Methane production of different forages in in vitro ruminal fermentation.
Methane emissions from ruminant livestock have increased five fold over the last century (Johnson et al., 2000) and now constitute ~15% of global C[H.sub.4] emissions (McAllister et al., 1996). In Australia, enteric C[H.sub.4] emissions account for 10.5% of the national greenhouse gas emission (Grainger et al., 2008). Methane production also represents a loss of 2 to 12% of dietary energy in ruminants (Johnson and Johnson, 1995), this is especially the case in Australia with the consumption of high fibre pastures producing ~1 t C[H.sub.4]/t of liveweight gain (Leng, 1993). However, improving forage quality (i.e. increasing dietary starch content) through the supplementation of alternative forages, such as leguminous and non-leguminous shrubs, has the potential to reduce C[H.sub.4] emissions per kg animal product as a result of increased diet digestibility and a shortened duration of feeding (Beauchemin et al., 2009). Dietary strategies such as this, have been successful in manipulating methanogenesis, at least in the short term, through either i) the direct inhibition of methanogens, ii) reducing the production of hydrogen in the rumen or iii) providing alternative sinks for the disposal of hydrogen (Beauchemin et al., 2009). For example, secondary plant compounds (e.g.: condensed tannins and saponins) have been shown to reduce enteric C[H.sub.4] emissions through the direct inhibition of methanogens (Carulla et al., 2005). Similarly, the inclusion of high starch feedstuffs, favour the production of propionate and reduce ruminal pH, thus inhibiting methanogen and protozoal growth (Boadi et al., 2004).
The objective of this study was to characterise common grasses, leguminous shrubs and non-leguminous shrubs used for livestock grazing in parts of Australia and Ghana based on the methanogenic activity of ruminal bacteria (C[H.sub.4] production at 24 h) using batch culture in vitro fermentation and to identify species which produce favourable fermentation profiles.
MATERIALS AND METHODS
Batch culture in vitro incubation
Twelve forage species were examined using batch culture in vitro fermentation. Grass species were Andropodon gayanus, Brachiaria ruziziensis and Pennisetum purpureum. Leguminous shrub species consisted of Cajanus cajan, Cratylia argentea, Gliricidia sepium, Leucaena leucocephala and Stylosanthes guianensis and non-leguminous shrub species were Annona senegalensis, Moringa oleifera, Securinega virosa and Vitellaria paradoxa. The forages were collected from native pastures near the Savanna Agricultural Research Institute at Nyankpala in the Guinea Savanna zone of Northern Ghana (9[degrees]54'N, 0[degrees]59'W). The location is characterized by a monomodal rainfall pattern with mean annual rainfall of 1,140 mm. Leaf samples of all leguminous and nonleguminous shrubs, and grasses were re-growths and collected ~60 d after the start of the rainy season. After harvest, leaves were dried at 55[degrees]C and ground through a 1 mm screen prior to in vitro incubation.
Rumen liquor was obtained from three ruminally fistulated lactating Holstein dairy cows (617[+ or -]8.9 kg body weight; 45[+ or -]13.1 d in milk) fed a total mixed ration containing 180 g crude protein (CP)/kg DM and 330 g neutral detergent fibre (aNDF)/kg DM. Cows were cared for in accordance with guidelines of the Canadian Council on Animal Care (1993). Ruminal liquor was collected from the anterior dorsal, anterior ventral, medium ventral, posterior dorsal and posterior ventral locations within the rumen 2 h after the morning feeding. Pooled ruminal fluid (e.g.: from the three cows) was strained through 4 layers of cheesecloth into an insulated thermos and immediately transported to the laboratory. Strained ruminal fluid was continuously purged under [O.sub.2]-free N gas and kept at 39[degrees]C in a water bath prior to use in in vitro incubations. The liquor was used for inoculum of in vitro bottles within 20 min of collection.
In vitro incubations were in 50 ml bottles fitted with rubber stoppers to prevent escape of fermentation gases (Wang et al., 2000). Bottles were placed in an incubator (Forma Scientific, model 39419-1, Marietta, OH, USA) with a capacity for 204 bottles. Incubator temperature was 39[+ or -]0.5[degrees]C and bottles were affixed to a rotary shaker platform at 120 oscillations/min (Lab-Line Instruments Inc, Melrose Park, IL, USA). On the day before incubation, 0.5 g DM of each forage sample (n = 2) was weighed into each bottle (n = 3 for each treatment). On the day of incubation, bottles containing substrate were warmed to 39[degrees]C in the incubator for 60 min, and gassed with [N.sub.2] before adding 20 ml of a 3:1 mixture of buffer:rumen fluid saturated with C[O.sub.2] with 0.5 ml cysteine sulphide reducing agent (Wang et al., 2000). Bottles were capped and placed in the incubator at 39[degrees]C. Three bottles containing inoculum only were also included at each time point as a blank control.
Gas samples were measured at 2, 6, 12 and 24 h of incubation. The procedure for sampling bottles was: 39 bottles (3 replicatesx12 treatments[+ or -]3 blanks) were removed from the incubator and gas production from each bottle was immediately determined using a water displacement apparatus (Fedorak and Hrudey, 1983). For C[H.sub.4] determination, 20 ml of headspace gas was collected from the bottles at 24 h by inserting a 20 ml syringe through the septum and immediately transferring it into a 6.8 ml evacuated exetainer (Labco Ltd., High Wycombe, England) thus ensuring a positive pressure in the containers. A 3 ml subsample of gas was removed from each exetainer and analyzed for C[H.sub.4] by gas chromatography as described by Chaves et al. (2006). Methane was expressed as mg C[H.sub.4]/g digested DM and total net gas production in ml/g DM incubated (Chaves et al., 2006).
At 24 h of incubation, incubation bottles (n = 3) of each forage were withdrawn from the incubator and put in ice to stop fermentation, and then processed for determination of volatile fatty acids (VFA), ammonia and in vitro DM disappearance (IVDMD) as described by Wang et al. (2008).
Determination ammonia : A sub-sample (1.5 ml) of the media culture from each bottle were transferred to 2 ml micro-centrifuge tubes containing 150 |al trichloroacetic acid (TCA; 0.25%; w/v) and centrifuge at 14,000xg for ten minutes (Spectrafuse 16M, National Labnet Co., Edison, NJ, USA) to precipitate particulate matter. The supernatant was transferred into 2 ml microcentrifuge tubes and stored frozen at -20[degrees]C until it was analyzed for ammonia-N by phenyl-hypochlorite reaction (Weatherburn, 1967). Blank 0 h samples were also used to analyze for ammonia and to calculate the net ammonia-N production.
Determination of volatile fatty acids (VFA) : An additional sub-sample (1.5 ml) of the culture in each bottle was also removed and 150 |al of metaphosphoric acid (20%; w/v) was added before the samples were centrifuged in the same manner as the ammonia analysis. The supernatant was stored frozen at -20[degrees]C and later analyse for VFA concentrations by high-performance liquid chromatography (HPLC; SHIMADZU model SPD-10A VP with an Ultra UV Detector waves lengths of 210 nm) equipped with a SCR-101 H silica 30 cmx7.9 mmx1 | m capillary column. Blank 0 h samples were also analyzed for VFA and to determine the net total VFA production.
In vitro DM disappearance : Following the collection of the supernatants samples for ammonia and VFA analyses after 24 h of incubation, the contents of the incubation bottles were transferred into preweighed 50 ml centrifuge tubes, rinsed with distilled water into the tubes, and centrifuged twice at 500xg for 10 min at 4[degrees]C. The supernatant was discarded, and the precipitate dried at 55[degrees]C for 48 h and weighed to estimate the in vitro DM disappearance (IVDMD).
Duplicate samples of each forage were analysed for neutral detergent fibre (aNDF) with a heat stable a-amylase and sodium sulphite (Mertens, 2002) and for acid detergent fibre (ADF) using method 973.18 (AOAC, 1990). Concentrations of aNDF and ADF are expressed inclusive of residual ash. Lignin (sa) was completed on ADF residues by solubilisation with sulphuric acid (Robertson and Van Soest, 1981). Ash was determined after 2 h of oxidation at 600[degrees]C in a muffle furnace using method 942 (AOAC, 1990).
Samples were re-ground using a ball grinder (Mixer Mill MM2000, Retsch, Haan, Germany) for determination of N by flash combustion with gas chromatography and thermal conductivity detection (Carlo Erba Instruments, Milan, Italy).
Statistical analyses and calculation
Methane production was calculated as: g C[H.sub.4]/g digested DM = ((gas [production.sub.24hx]([C[H.sub.4] 24 h]) -gas produced [blank.sub.24hx][C[H.sub.4] [blank.sub.24h]])) /g digested DM
according to Chaves et al. (2006).
In vitro data were analyzed as a completely randomized design using the MIXED procedure of SAS (2011). Means within forage family (e.g., leguminous shrubs, nonleguminous shrubs or grasses) were compared using the least squares mean linear hypothesis test included as fixed terms. Results are reported as least squares means ([+ or -]SEM). Significance was declared at p<0.05.
RESULTS AND DISCUSSION
Concentrations of crude protein (CP; g [kg.sup.-1] DM) and NDF (g [kg.sup.-1] DM) in P. purpureum, G. sepium, and M. oleifera are comparable to previously reported values of 96 and 709 (Nogueira Filho et al., 2000); 92 and 421 (Abdulrazak et al., 1997) and 214 and 333 (Njidda and Nasiru, 2010), respectively (Table 1). Dietary crude protein and NDF concentrations influence the amount of substrate organic matter (OM) fermented and the short chain fatty acids that are produced (Njidda and Nasiru, 2010). Crude protein concentrations below the threshold of 70 g CP [kg.sup.-1] DM, restrict microbial activity due to a lack of nitrogen (Hariadi and Santoso, 2010). However, protein levels above this threshold, as seen in this study, are considered to enhance microbial multiplication in the rumen, thus improving fermentation (Njidda and Nasiru, 2010). Similarly, ammonia accumulation varied (p<0.05) within legume and shrub species, yet remained above the threshold value for both maximum microbial growth (Satter and Slyter, 1974) and fibre digestion (Hariadi and Santoso, 2010). This suggests that CP concentrations did not impede gas production or forage digestibility.
In vitro DMD and cumulative gas production (ml/g DM) also differed (p<0.05) within forage type in the current study. B. ruziziensis, G. sepium and M. oleifera produced the highest (p<0.05) cumulative gas and had the highest IVDMD within the grasses, leguminous and nonleguminous shrubs, respectively (Table 2) indicating that these species are highly fermentable. It is widely accepted that feedstuffs which have higher gas production and IVDMD tend to have higher C[H.sub.4] production per gram DM incubated (Durmic et al., 2010; Njidda and Nasiru, 2010; Jayanegara et al., 2011). This trend was evident in nonleguminous shrub species, in addition to P. purpureum and S. guianensis (data not presented). This relationship is suggested to be a reflection of feed digestibility (Demeyer and Van Nevel, 1975; Holtshausen et al., 2009), in particular NDF concentration (Doane et al., 1997). Increasing cell wall content (i.e. NDF and ADF) is considered to suppress microbial activity through a reduction in the availability of rapidly fermented carbohydrates (Wilson and Hatfield, 1997). This is turn, is negatively correlated with gas production (Njidda and Nasiru, 2010). Similarly, in in vivo trials increasing fibre content is considered to reduce forage intake, ruminal residence time (Beauchemin et al., 2009; Archimede et al., 2011) and fermentability (Wilson and Mertens, 1995) resulting in an increase in C[H.sub.4] production per unit of OM digested (McAllister et al., 1996; Valenciaga et al., 2009).
In the current study, several forage species were able to favourably modulate rumen fermentation to produce C[H.sub.4] concentrations lower than expected when considering their cumulative gas production and IVDMD. The most notable of which, G. sepium and B. ruziziensis, produced moderate amounts of C[H.sub.4] compared with other species in their forage type, despite having the highest cumulative gas production, IVDMD and total VFA production. A strong positive relationship was observed between IVDMD and total VFA production, with total VFA production the greatest in species with high IVDMD, as would be expected. Interestingly, both G. sepium and B. ruziziensis, produced the highest proportion of propionate, and lowest acetate:propionate ratios, within their forage types.
Generally, the type of carbohydrate present in the forage is thought to dictate C[H.sub.4] production via shifts in the ruminal microbial population (Johnson and Johnson, 1995). High soluble carbohydrate content is suggested to promote the production of propionate in the rumen, lower ruminal pH and inhibit methanogen growth thereby reducing C[H.sub.4] production per unit of OM fermented (Van Kessel and Russell, 1996). Boadi and Wittenberg (2002) found C[H.sub.4] production (L C[H.sub.4]/kg digestible OM intake) was 25% higher for low versus medium or high nutritional quality diets in a feeding study where intake was restricted to 2% of body weight. Lower C[H.sub.4] losses with the high quality diet were expected as the lower fibre content shifted fermentation towards production of propionate. Chaves et al. (2006) demonstrated that diet quality affected C[H.sub.4] production in an in vitro study where low concentrations of non-fibrous carbohydrates in both legumes (e.g., alfalfa) and grasses contributed to a low IVDMD and consequently high C[H.sub.4] production per gram digested DM. Similarly, Boadi et al. (2002) showed that steers grazing early season pasture produced up to 45% less C[H.sub.4] than those grazing in the mid and late season. However, in the current study, no correlation between NDF concentration and C[H.sub.4] production was observed.
The presence of plant secondary metabolites (e.g. condensed tannins and saponins) may account for this, although, their presence was not examined in the current study. Tannins, common in tropical legumes (Waghorn, 2008), have been shown to reduce C[H.sub.4] production by reducing fibre digestion (Tiemann et al., 2008); binding with proteins thus reducing degradation of the plant protein in the rumen and through the direct inhibition of the growth of methanogens (Tavendale et al., 2005). A study by Pinares-Patino et al. (2003) reported a reduction in C[H.sub.4] emissions from grazing sheep, from 8% GEI to 3% GEI, following consumption of the tannin rich forage, Lotus corniculatus. Similarly, Carulla et al. (2005) found that an extract of Acacia mearnsii (61.5% CT) reduced C[H.sub.4] emissions by 12% without decreasing fibre digestibility.
G. sepium and B. ruziziensis, were able to successfully modulate rumen fermentation characteristics, such that moderate C[H.sub.4] emissions were produced without compromising forage digestion. Consequently, grazing of these two species may be a strategy to reduce C[H.sub.4] emissions in Australia. However, as our forages were examined at only one stage of maturity, any effects of NDF concentration on C[H.sub.4] production were not realised, as such there is a need for further assessment of fermentation characteristics of these species at various stages of maturity. Similarly, the relative scarcity of data on C[H.sub.4] production from in vivo trials, where ruminants are fed tropical forages, suggests a need for additional studies.
Received July 27, 2011; Accepted September 14, 2011
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* Corresponding Author : A. V. Chaves. Tel: +61-2-9036-9312, Fax: +61-2-9351-3957, E-mail: email@example.com
S.J. Meale, A.V. Chaves *, J. Baah (1) and T. A. McAllister (1)
The University of Sydney, Faculty of Veterinary Science, Sydney, NSW 2006, Australia (1) Agriculture and Agri-Food Canada, Lethbridge Research Centre, P. O. Box 3000 - Lethbridge, Alberta, Canada
Table 1. Chemical composition of forage species expressed in g/kg DM) used in the study Species CP aNDF ADF Lignin (sa) Ash Leguminous shrubs Cajanus cajan 199 478 387 173 61 Cratylia argentea 204 532 344 186 109 Gliricidia sepium 236 427 311 125 71 Leucaena leucocephala 301 377 289 95 81 Stylosanthes guianensis 112 590 472 133 78 SD 68.4 83.9 72.3 37.0 17.9 Non-leguminous shrubs Annona senegalensis 99 517 428 270 53 Moringa oleifera 249 288 175 53 73 Securinega virosa 170 307 263 87 65 Vitellaria paradoxa 89 355 451 298 57 SD 64.4 79.8 71.3 39.1 16.9 Grasses Andropodon gayanus 72 694 406 82 59 Brachiaria ruziziensis 87 671 387 64 84 Pennisetum purpureum 87 713 395 56 74 SD 8.2 20.1 10.0 15.1 11.3 DM = Dry matter; CP = Crude protein; aNDF = Neutral detergent fibre; ADF = Acid detergent fibre. Table 2. Cumulative gas and methane production, ammonia accumulation, concentration and proportions of volatile fatty acids (VFA) and in vitro dry matter (DM) disappearance (IVDMD) of 24 h in vitro ruminal fermentation of different forage species Gas ml/g Methane Ammonia, mg/g mM DM digested DM Leguminous shrubs Cajanus cajan 113.7 (c) 9.6 (ab) 22.5 (a) Cratylia argentea 125.1 (b) 11.1 (a) 1.1 (c) Gliricidia sepium 148.5 (a) 8.0 (bc) 4.4 (d) Leucaena leucocephala 126.8 (b) 7.3 (c) 17.4 (b) Stylosanthes guianensis 128.8 (b) 8.0 (bc) 0.8 (c) SEM 1.48 0.53 0.89 Non-leguminous shrubs Annona senegalensis 94.5 (b) 2.8 (c) 14.3 (a) Moringa oleifera 187 (a) 6.4 (c) 0.4 (b) Securinega virosa 101.4 (b) 4.4 (b) 0.9 (b) Vitellaria paradoxa 28.1 (c) 0.4 (d) 2.2 (b) SEM 2.93 0.34 1.5 Grasses Andropodon gayanus 116.7 (c) 15.6 (a) 6.3 Brachiaria ruziziensis 143.4 (a) 12.1 (b) 10.6 Pennisetum purpureum 131.2 (b) 11.6 (b) 9.2 SEM 2.36 0.43 1.88 mol/100 mol of total volatile fatty acids (VFA) Acetate (A) Propionate (P) Butyrate Leguminous shrubs Cajanus cajan 66.0 (b) 19.3 (d) 9.1 (a) Cratylia argentea 63.6 (c) 20.7 (b) 9.2 (a) Gliricidia sepium 66.2 (b) 21.7 (a) 6.9 (c) Leucaena leucocephala 67.0 (b) 20.0 (c) 8.2 (b) Stylosanthes guianensis 68.7 (a) 18.0 (e) 8.2 (b) SEM 0.49 0.16 0.19 Non-leguminous shrubs Annona senegalensis 68.0 (ab) 19.9 (ab) 8.7 (c) Moringa oleifera 61.2 (c) 20.7 (ab) 12.7 (a) Securinega virosa 69.1 (a) 16.5 (b) 10.5 (b) Vitellaria paradoxa 62.7 (bc) 24.2 (a) 10.7 (b) SEM 1.78 1.56 0.32 Grasses Andropodon gayanus 66.1 20.4 (b) 9.4 Brachiaria ruziziensis 64.8 22.6 (a) 8.8 Pennisetum purpureum 65.8 20.9 (b) 9.2 SEM 0.45 0.24 0.17 mol/100 mol of total volatile A:P Total fatty acids VFA mM (VFA) Minor VFA Leguminous shrubs Cajanus cajan 5.5 (b) 3.41 (b) 73.2 (b) Cratylia argentea 6.5 (a) 3.07 (c) 75.2 (b) Gliricidia sepium 5.2 (bc) 3.05 (c) 97.2 (a) Leucaena leucocephala 4.8 (c) 3.34 (b) 79.8 (b) Stylosanthes guianensis 5.1 (bc) 3.82 (a) 81.7 (b) SEM 0.19 0.047 3.81 Non-leguminous shrubs Annona senegalensis 3.3 (bc) 3.41 (ab) 68.7 (b) Moringa oleifera 5.4 (a) 2.95 (b) 102.4 (a) Securinega virosa 3.9 (b) 4.19 (a0 58.9 (c) Vitellaria paradoxa 2.5 (c) 2.59 (b) 18.4 (d) SEM 0.31 0.28 2.05 Grasses Andropodon gayanus 4.2 (a) 3.24 (a) 86.8 (c) Brachiaria ruziziensis 3.7 (b) 2.87 (b) 105.4 (a) Pennisetum purpureum 4.0 (a) 3.14 (a) 95.9 (b) SEM 0.09 0.051 2.2 IVDMD g/kg DM Leguminous shrubs Cajanus cajan 246 (d) Cratylia argentea 336 (c) Gliricidia sepium 404 (a) Leucaena leucocephala 376 (ab) Stylosanthes guianensis 348 (bc) SEM 12.8 Non-leguminous shrubs Annona senegalensis 257 (c) Moringa oleifera 540 (a) Securinega virosa 328 (b) Vitellaria paradoxa SEM 7.6 Grasses Andropodon gayanus 278 (c) Brachiaria ruziziensis 379 (a) Pennisetum purpureum 342 (b) SEM 5.6 Minor VFA = Iso-butyrate+iso-valerate+valerate+caproic acids. (a b c d) Least square means with different superscripts differ p<0.05 within forage family (e.g., leguminous shrubs, non-leguminous shrubs or grasses).
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|Author:||Meale, S.J.; Chaves, A.V.; Baah, J.; McAllister, T.A.|
|Publication:||Asian - Australasian Journal of Animal Sciences|
|Date:||Jan 1, 2012|
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