1Contribution paper no.1228 from Livestock Research Institute, Council of Agriculture, Executive Yuan, Taiwan.
2 Livestock Research Institute, Council of Agriculture, Executive Yuan, Taiwan, www.tlri.gov.tw Email jblin@mail.tlri.gov.tw
3 Diwan College of Management, Taiwan, www.dwu.edu.tw Email mclee@mail.dwu.edu.tw
4 Livestock Research Institute, Council of Agriculture, Executive Yuan, Taiwan, www.tlri.gov.tw
Email srchang@mail.tlri.gov.tw
5 Livestock Research Institute, Council of Agriculture, Executive Yuan, Taiwan, www.tlri.gov.tw Email Fhhsu@mail.tlri.gov.tw
Nilegrass (Acrocras macrum Stapf) and pangola grass(Digitaria decumbens Stent)are perennial C3 and C4 forage grasses, respectively, that produce high forage yield and quality in Taiwan. The objectives of this study were to measure aspects of the quality (metabolizable energy [ME], acid detergent fibre [ADF], neutral detergent fibre [NDF], crude protein [CP]), and observe changes in cell wall digestion, of nilegrass and pangola grass sampled after 4, 6, 8 and 10 weeks of regrowth in spring and fall crops. The contents of ADF and NDF of nilegrass were lower than those of pangola grass in both spring and fall crops. The 4-week crude protein content of both nilegrass and pangola grass were higher than those of the 6, 8 and 10-week growth stages. The ME content of the 6 and 8-week cuts of nilegrass were higher than those of 4 and 10-week cuts in both seasons. After 72 hours in the rumen, both stem and leaf of nilegrass up to 8 weeks growth stage had been digested by rumen micro organisms. For comparable samples of pangola grass the leaf had been digested while the stem tissue was mostly undegraded. The results showed that nilegrass has a higher quality and is more easily digested than pangola grass when grown under the same conditions and is a potential replacement for pangola grass in Taiwan.
Both nilegrass and pangolagrass had the highest metabolizable energy at 6 week growth stage. Nilegrass was more easily digested and had better forage quality than pangola grass.
Key words
Nilegrass (Acrocras macrum Stapf), Pangola grass(Digitaria decumbens Stent), digestibility, anatomy.
Nilegrass (Acroceras macrum Stapf) is a perennial C3 forage grass (Oliveira et al., 1973) and has been proposed by Shaug et al., (1999) as an alternative to pangola grass (Digitaria decumbens) for Taiwan. A study to compare the growth and forage quality of these grasses has been reported by Hsu et al. (2004). Plant samples from that study were used to develop a more comprehensive understanding of the morphological characteristics and quality attributes of these grasses.
Chemical contents and metabolizable energy: The contents of metabolizable energy (ME), ether extract (EE) , nitrogen-free extract (NFE), 24hr gas production (Gb24), crude protein (CP), acid detergent fibre (ADF) and neutral detergent fibre (NDF) were determined following the methods presented by Close and Menke (1986) and Olsen and Dean (1965) for oven-dried samples of Nilegrass cv. Taishi No. 1 and pangola grass line A254. Samples were taken from cuts at 4, 6, 8 and 10 week intervals in fall (October) and spring (April) in the second year of the experiment, with four replicates per grass per cutting interval.
Digestibility: Fresh samples of Nilegrass and pangola grass cut at 4, 6, 8 and 10 week intervals were collected at the spring (April) harvest. Fresh samples were enclosed in nylon bags (20 micron mesh) and suspended in the rumen of a cannulated dairy cow. The bags were removed from the rumen after 24, 48 and 72 hours for observation of changes in plant anatomy. Sections were obtained using the paraffin-cut technique reported by Lin and Yeh (1996).
Chemical contents and metabolizable energy: The contents of ADF and NDF in nilegrass were lower than those of pangola grass in both spring and fall crops (Table 1). For both grasses and in both seasons, the highest ME was achieved at the 6 and 8 week growth stages (Table 2, 3).
After 72 hours in the rumen, both stem and leaf of nilegrass had been mostly digested for the 4, 6 and 8 week cuts, while only the leaves of pangola grass cut at 4 and 6 weeks were easily digested (Fig. 1 A, B, C and D). Both stem and leaf of pangola grass cut at 8 and 10 weeks were not easily digested (Fig.1 F and H). The anatomical observations of plant tissues digested by rumen microorganisms, showed that most of the cell wall structure of nilegrass was degraded 72 hours after digesting in rumen of dairy cow. However, the cell wall of pangola grass was not completely degraded during the same period (Fig. 1).
In almost every measure of in vitro quality nilegrass was superior to pangola grass. The complete rumen digestion of both leaf and stem for samples of nilegrass cut up to 8-week intervals was in shape contrast to that for pangola grass.
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Table 1. Comparision of the chemical contents between nilegrass and pangola grass at different growth stages in spring and fall crops (%).
Growth stage week |
Spring |
Fall | |||||
Species |
CP |
ADF |
NDF |
CP |
ADF |
NDF | |
4 |
Nilegrass |
12.35a* |
35.14b |
59.23b |
11.96a* |
34.41b |
61.12b |
Pangolagrass |
10.48a |
39.67a |
63.09a |
9.39b |
39.08a |
70.89a | |
6 |
Nilegrass |
10.58a |
36.29b |
59.81b |
9.33a |
35.94b |
66.76b |
Pangolagrass |
9.88a |
39.09a |
59.83b |
7.26b |
38.47a |
69.96a | |
8 |
Nilegrass |
6.76a |
37.09b |
56.72b |
8.67a |
36.72b |
68.96b |
Pangolagrass |
6.64a |
39.48a |
68.13a |
5.92b |
41.50a |
73.46a | |
10 |
Nilegrass |
5.20a |
38.04b |
59.31b |
7.15a |
38.13b |
69.08b |
Pangolagrass |
5.15a |
39.22a |
64.99a |
5.68a |
42.13a |
72.82a |
*Means within columns and at the same growth stage with the same letter are not significantly different (P<0.05).
Table 2. Effects of different growth stages on the chemical contents and metabolizable energy of nilegrass and pangola grass in spring crop.
Growth stage |
Nilegrass |
Pangolagrass | ||||||
EE@ |
NFE |
Gb24 |
ME |
EE |
NFE |
Gb24 |
ME | |
week |
% |
% |
My/200mg |
Mcal/Kg |
% |
% |
My/200mg |
Mcal/Kg |
4 |
2.53c* |
61.5a |
40.3a |
9.79c |
2.18a |
64.7b |
40.1a |
8.97c |
6 |
1.56b |
59.3b |
42.2b |
10.08a |
1.98b |
63.3d |
40.4ab |
9.96a |
8 |
1.77a |
62.0a |
41.4ab |
9.92b |
1.41c |
65.7b |
41.7b |
9.20b |
10 |
1.83a |
65.9c |
41.0ab |
9.71d |
1.42c |
66.5a |
39.6a |
9.00c |
SEM |
0.036 |
0.422 |
0.570 |
0.017 |
0.027 |
0.410 |
0.530 |
0.020 |
*Means with the same letter in the same column are not significantly different (P<0.05).
Table 3. Effects of different growth stages on the chemical contents and metabolizable energy of nilegrass and pangola grass in fall crop.
Growth stage |
Nilegrass |
Pangolagrass | |||||||
EE@ |
NFE |
Gb24 |
ME |
EE |
NFE |
Gb24 |
ME | ||
week |
% |
% |
My/200mg |
Mcal/Kg |
% |
% |
My/200mg |
Mcal/Kg | |
4 |
1.42a* |
63.2c |
42.8a |
9.95c |
1.99a |
61.9a |
38.3a |
8.01c | |
6 |
1.57b |
65.6b |
49.5b |
10.97a |
2.06 b |
62.1a |
44.3b |
9.01b | |
8 |
1.61b |
63.3c |
45.5c |
10.22b |
2.17c |
67.6b |
42.8b |
9.59a | |
10 |
1.18c |
70.0a |
42.7a |
9.61d |
2.10 d |
67.3b |
36.5c |
8.33d | |
SEM |
0.021 |
0.400 |
0.516 |
0.021 |
0.012 |
0.379 |
0.521 |
0.019 |
*Means with the same letter in the same column are not significantly different (P<0.05).
Figure 1. The cell walls of nilegrass (left) and pangola grass (right) internodes at 4 (A, B), 6 (C, D), 8(E, F) and 10 (G, H) weeks after cutting digested by rumen micro-organisms in the rumen for 72 hours observed by transverse section, respectively. (x 100).