In-vitro screening of Kalahari browse species for rumen methane mitigation

Abstract

The nutritional value of browse foliage from the Thorny Kalahari Dune Bush veld of South Africa is not characterized. Most of this browse species is rich in tannin, but still palatable, and is consumed by ruminants during the dry season, as well as having a role to play in mitigating enteric methane emission from ruminants. In this study, the rumen methane mitigation potential of 19 browse species foliage collected from the Thorny Kalahari Dune Bush veld, was analyzed in terms of chemical composition, in vitro fermentation, digestibility and methane production. In vitro gas and methane production and organic matter digestibility (IVOMD) were determined by using rumen fluid collected, strained and anaerobically prepared. A semi-automated system was used to measure gas production (GP) from each browse species by incubating 400 mg samples in a shaking incubator at 39 °C with or without inclusion of 400 mg of polyethylene glycol (PEG). Data for all the parameters collected were statistically analyzed using the SAS (9.0) general linear model (GLM) procedure, and differences between foliage species were determined using Duncan’s multiple-range test. Acacia luederitzii and Monechma incanum showed the best potential for decreasing methane production by up to 90 % after 48 h of incubation. The secondary components (mainly tannins) of the browse species appeared to have a significant effect on volatile fatty acids (VFA), methane and gas production as judged by the comparison of samples incubated with or without PEG inclusion. The substantial amount of crude protein (CP) content coupled with their anti-methanogenic effect during fermentation would make these browses a potential mitigation option for small scale farmers and pastoralists in sub-Sahara Africa. However, it is also very important that systematic and strategic supplementation in a mixed diet should be looked at as the way forward in terms of best utilization.

in vitro fermentation; browse foliage; digestibility; tannin

Introduction

Methane is among the most important greenhouse gases responsible for a significant loss of energy by the ruminant through enteric methane (CH₄) fermentation (Jayanegara et al., 2011). Livestock, especially ruminants, contribute to CH₄ emissions through enteric fermentation and fermentation also taking place in the manure. This is especially the case when feeding highly fibrous diets which are prevalent in the tropics. In this regard, inclusion of feeds containing plant secondary metabolites, such as tannin in diets of ruminants, seems promising as a nutritional strategy to reduce CH₄ emissions from ruminants (Sebata et al., 2011; Sultan et al., 2012).

Tannins are polyphenolic compounds which bind to protein and act as chemical additives for protecting and decreasing ruminal degradation of proteins in ruminant feeds. Earlier studies suggested that feeding forages that contain tannins for ruminants generally effectively inhibit CH₄ produced during enteric fermentation (Puchala et al., 2005). In this regard, tannins of lower molecular weights were found to be more effective against methanogens than their monomeric precursors or tannins of higher molecular weight (Tavendale et al., 2005). However, there is huge diversity in tannin structure and concentration, and other chemical constituents among the browses, which may affect variably, the observed response in rumen fermentation, digestibility of nutrients and methanogen activity (Mueller-Harvey, 2006). This indicates that tannin from different plants might show a different response in gas production, true digestibility and methane production. The objective of this study was to investigate variations among palatable browse species foliage collected from the Kalahari bush dune veld in South Africa in terms of gas production characteristics, forage digestibility, VFA, ammonia-nitrogen (NH₃-N) and CH₄ production. The single effect of tannin was also studied and quantified for each browse species by incubating the browse plants with or without polyethylene glycol (PEG).

Materials and Methods

Study area description

Browse foliage sample collection for this study was carried out in the North West Province of South Africa in the Thorny Kalahari Dune Bush veld with an altitude of about 900 to 1100 m above sea level. The soil is sandy to sandy loam, and has excessive drain with high base status dunes that contain elevated concentrations of copper, which are bound in the soil in the form of secondary copper hydroxyl mineral atacamite (Cu₂ (OH)₃Cl). The area has highly erratic rainfall that ranges from 150 to 350 mm per year; however, it has barely exceeded 150 mm per year for the last two years and during the study period. The wettest months are usually from January to April and the extreme temperatures range from a winter low reaching -10.3 °C to summer highs of up to 45.4 °C (Van Rooyen, 2001).

Sample collection, preparation and chemical analysis

Samples of nineteen tannin rich browse plants (Table 1) were collected during the summer rainy season (Feb 2012). In this study, a shrub was considered as a small to medium-sized woody plant and distinguished from a tree by its multiple stems and shorter height, usually under 6 m tall. The browses were harvested at the same time when they were at the same maturity stage; almost at early vegetative stage. Fresh foliages (leaves and stems < 3 mm diameter) were harvested from at least five randomly selected and tagged representative plants of each species. During the sampling, fresh plant leaves and twigs (less than 3 mm in stem diameter) were hand plucked from 19 browse species to be used. Samples were dried at 55 °C for 48 h in a forced oven and ground to pass through a 1 mm sieve in a Wiley mill and used for chemical analysis. The neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) contents were determined using 200/220 Fiber Analyzer according to the methodology described by van Soest et al. (1991). Sodium sulphite and heat-stable amylase were used in an analysis of NDF. Nitrogen was analyzed following the method described in AOAC (2002) in a Nitrogen and Protein analyzer, and crude protein (CP) was calculated as N × 6.25. Determinations of total phenols (TP) and total tannins (TT) were made following the procedure described by Makkar (2003).

Table 1
− Mean chemical and phenolic composition of browse plants (g kg−1 DM) used in the study (n = 3).

Species name	OM	CP	NDF	ADF	ADL	Total phenol	Total tannin
Trees
Acacia erioloba	939.8c	169.8b	456.3c	391.8d	324.8a	182.4d	145.4d
Boscia albitrunca	924.4e	253.3a	369.2f	292.2g	128.5e	24.7h	9.1h
Acacia haematoxylon	932.8d	131.2e	533.4a	431.0b	275.7b	204.1c	163.4c
Olea europaea	939.1c	74.9j	355.6g	327.8f	131.3e	154.9f	73.0g
Ziziphus mucronata	908.9f	157.3d	364.6gf	291.3g	166.6c	136.2g	79.4g
Terminalia sericea	948.7b	97.4i	520.1b	445.7a	105.3f	223.4b	106.8f
Rhus lancea	951.0a	120.3h	454.0c	404.5c	95.0g	226.6b	197.0b
Acacia karroo	930.9d	124.7g	427.2d	351.8e	133.3ed	217.2b	200.7b
Prosopis glandulosa	937.8c	163.5c	403.6e	347.8e	101.8f	171.2e	132.0e
Acacia luederitzii	939.8c	130.6f	460.3c	385.8d	138.8d	314.5a	298.8a
Mean	935.3	142.3	434.4	366.9	160.1	185.5	140.6
SEM	0.728	0.01	0.413	0.386	0.197	3.4	3.14
Shrubs
Acacia mellifera	915.9gh	203.4c	373.6f	302.1f	80.1h	54.8f	30.6f
Acacia hebeclada	937.1dc	233.0b	401.2e	390.0dc	97.4f	30.5h	16.1g
Grewia flava	929.8de	125.1h	443.9d	399.5c	105.3e	233.7c	171.3c
Dichrostachys cinera	959.5a	141.5e	508.9a	376.8d	227.8d	386.5a	319.8a
Hermannia burchelli	924.7fe	177.2d	369.7f	353.2e	69.9i	189.3d	148.3d
Lycium cinereum	783.7i	328.9a	363.0f	277.2g	85.4g	24.3h	12.8g
Monechma genistifolium	790.5i	83.8i	494.2b	465.1a	266.2b	44.9g	28.2f
Hermanniato mentosa	915.0fe	136.2f	474.9c	426.4b	290.3a	97.3e	72.1e
Monechma incanum	919.4gf	130.6g	449.1d	350.1e	232.1c	307.6b	282.5b
Mean	892.8	173.3	430.9	371.2	161.6	152.1	120.2
SEM	2.5	0.01	0.356	0.499	0.14	3.08	2.9

• Means with different superscript (letters) across the column for each parameter are significantly (p < 0.05) different; OM = organic matter; CP = crude protein; ADF = acid detergent fibre; NDF = neutral detergent fibre; ADL = acid detergent lignin.

In vitro fermentation, digestibility and methane production

The rumen fluid was collected from three rumen cannulated Merino sheep fed ad libitum alfalfa hay. It was prepared and purged with CO₂ to maintain anaerobic conditions (Grant and Mertens, 1992). After blending, the rumen fluid was transferred to a large glass beaker inside a 39 °C water bath being continuously purged with CO₂ and continuously stirred as recommended by Goering and van Soest (1970). The buffer solution, macro and micro mineral solution were prepared in large volumes and utilized as needed as described in Goering and van Soest (1970).

Gas production was determined as described by Theodorou et al. (1994). Four hundred mg of the ground browse/shrub samples with and without PEG (molecular weight, 6000, analytical grade Sigma-Aldrich) were incubated with 40 mL of diluted rumen fluid (15 mL rumen fluid + 25 mL culture medium) in serum bottles in a CO₂ atmosphere. Two serum bottles containing rumen fluid inoculum were incubated as controls and used to account for gas production in the absence of the substrate. All serum bottles were returned to the incubator and the rotary shaker was turned on at 120 revolutions per minute (rpm). Two replicates of the same browse and four different cycles were executed for every browse sample studied. Fermentation was terminated after 48 h by removing the serum bottles from the incubator and placed on ice. Supernatants were taken immediately, pipetted and stored at -20 °C until analyzed for ammonia nitrogen (NH₃-N) (McDonald et al., 1960) and volatile fatty acid (VFA) (Ottenstein and Bartley, 1971). The in vitro organic matter digestibility (IVOMD) was done according to Tilley and Terry (1963), as modified Engels and van der Merwe (1967).

Methane production was measured from duplicate bottles incubated for each browse by taking gas samples at 2, 12, 24, and 48 h and analyzing the methane concentration using gas chromatography (GC) equipped with a stainless steel column packed with Porapak-Q and a Flame Ionization Detector. The GC was calibrated with standard CH₄ before injection of the sample. Gas produced from each bottle at various times was recorded and samples of the gas were taken using a Hamilton syringe. One mL of sampled gas produced was injected manually (pull and push method of sample injection) into the GC._.

Data were statistically analyzed using the general linear model (GLM) procedure from SAS (Statistical Analysis System, Version 9.2), considering each incubation run as a block for species. The average of the two bottles was considered as data from an experimental unit. The differences between means were determined using Duncan's multiple range test.

Results

Chemical composition

The browse studied showed significant variations in chemical and phenolic composition (Table 1). In this study, forage from shrub species had a higher mean value of crude protein concentration (173.3 g kg⁻¹ DM) than tree species (142.3 g kg⁻¹ DM). Among the tree forage species, Boscia albitrunca had the highest and Olea europaea the lowest CP concentrations. Within the shrub species, Lycium cinereum had the highest CP concentration while Monechma genistifolium had the lowest CP concentration. Acacia haematoxylon had the highest NDF and ADF concentrations while Acacia erioloba had the highest ADL concentrations among the tree species. The highest concentrations for NDF, ADF and ADL were found in Dichrostachys cinerea, Monechma genistifolium, and Hermannia tomentosa among shrubs, respectively.

Acacia luederitzii and Dichrostachys cinerea had the highest concentration of total phenols and total tannins among the tree and shrub species, respectively. Among the tree species, Boscia albitrunca had the lowest phenolic concentration, while Lycium cinereum had the lowest concentration of total phenols and total tannins.

In vitro gas and methane production

The in vitro gas and methane production of browse species studied at 12 and 24 h of incubation (± PEG) are shown in Table 2. Both in the presence and absence of PEG there was a significant (p < 0.05) variation amongst browse species in terms of gas and methane production. Inclusion of PEG in fermentation of tropical browses resulted in a significant (p < 0.001) increase in gas and methane profile particularly in browse forage species with a high secondary phenolic content. However, no effects of PEG on the gas and methane profiles of lower concentration tannin plants, such as Acacia mellifera, Acacia hebeclada and Lycium cinereum were detected. In the current study, the volume of methane produced at different incubation periods differed significantly (p < 0.001) between the browse species, depending on the concentration of tannin. In the presence of tannins, Rhus lancea and Acacia luederitzii showed significantly low methane volumes among tree browses, while Lycium cinereum and Monechma incanum presentedsignificantly low methane volumes among shrub browses.

Table 2
− Mean gas production and methane production (mL g−1 DM) of browse plants studied (n = 8).

Scientific name	Gas volume				Methane gas
	12 h		24 h		12 h		24 h
	PEG +	PEG -	PEG +	PEG -	PEG +	PEG -	PEG +	PEG -
Trees
Acacia erioloba	116.8d1	84.50d2	135.5dc1	106.5e2	17.25c1	9.45d2	39.5cbd1	28.25d2
Boscia albitrunca	150.0b1	120.0b2	182.0a1	154.3b2	22.58b1	19.50b1	64.5a1	63.25a1
Acacia haematoxylon	96.00f1	60.25f2	115.5f1	71.75g2	15.33c1	8.00e2	34.0ced1	20.00e2
Olea europaea	101.5f1	101.3e1	140.5dc1	137.8c1	8.83d2	17.20c1	25.5e2	50.0b1
Ziziphus mucronata	167.8a1	139.3a2	188.3a1	172.3a2	31.25a1	25.75a1	64.00a1	63.75a1
Terminalia sericea	96.00f1	55.50f2	117.5f1	68.25g2	15.70c1	6.58f2	33.50ced1	17.95e2
Rhus lancea	125.8dc1	36.75g2	157.5b1	54.50h2	18.63cb1	1.63h2	43.50cb1	7.08g2
Acacia karroo	130.0c1	72.00e2	145.3c1	92.00f2	23.00b1	3.88g2	45.00b1	12.25f2
Prosopis glandulosa	106.5fe1	103.8c1	121.0fe1	120.3d1	17.70c1	16.20c1	40.50ed1	30.5c2
Acacia luederitzii	116.3de1	36.00g2	130.8de1	44.75i2	22.00b1	0.13i2	43.25cb1	1.58h2
Mean	120.5	81.00	143.5	102.3	19.23	10.83	43.75	39.5
SEM	3.30	2.88	3.90	3.03	0.58	0.18	1.30	0.30
Shrubs
Acacia mellifera	75.30e2	92.25d	122.5d1	104.3c2	130.8e1	9.38c2	35.25e1	24.08de2
Acacia hebeclada	138.3a1	134.5a2	161.3a1	158.5a1	27.25c1	24.20b1	63.0b1	51.5b2
Grewia flava	108.5c1	55.50f2	141.8c1	85.75e2	19.63d1	8.25d2	48.25d1	28.25d2
Dichrostachys cinera	109.3c1	58.25f2	134.3c1	71.75f2	20.75d1	2.58e2	45.25de1	7.45e2
Hermannia burchelli	139.0a1	119.3b2	162.0a1	152.3a2	31.50b1	26.0a2	65.75b1	64.00a1
Lycium cinereum	69.00f1	68.75e	87.75e1	79.50e2	1.08f1	0.50f2	1.58f1	1.825f1
Monechma genistifolium	92.50d1	86.00d2	105.8d1	103.8d1	25.25c1	24.63b1	52.25c1	42.00c2
Hermanniato mentosa	126.5b1	100.5c2	151.5b1	132.8b2	35.75a1	24.95b2	77.25a1	58.0ba2
Monechma incanum	134.8a1	59.75f2	164.0a1	73.25f2	36.75a1	1.50fe2	77.00a1	4.45fe2
Mean	110.3	86.00	136.8	106.8	23.45	13.55	51.75	31.25
	2.8	2.58	2.93	3.13	0.15	0.40	0.36	1.063

• Means with different superscript (a,b,c,d,e,f,g,h) across the column for each parameter are significantly (p < 0.05) different; PEG = Polyethylene glycol; PEG (-) denotes presence of tannin, PEG (+) denotes absence of tannin.

Feed digestibility and certain rumen related parameters

The IVOMD, total VFA and methane expressed in mass are shown in Table 3. The IVOMD differed (p < 0.05) within trees and shrubs both in the presence and absence of PEG. As expected, browses with high tannin concentrations were found to be low in digestibility; however, inclusion of PEG significantly improved their digestibility. Among the tree foliage, Boscia albitrunca and Ziziphus mucronata have the highest IVOMD values both in the presence and absence of PEG. Among shrubs, Lycium cinereum showed the highest value of IVOMD both in the presence and absence of PEG.

Table 3
− Mean volatile fatty acid (mmol L−1) production, ammonia N (mg L−1), in vitro organic matter digestibility (g kg−1 DM) and methane (CH4) production in mass (g kg−1 IVOMD) from the browse plants studied after 24 h of incubation.

Species names	Total VFA		NH3-N		IVOMD		CH4
	PEG +	PEG -	PEG +	PEG -	PEG +	PEG -	PEG +	PEG -
Trees
Acacia erioloba	99.6i1	95.0h2	20.5f2	33.3b1	44.0d1	44.6c1	21.0b1	10.5fe2
Boscia albitrunca	113.9c1	106.7c2	22.8b2	36.6a1	62.2a1	62.1a1	17.2ed1	15.4ba2
Acacia haematoxylon	100.1h1	97.2g1	21.7c2	25.1e1	31.0f1	30.9d1	25.3a1	14.0bc2
Olea europaea	109.7d1	106.5d1	19.0j2	22.3g1	53.2b1	49.2bc2	11.9f2	13.1dc1
Ziziphus mucronata	156.3a1	119.7a2	20.7e2	29.2c1	63.2a1	64.7a1	16.1e1	12.4d2
Terminalia sericea	103.0g1	82.1j2	20.2g2	22.8f1	38.5e1	24.9d2	19.2cbd1	15.7a2
Rhus lancea	115.5b1	104.9e2	21.0d1	18.8h2	36.7e1	23.0d2	18.6cd1	11.8de2
Acacia karroo	108.1f1	98.6f2	26.9a1	16.1j2	48.8c2	56.1ba1	19.7cb1	4.72g2
Prosopis glandulosa	108.5e1	110.9b1	19.4i2	25.7d1	55.4b1	56.5ba1	13.8f1	10.1f2
Acacia luederitzii	99.0j1	84.0i2	19.9h1	17.2i2	43.3d1	44.9c1	17.5ced1	4.04g2
Mean	111.4	100.6	2	24.7	47.6	45.7	18.1	11.2
SEM	1.14	1.58	0.51	0.72	0.45	0.58	0.12	0.09
Shrubs
Acacia mellifera	104.3h1	107.0e1	21.5g2	29.9a1	57.1c2	59.2cd1	12.2d1	12.7b2
Acacia hebeclada	118.0b1	115.6b1	22.4b2	26.2c1	61.8b1	61.1cb1	13.0d1	10.0c2
Grewia flava	106.7g1	101.7h1	22.0d2	28.5b1	32.5g1	30.9g2	22.0b1	18.3a2
Dichrostachys cinera	111.8d1	83.5i2	21.2h1	20.0h1	33.5g1	31.0g2	25.7a1	7.21d2
Hermannia burchelli	107.0f1	107.7d1	21.5f1	22.3f1	56.2c	63.5b1	17.5c1	12.1b2
Lycium cinereum	107.9e1	105.7f1	22.7a2	25.3d1	77.1a	81.1a1	3.54e1	2.16f2
Monechma genistifolium	103.5i1	103.1g1	16.4i2	21.5g1	52.5d2	57.1d1	18.0c1	12.9b2
Hermanniato mentosa	133.1a1	116.2a2	22.3c2	24.0e1	40.9f2	47.3e1	25.6a1	17.4a2
Monechma incanum	114.8c1	114.0c1	21.9f1	19.9i2	47.6e1	38.7f2	20.7b1	5.42e2
Mean	111.9	106.0	2.13	24.7	51.0	52.2	17.6	10.9
SEM	3.54	5.12	0.57	0.68	0.58	0.36	0.17	0.089

• Means with different superscript (letters) within a column for each parameter are significantly (p < 0.05) different; PEG = Polyethylene glycol; PEG (-) denotes presence of tannin, PEG (+) denotes absence of tannin. VFA = volatile fatty acids; IVOMD = in vitro organic matter digestibility.

The VFA and NH₃-N concentrations differed significantly (p ≤ 0.001) between trees and shrubs species. The absence of tannin significantly increased the concentration of VFA. Ziziphus mucronata showed the highest concentration of VFA in both the presence and absence of PEG among tree browses, while Hermannia mentosa showed the highest VFA concentration among shrub browses both in the presence and absence of PEG.

The recorded NH₃-N concentrations were the highest for Boscia albitrunca of the tree browsesand for the shrubs, Acacia mellifera without PEG. Acacia karroo and Monechma incanum had the lowest NH₃-N concentrations among trees and shrubs, respectively, with PEG. With the inclusion of PEG, Acacia karroo and Lycium cinereum produced the highest concentrations of NH₃-N among trees and shrubs, respectively.

The correlation coefficients of ruminal fermentation parameters (IVOMD, CH₄) with the chemical composition and phenolic compounds of the trees and shrubs are presented in Table 4. Significantly (p < 0.05), positive correlations were observed between IVOMD and nitrogen and NFC content. There were significant (p < 0.001) negative correlations of IVOMD with fiber components (ADF, cellulose, hemi-cellulose) and phenolic compounds (total phenol, total tannin, condensed tannin and hydrolysable tannin). Methane production showed a significant (p < 0.001) negative correlation with phenolic compounds (TP, TT, CT and HT) and positive correlation with fiber components.

Table 4
− Correlation coefficients (r) between in vitro fermentation parameters with chemical composition and phenolic compounds of browse plants studied.

	IVOMD	TVFA	NH3-N	GP24	CH4
Chemical composition
Ash	0.00043	0.40475	0.30581	0.43446	0.38066
OM	0.00043	0.40475	0.30581	0.43446	0.38066
CP	0.66639*	0.28331	0.50042*	0.47026	0.08677
NDFN	0.0054	-0.31476	-0.2924	-0.3473	-0.46133
NDF	-0.74652*	-0.5932*	-0.5304	-0.67893*	-0.3723
ADF	-0.63965*	-0.38326	-0.34233	-0.50149*	-0.07653
ADL	-0.27028	-0.0922	0.04748	-0.18242	-0.00323
NFC	0.05584	0.01108	-0.01605	0.06941	-0.11949
Phenolic components
TP	-0.69493*	-0.5631*	-0.55093*	-0.73452*	-0.63429*
TT	-0.60308*	-0.4968*	-0.58449*	-0.7401*	-0.67445*
CT	-0.56258*	-0.47298*	-0.58643*	-0.73431*	-0.67601*
HT	-0.61957*	-0.50323*	-0.56955*	-0.72738*	-0.65773*

• OM = organic matter; CP = crud protein; NDFN= Nitrogen in neutral detergent fiber; NDF = neutral detergent fiber; ADF = acid detergent fibre; ADL = acid detergent lignin; NFC = non-fibre carbohydrates; TP = total phenols; TT = total tannins; CT = condensed tannins; HT = hydrolysed tannins; IVOMD = in vitro organic matter digestibility; TVFA = total volatile fatty acids; NH₃-N- rumen ammonia; GP_24- gas production; CH₄- methane.

Discussion

The Thorny Kalahari Dune Bush veldt is characterized by irregular rainfall all through the year and intense water stress, which results in limited herbaceous flora existing in this part of Africa for most of the year. Thus, browse tree and shrub foliages are the main feed sources for ruminants. In the current study, except for Olea europaea, Terminalia sericea and Monechma genistifolium, the CP values observed were within the optimal range of 110-160 g CP kg⁻¹ DM recommended by the NRC (2001) for maintenance requirements of small ruminants. In addition, results obtained in this study for browse species, phenolic components were similar to the results reported by Jayanegara et al. (2011). Although the phenolic concentrations were slightly high, these browse species can be a potential supplement during times of drought. Addition of PEG could overcome adverse effects of high tannins on nutrient availability, as indicated by cumulative gas production, IVOMD, VFA and NH₃-N concentrations. As observed in this study for Rhus lancea, Acacia luederitzii and Monechma incanum,inclusion of PEG during the incubation of tannin-rich plants led to an increase in gas production of 100 % and this has the potential to increase rumen fermentation. Feed fermentation in the rumen and digestibility determine nutritive values of browse and these parameters are further influenced by chemical and phenolic compositions. High gas production indicated more fermentation which supported high rumen microbial production (van Soest, 1994). In the current study, the main factors affecting gas production and IVOMD of browse were high fiber and tannin concentrations. In agreement with current findings, studies done on different tropical browses have showed negative effects of plant phenolic compounds on the fermentation rate and level of digestion (Bhatta et al., 2009; Sebata et al., 2011). The negative effect of tannins on fermentation and digestion could be related to the formation of tannin-carbohydrate and tannin-protein complexes that are less degradable or to its toxicity to rumen microbes (Bhatta et al., 2009). Moreover, it acted as a toxicant to methanogens, reduced acetate and butyrate production (i.e. reduced fiber degradation) or caused a decline in organic matter (OM) digestion (Patra and Saxena, 2011).

Production of methane is a sink for hydrogen in the rumen during the process of utilization of feed energy. However, with fermentation of tannin rich plants, its bacteriocidal and bacteriostatic effects on the rumen microbes, and inactivation of its enzymes, greatly suppresses fermentation and this could result in a decrease of CH₄ production (Patra and Saxena, 2011). In the current study, the presence of tannin decreased methane production in all the browse species. The decrease in CH₄ production with the inclusion of tannin in ruminant diets was similarly reported by several researchers (Sebata et al., 2011; Sultan et al., 2012). In addition, with an increase in tannin concentration in browse species, a reduction effect on methane production was found. The impact of tannins on methane production varies with tannin chemical structure (plant origin) as well as with its concentration.

In tropical ruminant production systems, it is also very important that systematic and strategic supplementation of these forages in a mixed diet should be the way forward in their utilization. In such a way it is possible to attain a maximal depressing effect on enteric CH₄ production with minimal detrimental effect on rumen fermentation characteristics of poor quality roughage based diets. This can also insure the best option of utilization of these browses in all systems of livestock production.

Conclusion

From the results obtained in this study, variations were observed in the fermentation of trees and shrubs as well as in methane gas production. For example, tree forage (Rhus lancea and Acacia luederitzii) and shrub forage (Dichrostachys cinera and Monechma incanum) decreased methane and gas production significantly and it seems that Acacia luederitzii and Monechma incanum have a prolonged effect on CH₄ production. The substantial amount of CP content of certain species coupled with anti-methanogenic effect during fermentation, would offer farmers and pastoralists farming in sub-Sahara Africa an opportunity to use some of the browses for reducing CH₄ production. However, further studies need to be undertaken to determine the variation in the efficacy of the browse samples collected in different seasons in reducing CH₄ and mechanisms to integrate these browses to complement low quality feeds for different ruminant groups.

Acknowledgments

The research leading to these results received funding from the European Community’s Framework Programme (FP7/2007-2013) under the grant agreement No. 266018 ANIMALCHANGE. The authors are also grateful for co-funding from the South African Department of Science and Technology. We also would like to thank the Theart family for permitting us access to their property and assistance offered during browse sample collection in the Kalahari district.

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Edited by

Edited by: Paulo Cesar Sentelhas

Publication Dates

• Publication in this collection
  Nov-Dec 2015

History

• Received
  07 Oct 2014
• Accepted
  22 June 2015