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In vitro gas production, methane production and fermentation kinetics of concentrate diet containing incremental levels of sodium humate

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The redox potentials of humic acids make it a veritable pathway to hydrogen consumption in the rumen that may be a strategy to mitigate methane production. This study assessed the fermentability indices and methane production of incremental levels of sodium humate by in vitro gas production technique. Five experimental diets containing sodium humate at 0, 5, 7.5 10 and 12.5 g/kg diet were formulated. Inoculum prepared was from rumen fluid of West African Dwarf (WAD) goats. Incubation period was 24 hours at 39°C. Fermentation kinetics, methane and rumen metabolites production were analysed using one-way analysis of variance as outlined in the GLM procedure of SAS. Results revealed a decrease (p < 0.05) in CH 4 , VFA, acetate, propionate, butyrate, hydrogen consumed via CH 4 /VFA pathway (HC), volume of gas from degradable fraction (A) and rate of gas constant (c) with addition of sodium humate in the diet up to 10 g/kg diet. There were increase (p < 0.05) in VFA, acetate, propionate, butyrate, HC, A and c at 12.5 g/kg diet humate inclusion. Also, hydrogen recovery (HR), metabolizeable energy (ME), adenosine triphosphate (ATP), microbial biomass, organic matter digestibility (OMD) and short chain fatty acids (SCFA) increased (p < 0.05) with incremental levels of sodium humate inclusion, but above 10 g/kg diet inclusion, ATP, MB, ME, OMD and SCFA were observed to decrease (p < 0.05). It was concluded that the impact of sodium humate in diet of goats is dose dependent and that supplementing the diet of WAD goats with sodium humate for up to 10 g/kg diet can effectively reduce methane production while also providing energy for rumen microbes and other metabolic activities of the animal.
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ORIGINAL SCIENTIFIC PAPER | 183
Agric. conspec. sci. Vol. 85 (2020) No. 2 (183-189)
aCS
In vitro gas production, methane production
and fermentation kinetics of concentrate
diet containing incremental levels of sodium
humate
Timothy Tertsegha IKYUME1,2 ()
Olusiji Sunday SOWANDE2
Azeez Olanrewaju YUSUF2
Adebayo Olusoji ONI3
Peter Aniwe DELE4
Olalekan Toheed IBRAHIM2
Summary
e redox potentials of humic acids make it a veritable pathway to hydrogen consumption
in the rumen that may be a strategy to mitigate methane production. is study assessed the
fermentability indices and methane production of incremental levels of sodium humate by
in vitro gas production technique. Five experimental diets containing sodium humate at 0, 5,
7.5 10 and 12.5 g/kg diet were formulated. Inoculum prepared was from rumen uid of West
African Dwarf (WAD) goats. Incubation period was 24 hours at 39°C. Fermentation kinetics,
methane and rumen metabolites production were analysed using one-way analysis of variance
as outlined in the GLM procedure of SAS. Results revealed a decrease (p < 0.05) in CH4, VFA,
acetate, propionate, butyrate, hydrogen consumed via CH4/VFA pathway (HC), volume of
gas from degradable fraction (A) and rate of gas constant (c) with addition of sodium humate
in the diet up to 10 g/kg diet. ere were increase (p < 0.05) in VFA, acetate, propionate,
butyrate, HC, A and c at 12.5 g/kg diet humate inclusion. Also, hydrogen recovery (HR),
metabolizeable energy (ME), adenosine triphosphate (ATP), microbial biomass, organic
matter digestibility (OMD) and short chain fatty acids (SCFA) increased (p < 0.05) with
incremental levels of sodium humate inclusion, but above 10 g/kg diet inclusion, ATP, MB,
ME, OMD and SCFA were observed to decrease (p < 0.05). It was concluded that the impact
of sodium humate in diet of goats is dose dependent and that supplementing the diet of WAD
goats with sodium humate for up to 10 g/kg diet can eectively reduce methane production
while also providing energy for rumen microbes and other metabolic activities of the animal.
Key words
in vitro, fermentation, methane, sodium humate, WAD goats
1 Department of Animal Production, Federal University of Agriculture, Makurdi, P.M.B. 2373, Nigeria
2 Department of Animal Production and Health, Federal University of Agriculture, Abeokuta, P. M. B.
2240, Nigeria
3 Department of Animal Nutrition, Federal University of Agriculture, Abeokuta, P. M. B. 2240, Nigeria
4 Department of Pasture and Range Management, Federal University of Agriculture, Abeokuta, P. M. B.
2240, Nigeria
Corresponding author: ikyumett@uam.edu.ng
Received: December 17, 2019 | Accepted: March 19, 2020
Agric. conspec. sci. Vol. 85 (2020) No. 2
184 | Timothy Tertsegha IKYUME, Olusiji Sunday SOWANDE, Azeez Olanrewaju YUSUF, Adebayo Olusoji ONI, Peter Aniwe DELE, Olalekan Toheed IBRAHIM
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Introduction
In ruminants, enteric methane (CH4) is a major energy loss for
the host animal. In addition, methane, a potent greenhouse gas, is
contributing to climate change. Attempts by animal nutritionist
are targeting at utilizing feed resources that will mitigate
methane output from ruminants, while improving their overall
performance. Feed additives such as garlic, humic substances,
plant derivatives, and other natural antimicrobials (herbs and
plant extracts) have been used as rumen modiers in order to
mitigate methane production (Busquet et al., 2005; Patra et al.,
2006; Wanapat et al., 2008a; Wanapat et al., 2008b; Abarghuei et al.,
2013; Ikyume et al., 2018; Sheng et al., 2018). However, literature
on the use of humate as rumen modiers in West African Dwarf
(WAD) goats is still scanty.
Previous studies have shown that humic substances (HS)
may have benecial eects on livestock nutrition. Few studies
on the use of humate or humic acid on feedlot performance,
health and production in ruminants indicated a positive eect
on the utilisation of carbohydrates and protein (Bell et al., 1997;
Covington et al., 1997; Brown et al., 2007; Cusack, 2008). Inclusion
of HS eectively reduced CH4 production and increased substrate
disappearance and the eciency of microbial protein synthesis in
vitro (Sheng et al., 2018). Terry et al. (2018) reported no eect of
HS on CH4 production in beef heifers under in vivo conditions.
Similarly, comparable results were obtained for rumen variables in
rams fed humic acid supplemented diets (Galip et al., 2010). e
contrasting reports give room for the need to delve further into
the use of humate as rumen modier. In addition, there is paucity
of information on the rumen modier eect of sodium humate in
ruminant nutrition with specic reference to WAD goats.
In v itro fermentation technique allows for estimation of methane
and other fermentation kinetics due to the cumulative production
of gases released during fermentation of the sample incubated in
buered rumen uid (Pell and Schoeld, 1993; eodorou et al.,
1994). In this milieu, this experiment evaluated the fermentation
kinetics and metabolite production of concentrate diet containing
incremental levels of sodium humate in WAD goats.
Materials and methods
Ingredient collection and formulation of diet
Sodium humate was purchased from a reputable company
in china via aliexpres.com®. Maize, wheat oal, palm kernel
cake, bone meal, mineral premix and salt were purchased from a
feed shop in Abeokuta, Ogun State. e ingredients were milled
into coarse form (not nely milled) and mixed together to form
concentrate diet that was supplemented with 0, 5, 7.5, 10 and 12.5
g/kg diet of sodium humate, respectively (Table 1). About 200 mg
of experimental diets were used as substrate for in vitro incubation.
In vitro gas production procedure and estimated values
e procedure of Babayemi and Bamikole (2006) was adopted
for rumen uid collection from three bucks that were fed a
concentrate diet containing maize, palm kernel cake, wheat oal,
and Panicum maximum. e rumen uid collected were ltered
with a 4-layer cheesecloth with the resulting ruminal uid purged
with deoxygenated CO2 and put in a warm (39°C) thermo ask
to be used with a buer for preparation of inoculum. e buer
solution used was 9.8 NaHCO3 + 2.77 NaPO4 + 0.57 KCl + 0.47
NaCl + 2.16 MgSO4.7H2O + 0.16 CaCl2.2H2O. e rumen uid and
the buer were mixed together in ratio 1:2 (v/v). e procedure
of Menke and Steingas (1998) was adopted for incubation of the
samples with the use of a 100 ml calibrated transparent glass
syringes tted with silicon tube. Twenty replicates per treatment,
each containing 200 mg of substrate (experimental diets), were
put into pre-weighed Dacron bre bags with a pore size of 50
µm and loaded in the syringes. irty milliliter of inoculum was
drawn and dispensed into the calibrated transparent syringes
containing the substrate under continuous CO2 ushing. e
piston of the syringes was pushed upwards to expel air bubbles.
e silicon tubes on the syringes were properly clipped to prevent
escape of gas before placement into the incubator at a temperature
of 39°C. Gas volume was measured aer 3, 6, 9, 12, 18, and 24 hr
of incubation. Ten syringes containing only the inoculum were
considered as the blank. e net gas productions of the samples
were determined by correcting gas volumes for blanks.
Determination of methane
At post incubation period of 24 hr 4 ml of NaOH was
introduced into six replicates, each per treatment, in the incubated
samples to estimate methane production (Fievez et al. 2005). e
introduction of NaOH was via silicon tube that was attached to
the syringes. e dierences between the volume of gas before
and aer introduction of NaOH was deduced to be the volume
of methane.
Estimation of other fermentation kinetics
Metabolizable energy (ME) (MJ/kg diet) and organic matter
digestibility (OMD) of dietary treatments during fermentation
were calculated as established by Menke and Steingas (1998)
while short chain fatty acids (SCFAs) produced during the period
of fermentation were calculated as reported by Gatechew et al.
(1989).
Total gas volume (GV) was expressed as ml/200 mg diet, CP
and ash as g/kg diet, ME as MJ/kg diet and SCFA as µmol/g diet.
ME =20+0.13GV−0.057CP+0.0029CF
OMD =4.88+0.889GV+0.45CP+0.0651XA
SCFA=0.0239GV−0.0601
Where GV is Net gas production (ml/200 mg diet) during
incubation
CP is Crude protein content of experimental diets
CF is Crude bre content of experimental diets
XA is Ash content of experimental diets
Cumulative gas production data were tted to non-linear
exponential model as:
Y= A (1-e-ct)
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In vitro gas production, methane production and fermentation kinetics of concentrate diet containing incremental levels of sodium humate | 185
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Table 1. Gross composition of experimental diets
Parameter ( kg ) Control 5HNa 7.5HNa 10HNa 12.25HNa
Maize offal 30 30 30 30 30
Wheat offal 34 34 34 34 34
Palm kernel cake 32 32 32 32 32
Bone meal 33333
Vitamin premix 0.5 0.5 0.5 0.5 0.5
Salt 0.5 0.5 0.5 0.5 0.5
**HNa - 0.5 0.75 1 1.25
Tot a l 100 100 100 100 100
Determined analysis
DM 88.00 88.00 88.00 88.00 89.00
CP% of DM 14.88 14.01 14.35 14.13 14.61
CF% of DM 9.50 9.50 10.00 9.00 10.00
Ash 5.00 5.40 5.45 6.00 6.50
EE% of DM 6.50 8.00 7.50 8.00 7.56
NDF% of DM 64.00 65.00 63.00 54.00 55.00
ADF% of DM 22.00 23.00 19.00 23.00 20.00
ADL% of DM 9.00 8.50 8.00 9.00 7.00
Control: 0 g/kg diet sodium humate inclusion
5HNa: 5 g/kg diet sodium humate inclusion
7.5HNa: 7.5 g/kg diet sodium humate inclusion
10HNa:10 g/kg diet sodium humate inclusion
12.5HNa: 12.5 g/kg diet sodium humate inclusion
**HNa - used as a supplement and does not add up in diet formulation
Where Y is gas production at time t, A is the volume of gas
produced from degradable fraction with time (ml/200 mg diet),
c is the gas production rate constant (h-1) and t is the incubation
lag time (h).
In vitro dry matter digestibility (IDMD)
e dry residues aer the incubation were weighed and the
digestibility was calculated as the percentage of the initial diet
input. e formula used was:
IDMD = (Dry samples before incubation − dry samples aer
incubation) / (Dry samples before incubation) × 100
Volatile fatty acids and ammonia nitrogen
Total volatile fatty acids (VFAs) and proportions of acetate (A),
propionate (P) and butyrate (B) were determined from incubated
samples as described by Samuel et al. (1997). e samples were
centrifuged at 3,000 xg for 10 min; they were allowed to settle and
decanted. e decant was titrated with 0.1 M of sodium hydroxide
(4/1000 gml-1 H2O) solution each with 2 – 3 drops of phenophtaline
(1/100 gml-1 ethanol) as the indicator. Determination of the various
fractions was as enumerated below:
Acetate = (Titre Value × 0.1 × 0.06 × 100) / 5
Propionate = (Titre Value × 0.1 × 0.04 × 100) / 5
Butyrate = (Titre Value × 0.1 × 0.006 × 100) / 5
Total volatile fatty acids = (Titre Value × 0.1 × 0.09 × 100) / 5
Ammonia nitrogen was determined as described in AOAC
(2005).
Hydrogen balance
Estimation of hydrogen balance was calculated according to
formula given by Demeyer (1991) as follows:
Agric. conspec. sci. Vol. 85 (2020) No. 2
186 | Timothy Tertsegha IKYUME, Olusiji Sunday SOWANDE, Azeez Olanrewaju YUSUF, Adebayo Olusoji ONI, Peter Aniwe DELE, Olalekan Toheed IBRAHIM
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Hydrogen recovery (HR):
HR(%) = (4M + 2P + 2B) / (2A + P + 4B) x 100
Hydrogen consumed via CH4 / VFA = 4M / (2P+2B)
Where M is methane (mmol), P is propionate (mmol), B
is butyrate (mmol) and A is acetate (mmol) produced during
fermentation of dietary treatments.
Adenosine triphosphate (ATP)
ATP pr is ATP produced during fermentation and it was
estimated using concentrations of the VFA proportions by the
following formula:
ATP pr (mol) = 2.5(A) + 2.75(P) + 3.5(B)
(Owens and Goetsch, 1988)
Microbial biomass
Microbial biomass was estimated as follows:
Microbial mass (g) = 10 × ATPpr
(Owens and Goetsch, 1988)
Chemical analysis
Proximate analysis of the substrate was done for dry matter,
crude protein, crude bre, ether extract and ash as described in
AOAC (2005), while neutral detergent bre, acid detergent bre
and acid detergent lignin were done as enunciated by Van Soest
et al. (1991)
Statistical analyses
e in vitro kinetics, hydrogen eciency, and production of
methane, microbial biomass and adenosine triphosphate were
analysed using one-way analysis of variance using the general linear
models (GLM) procedures of SAS (2000). Signicant dierences
among treatment means where applicable were seperated using
Duncan multiple range test. Probability signicance was declared
at P ≤ 0.05.
Results
Gas production parameters
e eect of incremental levels of sodium humate on in vitro
gas production parameters of dietary treatments using ruminal
uid of WAD goats is shown in Table 2. Total gas volume (GV),
ME, OMD and SCFA were the highest (p < 0.05) for the 10HNa
treatment and reduced (p < 0.05) in control, 5HNa, 7.5HNa
and 10.25HNa treatments, which had similar values of GV, ME,
OMD and in vitro dry matter digestibility (IDMD) decreased (p
< 0.05) at supplementation of sodium humate up to 10 g/kg diet.
e highest (p < 0.05) similar values of IDMD were observed in
control and 12.5HNa treatment (21.58% and 19.57%, respectively)
and reduced (p < 0.05) in 5HNa, 7.5HNa and 10HNa treatments,
which had the least similar values (15.95, 17.45 and 17.01%,
respectively). Methane production was the highest (p < 0.05) in
control group (9.40 ml/200 mg diet) and decreased (p < 0.05)
with increased humate supplementation. e highest (p < 0.05)
lag time was comparable in control and 10HNa treatments and
reduced (p < 0.05) in 5HNa, 7.5HNa and 12.5HNa treatments
that had the least comparable values. Gas production fractional
rate (c) was the highest in 10HNa group (0.012 ml/hr) that was
similar to the control and 7.5HNa groups (0.0088 and 0.0081 ml/
hr, respectively), and these diered signicantly from 5HNa and
12.5HNa groups (0.00052 and 0.0014 ml/hr, respectively). e
highest volume of gas produced from degradable fraction (A)
was estimated for 5HNa group (33539.67 ml/200 mg diet), and
this was similar to the control group (20256.93 ml/200 mg diet)
but diered signicantly (p < 0.05) from the 7.5HNa, 10HNa and
12.5HNa groups (5873.53, 3519.74 and 12474.86 ml/200 mg diet,
respectively). e ratio of methane to gas volume was statistically
similar (p > 0.05) for all treatment groups.
Rumen metabolites
Table 3 presents the rumen metabolites from in vitro
fermentation of diet containing supplemental levels of sodium
humates. Volatile fatty acids (VFA), acetate, propionate and
butyrate from post-incubated samples had similar pattern in all
the treatment groups. e highest (p < 0.05) comparable VFA,
acetate, propionate and butyrate concentrations of post incubation
samples were obtained in control and 12.5HNa treaments, while
they were reduced in 5HNa, 7.5HNa and 10HNa treatments.
Ammonia nitrogen and acetate to propionate ratio (A:P) were
similar (p > 0.05) for the dietary treatments.
Fermentability indices
Fermentability indices as inuenced by incremental levels of
sodium humate in treatments in vitro gas production using ruminal
uid of WAD goats are shown in Table 4. e highest (p < 0.05)
comparable amount of hydrogen recovery (HR) was observed
in 10HNa and 12.5HNa treatments, while the least comparable
amount of HR was found in control and 5HNa treatments. e
amount of hydrogen consumed via the ratio of CH4 and VFA
(HC) decreased (p < 0.05) with humate inclusion e highest (p
< 0.05) HC was observed in the control group (73.79), while the
least comparable HC means were observed in 7.5HNa, 10HNa
and 12.5HNa treatments. Production of adenosine triphosphate
(ATP) and microbial biomass (MB) had the highest (p < 0.05)
comparable amounts in 5HNa, 7.5HNa and 10HNa treatments,
while the least (p < 0.05) comparable values were observed in
control and 12.5HNa treatment.
Discussion
e volume of gas produced during fermentation reects
the products of the substrate fermentation to volatile fatty acids
microbial biomass and neutralization of the VFA, and this is
indication of the nutritional value of the substrate (Blummel and
Becker, 1997). e reason for increased gas volume in 10 g/kg
treatment may not have been inclusion of sodium humate in the
diet, since all gas volumes were not aected by all other sodium
humate supplemented treatment groups.
Dry matter digestibility is a measure of substrate disappearance.
Decrease in the IDMD in the current study may have been due to
the action of humic acid to prolong digestion period (Korniewicz
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In vitro gas production, methane production and fermentation kinetics of concentrate diet containing incremental levels of sodium humate | 187
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Table 2. In vitro gas production parameters from rumen of WAD goats fed diet containing supplemental levels of sodium humate
1Parameter Control 5HNa 7.5HNa 10HNa 12.5HNa SEM
GV(ml/200 mgDM) 21.54b22.00b22.80b25.40a22.90b0.82
Methane (ml/200 mg DM) 9.40a7.40b5.00c4.40c4.20c0.45
IDMD (%) 21.58a15.95b17.45b17.01b19.57ab 0.55
A (ml/200 mg DM) 20256.93ab 33539.67a5873.53b3519.74b12474.86b3146.74
c (ml/hr) 0.0088a0.00052c0.0081ab 0.012a0.0014bc 0.0012
lag (hr) -16.70ab -19.10b-17.13b-13.80a-18.83b0.51
ME (MJ/kg DM) 4.24b4.30b4.40b4.74a4.41b0.05
OMD(g/kg DM) 40.74b41.16b41.90b44.20a42.07b0.31
SCFA (µmol/g DM) 0.45b0.47b0.48b0.55a0.49b0.008
CH4/GV (%) 19.22 17.30 11.58 8.16 9.48 2.20
a,b,c Means with different superscript along the same row differ significantly (p < 0.05)
1 GV - gas volume, IDMD- in vitro dry matter digestibility, A - rate of gas production from soluble fraction, c - gas production constant, Lag - fermentation time, ME
- metabolizeable energy, OMD - organic matter digestibility, SCFA - short chain fatty acid, CH4/GV - methane-gas volume ratio
Table 3. Rumen metabolites of concentrate diet containing incremental levels of sodium humate from in vitro fermentation
Parameter Control 5HNa 7.5HNa 10HNa 12.5HNa SEM
NH3-N (g/100 ml) 40.26 30.06 43.09 39.69 37.99 2.05
VFA (Mm/100mol) 1.75ab 1.68b1.57b1.69b1.92a0.04
Acetate (Mm/100 mol) 1.17ab 1.12b1.05b1.10b1.28a0.02
Propionate (Mm/100 mol) 0.77ab 0.75b0.70b0.75b0.85a0.02
Butyrate (Mm/100 mol) 0.12ab 0.11b0.10b0.11b0.13a0.002
A:P 1.51 1.50 1.50 1.47 1.50 0.007
a,b Means with different superscript along the same row differ significantly (p < 0.05)
Table 4. Fermentability indices of concentrate diet containing incremental levels of sodium humates from in vitro fermentation
Parameter Control 5HNa 7.5HNa 10HNa 12.5HNa SEM
HR % 8.39c10.64c14.07b16.81ab 19.14a1.10
HC 73.79a52.62b34.39c32.34c36.66c4.37
ATP (mol) 5.51bc 5.78ab 6.17a5.84ab 5.06c0.12
MB (g) 55.06bc 57.77ab 61.70a58.39ab 50.56c1.22
a,b,c Means with different superscript along the same row differ significantly (p < 0.05)
HR-hydrogen recovery; HC - hydrogen consumed via CH4/VFA; ATP - adenosine tryphosphate; MB - microbial biomass
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188 | Timothy Tertsegha IKYUME, Olusiji Sunday SOWANDE, Azeez Olanrewaju YUSUF, Adebayo Olusoji ONI, Peter Aniwe DELE, Olalekan Toheed IBRAHIM
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et al., 1999; Suchy et al., 1999), thereby suggesting it will take
a longer time for the substrate to disappear. is implies that
substrate disappearance with humate supplementation may
increase if more time for incubation was given. is was further
armed by increase in the lag time observed in this study with
sodium humate supplementation. Increased lag time could result
in low feed intake by the animal. e observed decrease in IDMD
did not however aect the production of ATP, microbial biomass
and short chain fatty acids.
e decrease in methane production in this study is consistent
with the work of Sheng et al. (2018) who observed a reduction
in methane production in in vitro conditions when humic
substance was included for up to 30 g/kg diet. McMurphy et al.
(2011) has reported that humic substances (HS) could exhibit a
high anity for nitrogen (N), and this property is considered to
enhance rumen microbial biomass, reduce nitrogen excretion and
methane (CH4) release to the environment. e mechanism of
lowering methane production may be adjured to be because of the
redox capacity of humic substances that is attributed to the variety
of functional structures, such as quinone, phenolic, hydroxyl,
nitrogen and sulphur-containing molecules (Aeschbacher et al.,
2010). is capacity makes humic substances including humates
to act as electron acceptors for a wide variety of microorganisms
capable of extracellular electron transfer, with methanogens
inclusive (Martinez et al., 2013), and is evident in the decrease in
the hydrogen consumed (HC) via the methane/VFA pathway in
this study. e implication is that more of the hydrogen produced
during the process of fermentation would have undergone a redox
reaction with the humates instead of the methanogens. ese
redox potentials have been shown to lower methane production
in soil microorganisms (Tan et al., 2018).
e rate of gas produced from degradable fraction (A) of the
substrate decreased at higher concentration of sodium humate in
the diet. Crude protein availability in the rumen is reported to be
directly correlated with the rate of gas produced from degradable
fraction (A) of the substrate (Akinfemi et al., 2009). Summarily, the
crude protein available in the diets with sodium humates may not
have been available for degradation in the rumen. is is because
sodium humate reduces proteobacteria in the rumen (Mitsumori
et al., 2002). e relatively low fractional rate of gas production
(c) as aected by humate addition in this study is attributed to
lower protein degradation in the rumen. Dele (2012) reported that
higher values of fractional rate of gas production were attributed
to the amount of nitrogen that was available for degradation under
in vitro analysis. us, the lower fractional rate of gas production
in some of the sodium humate groups may be indication that fewer
nutrients were available for rumen microorganisms (Getachew et
al., 2004). e non-signicant dierence observed for NH3-N in
this study is not consistent with reports of Bell et al. (1997) and
Sheng et al. (2018). ese dierences could be attributed to the
type of humate used for the various studies as well as source of
rumen uid.
Volatile fatty acids (VFA) as well as the various proportion of
the VFA (acetate, propionate and butyrate) decreased at low-to-
relatively high doses (5, 7.5 and 10 g/kg diet) of sodium humate
used in this study compared to 12.5 g/kg diet. e addition of 12.5
g/kg diet did not aect the production of VFA, acetate, propionate
and butyrate as compared to the control. e comparable means
between the control group and the 12.5HNa group is consistent
with report of Terry et al. (2018) who did not observe signicant
dierences in VFA and its proportions when beef heifers were fed
a barley silage-based diet containing increasing concentrations
of humic substance. Higher production of volatile fatty acids in
the dietary treatment containing 12.5 g/kg diet of sodium humate
means more energy available to the animal for production.
Fermentability indices such as hydrogen, microbial biomass
and adenosine triphosphate (ATP) are indication of substrate
appreciation. e increase in the rate of H2 recovery (HR) with
incremental levels of sodium humate inclusion could be attributed
to less energy available. Energy available in form of ATP for the
microbes involved in dehydrogenase reactions releasing H2 was
observed to reduce in 12.5HNa with a corresponding rise in
HR in the same treatment group. It is worthy to note that while
incremental levels of sodium humate addition did not decrease H2
recovery (HR), its (HC) consumption was decreased via methane/
volatile fatty acids. e mechanism of reduction in H2 consumption
is explained by the redox properties of humic substances that are
hydrogen scavengers. e increase in microbial biomass in the
sodium humate group up to 10HNa with a subsequent decrease
in 12.5HNa group might be attributed to more hydrogen intake
by the microbes. Less amount of HC in this study imply more
hydrogen would have been available for the microbes. In addition,
Leng (2014) has reported that with less crude protein from the
diet for microbes, they will resort to use the non-protein-nitrogen
source (NPN source) which is bound to increase microbial
growth eciency and then, hydrogen intake. In this report as HC
decreased, MB increased. But this is also dose dependent as above
supplementation of 10 g/kg diet, microbial biomass decreased.
Conclusion
e supplementation of sodium humate in the diet of
WAD goats eectively reduced methane production while also
improving the fermentability of the diets. However, these eects
were dose dependent as supplementing sodium humate above 10
g/kg diet reduced energy and microbial biomass in the rumen.
Sodium humate can therefore be included in the diet of WAD
goats for up to 10 g/kg diet.
Conict of interest
e authors declare that there was no conict of interest in the
course of the research work.
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