5.3.1 Effects of season and plant species on in vitro degradability (Experiment 1) The effects of season and plant species (experiment 1) on in vitro pH, apparent degradability (ApDeg), true degradability (TrDeg), microbial yield (MY), total of short chain fatty acids (SCFA), partitioning factor (PF) and degradation efficiency factor (DEF) are shown in Table 5.1. Season affected (P<0.001) ApDeg, TrDeg, MY, PF and DEF, and
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also affected (P<0.05) SCFA, and did not affected the pH while browse species affected (P<0.001) all the parameters. The interaction of season x species affected (P<0.001) ApDeg, TrDeg, and DEF and also affected (P<0.05) the PF but did not affect the pH and MY. Among the seasons, ApDeg and TrDeg were higher in the dry season than in the early wet and the late wet seasons while MY was higher in the early wet season than in the dry and the late wet seasons. The SCFA was higher in the late wet season. The PF and DEF were higher in the early wet season than in the dry and the late wet seasons.
Among the five plant species, pH ranged from 6.81 in A. nilotica to 6.94 in S. myrtina.
Chromolaena odorata had the highest ApDeg, followed by A. nilotica while A. natalitia, D. cinerea and S. myrtina had similar and low ApDeg. Scutia myrtina had the highest TrDeg, followed in order by A. natalitia, D. cinerea, C. odorata and A. nilotica. Acacia natalitia had the highest MY whilst C. odorata had the lowest MY.Chromolaena odorata had the highest concentration of SCFA, followed by A. nilotica, S. myrtina, D. cinerea and A. natalitia. Acacia natalitia had the highest PF, whilst D. cinerea and S. myrtina had similar values and C. odorata had the lowest value. Acacia nilotica had the lowest DEF (0.99) while the others range from 1.20 to 1.95.
Interaction between season and browse species had different trends for the variables. For A. natalitia and A. nilotica ApDeg decreased from the dry season to the early and late stages of the wet season. The ApDeg for D. cinerea and S. myrtina decreased from the dry season to the early wet season from where it increased in the late wet season. Chromolaena odorata had similar ApDeg in the dry and the early wet seasons from where it decreased in the late wet season. The TrDeg of A. natalitia, D. cinerea and S. myrtina did not change across the three seasons. For A. nilotica and C. odorata TrDeg decreased from the dry season to the wet season. The SCFA did not change throughout three seasons in A.
natalitia, A. nilotica and S. myrtina, while in D. cinerea and C. odorata they increased from the dry to the early wet and the late wet seasons.
The PF for A. natalitia increased from the dry to the early wet seasons from where it decreased in the late wet season. For A. nilotica PF was similar during the three seasons.
The PF of D. cinerea and C. odorata decreased from the dry to the early wet seasons then decreased in the late wet season (D. cinerea) or remained similar between the early wet
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and the late wet seasons (C. odorata). For S. myrtina PF increased from the dry to the late wet seasons.
The DEF of A. natalitia increased from the dry to the early seasons from where it decreased in the late wet season. For A. nilotica, D. cinerea and C. odorata, DEF decreased from the dry to the early wet seasons then has been similar between the two wet seasons (A. nilotica) or decreased (D. cinerea) and increased (C. odorata) in the wet season. For S. myrtina DEF increased from the dry to the late wet seasons.
Within the five plant species and the three seasons, A. nilotica had the greatest ApDeg in the dry and the late wet seasons while C. odorata had the greatest value during the early wet season. The lowest ApDeg was observed with A. natalitia in the dry and the late wet seasons and S. myrtina in the early wet season. For TrDeg, S. myrtina had the highest value in the dry and late wet seasons while C. odorata had the highest value in the early wet season and the lowest value in the dry season and A. nilotica the lowest values in the two wet seasons. For MY, A. natalitia had highest values during the three seasons. The lowest MY was observed with C. odorata in the dry season as well as A. nilotica in the early and late wet seasons. For SCFA, C. odorata had the greatest concentration in the three seasons followed in decreasing order by A. nilotica, S. myrtina, A. natalitia and D. cinerea in the dry and the early wet, except A. natalitia in the dry season switched with D. cinerea in the early wet season. Whilst the concentration of SCFA in the late wet season followed this decreasing trend: C. odorata, D. cinerea, A. nilotica, A. natalitia, and S. myrtina. For the PF and DEF, D. cinerea, A. natalitia and S. myrtina had the highest values during the dry, early wet and late wet seasons, respectively, while C. odorata had the lowest PF and A.
nilotica had lowest DEF in the three seasons.
5.3.2 Effects of PEG on in vitro degradability (Experiment 2)
Table 5.2 shows the effect of PEG on in vitro pH, apparent degradability (ApDeg), true degradability (TrDeg), microbial yield (MY), the total short chain fatty acids (SCFA), partitioning factor (PF) and degradation efficiency factor (DEF) (experiment 2). The addition of PEG affected (P<0.001) all the above parameters. Season and its interaction with PEG (Se x PEG) affected (P<0.001) the MY, SCFA, PF and DEF while plant species affected (P<0.001) all variables (pH, ApDeg, TrDeg, MY, SCFA, PF and DEF). The
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interaction between plant species and PEG (Sp x PEG) affected all the above variables except pH while the interaction between season and plant species (Se x Sp), and between season, plant species and PEG (Se x Sp x PEG) affected only the ApDeg, SCFA, PF and DEF.
Table 5.1 Effects of season and plant species on in vitro pH, apparent and true degradability, microbial yield, total of short chain fatty acids, partitioning factor and degradation efficiency factor of plant species harvested from sub-humid subtropical savannah and fermented using rumen fluid (Experiment 1)
Season Species pH ApDeg TrDeg MY SCFA PF DEF
Dry A. natalitia a 6.88 195 833 640 25.8 27.9 1.50
A. nilotica 6.78 524 844 321 31.3 17.0 1.17
D. cinerea 6.97 200 805 605 21. 5 30.7 1.76
S. myrtina 6.91 223 848 619 28.0 19.1 1.27
C. odorata b 6.81 530 734 210 50.2 9.7 1.40
Early A. natalitia 6.90 175 809 636 16.7 35.9 3.05
Wet A. nilotica 6.85 400 681 286 29.6 16.8 0.89
D. cinerea 6.88 169 789 630 26.5 27.2 1.63
S. myrtina 6.94 176 815 635 23.4 - -
C. odorata 6.80 521 845 324 57.2 07.1 0.99
Late A. natalitia 6.86 174 836 662 25.4 19.9 1.30
Wet A. nilotica 6.81 421 680 315 28.1 15.8 0.92
D. cinerea 6.84 227 778 551 28.9 15.9 1.27
S. myrtina 6.92 212 862 650 25.3 30.1 1.47
C. odorata 6.79 366 718 350 55.6 7.0 1.21
P < 0.001 0.001 0.001 0.001 0.001 0.001 0.001
RMSE 0.239 49.12 71.65 86.14 2.092 6.766 0.112
LSD 0.062 12.78 19.02 6.2011 1.124 2.841 0.086
Sources of variation effects 25.8
Season ns *** *** *** * *** ***
Species *** *** *** *** *** *** ***
Interaction ns *** *** ns *** * ***
a Formerly part of Acacia karroo (Coates Palgrave, 2002); b invasive non-native species; ApDeg - the apparent degradability (g kg-1 DM); TrDeg – true degradability (g kg-1 DM); MY – microbial yield (g kg-1 DM); SCFA – total of short chain fatty acids (mmol L-1); PF – portioning factor; DEF=degradation efficiency factor; RMSE - root mean square error; ns (P>0.05), * (P<05); *** (P<0.001).
With the addition of PEG, the ApDeg increased during the two seasons (early and late wet) with two exceptions: C. odorata and A. nilotica decreased during the early wet and the late wet seasons, respectively. The five plant species decreased in TrDeg, MY, PF and DEF during the early wet and the late wet seasons. However, with regards to TrDeg, A. nilotica and C. odorata increased during the early wet and the late wet season, respectively. The addition of PEG resulted in a higher increase in concentration of SCFA during the early
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wet than the late wet seasons. In the early wet season, S. myrtina had a high increase in SCFA followed by A. natalitia, A. nilotica and D. cinerea, while C. odorata had a slight decrease. The increasing in SCFA during the late wet season followed this order: S.
myrtina, A. nilotica, A. natalitia, D. cinerea and C. odorata.
Table 5.2 Effects of PEG on in vitro apparent and true degradability, microbial yield, total of short chain fatty acids, partitioning factor and degradation efficiency factor of browse species (Sp) samples in two seasons (Se) at Zululand Thornveld and fermented using rumen fluid (Experiment 2)
Se Sp PEG pH ApDeg TrDeg MY SCFA PF DEF
Early Ana a - 6.92 173 821 652 17.7 34.7 3.6
wet Ana + 6.80 194 625 440 36.0 8.2 0.81
An - 6.86 408 688 291 28.1 16.7 0.88
An + 6.70 436 710 274 45.7 8 0.71
Dc - 6.87 166 793 625 24.7 25.3 1.57
Dc + 6.84 249 691 442 37.5 9.7 1.05
Sm - 6.97 171 816 649 25.8 - -
Sm + 6.81 294 647 353 45.3 7.2 0.68
Co b - 6.83 532 738 209 56.2 6.7 0.94
Co + 6.78 510 728 218 50.4 6.4 0.88
Late Ana - 6.86 163 831 665 27.3 17.9 1.22
wet Ana + 6.82 224 678 451 33.0 9.8 1.14
An - 6.78 392 684 300 29.1 15 0.9
An + 6.72 383 643 257 35.6 8.2 0.75
Dc - 6.83 220 782 562 30.6 16.5 1.3
Dc + 6.81 280 695 415 35.0 9.3 1.18
Sm - 6.94 210 856 657 24.1 27.2 1.2
Sm + 6.78 287 696 414 44.1 7.9 0.72
Co - 6.77 369 710 331 54.5 7.2 1.39
Co + 6.76 529 725 196 56.1 7.0 1.00
P < 0.001 0.001 0.001 0.001 0.001 0.001 0.001
RMSE 0.206 59.57 76.12 74.72 2.700 1.554 0.278
LSD 0.051 14.79 18.9 18.55 1.254 0.438 0.078
Sources of variation effects
Se ns ns ns *** ns *** *
Sp *** *** ** *** *** *** ***
PEG * *** *** *** *** *** ***
Se x Sp ns * ns ns *** *** ***
Se x PEG ns ns ns *** *** *** ***
Sp x PEG ns ** *** *** *** *** ***
Se x Sp x PEG ns *** ns ns *** *** ***
Ana – Acacia natalitia; An – Acacia nilotica; Dc – Dichrostachys cinerea; Sm – Scutia myrtina; Co –
Chromolaena odorata; a Formerly part of Acacia karroo (Coates Palgrave, 2002); b invasive non-native species; ApDeg - the apparent degradability (g kg-1 DM); TrDeg – true degradability (g kg-1 DM); MY – microbial yield (g kg-1 DM); SCFA – total of short chain fatty acids (mmol L-1); PF – portioning factor;
DEF=degradation efficiency factor; LSD – least significant difference; RMSE - root mean square error; ns (P>0.05), * (P<05); ** (P<0.1); *** (P<0.001).
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