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Effect of level of monensin on rumen fermentation characteristics in Awassi lambs

Authors:
  • Al-Qasim Green University

Abstract and Figures

The current study was conducted in the Animal field of the Department of Animal Production – College of Agriculture - Al-Qasim Green University for the period from 10/10/2019 to 19/1/2020 to investigate the effect of addition of monensin at levels of 15, 30 and 45 mg/kg concentrate on growth performance of Awassi lambs. First treatment in which lambs were fed concentrate diet without addition of monensin was considered the control treatment. Sixteen male Awassi lambs were used with an average weight of 24.85 and 4-6 months of age. The lambs were randomly distributed to the experimental treatments, four lambs per each using the individual feeding in the cages. The concentrate diet was offered at a level of 2.75% of the body weight at 2 meals, morning and evening meals, while the ground wheat straw was offered at free choice. Results revealed no significant effect of level of monensin on pH values, whereas ruminal ammonia concentrations were significantly decreased (P˂0.05) from 7.54 in the control treatment to 6.08 and 6.45 mg/100 ml due to addition of monensin at levels of 30 and 45 mg/kg. Moreover, addition of monensin at a level of 30 mg/kg concentrate diet significantly increased (P˂0.05) ruminal concentration of total volatile fatty acids to 13.76 as compared with 10.99 mM/100 ml for control treatment. Concentrations of all rumen fermentation characteristics were significantly affected (P˂0.01) by time of ensiling.
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Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
1
Effect of level of monensin on rumen fermentation characteristics in Awassi
lambs
Razzaq S. M. Baiee* Ali A. Saeed**
* Directorate of Agriculture in Babylon razaq_1989@yahoo.com 07601332360
** College of Agriculture Al-Qasim Green University aliameensaeed@yahoo.com 07802893603
Received date:23July.2020 Accepted:(469) 27Aug.2020 page: (1-11) Published: 30Dec.2020
DOI: http://dx.doi.org/10.36326/kjvs/2020/0110201
Abstract
The current study was conducted in the Animal field of the Department of Animal
Production College of Agriculture - Al-Qasim Green University for the period from 10/10/2019 to
19/1/2020 to investigate the effect of addition of monensin at levels of 15, 30 and 45 mg/kg
concentrate on growth performance of Awassi lambs. First treatment in which lambs were fed
concentrate diet without addition of monensin was considered the control treatment. Sixteen male
Awassi lambs were used with an average weight of 24.85 and 4-6 months of age. The lambs were
randomly distributed to the experimental treatments, four lambs per each using the individual
feeding in the cages. The concentrate diet was offered at a level of 2.75% of the body weight at 2
meals, morning and evening meals, while the ground wheat straw was offered at free choice.
Results revealed no significant effect of level of monensin on pH values, whereas ruminal ammonia
concentrations were significantly decreased (P˂0.05) from  in the control treatment to 6.08 and
6.45 mg/100 ml due to addition of monensin at levels of 30 and 45 mg/kg. Moreover, addition of
monensin at a level of 30 mg/kg concentrate diet significantly increased (P˂0.05) ruminal
concentration of total volatile fatty acids to 13.76 as compared with 10.99 mM/100 ml for control
treatment. Concentrations of all rumen fermentation characteristics were significantly affected
(P˂0.01) by time of ensiling.
Key words: Monensin, lambs, fermentation, rumen
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Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
2
Introduction
The livestock industry in Iraq faces
many problems and constraints, natural
problems related to climate, water scarcity
and human problems related to nutrition and
the failure of animals to gain its requirements
of nutrients. These conditions led to decrease
the number of sheep by more than 45% in
2010 as compared with its number at 1961, it
was about 6.663 million at 2017 (1). Due to
the unique anatomical characteristics of
ruminants in the presence of the rumen, where
different species and strains of anaerobic
microorganisms live, these animals are
characterized with its ability to utilize poor
quality roughages (2).
Ruminant nutritionists have made great
efforts focused on improving rumen
fermentation to increase production
efficiency. In the last two decades, a number
of active compounds that can be introduced as
feed additives in ruminant diets such as
monensin, the most important polycarboxylic
antibiotic Ionophore compounds, have been
found to achieve this goal by increasing the
production of propionate while reducing the
production of methane, (3).
Rutkowski and Brzezinski (4) indicated
that monensin was also used as a growth
promoter for ruminants and targeted specific
bacterial groups in the rumen, leading to
increase production efficiency. The increase
in the pH of the rumen is associated with an
increased level of addition of monensin to the
diets offered to the ruminants (5). This is
explained by the effectiveness of monensin in
inhibiting lactic acid-producing bacteria such
as Streptococcus bovis and lactobacilli
directly (6).
Most studies indicated that introduction
of monensin into ruminant diets improved the
efficiency of rumen fermentation. This
improvement was attributed to its positive
effects on rumen fermentation, including
increasing the concentration of propionate and
reducing ammonia (7). Therefore, the present
study aims to investigate the effect of
introducing different levels of monensin on
rumen fermentation characteristics.
Materials and methods
The study was conducted at the Animal
fields of Animal Production Department /
College of Agriculture - Al-Qasim Green
University from 10/10/2019 to 1/19/2020,
including a preliminary period for 30 days.
Sixteen male Awassi lambs bought from local
markets with an average weights of 24.85 ±
0.83 kg and 4-6 months of age were used.
They were randomly distributed to
experimental treatments and housed
individually with four pens per each
treatment. There were 4 experimental
treatments based on concentrate diet offered
at a level of 2.75% of body weight at 2 meals
a day. Concentrate diet was offered without
monensin for the first treatment (control) and
with addition of monensin at level of 15, 30
or 45 mg/kg concentrate diet for the second,
third and fourth treatments respectively. Table
1 shows the chemical composition of
concentrate diet, its ingredients and wheat
straw.
Table 1- Chemical composition of concentrate diet, its ingredients* and wheat straw (%)
ME
MJ/100 g
% inDM
DM
Ingredients
NFE
EE
CP
OM
1.23
62.52
4.39
14.14
95.31
93.55
Wheat bran
1.37
80.80
5.84
7.20
98.86
89.09
Yellow corn
1.27
75.49
3.75
11.86
97.12
92.69
Barley
1.18
39.35
1.47
42.79
78.62
94.31
Soybean meal
-
-
-
*
287.5
*
-
-
Urea
1.25***
74.68
4.43
14.47
95.13
89.75
Concentrate
1.00***
52.09
2.13
2.69
91.09
91.19
Wheat straw
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
3
* % barley, % yellow corn, 30% wheat bran and 4.90% soybean meal ** 46 × 6.25
***Level of ME in diets was estimated according to MAFF (8) equation with subsequent conversion of values from
MJ/kg DM to MJ/ 100 g DM:
MAFF (MJ/ Kg DM) = 0.012 CP + 0.013 EE + 0.005 CF + 0.014 NFE.
Level of RDN was estimated according to previous studies in which the ruminal effective degradability of protein
fraction in the different ingredients of concentrate diet had been determined as follows: 80 and 60% for barley and
yellow corn respectively (9), 70% for soybean meal (10) and 67% for wheat bran (11).
NaCl and mineral-vitamin mix manufactured by Turkish Profeed Company were added to concentrate at rate of 1% for
each. Urea was added at rate of 0.536% to ensure existence of a standard ratio of 1.34 g RDN/MJ of ME (12). The
estimated level of RDN in concentrate diet was about 1.67 g/100 g DM.
Withdrawal of rumen fluid sample
Rumen fluid samples were withdrawn
from all lambs according to the method
described by Saeed (13) using stomach tube.
The samples were withdrawn within one day
at 3 times, before the morning meal of
concentrate diet, 3 and 6 hours after that. The
samples were filtered through 4 layers of
cheese cloth. The pH was measured
immediately using the Mi 180 Bench Meter.
Then a few drops of the 50% sulfuric acid
solution were added to stop fermentations.
Two fractions of acidic samples were
transferred into clean pipes and kept frozen
until determinations of fermentation
characteristics were performed.
Determination rumen fermentation
characteristics
The first part of the frozen samples
were thawed and the remaining solid parts
were separated using a centrifuge at 3000 rpm
for 20 minutes, the supernate was then used to
determine the concentration of ammonia
nitrogen (NH3-N) in the rumen liquid. 0.5 ml
of the rumen liquid sample was transferred
into the digestion tube of the Kjildahl
apparatus and fixed in the distillation unit
after addition of 0.5 g of MgO, 0.25 g of
boiling stone, and 1 ml of a 25% CaCl2
solution. 10 ml of distilled water were added
automatically to the tube before the start of
boiling and condensation operations. The
released ammonia was collected in a beaker
containing 10 ml of 2% solution of boric acid
with a few drops of the methyl red and green
bromocresol indicator. The collected
ammonia was titrated against 0.05 M of HCl
solution and NH3-N concentration was
estimated according to the following
equation:
(ml acid in titration - ml blank) × M × 0.014
NH3-N mg/100ml =  100
Sample volume, ml
To determine the concentration of total
volatile fatty acids (TVFA) in the rumen
liquid, the method proposed by Markham (14)
was used. The second part of frozen samples
were used as shown above. One ml of the
rumen liquid sample was transferred into the
digestion tube of the Kjildahl and 1 ml of
50% orthophosphoric acid was added. The
tube was fixed in the distillation unit. Soon
after operation of this unit 10 ml of distilled
water were added automatically. About 50-
100 ml of the condensate solution was
collected in a beaker containing 3-4 drops of
the methyl red and green bromomresol
indicator. The collected solution was then
titrated against 0.1 N of NaOH solution and
the concentration of TVFA was estimated
according to the following equation
(ml, base in titration - ml Blank) × N
TVFA mM/100ml =  100
Sample volume
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
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Statistical analysis
The data were analyzed statistically
according to the Completely Randomized
Design (CRD) to study the effect of the level
of monensin. The statistical program SAS
(15) was used to analyze the data of rumen
fermentation characteristics obtained in the
study.
Results and Discussion
Effect of level of monensin on rumen
fermentation characteristics
Table 2 shows the effect of level of
monensin on rumen fermentation
characteristics. Results revealed no significant
effect of level of monensin on pH values. This
result agrees with those obtained by many
studies (16)-(19). Monensin inhibits lactic
acid producing bacteria keeping pH at values
within those supporting best rumen
fermentation rate (20).
Table 2- Effect of level of monensin on rumen fermentation characteristics
(as shown in the table ± SE).
Items
Level of monensin, mg/kg concentrate
P



pH

0.11

0.10

0.

0.
NS
NH3-N, mg/100 ml
a

0.
ab

0.
b

0.34
b

0.
*
TVFA, mM/100 ml
b

0.
ab

0.
a

0.
ab

0.
*
* Means with different letters are significantly differed (P˂0.05)
However, inconsistent result was
reported by Rowghani, et. al., (21), addition
of monensin to lambs diet at levels of 5, 11
and 22 mg/kg DM significantly (P˂0.05)
increased ruminal pH value from 5.83 to 5.94,
5.91 and 5.90 respectively. Similarly, Silva,
et. al., (22) found a significant (P˂0.05)
increase in ruminal pH values from 6.07 to
6.13 due to addition of monensin to the
concentrate diet offered to castrated lambs at
level of 30 mg/kg.
Regarding ruminal NH3-N
concentration, results showed that it was
decreased (P˂0.05) from  in the control
treatment to 6.08 and 6.45 mg/100 ml due to
addition of monensin at levels of 30 and 45
mg/kg respectively. This result agrees with
that revealed by Anassori, et. al., (17), in
which introduction of monensin into the diet
of Makoui lambs at a level of 33 mg/kg DM
decreased (P˂0.05) ruminal NH3-N
concentration after 14 days from 20.89 to
11.68 and from 21.38 to 13.33 mg/100 ml
after 21 days. In other study, addition of
monensin to the diet of Chall sheep decreased
(P˂0.05) ruminal NH3-N concentration from
18.53 to 13.95 mg/100 ml (23).
Taghizadeh, et. al., (24) noticed a
significant (P˂0.05) decrease in ruminal NH3-
N concentration from 10.1 to 9.77, 9.17 and
8.63 after 2 hours and from 10.55 to10.03,
9.62 and 9.23 mg/100 ml after 4 hours of
feeding due to increasing level of monensin
added to the diet of Ghizel lambs from 20 to
25, 30 and 35 mg/kg. Similar results were
reported by many other studies (25), (21),
(22), (18).
The reduction of ruminal NH3-N
concentration observed with feeding
monensin may be due to the decrease in the
number of ruminal protozoa (23), (17). Many
studies demonstrated that the overall and
partial reduction in ruminal protozoa of sheep
led to increase propionate production on
expense of acetate and butyrate with a
decrease in the recycled bacterial N and
ruminal NH3-N concentration (26).
Bohnert, et. al., (27) indicated that the
reduction of ruminal NH3-N concentration
may associate with a decrease in the ruminal
degradation of protein and peptides and in
deamination of amino acids. Moreover, the
reduction of ruminal NH3-N concentration
may be resulted from a decrease in the
number of proteolytic bacteria or that
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
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involved in the deamination of amino acids in
the rumen (28). Joyner, et. al., (29) concluded
that animal fed monensin containing diets
efficiently utilize its N allowances in protein
synthesis.
Inconsistence with the current study,
Maas, et. al., (30) found that ruminal NH3-N
concentration was not significantly affected
by the addition of monensin to the diet of
castrated lambs in the Autumn (18.6 and 17.7)
and Spring seasons, concentrations were 18.2
and 17.3 mg/100 ml for the addition and
control treatments respectively. Similar result
was obtained by Aguilera-Soto, et. al., (31), in
which, ruminal NH3-N concentration was not
affected by addition of monensin to the diet of
Pelibuey × Rambouillet cross bred lambs at a
level of 33 mg/kg, values were 16.9 and 15.6
mg/100 ml for the addition and control
treatments respectively.
Al-Shemary (19) reported different
result as compared with the result of a current
study. The worker fount that introduction of
monensin into the concentrate diet of Awassi
lambs at a level of 30 mg/kg DM increased
P<0.01 ruminal NH3-N concentration from
6.21 to 6.97 mg/100 ml when lambs were fed
the concentrate diet at a level of 2.5% of BW.
However, no significant difference was
shown when the diet was offered at 3% of
BW, mean values were 6.97 and 7.29 mg/100
ml for the addition and control treatments
respectively.
Results of a current study revealed also
that concentration of ruminal TVFA was
increased P<0.05 from 10.99 to 13.76
mM/100 ml due to addition of monensin at a
level of 30 mg/kg DM as compared with the
control treatment. This result disagree with
that obtained by Mirzaei, et. al., (23) where,
addition of monensin to the diet of goat at
level of 15 mg/kg had no significant effect on
ruminal concentration of TVFA, values were
5.67 and 5.74 mM/100 ml for addition and
control treatments respectively.
Anassori, et. al., (17) clarified that the
concentration of ruminal TVFA was not
significantly affected by addition of monensin
to the diet of Makoui lambs at a level of 33
mg/kg DM after 14 and 21 days of the start of
the study, values were 9.68 vs. 9.78 for the
control treatment and 9.72 vs. 9.76 mM/100
ml for the addition treatment respectively. Al-
Shemary (19) found that addition of monensin
to concentrate diet of Awassi lambs at a level
of 30 mg/kg decreased P<0.01 ruminal
concentration of TVFA from 15.18 to 11.44
mM/100 ml. Similar results were obtained by
other studies (16), (25), (32), (31), (18), (24),
(33). The significant increase in ruminal
concentration of TVFA due addition of
monensin may be due to the improve of
rumen condition and enhance activity of
rumen microbes (17). In addition to the
decrease of outflow rate of feed particles via
fermentation area, improve digestion and
processes of chewing and rumination that lead
to decrease those particles and increase
surface area of diets exposed to the action of
microbial enzymes (34).
The differences among a current study
and other studies in rumen fermentation
characteristics may be due to levels of
nutrients, chemical composition of organic
materials, physical state of diet, concentrate to
roughage ratio and method of sampling as
indicated by Rowghani, et. al., (21). In that
study, the ratio was 83:17%, samples were
taken and data was obtained using cannulated
lambs. The differences can also be attributed
to the differences in study condition, such as
period, formulation of diets and its
characteristics, treatment or additives, level of
addition and other factors (17). In addition to
the level of dietary crude protein. Dung, et.
al., (35) reported that ruminal NH3-N
concentration can be affected by the level of
dietary CP and its ruminal degradability.
Diurnal changes in rumen fermentation
characteristics
Table 3 shows the effect of sampling
time on rumen fermentation characteristics in
Awassi lambs. Results revealed that all
studied characteristics were significantly
altered. Higher P<0.01 pH value of 7.36 was
recorded in rumen liquid samples withdrawn
before feeding in comparison with 6.37 and
6.44 recorded in samples withdrawn 3 and 6
hours post feeding. This may be due to the
effect of saliva produced during chewing and
rumination of roughage throughout the night
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
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and passed to the fermentation chamber (36).
Large quantities of saliva containing
bicarbonate and urea may therefore flow into
this chamber leading to increase ruminal pH
(19). The reduction of the ruminal pH in
samples withdrawn 3 hours post feeding may
be attributed to the effect of concentrate diet
offered to the lambs at morning meal, in
which readily fermented carbohydrates was
converted by rumen microbes to lactic acid
(LA) and VFA (13). Reduction of ruminal pH
is mainly associated with increased LA
concentration in the rumen (22).
Table 3- Effect of sampling time of rumen liquid on rumen fermentation characteristics (as
shown in the table ± SE)
P
Post feeding
Before feeding
Time of sampling
6
3
0
Fermentation characteristics
**
b
6.44

b
6.37

a
7.36 
pH
**
c


b


a


NH3-N, mg/100 ml
**
b


a


b


TVFA, mM/100 ml
** Means with different letters are significantly differed (P˂0.01)
Chamley (37) reported that there is a
reverse relationship between intake of
concentrate diet and ruminal pH. Increased
acids concentration in the rumen by the time
lead to reduce the pH until acids would
absorbed via rumen wall (38). The linear
increase in the ruminal pH at 6 hours post
feeding in a current study can be explained by
the fact that lambs were often moved to
consume straw after it finished its concentrate
meal. Taghizadeh, et. al., (24)
observed that addition of monensin to
the diet of lambs stabilized ruminal pH values
after 2 and 4 hours of feeding. Stability of
ruminal pH values nearby neutralization limit
as affected by addition of monensin have been
attributed to the decrease in the number of LA
producing bacteria, while those which
ferment LA as a substrate are still active (5).
In consistent with a current study,
Hassan and Saeed (39); Hadi (40) and Al-
Shemary and Saeed (41) reported similar
result. In later two studies, values of the
ruminal pH in samples withdrawn 3 hours
post feeding were significantly (P˂0.01)
decreased to 6.48 and 5.80 as compared with
7.51 and 7.18 in samples withdrawn before
feeding for those studies respectively.
However, inconsistently, a significant
increase (P˂0.01) to 6.86 and 6.26 was
recorded by those workers in samples
withdrawn at 6 hours post feeding. No
significant difference in ruminal pH was seen
in a current study between samples withdrawn
3 and 6 hours post feeding.
Regarding ruminal concentration of
NH3-N, results revealed that higher (P˂0.01)
value of 9.52 mg/100 ml was detected in
samples withdrawn before feeding. This may
be due to the effect of consuming roughage
throughout the night and early morning. In
this case, large quantities of saliva would
excreted to moisten rough materials and
facilitating swelling.
Ruminal concentration of NH3-N was
decreased (P˂0.01) in samples withdrawn at 3
hours post feeding to 7.44 mg/100 ml. This
decrease can be explained on basis of
supplying rumen microbes with energy
through morning meal of concentrate diet.
This additional energy stimulates
incorporation of ammonia produced from
degradation of protein, non-protein nitrogen
and recycled urea into microbial protein, or be
utilized by rumen microbes which prefer
ammonia as a N source for metabolic activity
(42). Moreover, monensin plays an important
role in reducing ruminal degradation of
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
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protein and deamination of amino groups
from amino acids. Taghizadeh, et. al., (24)
confirmed that feeding monensin containing
diets resulted in low ruminal concentration of
NH3-N due to the decrease of proteolytic
bacterial activity and increased flow of
protein into small intestine.
Results of a current study also showed
that there was a significant (P˂0.01) decrease
in ruminal concentration of NH3-N to 3.09
mg/100 ml in samples withdrawn 6 post
feeding. This may be due to more
incorporation of ammonia N in microbial
protein synthesis. Al-Shemary (19)
demonstrated that a decrease in ruminal
concentration of NH3-N refers to the improve
of utilization of dietary N due to increase
microbial protein synthesis. In addition to the
inhibition effect of monensin on ruminal
degradability of protein and deamination of
amino groups from amino acids resulted from
a decrease in the number of proteolytic
bacteria and urease activity (43). Lower
ruminal concentration of NH3-N may
associate with high sensitivity of ammonia
producing bacteria to monensin (44), (45).
The negative effect of monensin on
protozoan activity and recycling of bacterial
N proposed by Jouany (46) may explain the
lower ruminal concentration of NH3-N
detected in samples withdrawn 6 hours post
feeding. Hussian and Saeed (47) obtained
similar trend of diurnal changes in ruminal
concentration of NH3-N, there was a
significant (P˂0.01) decrease from 12.10 to
10.66 mg/100 ml in samples withdrawn 3 and
6 hours post feeding respectively. In another
study, Hadi (40) found that ruminal
concentration of NH3-N was significantly
(P˂0.01) decreased from 7.57 to 6.65 mg/100
ml in samples withdrawn 3 and 6 hours post
feeding respectively. The difference in the
levels of ruminal concentration of NH3-N
between both studies may be due to basic diet,
concentrate to roughage ratio, level of
additives and how samples of rumen liquid
were taken. In the first study reed silage
prepared with addition of urea at 1 and 2%
was used as a roughage, then degradation of
dietary protein was probably occurred in
addition to the rapid dissociation of urea.
Regarding diurnal changes in ruminal
concentration of TVFA, higher (P˂0.01)
value was detected in samples withdrawn 3
hours post feeding, whereas lower value was
detected in samples withdrawn before
feeding, values were 15.26 and 10.35
mM/100 ml respectively. In those withdrawn
6 hours post feeding, a significant (P˂0.01)
decrease was detected in ruminal
concentration of TVFA to 11.58 mM/100 ml.
The lower ruminal concentration of
TVFA in samples withdrawn 3 hours post
feeding was probably resulted from the slow
degradation of structural carbohydrates
presented in roughages, which its ruminal
fermentation is rarely completed. While, rapid
fermentation of soluble carbohydrates
presented in the concentrate diet offered to
lambs at morning would increase ruminal
concentration of TVFA. Resende-Junior, et.
al., (48) confirmed that the intake of rich
carbohydrate diets may increase ruminal
concentration of TVFA and decrease pH.
Such case may occurred in a current study
since ruminal pH was significantly (P˂0.01)
decreased 3 hours post feeding. Kim, et. al.,
(49) mentioned to the reverse relationship
between ruminal concentration of TVFA and
pH. The decrease in ruminal concentration
of TVFA in samples withdrawn hours post
feeding may be due to the absorption of those
acids via rumen wall by simple diffusion or as
negative ions. Ruminal concentration of
TVFA is a result of production and absorption
of these acids (50). The increase in ruminal
concentration of TVFA is associated with the
improve of ruminal microbial activity,
especially that of cellulolytic bacteria, higher
crude fiber degradation and absorption of
VFA via rumen wall, it may also associate
with the improve of rumen condition
including stability of pH at levels that support
better microbial fermentations (51).
Al-Shemary (19) reported similar trend
in diurnal changes of ruminal concentration of
TVFA. In his study, higher (P˂0.01) value of
15.42 was detected in samples withdrawn 3
hours post feeding as compared with 7.35
mM/100 ml which detected in samples
withdrawn before feeding. In that study,
Kufa Journal For Veterinary Medical Sciences Vol. (11) No. (2)  2020
8
ruminal concentration of TVFA in samples
withdrawn 6 hours post feeding was 16.61
mM/100 ml. Figure 1 shows the diurnal
changes in rumen fermentation
characteristics.
Figure 1: The diurnal changes in rumen fermentation characteristics
Conclusions
Addition of monensin to the diet of lambs
enhance rumen fermentation characteristics
particularly, at higher levels of 30 and 45
mg/kg concentrate diet as evidenced by low
ruminal ammonia and high volatile fatty acids
concentrations.
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