F. Mould, J. Øyen and M. Pestalozzi Særheim Research Station, N-4062 Klepp Stasjon, Norway
Introduction
Materials and methods
Results and discussion
References
Grass/clover swards have a major role in sustainable and environmentally aware grassland-based animal production. Field studies to investigate the use of perennial ryegrass/white clover mixtures and pure ryegrass as silage for beef cattle were initiated in spring 1992. The objective was to verify if a clover based system could give a satisfactory production and economic return compared with a conventional pure grass/high N fertiliser input. Although the viability of such systems has been demonstrated e.g. in the UK (Bax and Roberts 1992), there is at present little knowledge or experience of the utilization of such swards under Norwegian conditions.
In spring 1991, 5.5 ha was sown with a mixture of perennial ryegrass 'Tove' and white clover 'Milkanova' (GC) using 25 and 5 kg seed/ha, respectively. Adjacent areas were sown with pure ryegrass (G) using 35 kg ha-1. Swards were established using a cover crop of barley, subsequently harvested at heading. The soil was a sandy loam, with a pH of 6.2. All fields received 32 kg P and 100 kg K ha-1 in spring 1992. In addition pure ryegrass received 100+ 100 kg N and the grass/clover fields 50+ 50 kg N ha-1 in the spring and after first harvest, respectively. Two cuts were taken for ensiling (weeks 22 and 29) and 'Foraform' (Norsk Fôrkonservering a/s) included at the rate of 4.5 1 t-1 ensiled material. Samples of herbage were taken for chemical analyses (NIRR). Clover content was assessed by separation of three samples per field and by visual scoring of 40 random plots (0.25m2) taken along the diagonal of each field. Representative samples of the silages were obtained for in vivo digestibility studies in which three sheep were offered each silage at maintenance for 14 days. Metabolisable energy and net energy content, expressed as feed units milk (FEm), were then calculated using standard formulae. Silage feed value was assessed in a series of beef production studies, each with a duration of eight weeks using Norwegian Red bulls (46) and steer calves (38). The bulls, blocked in pairs by live weight and rate of gain, were randomly allocated to one of the two treatments - ryegrass or ryegrass/clover silage. Second-cut silage was offered during the first period followed by first-cut. The cattle were not reblocked between periods. Silage was offered ad libitum (5% more than that consumed during the previous day) on an individual basis and all cattle received 1.0 kg concentrate (12% crude protein, 1.3 FEm kg DM-1, -17g PBV FEm-1) daily. Feed refusals were taken daily and the cattle weighed every 14 days. The calves were managed in a similar way except that following allocation to treatment they were group fed by live weight (three groups per treatments).
Clover content increased markedly from 1st to 3rd cut. The SD did not increase from 2nd to 3rd cut, indicating a more even distribution of clover in late season (Table 1). White clover fully compensated for the reduced N fertiliser level, with yields of dry matter similar at each harvest. The second-cut DM yield was especially high in the GC-fields (Table 2). The high proportion of clover in the second cut was also reflected in a higher content of crude protein (Table 2). Growth rate of the bulls over the study period was rapid, about 1100 g day-1, but no differences were found between treatments with either the first or second cut silages (Table 3). As each animal received only 1.0 kg concentrate daily, these growth rates reflect the high quality of the silages available. No effect of treatment on silage dry matter intake (DMI) was observed with second-cut material, although those offered first-cut ryegrass/clover silage consumed significantly (P<0.01) more than those given ryegrass silage. The cattle offered first-cut ryegrass silage had a significantly (P<0.05) better feed/gain (F/G) ratios than those given ryegrass/clover silage. The low intake of first-cut silages, and especially that of the ryegrass group, is probably due to the high DM of these silages (ca. 30%) and the low observed leaf: stem ratio. This resulted from extreme weather conditions during growth (high temperatures and below normal rainfall) and a delayed harvesting. This effect on intake was also observed in the digestibility studies where approximately 2% of first-cut material offered was rejected, while all second-cut silage was consumed. Like the bulls, the calves showed good growth rates on both silages (Table 3). No difference between treatment groups was observed with second-cut material but calves offered first-cut ryegrass silage grew significantly (P<0.001) faster than those given grass/clover silage. This effect may be related to an interaction between crude protein content of the two silages and animal requirements, however no such effect occurred when the bulls were offered these silages. Within cuts no difference in feed intakes were observed between silages. The variation in daily gain with the first-cut silage, as found with the bulls, produced a better F/G ratio for the calves offered ryegrass silage however this difference was not significant. The in vivo studies identified significant (P<0.05) differences in DM digestibility between pure ryegrass and the grass/clover combination at both harvests, although the effect was not consistent (Table 4). Digestibility of first-cut was slightly higher than second-cut and pure grass silage higher than the grass/clover silage, but none of these differences were significant.
Table 1 Clover content (%), max/min, standard deviation and coefficient of variation. GC swards only.
|
|
Cut no. |
|
Cut no. | ||||
|
Character |
1 |
2 |
3 |
Character |
1 |
2 |
3 |
|
Clover, % |
18 |
28 |
34 |
SD |
11 |
16 |
16 |
|
Max field |
26 |
44 |
39 |
CV% |
60 |
57 |
45 |
|
Min field |
8 |
17 |
29 |
|
|
|
|
Table 2 Yield and herbage quality of pure ryegrass (G) and ryegrass/clover (GC).
|
|
Dry matter, t ha-1 |
CP, % no. Fem 100 kg-1 |
||||||
|
Cut no. |
Cut no. |
Cut no. |
||||||
|
Treatment |
1 |
2 |
3 |
Total |
1 |
2 |
1 |
2 |
|
G |
5.80 |
2.10 |
2.20 |
10.10 |
16.5 |
18.9 |
89.8 |
85.2 |
|
GC |
6.80 |
3.20 |
2.50 |
11.70 |
13.3 |
16.7 |
88.8 |
86.6 |
Table 3 In vivo digestibility and feed energy contents of pure ryegrass (G) and ryegrass/clover (GC), first- (1) and second-cut (2).
|
Silage |
DMD (g g-1) |
OM (MJ kg DM-1) |
FEm (kg DM-1) |
|
G1 |
0.718a |
10.48 |
88.9 |
|
GC1 |
0.733b |
10.73 |
91.5 |
|
G2 |
0.732b |
10.72 |
91.4 |
|
GC2 |
0.702C |
10.23 |
86.3 |
Table 4 Growth performance and feed intake of pure ryegrass (G) and ryegrass/clover (GC), first- (1) and second-cut (2).
|
Cattle |
Silage |
Initial |
Gain |
DMI |
Silage |
F: G |
|
wt. (kg) |
(kg d-1) |
(kg d-1) |
(g kgw-0.75) |
ratio |
||
|
Bulls |
G1 |
450.3 |
1.159 |
6.66 |
64.7 |
6.51 |
|
GC1 |
450.9 |
1.157 |
7.44 |
72.2 |
7.20 |
|
|
G2 |
387.0 |
1.130 |
6.87 |
74.2 |
6.87 |
|
|
GC2 |
389.4 |
1.098 |
6.95 |
74.9 |
7.14 |
|
|
Calves |
G1 |
170.9 |
1.049 |
3.59 |
67.4 |
4.27 |
|
GC1 |
169.8 |
0.867 |
3.57 |
68.7 |
5.14 |
|
|
G2 |
122.0 |
0.873 |
2.59 |
61.5 |
3.99 |
|
|
GC2 |
120.9 |
0.872 |
2.45 |
58.5 |
3.83 |
Bax, J.A. and Roberts, D.J. (1992) The viability of a grass/white clover based dairy system at two levels of intensity. Proceedings of the 14th General Meeting of the European Grassland Federation. Lahti. Finland. pp. 392-396.
