30 H
. Valk et al. Livestock Production Science 63 2000 27 –38
dung patch excreted between 06.30h to 15.00h was above. Statistical analysis was carried out using
sampled and pooled to one sample per cow per Genstat Genstat 5 Committee, 1993. Treatment
week. Samples were dried at 708C and analyzed for means were compared by Student’s t-test. In experi-
DM, ash, NDF and Cr content and Kjeldahl N was ment A
one cow was infected by a severe form of
93
analyzed in a fresh subsample. The fixed amount of mastitis and was assigned as a missing value in the
Cr ingested each day and the Cr content in the faeces statistical analysis of the data. The effect of N
assuming a Cr recovery of 94, were used to fertilizer on chemical composition and nutritive
estimate daily faecal output per cow per week faecal value of grass was tested for significance using a
output 5 ingested Cr faecal Cr content. linear regression model with N treatment as the only
Cows were milked twice daily with milk yields variable.
being recorded at each milking. Milk samples were taken during six consecutive milkings per week for
fat and protein analyses, which were determined by
3. Results
infrared analysis Melkcontrolestation Noord-Neder- land, Leeuwarden.
3.1. Weather conditions during the experiments 2.4. Statistical analyses
For the spring experiments, in 1991 S weather
91
was relatively cold and wet, whereas in 1992 S
92
Intake, digestibility of nutrients and milk per- temperature was high and the experimental period
formance data were analyzed in a completely ran- was characterised by drought with occasional rain
domised block design and were subjected to analysis showers Fig. 1. Also the late summer experiment
of variance, using per experiment the model: Y 5 of 1992 A was carried out in hot weather
ij 92
m 1 a 1 b 1 e , where m 5 mean, a 5 effect of conditions with drought, whereas in 1993 A ,
i j
ij i
93
block i, b 5 effect of treatment j, and e 5 variation
weather was cold with high amounts of rainfall
j ij
within a block. Data from the experiments carried especially at the end of the experiment.
out in the same season were pooled and analyzed by Due to the drought in 1992, crown rust was
including the effect of year in the model described observed, notably at the 150N plots. During harvest-
Fig. 1. Mean maximum daily temperature in 8C per week and the accumulative amount of rainfall per week during the experiments.
H . Valk et al. Livestock Production Science 63 2000 27 –38
31
ing, the infected plots were avoided as much as N150 versus 77.7 and 76.3 for N450 and N300
possible. grass, respectively.
3.2. Grass growth 3.4. Feed intake and digestibility of nutrients
The mean age of grass in S was five days lower
91
Both compound feeds were consumed according than in S
Table 2, which reflected the better
92
the amounts offered daily 1.8 and 2.7 kg DM cow growing conditions in spring of 1991 as compared
in spring and late summer, respectively. When year with 1992. Grass growth in A
was not limited by
93
effect is accounted for, no distinct effect of N drought which resulted in a higher growth rate in
fertilizer on VI was observed in spring whereas in contrast to A
especially at the highest level of N
92
late summer, but VI was reduced significantly on fertilizer. However, except for N
in A , days of
150 92
N compared with the other treatments 15.3
150
regrowth differed not markedly between the late versus 16.2 kg DM. When compared within each
summer experiments which means that in A DM
92
experiment, a systematic reduction in VI with de- yield of grass was lower than in A .
93
creasing N fertilization was only obvious in A
93
Within the spring experiments, the reduction of N Table 3. If grass intake was expressed per kg
fertilizer resulted in a systematic increase of up to
0.75
metabolic weight W , treatment effects were
2.5 growing days to achieve 1500–2000 kg DM ha. significant only in S
and A . In A , the extra N
92 93
92
In the late summer experiments, grass was harvested on the 150N plots resulted in an increase in VI
at similar days after regrowth for the three treat- during the last two weeks of this experiment. Fur-
ments, except for N in A
which was retarded by
150 92
ther, VI of cows fed 450N grass in A was unexpec-
92
seven days. tedly low in two of the six weeks thereby reducing
the mean VI. Nevertheless, grass VI of cows fed N
450
3.3. Chemical composition and nutritive value was markedly higher than of cows fed 150N grass
during A .
92
Chemical composition and nutritive value of grass Differences in NDF intake reflected the differ-
samples are shown in Table 2. Because of dry ences in DM intake. Differences in kVEM, DVE and
weather conditions, DM content of grass cut in S
92
OEB intakes were a result of differences in VEM, was higher than in the other experiments 194 versus
DVE and OEB contents and differences in DM 145 g DM content. In A
sugar content and in-vitro
92
intake. In general, the intake of VEM, DVE and d
of grass were relatively low as compared to the
OM
OEB decreased with a reduction in N fertilizer other experiments.
especially from 300 to 150 kg N ha per year. In all Grass DM, sugar and crude fibre except in S
91
experiments the apparent in-vivo digestibility of OM content increased significantly P , 0.05 with de-
d , N d and NDF d
was significantly
OM N
NDF
creasing N application. Ash content was not affected P , 0.05 lower on diet N
compared with diet
150
by fertilizer N. The CP content decreased signifi- N
. For these response variables, the results of
450
cantly P , 0.05 with about 80 to 90 g kg DM in N
varied between the other two treatments and
300
spring and 60 to 70 g kg DM in late summer when differed more significantly from N
than from
150
N application decreased from 450 to 150 kg ha per N
. The in-vitro d calculated for the total ration
450 OM
year. The content of NDF was not affected by N was not different between N treatments following the
fertilizer except in A where NDF increased sig-
92
in-vitro d differences of grass shown in Table 2.
OM
nificantly P , 0.05 with decreasing N application. In all experiments VEM, DVE and especially OEB
declined significantly P , 0.05 by using lower 3.5. Yield, composition of milk and liveweight
amounts of N fertilizer with no seasonal effect. Except in S , in-vitro d
of 150N grass was From the overall analysis with allowance for year
91 OM
significantly lower than of 450N and 300N grass effect, daily milk yield per cow did not differ
with the most markedly difference in A 73.7 for
significantly in spring between treatments whereas in
92
32
H .
V alk
et al
. Livestock
Production Science
63 2000
27 –
38 Table 2
1 2
3
Mean days after regrowth and mean content of dry matter DM, crude protein CP, neutral detergent fibre NDF, sugar, DVE , OEB , VEM and in-vitro digestibility in-vitro d
of grass, fertilized with different amounts of N 450, 300 and 150 kg ha year, and offered to dairy cows in four zero-grazing experiments S , S , A and A
OM 91
92 92
93
Experiment S
S A
A
91 92
92 93
N N
N S.E.
N N
N S.E.
N N
N S.E.
N N
N S.E.
450 300
150 450
300 150
450 300
150 450
300 150
a a
b
Days after regrowth d 20
22 23
2 27
28 29
2 28
28 35
3 26
27 26
1 Grass
a b
c a
a b
a a
b ab
a b
DM g kg 138
147 163
3.1 182
191 208
4.1 143
141 152
4.2 142
137 145
2.9 DM composition g kg
Ash 108
105 102
1.7 106
107 105
1.4 114
113 117
3.5 105
103 106
3.4
a b
c a
b c
a b
c a
b c
CP 250
200 163
4.7 213
175 131
5.3 238
213 169
4.4 244
206 181
5.9
a b
b a
b c
a b
b
Crude fibre 214
222 219
2.5 216
222 228
4.0 225
237 244
2.2 203
213 210
2.2
a b
c
NDF 462
467 459
3.6 480
482 486
5.7 495
510 522
4.2 459
462 461
3.9
a b
c a
b c
a ab
b a
b c
Sugar 92
125 159
4.4 119
144 172
6.9 79
86 98
5.8 111
128 147
5.9
1 a
b c
a b
c a
b c
a a
b
DVE 106
99 93
0.9 97
90 80
1.2 94
89 78
1.2 100
95 89
1.4
2 a
b c
a b
c a
b c
a b
c
OEB 86
39 11
4.4 54
26 2 9
4.4 82
60 27
4.1 84
51 30
5.5 Net energy
3 a
b c
a b
c a
b c
a a
b
VEM kg DM 1029
996 976
5.8 964
934 893
7.5 934
901 837
7.6 984
960 926
9.8 In vitro
a a
b a
a b
a a
b
d 83.6
83.2 82.9
0.4 80.4
79.8 78.4
0.5 77.7
76.3 73.7
0.5 80.4
80.0 78.8
0.6
OM
a, b, c: Means in the same row and experiment with different superscripts differ significantly P , 0.05.
1
DVE 5 True protein digested in small intestine Tamminga et al., 1994.
2
OEB 5 Degraded protein balance in the rumen Tamminga et al., 1994.
3
1 kVEM 5 6.9 MJ net energy lactation Van Es, 1978.
H .
V alk
et al
. Livestock
Production Science
63 2000
27 –
38
33 Table 3
0.75
The effect of lowering N fertilizer on voluntary grass intake VI in kg DM d and g DM kg LW and total intake grass 1 compound of NDF, net-energy VEM and protein
DVE and on the apparent digestibilities of OM, N and NDF
Experiment S
S A
A
91 92
92 93
N N
N S.E.
N N
N S.E.
N N
N S.E.
N N
N S.E.
450 300
150 450
300 150
450 300
150 450
300 150
DM-intake of grass
ab b
a a
a b
VI kg d 15.4
15.9 16.0
0.5 17.2
16.7 16.6
0.4 15.4
16.1 15.0
0.4 16.7
16.6 15.5
0.4
0.75 a
ab b
a a
b
VI g kg LW 123
122 126
4.2 137
132 129
3.8 129
130 124
3.9 140
135 127
3.5 Total intake
a b
a a
a b
NDF kg d 7.8
8.0 8.0
0.2 8.9
8.7 8.8
0.2 8.6
9.2 8.7
0.2 8.6
8.6 8.1
0.2
a b
c a
a b
a a
b
kVEM 17.7
17.7 17.5
0.5 18.5
17.4 16.7
0.3 17.2
17.3 15.4
0.3 19.3
18.8 17.2
0.4
a ab
b a
b c
a a
b a
b c
DVE g d 1809
1742 1666
50 1840
1675 1507
33 1736
1711 1444
31 1948
1860 1658
39
a b
c a
b c
a b
c b
c
OEB g d 1345
630 175
28 934
435 2 135
19 1239
955 380
22 1406
853 443
27 Total diet apparent digestibility
In-vivo
a a
b a
b b
a a
b a
ab b
d 79.9
79.4 77.1
0.5 77.9
76.6 76.6
0.5 76.3
75.9 73.1
0.5 77.4
76.4 75.9
0.8
OM a
b c
a b
c a
b c
a b
b
d 78.1
73.5 68.5
0.7 76.5
72.6 69.2
0.8 75.2
73.5 68.6
0.7 74.3
71.0 69.8
1.1
N a
b c
a b
b a
a b
a b
c
d 77.3
75.1 70.1
0.8 75.3
72.9 71.5
0.8 75.5
74.2 70.5
0.9 76.1
73.1 70.5
1.1
NDF
In-vitro d
83.3 83.5
82.7 –
80.6 80.0
78.8 –
78.1 76.9
74.7 –
80.6 80.7
79.3
OM
a, b, c: Means in the same row and experiment with different superscripts differ significantly P , 0.05.
34
H .
V alk
et al
. Livestock
Production Science
63 2000
27 –
38 Table 4
Mean milk yield and composition, liveweight LW and liveweight change during the experiments of cows offered different rations N , N
and N in four experiments
450 300
150
S , S , A and A
91 92
92 93
Experiment S
S A
A
91 92
92 93
N N
N S.E.
N N
N S.E.
N N
N S.E.
N N
N S.E.
450 300
150 450
300 150
450 300
150 450
300 150
Yield
a b
b a
a b
a a
b
Milk kg d 22.1
22.1 21.7
0.7 23.7
21.5 20.8
1.1 24.3
24.4 21.8
0.6 24.8
24.3 20.7
0.9
a b
b a
a b
a a
b
FPCM kg d 24.1
23.6 23.4
0.8 25.3
23.2 22.4
1.1 24.8
25.2 22.4
0.8 26.2
25.5 22.0
0.9
a b
b a
a b
a a
b
Fat g d 1028
985 985
42 1070
982 960
49 1017
1048 937
36 1111
1060 926
43
a ab
b a
a b
a a
b
Protein g d 782
794 784
27 814
764 714
31 792
806 695
21 823
837 722
26 Milk composition
Fat g d 46.6
44.6 45.5
1.2 45.2
45.6 46.1
0.7 41.8
42.9 42.9
0.8 44.8
43.6 44.8
1.0
a b
a a
b b
Protein g d 35.4
35.9 36.2
0.6 34.4
35.5 34.3
0.6 32.5
33.0 31.8
0.7 33.2
34.4 34.9
0.6 Liveweight
a b
a
LW kg 620
651 629
6 619
632 652
22 596
608 599
13 590
613 612
18 LW change kg week 1 1.1
1 2.1 1 1.0
2.1 1 1.6
1 2.5 2 0.1
2.8 1 0.6
1 0.4 2 1.8
3.1 2 0.6
2 0.2 1 0.4
3.1 a, b, c: Means in the same row and experiment with different superscripts differ significantly P , 0.05.
H . Valk et al. Livestock Production Science 63 2000 27 –38
35
late summer cows on N produced significantly
were smaller. One of the factors that influence the
150
less milk than the cows in the other treatments 21.2 magnitude of the effects is stage of maturity. This is
on N versus 24.6 and 24.4 kg milk on N
and emphasised in A
where the differences in chemical
150 450
92
N , respectively. When compared within each
composition and nutritive value were much larger
300
experiment, milk yield on treatment N was sig-
caused by a substantial difference in growing days
150
nificantly P , 0.05 lower than on N Table 4,
for 150N grass Table 2. Also Salette 1982 and
450
except in S . In S cows on N
produced Peyraud and Astigarraga 1998 stated that NDF
91 92
300
significantly less milk than cows on N 21.5
content and d value of grass are more influenced
450 OM
versus 23.7 kg milk. In late summer, cows on N by stage of maturity than by N fertilization.
300
produced significantly more milk than cows on N ,
Nutritive value decreased with decreasing levels of
150
but no difference between N and N
was N application. The reduction of DVE and OEB with
300 450
observed. Yields of FPCM, fat and protein followed decreasing N fertilizer reflected the decrease in CP
the differences in milk yield. Except in S and A
content. The reduction in DVE ranged between 11
92 93
where milk protein content between treatments was and 18 g kg DM and was much smaller than the
significantly affected in a non-consistent way, no reduction in OEB, which decreased between 54
differences in milk constituents between treatments A and 75 S g kg DM. This agrees with
93 91
were observed. Mean liveweight LW of cows in estimates based on nylon bag studies Valk et al.,
S fed N
was significantly higher than of those in 1996; Van Vuuren et al. 1991. The reduction in VEM
91 300
the other groups. In spring, live weight changes were content with decreasing N fertilizer was mainly
positive in contrast to experiment A where live
caused by the reduction in digestible CP which is an
93
weight changes were tended to be negative. arithmetical component in the VEM equation Van
Es, 1978. In A , also the reduction in OM di-
92
gestibility attributed to the decrease in calculated
4. Discussion VEM content.
