Livestock operations have shifted from small farms to
industrial facilities. Industrialized farms have benefits with improved
the efficiency of animal management however there are problems with
these operations, such as infectious disease and waste disposal. In the
case of waste disposal, especially odors such as ammonia (NH3) and
hydrogen sulfide (H2S) are problematic on farms. NH3 and H2S emissions
can have severe negative effects on farm workers, such as chronic or
acute pulmonary disorders, as well as on domestic animals like swine and
poultry. Probiotics are a potential solution for this critical problem. Bacillus
-based probiotics complex are generally recognized as useful
microorganism to decrease the malodor and enhance the growth performance
in livestock. Various studies of dietary supplementation with Bacillus
have been conducted on monogastric animals. The dietary supplementation of Bacillus
spp. showed several beneficial effects in swine as follows; the
reduction of noxious gases (NH3, H2S and mercaptan) emission, and the
improvement of growth performance parameters such as average daily gain,
average daily feed intake and feed conversion ratio. It has been
reported that feed supplementation with Bacillus
spp. was definitely effective to improve the growth performance and egg production quality in chickens. Moreover, NH3 and H2S emissions from poultry manure were dramatically decreased after dietary Bacillus
spp. supplementation. Some authors have suggested that the beneficial effects of Bacillus
supplementation may be boosted by the addition of other probiotics, such as Lactobacillus
spp. However, probiotics have a disadvantage as feed additives, namely
the inconsistency in results caused by variation in dietary
compositions, dose levels, strains, and environmental factors.
Additional studies of complex probiotics are needed to find appropriate
combinations of microbial sources, that satisfy both odor reduction and
growth performance requirements in monogastric animals.
Keywords: Odor; Gas emission; Bacillus
; Ammonia; Hydrogen sulfide; livestock
Abbreviations:
ADG: Average Daily Gain; ADFI: Average Daily Feed Intake; FCR: Feed
Conversion Ratio; DFM: Direct Fed Microbial; DM: Dry matter; CP: Crude
Protein; EE: Ether Extract; CF: Crude Fiber; GE: Gross Energy; ME:
Metabolic Energy; PKM: Palm Kernel Meal
Livestock operations have transitioned over time from
small farms to industrial facilities. Industrialized farms have
improved the efficiency of animal management. However, there are
problems with these large-scale operations, such as infectious disease
and waste disposal [1]. Waste disposal can cause environmental issues,
including soil erosion and the production of global greenhouse gases and
air pollutants [2,3]. In terms of air pollutants, various emissions such as ammonia (NH3), hydrogen sulfide (H2S), methane (CH4), nitrous oxide (N2O),
volatile organic compounds (VOCs), and other odors are released from
livestock production facilities [4]. These emissions are not only a
nuisance to people living in nearby residential areas [5] but can also
result in health problems for farm workers. Ammonia and H2S have shown critical negative effects on farm workers,
including chronic or acute pulmonary disorders, as well as on domestic animals like swine and poultry.
Ammonia is generated from livestock barns, open
feedlots, and manure storage facilities on farms, as well as during
manure handling, treatment, and spreading. Ammonia dissolves readily in
water (e.g., swine urine and drinking water) where it ionizes to form an
ammonium ion. The atmospheric pressure and temperature affect ammonia
solubility in water from dissolved or suspended materials [6]. On the
other hand, ammonia produced in poultry facilities is created by urea
and uric acid degradation [7]. Another source of odor in livestock production is H2S,
which has been recognized as harmful to humans, and animals in deep-pit
production systems [8,9]. Hydrogen sulfide is formed under anaerobic
conditions by bacteria reducing sulfate to sulfide;sulfide then combines
with hydrogen ions to form hydrogen
sulfide [10]. Pigs are affected by different levels of hydrogen
sulfide. Severe distress, eye irritation, and drooling can be caused
by concentrations of 100 ppm. Pigs exposed to 250 ppm of H2S
may exhibit cyanosis, convulsions, and death [11]. Farm workers are also affected negatively by hydrogen sulfide
exposure. Humans can detect a smell like rotten eggs when
exposed to 0.1 to 5 ppm of H2S, even though these levels are not
toxic. Eye and respiratory irritation in humans can occur at H2S
levels of 100 ppm. High levels of H2S, (e.g., 150 to 200 ppm) cannot
be detected by humans due to olfactory paralysis. At levels >200
ppm, H2S affect the nervous system and levels >1,000 ppm result
in immediate collapse and respiratory paralysis [12].
There are several possible solutions to mitigate the
environmental pollution from animal housing. Excretion of
nitrogen and phosphorus can be reduced by formulating diets
that improve nutrient digestibility [13]. Feed utilization and dry
matter intake can be improved by fine grinding and pelleting,
which reduce the size and increase the surface area of grains,
thereby increasing the potential for interaction with digestive
enzymes [13]. Enzymes can also be used to increase nutrient availability
in animal feed. Enzymes can supplement the host’s endogenous
enzyme production, increasing the availability of nutrients,
improving the digestibility of fibrous material, and decreasing
any anti-nutritional factors present in feed ingredients [14]. For
example, protease can degrade protein sources such as soybean
meal and improve protein digestibility [13]. Other indirect
contributors to improving swine house environments include
antibiotics, probiotics, and organic acids. Low crude protein
formulations using synthetic amino acids can also be used to
reduce N excretion. Probiotics can protect young animals against enteropathogenic
disorders and improve growth performance [15]. Studies
have shown that probiotics can create a gastrointestinal tract
environment that is unfavorable to pathogenic growth [16].
Probiotics can decrease intestinal microbial catabolism and have
a protein sparing effect, leading to reduced nitrogen flows [17]. A number of Bacillus
strains could be used for feed additive
in livestock industry. Bacillus
are aerobic or facultative anaerobic,
gram-positive, rod-shaped, and spore-forming bacteria. The
spore-forming habit of Bacillus
is highly beneficial for long term
storage without a loss of activity, compared with non-sporeforming
bacteria. Spores also have the ability to survive low pH,
harsh environments, meaning their probiotic properties can
benefit the small intestine [18].
Bacillus
in swine can help to improve gut health and immunity
for piglets and reduce environmental pollutants such as odor gas
emissions from pig manure [19]. Upadhaya et al. [20] proposed that
the reduction of fecal NH3 emissions was observed when Bacillus
including Bacillu including
feed was supplied to pigs, suggesting the improvement
of nutrient digestibility by probiotics. However, Wang et al. [21]
reported that it has no influence to enhance nutrient digestibility
but indicates the effectiveness for the reduction of slurry NH3
emissions. The roles of Bacillus
in poultry are similar to those in swine.
Various effects have been observed in poultry fed with Bacillus,
including histological changes in the intestine of broilers,
increased villus height and villus height to crypt depth ratio,
improved nutrient digestibility and absorption capacity of the
small intestine [22], reduced digesta viscosity caused by soluble
non-starch polysaccharides (which affect nutrient availability and
absorption) [23], improved quality of meat and eggs [24], and
reduced NH3 emissions from manure [25].
Ammonia and hydrogen sulfide are negative substances
on farm workers as well as animals in swine production and
cause environment pollution [26]. Nguyen et al. [27] found
that the supplementation of Bacillus
-containing feed showed
an advantageous effect to decrease NH3 emissions but have no
effect on the reduction of other gases (H2S and mercaptan). A
recent study [27], showed that the addition of the increase in
Lactobacillus
inhibited pathogenic microorganisms and improved
nutrient digestibility, resulting in reduced fecal NH3 emissions. Growing pigs fed diets with Bacillus
licheniformis and Bacillus
subtilis for 15 weeks, showed improved performance and reduced
gas emissions due to increased fecalLactobacillus
counts and improved utilization of sulfur-containing amino acids [28]. It was
concluded that the increase in Lactobacillus
reduced intestinal pH through the production of organic acids, and that the bacitracin
(bacteriocin) secreted by B. licheniformis inhibited the microbes
that produce urease, thereby reducing NH3 gas emissions. These
results are supported by our research data, which showed that
pigs fed diets with B. subtilis complex probiotics produced
lower NH3 and H2S emissions after a three-week growing period
(unpublished data). These results suggest that three weeks of
feeding is needed for probiotic adherence in the gut to have
positive effects in swine.
According to Balasubramanian et al. [29], when probiotics
containing Bacillus
coagulans, B. licheniformis, and B. subtilis were
fed to growing and finishing pigs over 16 weeks, no reduction in
fecal noxious gas (NH3, H2S) emissions was observed. Yan et al. [30]
found that increased nutrient digestibility reduced the substrate
for microbial fermentation in the large intestine, which resulted
in a decrease in fecal gas emissions. Chen et al. [31] showed
that dietary Bacillus
supplementation decreased NH3 emissions,
however, other odor substances such as H2S and mercaptan did
not decrease. Bacillus
spp. as probiotics can also affect the production of
malodorous substances such as skatole. Skatole is a malodorous
compound in meat and fecal that causes an off-flavor, so called
“boar taint” [32]. Sheng et al. [33] demonstrated that dietary B.
subtilis natto and B. coagulans supplementation decreased the
skatole content of meat and feces. Doerner et al. [34] found that
the reduced number of Clostridium in the feces of pigs fed Bacillus
spp. was consistent with a lower skatole concentration in the
meat and feces; Clostridium in feces is involved in the conversion
of tryptophan to skatole.
Nguyen et al. [27] reported that dietary supplementation
with probiotics-based Bacillus
in weaning pigs linearly improved
average daily gain (ADG) and average daily feed intake (ADFI) on
days 0 to 7 of the experiment, as well as ADG and feed conversion
ratio (FCR) on days 8 to 21. According to research by Lan et al.
Kim et al. [28], dietary supplementation with B. licheniformis and
B. subtilis complex probiotics (Bioplus YC) in growing pigs for 15
weeks resulted in improved growth performance in some periods
but there was no significant difference from the control over the
study period as a whole. The reasons for improved performance
may be explained by changes in intestinal microorganisms and an
increase in the secretion of digestive enzymes. Hu et al. [35] observed that the ADG and FCR of piglets were
improved and diarrhea occurrence was reduced when weaning
pigs were fed B. subtilis KN-42 for 26 days. Greater bacterial
diversity in the intestinal environment indicated an increase in
the relative number of Lactobacillus
and reduction in the relative
number of E. coli in the feces. Wang et al. [21] also reported that
ADG tended to increase linearly and ADFI increased as the levels of
probiotic (Bioplus 2B®) increased, however, no linear or quadratic
effects were observed in FCR. In growing and finishing pigs, dietary direct-fed microbial
(DFM) supplementation has been shown to have negative effects
on growth performance. Growing and finishing pigs have better
digestibility, improved immunity, and increased resistance to
intestinal disorders [36]. Balasubramanian et al. [29] reported
that dietary supplementation of three probiotic Bacillus
strains
(B. coagulans, B. licheniformis, and B. subtilis) did not show
a positive effect on the ADG and FCR without affecting ADFI
in growing and finishing pigs. Upadhaya et al. [37] reported
that there were significantly effective to ADG and ADFI, when
two probiotic complexes (B. licheniformis and B. subtilis) was
supplied to growing and finishing pigs as feed additive during the
experimental period.
According to Patarapreech et al. [38], both types of probiotic
additives (Bacillus
subtilis + Sanizyme®) improved the nutrient
utilization of feed components [dry matter (DM), crude protein
(CP), ether extract (EE), crude fiber (CF), and gross energy (GE)]
in the starter and grower periods, as well as growth performance
(ADG, ADFI, FCR). Such improvements in nutrient digestibility
may be due to the enzymes secreted by Bacillus
spp., such as
lipase, cellulose, amylase, and protease [39].
The results of probiotic complex supplementation are not
consistent. The use of Bacillus
-based probiotics in diets fed to
finishing pigs did not affect ADG, FCR [40], ADFI, and FCR [31].
Davis et al. [39] also reported that two probiotic Bacillus
strains
(B. licheniformis and B. subtilis) were ineffective in improving
the growth performance in growing and finishing pigs, when they
were supplied in feed during test period. Moreover, Sheng et al. [32] also found that the dietary
supplementation of two probiotic complex (B. subtilis natto
and B. coagulans) did not show a remarkable improvement of
growth performance in growing pigs, but indicate dramatical
effects in terms of meat quality, antioxidant function, and the
skatole content of meat. The effects of Bacillus
-based probiotics
are influenced by a variety of factors, (e.g., age of the pigs, diet
composition, differences in strains of bacteria, dosage levels, and
breeding environment) [41].
Growing pigs fed a diet with 10% palm kernel meal (PKM)
and added probiotics (B. subtilis and Saccharomyces cerevisiae),
showed a reduction in fecal NH3, total mercaptans, and H2S content
[42]; pigs fed a diet without PKM produced less mercaptans than
pigs fed diets with PKM. The addition of probiotics to a non-PKM
diet had a significant effect on ADG and FCR, but the addition of
probiotics to a diet with PKM did not have a positive effect on
performance. These results may be due to the presence of nonstarch
polysaccharides in PKM creating a viscous environment in
the gut.
Chen et al. [43] found the dietary supplementation of three
probiotic complex (Lactobacillus
acidophilus, S. cerevisiae, and B.
subtilis) enhance ADG, when it was provided to the growing pigs
for six weeks. In addition, fecal NH3-N excretion was reduced when
pigs were fed a probiotic complex, however, there was no effect on
volatile fatty acid (VFA) production. Chen et al. [31] reported that
dietary supplementation probiotics combination (B. subtilis, B.
coagulans, and L. acidophilus) in finishing pigs reduced fecal NH3-N
production and improved ADG, however, there was no effect on
ADFI or FCR. In their study, digestibility of N was not increased,
therefore, the reduction in fecal NH3-N may not have resulted from
nutrient digestibility but rather changes in intestinal microflora.
In the poultry industry, Bacillus
spp. probiotics are widely
used. A reduction in NH3 gas emissions from excreta was observed
for poultry fed metabolic energy (ME)- and crude protein (CP)-
reduced diets [44]. Poultry fed probiotic-supplemented diets also
showed reduced NH3 gas emissions compared with those fed diets without probiotics. Decreasing the CP content of the feed reduces
the amount of synthetic amino acids supplied, thereby reducing
the amount of N that is excreted by the poultry [45]. In addition,
the feeding of probiotics can lead to increased nutrient utilization
and changes in the balance of intestinal microorganisms, which
can reduce NH3 gas emissions. According to research by Jeong et al. and Kim et al. [25], broilers
fed a diet supplemented with B. subtilis C-3102 for five weeks,
showed a reduction in NH3 due to an increase in the number of
Lactobacillus
and reduction in the number of pathogenic bacteria.
However, there were no effects on H2S, mercaptan, or acetic acid
production. Ahmed et al. [46] reported that the supplementation of feed
containing Bacillus
amyloliquefaciens showed the effect of NH3
reduction in feces during raising term. The observed reduction
in NH3 emissions from broiler excreta may be due to increased
nutrient utilization and changes in intestinal microbiota. Another
reason is that B. amyloliquefaciens reduced the pH of the feces. A
reduced concentration of E. coli and improved utilization of sulfur
amino acids in the intestine could reduce the conversion of fecal
ammonium to volatile ammonia. Tang et al. [47] indicated that inclusion of B. amyloliquefaciens
product in laying hens reduced NH3 production in a six-week
feeding trial; the number of cecal Lactobacillus
was increased,
but the number of E. coli and Salmonella bacteria and NH3 gas
emission was reduced.
The use of antibiotics in the poultry industry to control
pathogenic infections, such as necrotic enteritis, has been banned
in some places due to concerns about consumer safety. In such
cases, Bacillus
spp. have been used to improve performance
through positive changes in intestinal microbiota. Bacillus
subtilis was added to a ME- and CP-reduced diet to
evaluate the effects of probiotic supplementation related to energy
and protein [44]. Poultry fed diets with reduced energy and protein
content showed a decreased in ADG and FCR. However, animals
fed diets with probiotics showed significant improvements in ADG
and FCR in the growing and finishing periods. These performance
improvements did not appear immediately; three weeks were
required for normal enzyme production that produced effects. A recent study by Jeong et al. & Kim et al. [25] found that
broilers fed a diet with B. subtilis C-3102 showed improved ADG
and FCR, however, there was no effect on meat quality. In this
study, Lactobacillus
counts in the cecum, ileum, and excreta were
significantly increased, and E. coli counts in the cecum and excreta
were decreased with dietary B. subtilis supplementation. Ahmed et al. [46] reported that ADG, ADFI, and FCR were
improved when broilers were fed a diet with a B. amyloliquefaciens
probiotic; serum IgG and IgA were also increased. Tang et al. [47] reported that laying hens fed a diet with B. amyloliquefaciens
commercial product for six weeks had better egg production,
eggshell strength, and eggshell thickness than hens that received a
non-supplemented diet. Bacillus
amyloliquefaciens has the ability to produce
extracellular enzymes, such as cellulose, α-amylases, protease,
and metalloproteases. Those enzymes can help to increase
the efficiency of digestion and absorption of nutrients [48].
Bacillus
amyloliquefaciens also produce bacteriocins, such as
subtilin, which have antibacterial effects against pathogenic
microorganisms [49].
Probiotics have been used to reduce NH3 emissions, improve
performance, and maintain livestock product safety in the poultry
industry, most commonly with a Bacillus
spp. complex. In one study,
a combination of Pichia guilliermondii, B. subtilis, and Lactobacillus
plantarum, at a ratio of 1:2:1, reduced NH3 gas emissions by 46%
in vitro test [50]. This probiotic complex significantly decreased
crude protein digestibility, pH, NH3-N, urease, and uricase activity.
Furthermore, the number of microorganisms responsible for
fermenting carbohydrates to produce short chain fatty acids was
increased.
In conclusion, dietary Bacillus
spp. probiotic supplementation
in monogastric animals can reduce NH3 and H2S production
depending on the conditions. In terms of performance, there
were various effects of supplementation level, viability, and
composition of probiotic species, diet formulation, age of animals,
livestock house environment, and so on. Nutrient digestibility can
be improved by the enzymes or bacteriocin produced by Bacillus
spp. In addition, supplementation with Bacillus
spp. can help reduce
fecal odor production, gas emission, and improve the performance
of monogastric animals. Additional studies of complex probiotics
that satisfy both odor reduction and performance requirements
for monogastric animals are recommended.
