Effect of Age of Guinea Grass (Panicum Maximum) on Silage Quality and Its Nutritive Value in West African Dwarf Goat (Wad)
Objectives of the Study
The general objective of this study is to determine the effect of age of Guinea grass on the silage quality and nutritive value in West African dwarf goat (WAD).
Specific objectives of this study are;
- To determine the chemical composition of silage produced from Guinea grass harvested at different age.
- To determine the invitro gas production characteristics of ensiled Guinea grass at different ages.
Potential of Guinea grass (Panicum Maximum) as forage in livestock production Panicum maximum (guinea grass) is native to Africa but this grass was introduced to almost all tropical countries as a source of animal forage. It grows well on a wide variety of well drained soils of good fertility and it is suitable to stop soil erosion. It can survive quick moving fires which does not harm the underground roots and drought because of the deep, dense and fibrous root system. Guinea grass is a clump-forming perennial which grows best in warm frost free areas receiving more than 900 mm rainfall. Crude protein (CP) content of fresh guinea grass varied from 5.0 to 5.6% while guinea grass silage contains 5.0 to 5.5% CP. The digestibility (IVDOM) varied with the variety from 56.9% for Gatton to 87.7% for Vencidor. This paper reviews the potential of P. maximum as a forage for animal production in the tropics and Sub tropics.
Morphology Guinea Grass (Panicum Maximum)
Guinea grass is a large tufted, fast-growing perennial grass. It has a broad morphological and agronomic variability, ranging in height from 0.5 to 3.5 m, with stems of 5 mm to 10 mm diameter. There are two main types: a tall/medium tussock type, taller than 1.5 m at flowering, and a short tussock type (Cook et al., 2005). The root is a short creeping rhizome; culms are erect, hirsute at the nodes. Leaves are blade-shaped, glabrous to pubescent up to 35 mm broad. Inflorescence is a panicle, 15 to 50 cm long. Spikelets are 3-4 mm green to purple (Ecoport, 2009).
Utilization Guinea Grass (Panicum Maximum)
Guinea grass is suitable for pasture, cut-and-carry, silage and hay. Many Guinea grass cultivars have been developed for different purposes and agronomic situations (FAO, 2009).
Distribution Guinea Grass (Panicum Maximum)
Guinea grass is native to tropical Africa and is now widely naturalized in the tropics. It is naturally found in open grasslands, woodland and shady places within 16.3°N and 28.7°S. It grows best under an annual rainfall above 1000 mm with no more than a 4 to 5 month dry period. Average annual day-temperature should range from 19.1°C to 22.9°C. Small types are more tolerant of cooler temperatures than tall types. It prefers well-drained, moist and fertile soils (Cook et al., 2005). It is tolerant of light frost and low soil pH if drainage is good (FAO, 2009) and also of high Al3+ saturation (Ecoport, 2009). It is well adapted to sloping, cleared land in rainforest areas (FAO, 2009). Drought tolerance depends on the cultivar, but should not generally exceed 4 or 5 months. Guinea grass can be sown with companion legumes such as Centrosema pubescens, Leucaena leucocephala, Pueraria phaseoloides or Macroptilium atropurpureum (Cook et al., 2005).
MATERIALS AND METHODS
The experiment was carried out in a greenhouse, located at the Plant Growth Unit, Massey University, Palmerston North (408169 S, 1758179 E) from May–July 1999 (Southern Hemisphere winter). Over the experimental period, daily minimum and maximum temperatures were maintained between approximately 18 8C and 32 8C, respectively.
Seeds of the two Guinea grass cultivars, cvs Kaduna and Jos, were germinated in soil in flat trays for 2 weeks in a greenhouse maintained at 25 8C. At this point, pairs of similar-sized seedlings were transplanted to 4.0 l plastic pots filled with a mixture of sand and soil (1:1) from the B horizon of an alluvial silt deposit (Karipoti soil series). A controlled release fertilizer was added (3 g pot1, Osmocote brand) containing 15% N, 4.8% P, 10.8% K, 1.2% Mg, 3.0% S, 0.4% Ca plus trace elements, B, Cu, Fe, Mn, Mo, and Zn. One week later seedlings were thinned to one per pot to leave seedlings of similar size in all pots. Plants were grown for a further 5 weeks, then one adult tiller in each plant was randomly selected for application of 14C treatments. In replicate plants, different categories of tiller were labelled; the main tiller (TM); the first or second most recently developed primary tiller on the main stem, with at least three fully emerged leaves (TY); and an old primary tiller (TO), the fourth or fifth tiller on the main stem with at least two daughter tillers (Treatments TM, TY, and TO; Table 1). These treatments were replicated four times, making a total of 12 plants for each cultivar.
The labelled tillers were enclosed in a plastic bag with a clip seal, and silicon rubber used to seal bags around the base of the stem. Atmospheric 14CO2 enrichment was achieved by injecting with a hypodermic syringe 1 ml dilute NaH14CO3 (Amersham product CFA2, diluted to a specific activity of approximately 740 kBq ml1) into a pocket in the plastic bag, followed by an equal quantity of 10% (v/v) acetic acid to release 14CO2 gas inside the plastic bag for uptake by the enclosed tiller. This would result in a transiently higher concentration of CO2 inside the bag, however, this would ensure that the tiller had adequate 14CO2 during labelling. In previous studies with temperate plants such as Lolium perenne, a typical dose rate would be 37 kBq (1 lCi) tiller1, and the dose rate used here of 740 kBq tiller1 was estimated, based on the much larger size of tropical grass tillers, as the dose required to achieve specific activities in labelled tillers similar to those previously used in studying photoassimilate distribution in temperate grasses. The needle holes were sealed with petroleum jelly and bags were left in place for 20 h until Geiger counter readings showed that radioactivity had transferred from solution to the tiller being labelled. Since the CO2 was present in the labelling bags until near the end of the labelling period, in quantities detectable by Geiger counter.
Tiller number and dry weight
On average, total tiller number per plant was 22% higher in Kaduna than Jos (15.760.57, and 12.860.57, P <0.01) with secondary tillers accounting for this difference rather than primary tillers. The mean plant dry mass was 28% higher in Jos (17.360.81 and 13.560.89 g plant1; P=0.009, for Jos and Kaduna, respectively) however, no differences in plant mass were noted between treatments (P=0.616, 2-way ANOVA). Both shoot (14.360.73 and 10.860.75 g plant1; P=0.005) and root (3.260.14 and 2.760.16 g plant1, P=0.04) dry mass were higher in Jos than Kaduna. Neither main shoot, primary tiller nor old tiller masses varied between treatments, however, genotypic differences were noted in the main shoot and primary tiller masses (P >0.05 and P=0.001, respectively, 2-way ANOVA). The difference in root–shoot ratios approached significance between the two genotypes (0.22960.011 and 0.25560.007; P= 0.0519, for Jos and Kaduna, respectively). Table 2 shows the breakdown of shoot and root masses for each tiller group within the three treatments. The tiller masses for each of the three treatments are similar, although differences between cultivars in one treatment were not always evident in the other treatments. For example, in the treatment TM, the masses of both the main stem and the root associated with it were significantly different between cultivars, with Jos being heavier in both cases. In treatment TY, however, only the root masses exhibit significant difference, and in TO only the stem masses are statistically different. Root masses were, in most cases, significantly lower than the shoot mass for each tiller group.
Distribution of radiocarbon
528670 and 428658 kBq plant1 (P=0.059, 2-way ANOVA) were recovered from Kaduna and Jos plants, respectively. TM treatments tended to exhibit a higher recovery than plants in TY and TO treatments (5666 115, 350637, and 322640, and 6496106, 5006169, and 436667 kBq plant1, for Jos and Kaduna, respectively), although within cultivars this was not significant (P=0.341, 2-way ANOVA). Only when the two cultivars were pooled were the TM and TY recoveries significantly different. Generally, the proportion of exported carbon from a labelled tiller was in the order of 10–22% (Table 3) of the total 14C recovered from the plant; there were no significant differences in the proportion of C exported either between cultivars (P=0.543) or treatments (P=0.189, 2-way ANOVA). This value tended to be numerically higher (although not statistically different), for young tillers than either older tillers or the main stem (20.563.1%, 14.363.1%, and 12.663.1%), respectively.
This study compared two P. maximum cultivars with differing agronomic behavior, cv. Jos consistently having fewer tillers per plant but higher total plant dry weight, than cv. Kaduna, but did not find a common physiological trait expressed in all categories of tiller that would explain agronomic performance differences between the two cultivars. The situation seems to be far more complex than first suspected, with cultivar differences in radiocarbon distribution clearly demonstrated only in old primary tillers, and indicating quite complex interactions between parent and daughter tillers, such as the preferential feeding of young parent tiller roots by daughter tillers or differential diurnal sink–source behaviors. A mechanism that would account for both the observed agronomic behavior differences and radiocarbon distribution differences between cultivars is greater sink strength in Kaduna in tillers that are net importers of photosynthate, however, this must be regarded as a speculative hypothesis for future study, and not as a definitive research finding.
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