The effects of concentrate energy source on silage intake and
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Keady, T.W.J., Mayne, C.S., Fitzpatrick, D.A., 1999b. An examination of the effect of concentrate energy source
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Keady, T.W.J., Steen, R.W.J., Kilpatrick, D.J., Mayne, C.S., 1994. Effects of inoculant treatment on silage
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Nicholson, J.W.G., Sutton, J.D., 1971. Some effects of unsaturated oil given to dairy cows with rations of
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81 (1999) 57±68
The effects of level of fish oil inclusion in the diet
on rumen digestion and fermentation parameters
in cattle offered grass silage based diets
T.W.J. Keadya,*, C.S. Maynea,b
a
Agricultural Research Institute of Northern Ireland, Hillsborough, Co. Down BT26 6DR, UK
b
Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK
Received 7 December 1998; received in revised form 26 April 1999; accepted 19 May 1999
Abstract
A partially balanced changeover design experiment was undertaken to evaluate the effects of
level of fish oil inclusion in the diet on rumen fermentation parameters and digestion with 10 beef
cattle offered grass silage ad libitum as the basal forage supplemented with 5 kg concentrates
headÿ1 dayÿ1. Concentrates were prepared to provide either 0 (T0), 150 (T150), 300 (T300) or
450 g (T450) fish oil (Fish Industries, Killybegs, Co. Donegal, Ireland) or 300 g (T300B) fish oil
premix (J. Bibby Agriculture) per head per day. The concentrates were formulated to have similar
concentrations of crude protein, effective rumen degradable protein, digestible undegradable
protein and starch. The dry matter (DM), pH and ammonia nitrogen (N) concentrations of the silage
were 194 g kgÿ1, 3.98 and 94 g kgÿ1 N, respectively. Level or source of fish oil did not alter
(P > 0.05) the disappearance of DM, neutral detergent fibre or acid detergent fibre after 12 or 24 h
rumen incubation intervals. Increasing the level of fish oil increased rumen ammonia concentration
(P < 0.001) but did not alter (P > 0.05) rumen pH or the molar concentrations of the volatile fatty
acids. The fish oil premix decreased rumen ammonia concentration (P < 0.001), the molar
concentrations of acetate (P < 0.05), the acetate : propionate (P < 0.05), acetate + butyrate/
propionate (P < 0.01) and non-glucogenic (P < 0.05) ratios and increased the molar concentration
of propionate (P < 0.01). It is concluded that changes in rumen fermentation parameters do not
account for the depressions in milk butterfat content with fish oil inclusion observed in a concurrent
production study in which lactating dairy cows were offered similar diets to those used in the
present study. Furthermore, the changes in rumen fermentation parameters with inclusion of a fish
oil premix are probably associated with the carrier or the source of fish oil used in that product.
# 1999 Elsevier Science B.V. All rights reserved.
Keywords: Cattle; Fish oil; Rumen; Fermentation; Digestibility
*
Corresponding author. Tel.: +44-1846-682484; fax: +44-1846-689594
E-mail address: [email protected] (T.W.J. Keady)
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 7 3 - 5
58
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
1. Introduction
Given the current constraints on milk fat production within the European Union (EC),
there is considerable interest in developing strategies to reduce milk butterfat content
whilst maintaining milk output. It is generally accepted that inclusion of fish oil in the
diet depresses butterfat content of milk when animals are offered hay (Beitz and Davis,
1964; Nicholson and Sutton, 1971; Brumby et al., 1972) or maize silage (Chilliard and
Doreau, 1997) as the basal forage. More recently, Keady et al. (1999a) concluded that
increasing the level of fish oil in the diet decreased milk fat content of dairy cows offered
grass silage as the basal diet, regardless of the level of concentrate supplementation.
Possible reasons for the decreased milk fat content with fish oil supplementation include
inhibition of de-novo fatty acid synthesis and mammary gland uptake of plasma fatty
acids (Brumby et al., 1972), inhibition of lipoprotein lipase activity (Storry et al., 1969) or
mammary acetyl-CoA carboxylase (Moore and Steele, 1968), or as a result of trans fatty
acid production. It is also possible that fish oil inclusion in the diet may alter the rumen
environment, consequently decreasing fibre digestion and the ratio of lipogenic : glucogenic fatty acids. Several previous studies have shown that fish oil supplementation of
cows offered hay (Nicholson and Sutton, 1971; Brumby et al., 1972; Storry et al., 1974)
or maize silage (Chilliard and Doreau, 1997) as the basal forage, resulted in a reduction in
the ratio of lipogenic to glucogenic fatty acids in the rumen. However, in these studies the
fish oil was offered in one feed and samples of rumen fluid were collected on a few
occasions, within a maximum period of 10 h post feeding.
Given the paucity of experimental data on the effects of fish oil supplementation on
rumen digestion and fermentation patterns of cattle offered grass silage based diets the
present study was initiated to determine if the effects of fish oil inclusion on milk fat
concentration in the concurrent study (Keady et al., 1999a) were mediated through
changes in rumen fermentation parameters. The effects of fish oil inclusion on the
disappearance of dry matter (DM), neutral detergent fibre (NDF) and acid detergent fibre
(ADF) in the rumen were also examined.
2. Material and methods
2.1. Silage
Grass silage was produced from herbage harvested from the primary growth of
predominantly perennial ryegrass swards which had received 7.6 m3 cattle slurry and 127,
17.5 and 35 kg haÿ1 of nitrogen (N), P2O5 and K2O, respectively. It was mown between 4
and 7 June using a mower fitted with a V-spoke grass conditioner (Taarup, Model 307)
and harvested after a wilting period of 24 h using a precision chop forage harvester
(Reco-Mengele, Model SH40N). At ensiling the herbage was treated with an inoculant
(Ecosyl, Zeneca Bio Products) which was applied through a pump applicator and
discharged into the auger chamber of the harvester at the rate of 2.98 l tÿ1 herbage.
During filling, the silo was consolidated between loads by rolling with an industrial
loader and for a further 60 min after filling was completed. Following consolidation, two
59
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 1
Ingredient composition of concentrates (g kgÿ1 fresh weight)
Concentrate
Ingredients
Barley
Wheat
Maize gluten
Molassed sugar beet pulp
Soyabean
SoyPass
Rapeseed
Fish oil
Fish oil premix
Minerals and vitamins
Molasses
Urea
a
b
Control
FOa
FOPb
135
310
140
100
110
80
55
0
0
40
30
0
25
397
35
95
138
90
60
90
0
40
30
0
30
400
20
100
85
115
55
0
120
40
30
5
FO = fish oil included.
FOP = fish oil premix included.
polythene sheets were used to seal the silo. The entire surface was then weighed down
with a layer of tyres.
During the feeding period, silage was removed from the silos with a shear grab in
blocks containing approximately 0.5 m3.
2.2. Concentrate
Five concentrates were formulated containing different levels and sources of fish oil.
Initially three concentrates were prepared containing no fish oil (Control) and fish oil
(FO) (Fish Industries, Killybegs, Co. Donegal, Ireland) at 90 kg tÿ1 or a commercial fish
oil premix (FOP) (J. Bibby Agriculture) at 120 kg tÿ1. Two further concentrates were
prepared by mixing the control and FO concentrates in different proportions. The
concentrates were formulated to supply either 0 (T0), 150 (T150), 300 (T300) or 450 g
(T450) fish oil animalÿ1 dayÿ1 or 300 g (T300B) animalÿ1 dayÿ1 of the alternative
commercial fish oil premix, when offered at 5 kg headÿ1 dayÿ1. The concentrates were
formulated to have similar concentrations of crude protein (CP), effective rumen
degradable protein (ERDP) and digestible undegradable protein (DUP) using AFRC
(1993) published values for individual feed ingredients and starch. Concentrate
formulations are presented in Table 1. Cereals and pelleted ingredients were ground
through a 3 mm screen before mixing and pelleting through a 12 mm die.
2.3. Animals and management
The diets were offered to 10 mature steers fitted with rumen fistulae in a partially
balanced, changeover design experiment consisting of three 4-week periods giving a total
of six animals per treatment. During changeover, the concentrate treatments were
60
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
gradually introduced during a 3-day period. Silage was offered once daily at 09:00 in
sufficient quantities to allow a refusal of 50 to 100 g kgÿ1 intake. The concentrates
were offered in two equal feeds at 05:00 and 16:00 h. The animals were housed in
individual tie-up stalls. Individual intakes of silage and concentrates were recorded daily
for the duration of the study, with the last week of each period being the main recording
interval.
2.4. Measurements
Samples of offered and refused silage were retained daily for oven DM (858C)
analysis. The dried samples of offered silage were bulked weekly and analysed for ADF,
NDF, ash and acid detergent insoluble nitrogen (ADIN) concentrations. Fresh samples of
offered silage were obtained twice weekly for the determination of pH, buffering capacity
and concentrations of toluene DM, CP, ammonia N, ethanol, propanol, acetate,
propionate, valerate, butyrate and lactate.
A sample of each concentrate type was retained weekly for the determination of oven
DM (1008C), CP, ash, ether extract (EE), NDF, water soluble carbohydrates (WSC), gross
energy, starch, NDF cellulose digestibility and ADIN.
2.5. Rumen digestion study
The effects of fish oil supplementation on rumen digestion of hay were determined by
the polyester bag method as described by Mehrez and érskov (1977). Eight polyester
bags (pore size = 1600 mm2) containing the equivalent of 5 g DM of fresh chopped hay
(ADF and NDF concentrations of 420 and 722 g kgÿ1 DM, respectively) were suspended
in the rumen of the steers fitted with rumen fistulae on day 26 of each sampling period.
Four polyester bags were removed after the 12 and 24 h incubation periods, respectively.
2.6. Rumen fermentation study
On day 28 of each period samples of rumen liquor were collected via the fistulae at
05:00, 06:00, 07:00, 09:00, 10:00, 13:00, 16:00, 17:00, 19:00, 22:00 and 05:00 h
representing 0, 1, 2, 4, 5, 8, 11, 12, 14, 17 and 24 h after the morning feed, respectively.
The samples of rumen liquor were obtained as described by Keady and Steen (1996) and
were analysed for pH, ammonia N, acetate, propionate, butyrate and valerate as described
by Keady et al. (1994). Other methods of chemical analysis of the silages and
concentrates were as described by Keady et al. (1998).
2.7. Statistical analysis
Data on food intake, rumen digestion and fermentation parameters were analysed as
partially balanced changeover design experiment using the residual maximum likelihood
(REML) directive in the GENSTAT 5 statistical software package. For food intake and
rumen digestion data, the effect of oil was investigated using the REML, while for the
rumen fermentation data, REML was used to investigate the effects of oil, time and the
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
61
Table 2
Chemical composition of the silage at feeding
Dry matter (alcohol corrected toluene) (g kgÿ1)
pH
Buffering capacity (mEquiv kgÿ1 DM)
Composition of DM (g kgÿ1)
Crude protein
Ammonia nitrogen (g kgÿ1 total N)
Ethanol
Propanol
Acetate
Propionate
Butyrate
Valerate
Lactate
ADF
NDF
ADIN
Ash
194
3.98
1045
135
94
9.2
1.2
25
0.2
0.4
0.5
75
403
664
4.4
74
interaction between oil and time. Linear and quadratic contrasts were calculated for the
four levels of fish oil. Differences between treatments were tested using the student t-test.
3. Results
3.1. Chemical composition of the silages and concentrates
The chemical composition of the silage as fed is presented in Table 2. The silage was
well preserved as measured by its pH and low concentrations of ammonia N and butyrate.
The chemical composition of the concentrates at feeding is presented in Table 3. The
concentrates had similar concentrations of DM, CP and starch. Increasing the level of fish
oil in the concentrate decreased the concentrations of WSC and ash, and increased the
concentrations of ADIN, EE and gross energy. Relative to T300, T300B had lower
concentrations of WSC and gross energy and higher concentrations of ADIN and ash.
The fatty acid profiles of the fish oil, fish oil premix and the concentrates at feeding are
presented in Table 4. Increasing the level of fish oil inclusion in the concentrates
increased the concentrations of C12:0, C14:0, C18:0, C20:0, C20:4w3, C20:4w6, C22.0, C22:1,
C20:5w3, C24:0, C24:1w9 and C22:6w3 and decreased the concentrations of C18:2, and C18:3 in
total fat. Relative to T300, T300B increased the concentrations of C18:2 and C20:5w3 and
decreased the concentrations of C14:0, C20:0 and C22:6w3.
3.2. Food intake
The effects of fish oil treatment on silage and total DM intake are presented in Table 5.
Increasing the level of fish oil supplementation tended (P > 0.05) to decrease silage and
total DM intakes. There were no significant (P > 0.05) linear or quadratic contrasts across
62
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 3
Chemical composition of the concentrates at feeding
Concentrate
Chemical composition
Dry matter (g kgÿ1)
Composition of dry matter (g kgÿ1)
Crude protein
Water soluble carbohydrate
Neutral detergent fibre
Starch
NDF cellulose digestibility
Acid detergent insoluble nitrogen
Ash
Ether extract
Gross energy (MJ kgÿ1 DM)
T0
T150
T300
T450
T300B
861
864
867
870
862
219
101
308
307
824
2.94
84
28
17.87
217
98.7
307
301
811
3.13
83.3
54
18.33
215
96.3
305
296
797
3.32
82.6
79
18.80
213
94
304
290
784
3.52
82
105
19.26
218
90
332
303
777
4.54
86
81
18.52
Table 4
Fatty acid profile of the fish oils and of the concentrates at feeding
Fatty acid
(g kgÿ1 fat)
C12:0
C14:0
C14:1
C15:0
C16:0
C16:1
C17:0
C17:1
C18:0
C18:1
C18:2
C18:3
C20:0
C20:1
C20:2
C21:0
C20:3w6
C20:3w3
C20:4w6
C22:0
C22:1
C20:5w3
C24:0
C24:1w9
C22:6w3
Fish oil
0.8
58
0.5
5.2
136
41
3.5
3.2
26
158
22
22
59
79
5.0
4.5
2.3
9.3
3.8
12.2
123
81
12.2
28.8
108
Fish oil
premix
10.0
9.9
1.9
5.2
200
2.0
1.7
1.7
44
206
15.7
6.6
54
11.7
4.7
2.1
3.8
20
16.7
8.6
13.7
190
8.8
9.8
7.7
Treatment
T0
T150
T300
T450
T300B
0.0
2.4
0.0
1.1
164
3.2
1.0
0.0
16.3
184
558
66
1.6
3.7
1.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
5.3
0.0
1.2
165
3.1
1.0
0.0
17.2
184
541
64
3.1
3.9
1.1
0.1
0.1
0.6
0.5
0.3
0.4
5.7
0.3
0.3
2.3
0.6
8.2
0.1
1.4
166
3.1
1.0
0.1
18.0
185
525
62
4.7
4.1
1.2
0.1
0.2
1.2
1.0
0.5
0.8
11.4
0.5
0.6
4.6
0.9
11.1
0.2
1.5
167
3.1
1.1
0.2
18.8
186
509
60
6.3
4.4
1.3
0.2
0.3
1.8
1.5
0.8
1.2
17.1
0.8
0.9
7.0
1.2
14
0.2
1.6
168
3.0
1.1
0.2
19.6
186
490
58
7.9
4.6
1.4
0.3
0.5
2.4
2.0
1.0
1.6
22.8
1.1
1.2
9.3
63
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Table 5
Effect of fish oil treatment on food intake and rumen fermentation parameters
Treatment
T0
T150
s.e.m.
T300
T450
Significance
Treatmenta Time Treatment
time
T300B
Food intake (kg DM dayÿ1)
Silage
7.50 6.80 7.21 6.76
Total
12.14 11.47 11.88 11.45
6.95
11.59
0.251
0.249
NS
NS
Rumen fermentation
pH
Ammonia (m mol lÿ1)
Ethanol (m mol lÿ1)
Propanol (m mol lÿ1)
Total VFA (m mol lÿ1)
6.14
8.46bc
0.69
0.04
110
6.21
8.97c
0.82
0.00
105
0.035
0.364
0.152
0.021
3.4
NS
***
NS
NS
NS
***
***
***
***
***
NS
**
NS
NS
NS
Molar concentrations of VFAs (mmol/mol total VFAs)
Acetate (Ac)
667b 662ab 672b 652ab
Propionate (Pr)
184a 185a 182a 195ab
Butyrate (But)
124
127
123
126
Valerate (Va)
24
26
24
27
Ac/Pr
3.76b 3.75b 3.86b 3.46ab
Ac + But/Pr
4.45b 4.45b 4.55b 4.12ab
Non-glucogenic ratio
4.64bc 4.62bc 4.72c 4.25ab
641a
203b
126
30
3.24a
3.87a
4.07a
7.8
5.8
4.7
3.2
0.169
0.183
0.159
*
**
NS
NS
*
**
***
***
***
***
*
***
***
***
NS
NS
NS
NS
NS
NS
NS
6.17
6.82a
0.51
0.00
114
6.11
7.72ab
0.61
0.06
110
6.14
7.22a
0.67
0.00
109
a
Other than for the linear effect of ammonia (P < 0.05), there were no significant (P > 0.05) linear or quadratic
contrasts across the four levels of fish oil.
the four levels of fish oil. Source of fish oil did not alter (P > 0.05) either silage or total
DM intakes.
3.3. Rumen fermentation parameters
The effects of fish oil treatment on rumen fermentation parameters are presented in
Table 5. Relative to T0 and T300, T450 increased (P < 0.05) the concentrations of rumen
ammonia. T450 decreased (P < 0.05) the non-glucogenic ratio relative to T300. Other
than for the linear effect of ammonia (P < 0.05) there were no significant (P > 0.05)
linear or quadratic contrasts across the four levels of fish oil. Level of fish oil did not
significantly (P > 0.05) alter rumen pH, the concentrations of ammonia, total volatile
fatty acids (VFA), ethanol or propanol, or the molar concentrations of acetate, butyrate,
propionate or valerate. Relative to T300, T300B increased the concentrations of ammonia
(P < 0.001) and the molar proportion of propionate (P < 0.01) and decreased the molar
proportions of acetate (P < 0.01) and the acetate + butyrate/propionate (P < 0.01) acetate/
propionate (P < 0.01) and the non-glucogenic ratios (P < 0.01).
All the rumen fermentation variables determined in the present study were significantly
(P < 0.05 or greater) altered by time of sampling.
There was a significant fish oil treatment by sampling time interaction (P < 0.01) for
the concentration of rumen ammonia (Fig. 1). Treatment T300B significantly increased
the concentrations of ammonia at 1 and 2 h relative to the other treatments and at 4 h
64
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
Fig. 1. The effects of fish oil treatment on rumen ammonia concentration (Control ±&± 150 g fish oil/cow/day
±^± 300 g fish oil/cow/day ±~± 450 g fish oil/cow/day ±$± 300 g fish oil/cow/day from premix ±*±).
relative to the control. At 8 h T150 increased ammonia concentrations relative to T300.
Relative to the control, rumen ammonia concentration was increased for T300B at 12 h
and for T450 at 12 and 14 h after the morning concentrate feed. Treatment had no effect
(P > 0.05) on rumen ammonia concentrations at 0, 5, 11, 17 or 24 h post feeding. There
were no treatment by time interactions (P > 0.05) for rumen pH, the molar concentrations
of acetate, propionate, butyrate, the ratios of acetate : propionate, acetate + butyrate/
propionate and non-glucogenic ratios or the concentrations of ethanol or propanol.
The effects of fish oil treatment on the disappearance of DM, ADF and NDF of hay
incubated in the rumen for 12 and 24 h are presented in Table 6. Fish oil treatment did not
alter (P > 0.05) the disappearance of DM, ADF or NDF following 12 and 24 h incubation
periods, respectively. There were no significant (P > 0.05) linear or quadratic contrasts
across the four levels of fish oil.
Table 6
The effects of fish oil treatment on the proportion of hay disappearance in the rumena
Dry matter
Acid detergent fibre
Neutral detergent fibre
a
Incubation
period (h)
Treatment
T0
T150
T300
T450
T300B
12
24
12
24
12
24
0.189
0.380
0.067
0.259
0.048
0.240
0.180
0.363
0.073
0.258
0.041
0.227
0.180
0.366
0.071
0.255
0.030
0.222
0.186
0.385
0.082
0.278
0.056
0.257
0.192
0.375
0.098
0.274
0.053
0.247
s.e.m.
Significance
0.0102
0.0185
0.0183
0.0241
0.0112
0.0229
NS
NS
NS
NS
NS
NS
There were no significant (P > 0.05) linear or quadratic contrasts across the four levels of fish oil.
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
65
4. Discussion
In a concurrent study (Keady et al., 1999a) inclusion of 450 g fish oil cowÿ1 dayÿ1 in
the diet of lactating dairy cattle altered milk composition by decreasing the
concentrations of fat and protein by 15 and 3.86 g kgÿ1, respectively. The present study
was undertaken to elucidate if the mode of action of fish oil was occurring in the rumen,
due to changes either in fermentation parameters or digestibility. In the present study
concentrates accounted for approximately 0.60 of the total diet which is similar to the
mean of the two concentrate treatments offered in the concurrent study (Keady et al.,
1999a) in which there were no fish oil by concentrate feed level interactions for milk
composition. As in the concurrent study the concentrates were formulated to contain
similar concentrations of CP, starch, ERDP, DUP, WSC and sugars. The ERDP and DUP
concentrations were based on AFRC (1993) published values.
4.1. Effects of fish oil on silage intake
Although fish oil treatment did not significantly decrease silage intake, fish oil
inclusion resulted in similar proportional decreases in intake as occurred at the higher
level of concentrate supplementation in the concurrent study (Keady et al., 1999a). Also
Wonsil et al. (1994), Chilliard and Doreau (1997) and Cant et al. (1997) reported
reductions in food intake due to fish oil inclusion in the diet. Furthermore, the absence
of an effect of fish oil type on silage DM intake in the present study is similar to the
results obtained by Keady et al. (1999a). The decrease in silage intake recorded in the
present study with fish oil supplementation may be due to a metabolic control mechanism
related to the effect of some fatty acids of fish oil on biohydrogenation in the rumen as
suggested by Doreau and Chilliard (1997) rather than to a negative effect on rumen
function, as fish oil inclusion did not affect rumen fermentation patterns or digestion of
fibre fractions, which have been identified as major factors affecting silage intake (Steen
et al., 1998).
4.2. Effects of fish oil on rumen digestion
Previous studies (Devendra and Lewis, 1974; Kowalczyk et al., 1977; Knight et al.,
1978) have shown that free oil supplementation reduced the apparent digestion of organic
matter due primarily to a reduction in fibre digestibility. Also more recently Ikwuegbu
and Sutton (1982) concluded that inclusion of free oil shifted the site of digestion of
digestible ADF to the intestines. Lipid supply generally causes no variation in retention
time of particles in the rumen (Ferlay et al., 1992). The absence of an effect of fish oil
treatment on the disappearance of DM after 12 or 24 h rumen incubation periods, is
similar to the results of Doreau (1992) and Wonsil et al. (1994). Similarly, the lack of
effect of fish oil treatment on ADF disappearance is in line with the observations of
Sutton et al. (1975) and Wonsil et al. (1994). The absence of any detrimental effects of
fish oil treatment on DM and fibre disappearance from the dacron bags in the present
study, or total diet digestibility in the concurrent study (Keady et al., 1999a), which
involved lactating dairy cows offered two level of concentrates, clearly illustrate that the
66
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
levels and type of fish oil supplementation had little effect on bacteria or protozoa growth.
Dong et al. (1994) observed no effect of including cod liver oil at levels up to 0.10 of total
DM on total or cellulolytic bacterial numbers in an artificial fermenter containing forage
or grain based diets.
4.3. Effects of fish oil on rumen fermentation
Fish oil inclusion had no effect on the composition of fatty acid in the rumen liquor in
accord with the results of Beitz and Davis (1964); Doreau (1992) and Wonsil et al.
(1994). However Nicholson and Sutton (1971), Brumby et al. (1972), Sutton et al. (1975)
and Doreau and Chilliard (1997) concluded that inclusion of fish oil in the diet decreased
the molar concentration of acetate and increased the molar concentration of propionate.
The absence of any effect of fish oil on rumen volatile fatty acid concentrations may be
associated with the sampling procedure employed in the present study, i.e., 11 samples
being taken during the 24 h sampling period. In previous studies, (Beitz and Davis, 1964;
Brumby et al., 1972; Nicholson and Sutton, 1971; Storry et al., 1974; Sutton et al., 1975;
Doreau, 1992; Wonsil et al., 1994; Doreau and Chilliard, 1997) normally only 1 to 3
samples of rumen liquor were obtained within the first 10 h after feeding. In the present
study increasing the level of fish oil tended to increase propionate concentrations at 1, 5
and 14 h after feeding but had no effect on propionate concentrations at the other
sampling times. Secondly in the present study the fish oil was offered in two equal feeds
per day, reducing total oil intake at any one period and consequently reducing potential
changes in rumen fermentation pattern. For example, Doreau and Chilliard (1997) offered
fish oil in one feed daily and concluded that the inclusion of 200 g fish oil had no effect
on rumen fermentation patterns whereas inclusion of 400 g fish oil in one feed reduced
the molar proportions of acetate and increased the proportions of propionate. In the
present study the maximum level of fish oil offered at any one time was 225 g. Finally
grass silage formed the basal forage in the present study whereas in previous studies the
basal diet consisted of either hay (Beitz and Davis, 1964; Brumby et al., 1972; Nicholson
and Sutton, 1971; Storry et al., 1974; Sutton et al., 1975) or maize silage (Doreau, 1992;
Wonsil et al., 1994; Doreau and Chilliard, 1997). Grass silage has a major impact on
rumen fermentation parameters. Keady et al. (1999b) offered three grass silages
supplemented with concentrates varying in starch content from 17 to 304 g kgÿ1 DM to
dairy cows and concluded that relative to concentrate type, silage type had a greater
impact on rumen fermentation patterns. Furthermore the rumen fermentation pattern
measured at a particular time depends not only on silage composition but also on rate of
eating (Offer and Percival, 1998). Although feeding behaviour was not measured in the
present study, in the concurrent study Keady et al. (1999a) concluded that as the level of
fish oil increased silage intake decreased from 6 to 24 h after the a.m. feed.
It is interesting to note that in the present study the fish oil premix significantly
decreased the molar proportions of acetate and increased the proportions of propionate
relative to the other fish oil source. These changes in rumen VFA concentrations are
possibly associated with the carrier used in this product, namely palm kernel, and/or its
fatty acid profile. The fish oil premix had a greater proportion of the longer chain fatty
acids (i.e. C20:0 and greater) which may have resulted in a modification of the ruminal
T.W.J. Keady, C.S. Mayne / Animal Feed Science and Technology 81 (1999) 57±68
67
microbial ecosystem. Also the fish oil premix resulted in higher intakes of unsaturated oil
which are prone to cause changes in the rumen environment.
It is concluded that increasing the level of fish oil up to 450 g per day did not alter rate
of rumen digestion or fermentation parameters. However, the fish oil premix decreased
the ratio of lipogenic to glucogenic precursors. Consequently the depression in milk
butterfat content obtained in the concurrent study cannot be attributed to changes in
rumen fermentation parameters (Keady et al., 1999a). The depression in milk fat recorded
in the concurrent study (Keady et al., 1999a) was probably due firstly to the inhibition of
de-novo fatty acid synthesis and mammary uptake of plasma fatty acids which may have
occurred given the presence of C20 to C22 polyunsaturated acids in fish oil and, secondly,
to the production of trans fatty acids, particularly trans C18:1, which has been shown to
depress de-novo fatty acid synthesis.
Acknowledgements
The authors wish to thank Mr W. Clews and the staff of the dairy unit and Mr M. Porter
and the laboratory staff for their assistance.
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