Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous Forage in Ruminant

Abstract

Ruminant feeding efficiency will always be an important research topic. Thus there is a need to enhance the digestibility of poor-quality fibrous forages due to their lignified cell walls that restrict nutrient availability. A potentially cost-effective means of improving nutrient availability is by supplementation with exogenous enzymes. This chapter explores the influence of exogenous enzymes added to fibrous forages on the nutritive value of diets for ruminants. The sources of exogenous enzymes and their role in improving the utilization of animal feeds are discussed. Moreover, the effects of exogenous enzyme supplementation on ruminal degradation, microbial protein synthesis, and nutrient digestibility were reviewed, together with their effects on animal growth performance, milk yield and the quality of milk and meat.KeywordsExogenous enzymeFiber digestibilityProductivityNutritive value

Full text

45
Effects of Exogenous Enzymes on the
Nutritive Value of Some Fibrous Forage in
Ruminant
AbdelfattahZeidanMohamedSalem,
MonaMohamedMohamedYasseenElghandour, MoyosoreJosephAdegbeye,
JavierHernándezMeléndez, JoséLuisPonce- Covarrubias,
andPedroEnriqueHernándezRuiz
Abstract Ruminant feeding efciency will always be an important research topic.Thus
there is a need to enhance the digestibility of poor-quality brous forages due to their
lignied cell walls that restrict nutrient availability. A potentially cost-effective means of
improving nutrient availability is by supplementation with exogenous enzymes. This
chapter explores the inuence of exogenous enzymes added to brous forages on the
nutritive value of diets for ruminants. The sources of exogenous enzymes and their role
in improving the utilization of animal feeds are discussed. Moreover,the effects of exog-
enous enzyme supplementation on ruminal degradation, microbial protein synthesis,
and nutrient digestibility were reviewed, together with their effects on animal growth
performance,milk yield and the quality of milk and meat.
A. Z. M. Salem (*) · M. M. M. Y. Elghandour
Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma del Estado de México,
Toluca, Estado de México, Mexico
M. J. Adegbeye
Department of Animal Production and Health, Federal University of Technology,
Akure, Nigeria
J. H. Meléndez
Facultad de Ingeniería y Ciencias, Universidad Autónoma de Tamaulipas,
Centro Universitario “Adolfo López Mateos” Cd Victoria Tamaulipas, Mexico
J. L. Ponce-Covarrubias · P. E. H. Ruiz
Escuela Superior de Medicina Veterinaria y Zootecnia No. 3, Universidad Autónoma de
Guerrero, Tecpan de Galeana, Mexico
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2023
A. Z. M. Salem et al. (eds.), Exogenous Enzymes as Feed Additives in
Ruminants, https://doi.org/10.1007/978-3-031-27993-5_3

46
1 Introduction
Many local plant species are undervalued as forages for ruminants, because of inade-
quate knowledge on their nutritive value, especially the ber content and level of antinu-
tritional factors, which can limit feed efciency and overall animal performance. The
prociency with which ruminants acquire energy from diets comprising complex plant
polysaccharides has been an enduring important research question. Improvements in
the efciency of feed use may enable ruminants to produce more and better-quality
meat and milk, thereby contributing to meeting the ever- increasing demands of food for
the increasing human population. Considering the economy of food production from
animals and their physiological requirements to maintain rumen health, forage consti-
tutes the major bulk of ruminant diets (Krause etal. 2003). However, the conditions
within the rumen for effective ber digestion are often suboptimal, leading to poor
digestibility of forage cell walls, which in turn limits nutrient availability to the animal.
The use of exogenous enzymes is regarded as an inexpensive method of enhancing
feed conversion efciency (Krause etal. 2003). There has been a considerable amount
of published research on benecial effects of using exogenous enzymes to improve feed
efciency, nutrition, and productivity in ruminants (Krause etal. 2003; Beauchemin
and Holtshausen 2010). The application of brolytic enzymes in ruminants feed often
results in boosting ber digestion and improving intake of feed invivo. Also, they have
been reported to increase yield and better composition of milk (Gado etal. 2009).
Exogenous brolytic enzyme treatment resulted in increased milk production
efciency in early lactation of dairy cows (Holtshausen etal. 2011). Arriola et al.
(2011) ascribed the improvement in feed efciency to a rise in the total gastro-
intestinal tract digestibility without a change in ruminal degradability. Holtshausen
etal. (2009) ascribed the increase in milk production efciency to an increase in
ber digestibility (based on invitro assay) of dietary forages. However, responses to
ruminal fermentation were not investigated in that study. It is apparent that exoge-
nous enzymes added to brous, poor-quality forages, or crop residues can be prac-
ticed in animal feeding without compromising the energy intake and milk production.
A prepared exogenous enzyme mixture of polysaccharidases (ZADO®), obtained
from anaerobic bacteria, was reported to increase nutrient digestibility, N balance
and ruminal fermentation, and milk yield of cows receiving diets based upon crop
residues and by-products (Gado etal. 2009). Salem etal. (2011) found higher feed
efciency, average daily gain, in goat and sheep fed on wheat straw.
The purpose of this chapter is to elucidate the benet of using exogenous enzymes
on some brous feed ingredients fed to ruminants.
2 Denition ofExogenous Enzymes
Exogenous enzymes are enzyme productsthatcan be used to supplement animal feeds
to enhance the digestion process. Examples of exogenous enzymes include cellulases
(hydrolyzing cellulose), proteases (hydrolyzing proteins), and amylase (hydrolyzing
starch). Recent advances in biotechnology, which makes enzyme production cost-effec-
tive, have led to a wide range of enzyme products becoming available. With
A. Z. M. Salem et al.

47
improvements in knowledge of rumen functioning and techniques for evaluating enzyme
activity, interest in the use of exogenous enzyme products in ruminant production sys-
tems has increased (Sujani and Seresinhe 2015). Exogenous enzymes used in ruminant
diets can be mainly categorized as proteolytic, amylolytic, and brolytic enzymes,
depending on the substrate on which the enzyme acts (Sujani and Seresinhe 2015).
The aim of supplementing ruminant diets with exogenous enzymes is to improve
the digestibility of the dietary plant cell walls, and consequently improve the ef-
ciency of feed utilization. Having knowledge of the complexity of the rumen eco-
system and understanding the nature of interactions between rumen microbes and
plant cell walls is key for efcient use of exogenous enzymes in enhancing the uti-
lization of feeds by ruminant (Meale etal. 2014).
The use of invitro methods to screen exogenous enzymes offers a fast and inex-
pensive way to evaluate a large number of different products with various substrates
and could be applied for prediction of possible invivo responses (Jalilvand etal.
2008). However, invivo animal trials measuring production responses to different
known doses of exogenous enzymes represent the nal proof of the benecial
effects of enzyme supplementation of animal feeds.
3 Sources ofExogenous Enzymes
The exogenous enzymes used to enhance the nutritive value of ruminant feeds are
mostly sourced from microbial cultures involving four bacterial species and three
fungal species, in addition to some yeasts. The main processes used to produce the
enzymes are submerged fermentation, in which the substrates and other nutrients
are in liquid form, and solid-state fermentation, which use solid substrates associ-
ated with low levels of moisture being present; several other biotechnological meth-
ods are also involved (Sujani and Seresinhe 2015). The exogenous brolytic
enzymes are classied according to the specic substrates upon which they act. The
enzyme cellulase hydrolyzes the plant cell wall ber to cello-oligosaccharides, cel-
lobiose, or glucose with a collective activity of three enzymes, including exogluca-
nase, β-glucosidase, and endoglucanase (Zhang and Lynd 2004). Xylanase
hydrolyses 1,4-β-D-xylosidic linkages in xylans found in the structural component
of plant cell walls, generally known as hemicellulose. The group of xylanolytic
enzymes includes endo-β-1,4-xylanase (EC 3.2.1.8, 1,4-β-D xylanxylanohydrolase)
that breaks the main chain of xylans, β-D-xylosidase (EC 3.2.1.37,
1,4-β-xylanxylohydrolase) that hydrolyzes xylo-oligosaccharides to D-xylose, as
well as a selection of debranching enzymes such as acetyl esterases, α-glucuronidases,
and α-L-arabino-furanosidases (Kamble and Jadhav 2012).
Most enzymes used in the livestock industry are obtained from the bacteria,
Enterococcus faecium spp., Lactobacillus plantarum, L. acidophilus, and Bacillus
subtilis and the fungi, Trichoderma reesei and Aspergillus oryzae (McAllister etal.
2001). The enzymes are produced by microbial fermentation that starts with a
growth media and a seed culture. The activity and types of enzymes generated vary
based on the conditions and substrates used for the culture and the selected strain of
the microbes (Lee etal. 1998).
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

48
A wide range of enzymes are required for the degradation of complex structural
carbohydrates that comprise plant cell walls (Morgavi etal. 2013). Although con-
ventional enzymes are mainly xylanases or cellulases, secondary enzymes, such as
proteases, esterases, pectinases, and amylases, are normally present, since the prep-
arations rarely comprise only a single pure enzyme (McAllister etal. 2001). This
diversity is benecial since several substrates could be targeted with a single prod-
uct. Degradation of hemicellulose and cellulose alone needs several glycosidic
hydrolases (Krause etal. 2003) and alterations in the activity of specic enzymes
and their relative proportions affect the overall efciency of degradation of the for-
age cell wall (McAllister etal. 2001). Research results indicate that a mixture of
enzymes developed for enhancing the digestibility of a particular diet is better than
targeting a specic enzyme for a particular feed (Beauchemin et al. 2003). The
inclusion of exogenous enzymes in feeds without considering the relevant substrates
could lead to a variation in results. Highly variable results of enzyme supplementa-
tion may discourage farmers from using enzymes in ruminant feeds (Table1).
Table 1 Summary of the effects of adding exogenous enzymes to ruminant feeds
Enzyme Dose Impact
Animal
species References
ZADO®a 10g/h/d OMb and DM
digestibility and live
weight
Growing
lamb
Valdes etal.
(2015)
ZADO®40g/h/d ADF and NDF
digestibility
Cows Gado etal. (2009)
ZADO®Not specied Fiber digestibility Ossimi male
lambs
Gado etal. (2011)
Celluase plus®2mL cellulase
per kg DMI
DM and NDF Alpine goats Rojo etal. (2015)
Cellulases Not specied OM, ADE and NDF
digestibility
Pelibuey
lambs
López-Aguirre
etal. (2016a)
Xylanase and
cellulase
0, 1, 3μL per
0.5g DM
OM digestibility In vitro López-Aguirre
etal. (2016b)
ZADO®0, 6, 12,
24mg/g DM
OM digestibility In vitro Elghandour etal.
(2013)
Xylanase and
cellulase
2g/h/d Nutrient digestion and
milk yield
Cows Yang etal. (1999)
ZADO®10g/h/d Growth performance Suffolk
lambs
Rivero etal.
(2012)
aZADO®: a commercial product comprising an enzyme mixture of cellulase, xylanase, protease,
and α-amylase
bOM organic matter, DM dry matter, ADF acid detergent ber, NDF neutral detergent ber, DMI
dry matter intake
Cellulase Plus®: a commercial cellulase product
A. Z. M. Salem et al.

49
4 Roles of Exogenous Enzymes in Improving Nutritive
Value of Animal Feeds
The use of exogenous enzymes as a feed additive has been shown to enhance the
nutritive value of tree foliage in animal feeds due to an increase in the degradation
of the dietary ber (Salem etal. 2015a). Salem etal. (2015a) reported that the appli-
cation of exogenous enzymes can improve the nutritive value of fodder trees used as
supplements in ruminant diet. The inclusion of exogenous enzymes can enhance the
number of bacteria, ber digestibility, and capabilities of rumen bacteria for degra-
dation of feed consumed by the animal. The supplementary enzymes may also help
to increase the availability of protein for microbial metabolism, thereby increasing
the amount of metabolizable energy and ber digestibility in the diet (Polderman
etal. 1955; Salem etal. 2012). The exogenous brolytic enzymes can work syner-
gistically with endogenous enzymes produced by the rumen microbes with a resul-
tant increase in the nutritive value and digestion of brous feeds (Morgavi
etal. 2001).
Dairy cows fed forages supplemented with exogenous enzymes had more dry
matter intake and produced 5–25% more milk than their counterparts receiving no
enzyme supplements (Gado et al. 2009). In feedlot cattle, exogenous brolytic
enzyme was successfully used to boost live weight gain by up to 16% (Salem etal.
2013). In lactating goats, exogenous enzyme supplementation resulted in an
increased yield of milk with a lower fat content (Stella etal. 2007). Titi and Lubbadeh
(2004) reported that exogenous enzyme supplementation increased milk yield and
milk fat and protein levels in lactating sheep, but in goats, enzyme supplementation
increased milk yield, but milk composition was not affected.
Application of exogenous enzymes phytases and nonstarch polysaccharidases is
very common in poultry diets and frequently used in swine rations. The bulk of
research carried out using these enzyme products in diets for poultry and pigs has
focused on the determination of their inuence on nutrient digestibility and/or ani-
mal performance (Bedford and Cowieson 2012).
5 Impact ofExogenous Enzymes
5.1 Fermentation ofFibrous Feeds
Considerable variation in responses to exogenous enzyme supplementation of feeds
on ruminal fermentation has been reported in literature. Many studies have reported
increases in diet digestibility after treatment of feeds with exogenous enzymes.
Arriola etal. (2011) observed a decrease in the acetate: propionate ratio in rumen
uid and an increase in total volatile fatty acid concentration. In contrast, increases
in the proportion of acetate in rumen uid following exogenous brolytic enzyme
supplementation have been reported by Gado etal. (2009) and Beauchemin etal.
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

50
(2000). However, Beauchemin etal. (1999) and Yang etal. (1999) found no effect
of exogenous brolytic enzymes on ruminal fermentation.
Pretreatment of total mixed ration with exogenous enzymes may help increase
the availability of nutrients to ruminal microbes, due to increased colonization and
attachment of microbes to feed particles (Wang etal. 2001). Fibrobacter succino-
genes, which is a fermentation product from primary digesters, can attract
Ruminobacter amylophilus and Selenomonasruminantium as secondary digesters
to attach to and colonize feed particles (Cheng and McAllister 1997). McGinn etal.
(2004) reported that supplementation with a proteolytic enzyme obtained from
yeast had no effect on enteric CH4 emissions from cattle receiving a diet based on
barley silage and barley grain. Arriola etal. (2011) examined the effects of exoge-
nous brolytic enzyme supplementation of high and low concentrate rations fed to
dairy cows. Using a fermentation balance approach to estimate methane production
from volatile fatty acid data, a reduction in methane production was observed in
cows receiving the high-concentrate diet. Results of invitro studies have shown that
enhancement in ber degradation by exogenous brolytic enzymes was often
accompanied by a decrease in acetate: propionate ratio in the fermentation uid
(Eun and Beauchemin 2005; Eun etal. 2007). Beauchemin etal. (2008) suggested
that exogenous enzyme feed supplements could assist in reducing emissions of
enteric CH4. However, increased enteric CH4 production with an increase in enzyme
dosage reported by Chung etal. (2012) reinforces the need for in vivo evaluation
with direct measurement of CH4 emissions. An increase in CH4 production with
increasing enzyme dosage implies that more energy was lost in form of CH4 during
ruminal fermentation. This suggests that if enzyme supplementation increases rumi-
nal nutrient availability, methane production would be increased (Zhou etal. 2011).
The increase in feed efciency is perhaps due to a change in the microbial commu-
nities in response to enzyme supplementation (Holtshausen etal. 2011). Using the
same enzyme preparation and diet, Zhou etal. (2011) observed that enzyme supple-
mentation had no effect on the overall microbe population size, although the relative
activities of individual methanogen species was altered. A detailed study is required
to investigate the long-term effect of exogenous brolytic enzyme on rumen fer-
mentation characteristics and enteric CH4 production.
5.2 Nutrient Digestibility
The incorporation of a high proportion of grain into ruminant diets decreases ber
digestion because of poor brolytic enzyme activity in the rumen, caused by seem-
ing preference of rumen microbes for different feed structures like nonstructural
carbohydrates and depression in rumen pH (Nozière etal. 1996; Faniyi etal. 2019).
This may bring about conditions in which addition of exogenous enzymes could be
advantageous (Vallejo etal. 2016). Rumen microbial enzymes can work synergisti-
cally with exogenous brolytic enzymes to increase the digestibility and nutritional
value of brous feeds (Morgavi etal. 2001).
A. Z. M. Salem et al.

51
Following exogenous enzyme supplementation, Arriola et al. (2011) associated
the enhanced feed utilization efciency with increased total-tract digestion, since
ruminal degradability, measured in sacco, was not affected. Gado et al. (2009)
investigated the effect of the multienzyme preparation, ZADO®, added to a total
mixed ration of dairy cows on nutrient digestion. They reported an 8–16% higher
digestibility of acid detergent ber, neutral detergent ber, dry matter, and organic
matter compared with values obtained from those receiving the control treatment
(no enzyme added). Table2 shows data from Gado etal. (2009), indicating the inu-
ence of enzyme supplementation on intake, digestibility, nitrogen balance and rumi-
nal characteristics.
Using Ossimi male lambs, Gado etal. (2011) investigated the effect on growth
performance and digestion of ensiled orange pulp (EOP) supplementation of feed
with or without ZADO® exogenous enzyme product. They reported lower nutrient
digestion in the EOP treatment compared with the EOP plus ZADO® treatment.
Digestibility of dry matter, acid detergent ber (ADF), and neutral detergent ber
(NDF) was increased by 18, 47, and 93%, respectively, in lambs fed with EOP plus
ZADO®. The feed conversion efciency was increased by 31% and 19% in lambs
on the EOP plus ZADO® and EOP treatments, respectively, compared with the
lambs on the control (unsupplemented) treatment. Compared with the lambs on the
control treatment, liveweight gain increased by 54% in the EOP lambs and by 92%
in EOP plus ZADO® lambs. Nevertheless, dry matter intake was low in all treat-
ment groups.
Gado etal. (2009) studied the effects of supplementing a total mixed ration based
on maize silage and cereal concentrate with exogenous brolytic enzymes on milk
yield and composition in dairy cows. Enzyme supplementation generallyinduced
changes in ruminal volatile fatty acid concentrations. The total short chain fatty acid
concentrations were increased by 7.4%, acetate concentration by 6.7% and propio-
nate by 13.7%. Consequently, the acetate: propionate ratio was reduced by 6.5%. In
addition, enzyme supplementation increased ruminal microbial nitrogen synthesis.
Using Alpine dairy goats, Rojo etal. (2015) reported that supplementing diets with
an exogenous cellulase preparation (Celluase Plus®) increased dry matter intake
and digestibility of dry matter, neutral detergent ber and organic matter compared
with the unsupplemented diet. López-Aguirre et al. (2016a, b) investigated the
effect of exogenous cellulase (Cellulase Plus®) and its mode of administration on
nutrient digestibility in Pelibuey lambs. They reported that digestibility of acid
detergent ber, neutral detergent ber, organic matter, and dry matter when the
enzyme was administered either by incorporation in the feed or by direct oral dos-
age; the digestibility of crude protein was not affected. However, feed conversion
ratio and digestibility of acid detergent ber were improved only when the enzyme
was incorporated in the diet. Thus, the inuence of exogenous enzyme addition is
dependent to some degree on the method by which the enzyme is administered.
Data from previous studies reported by Valdes etal. (2015), Rojo etal. (2015), and
Salem etal. (2013) are summarized in Table3.
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

52
Table 2 Feed intake, digestibility, nitrogen balance, and rumen uid characteristics in dairy cows
fed with a total mixed ration (control treatment) and the total mixed ration supplemented with a
mixed enzyme preparation (ZADO®)- (Gado etal. 2009)
Control ZADO®aSEM P value
Intake (kg/d)
Dry matter 16.1 18.2 0.21 0.049
Organic matter 14.1 16.4 0.14 0.048
Neutral detergent ber 7.1 7.4 0.23 0.192
Acid detergent ber 4.04 4.57 0.111 0.087
Digestibility (g/kg)
Dry matter 663 743 2.1 0.045
Organic matter 667 741 2.9 0.047
Neutral detergent ber 418 584 2.8 0.049
Acid detergent ber 401 532 2.3 0.046
Nitrogen balance
N intake (g/d) 1654 1870 54.1 0.07
Urinary N (g/d) 509 542 12.6 0.11
Fecal N (g/d) 659 711 14.3 0.17
N balance (g/d) 468 617 11.9 0.06
Rumen uid characteristics
pH 6.1 5.9 0.24 0.41
Before feeding (0h)
Total short chain fatty acids
(mmol/L)
111 122 2.1 0.34
Individual SCFA (molar %)
Acetate (A) 61.0 64.8 1.30 0.05
Propionate (P) 17.8 18.1 0.83 0.13
Butyrate 11.3 11.9 0.81 0.24
Acetate: Propionate ratio 3.43 3.85 1.162 0.14
Ammonia N (mg/L) 55 67 0.37 0.04
Post feeding (3h)
Total short chain fatty acids
(mmol/L)
119.2 128 3.6 0.04
Individual SCFA (molar %)
Acetate (A) 60.0 64.0 1.2 0.04
Propionate (P) 18.3 20.8 0.87 0.01
Butyrate 10.9 11.0 0.96 0.31
Acetate: Propionate ratio 3.28 3.08 0.071 0.01
Ammonia N (mg/L) 110 126 2.3 0.05
Microbial N synthesis (g/d) 190 220 9.6 0.04
Urinary purine derivative excretion
Uric acid (mmol/d) 22.4 24.6 0.67 0.16
Allantoin (mmol/d) 308 304 10.4 0.26
aZADO®: A commercial product obtained from Ruminococcus avefaciens comprising cellulase,
xylanase, protease, and α-amylase enzymes
A. Z. M. Salem et al.

53
Table 3 Data from Valdes etal. (2015), Rojo etal. (2015), and Salem etal. (2013) summarizing
the impact of exogenous enzymes on feed intake and nutrient digestibility in various livestock species
Treatment
ParameteraControl Enzymeb
Salix
babylonicac
Enzyme plus S.
babylonica SEM
P
value
No plant
extract
No plant
extract
Plant extract
30mL/h/day
Plant extract
30mL/h/d
Valdes etal.
(2015)
No
enzyme
ZADO® No enzyme ZADO®
Suffolk
lambs
10g/h/d 10g/h/d
DM intake
(g/d)
567 636 574 699 21.4 <0.001
OM intake
(g/d)
521 578 528 685 15.9 0.01
CP intake
(g/d)
412 465 437 452 14.3 0.002
NDF intake
(g/d)
160 228 186 201 13.6 0.001
ADF intake
(g/d)
108 154 125 135 10.4 <0.001
DM
digestibility
OM
digestibility
0.746 0.878 0.810 0.889 0.0316 0.001
CP
digestibility
0.721 0.724 0.727 0.722 0.0245 0.001
NDF
digestibility
0.601 0.665 0.676 0.694 0.1625 0.001
ADF
digestibility
0.455 0.539 0.592 0.561 0.0943 0.001
Rojo etal.
(2015)
Cellulase
plus®
Alpine dairy
goats
2ml/kg
DM
DM intake
(g/d)
3.1 3.5 – – 0.12 0.049
OM intake
(g/d)
2.9 3.2 – – 0.11 0.049
NDF intake
(g/d)
1.11 1.23 – – 0.041 0.049
OM
digestibility
0.76 0.80 – – 0.013 0.001
DM
digestibility
0.74 0.77 – – 0.011 0.001
NDF
digestibility
0.62 0.68 – – 0.011 <0.001
(continued)
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

54
Table 3 (continued)
Treatment
ParameteraControl Enzymeb
Salix
babylonicac
Enzyme plus S.
babylonica SEM
P
value
Salem etal.
(2013)
ZADO®
Beef cattle 40g/h/d
DM intake
(kg/d)
7.3 7.8 – – 0.3 0.11
DM
digestibility
617 691 – – 12.2 0.04
OM
digestibility
674 753 – – 151 0.01
CP
digestibility
835 874 – – 7.6 0.04
NDF
digestibility
417 508 – – 12.3 0.01
ADF
digestibility
322 408 – – 15.1 0.01
aDM dry matter, OM organic matter, NDF neutral detergent ber, ADF acid detergent ber, CP
crude protein
bZADO®: A commercial product obtained from Ruminococcus avefaciens comprising cellulase,
xylanase, Protease, and α-amylase enzymes; Cellulase Plus®: A commercial product obtained
from Trichoderma longibrachiatum, containing cellulase and β-glucanase
cExtract of the willow species Salix babylonica, obtained by macerating leaves in methanol/etha-
nol/water
5.3 Ruminal Degradability andGas Production
Generally, ber degradation in rumen is not fully efcient as indicated by the presence
of fermentable ber in feces (Krause etal. 2003). Mendoza etal. (2014) suggested
that feed supplementation with exogenous brolytic enzymes may be effective in act-
ing on the potentially digestible fraction of dietary ber. Enzymes added to feeds are
effective in increasing ber degradation when structural barriers that interrupt micro-
bial colonization of digestible fractions in the consumed plants are eliminated (López-
Aguirre etal. 2016a). Gado etal. (2013) investigated the effect of ensiling rice straw,
dried distillers’ grains and a 9:1 mixture of the two feedstuffs, for 30days with a liquid
exogenous enzyme product containing cellulases, xylanases, and α-amylase (ZAD®),
on levels of ber fractions and on invitro ruminal degradability. Treatment with the
exogenous enzyme product enhanced degradation of acid detergent ber, dry matter,
and neutral detergent ber. The feed degradation fractions (rapid soluble fraction and
insoluble, but potentially degradable fraction) and degradation rate were increased
when the enzyme inclusion rate was 3L/tonne, except for rice straw where the degra-
dation rate values for acid detergent ber and neutral detergent ber were not inu-
enced by the exogenous enzyme treatment.
Togtokhbayar etal. (2015) investigated the effect of xylanase on in sacco degra-
dation of wheat straw and showed that the dry matter degradation decreased linearly
A. Z. M. Salem et al.

55
with increasing enzyme dosage. Although the in sacco neutral detergent ber deg-
radation remained unchanged with xylanase addition, an intermediate xylanase dos-
age level enhanced rumen degradability. Salem et al. (2015b) reported positive
effects of glucoamylase extracts on invitro degradability of two total mixed rations
that contained 25% sorghum grains and 25% maize. For both diets, supplementation
with glucoamylase had no effect on the digestibility of acid detergent ber, neutral
detergent ber, and dry matter. Regardless of the level of exogenous enzyme supply,
the pattern of degradation of sorghum was generally lower than that of maize.
López-Aguirre etal. (2016a, b) studied the effect of three exogenous brolytic
enzyme products (xylanase, cellulase and a 1:1 blend of xylanase and cellulase) at
varying dosages (0, 1, 3μL/0.5g DM) on the invitro fermentation of feeds formu-
lated for growing lambs. Bottles containing the samples were incubated at 39°C for
96h. Data showed that the use of cellulases improved degradation of dry matter and
acid detergent ber and increased the asymptotic gas production value; interactions
between the enzyme dosage and products were signicant.
5.4 Nitrogen Balance andMicrobial Protein Synthesis
Most tropical forages and brous crop residues have a poor digestibility and low
protein content (Salem etal. 2015c). Microbial protein is a vital component of the
nitrogen ow after foregut fermentation in ruminants (Valdes et al. 2015).
Supplementation of animal diets with exogenous enzymes has been shown to
improve the nutritional value of tree foliage owing to the actions of enzymes in
enhancing the degradation of dietary ber (Salem etal. 2015a). Wang etal. (2001)
investigated the effects of exogenous enzyme by different modes of application on
the synthesis of microbial protein by using the rumen simulation technique (Rusitec)
and reported an increased microbial protein synthesis (assessed by 15N incorpora-
tion) when crude xylanase was added to a diet 24h before fermentation began.
5.5 Milk Production, Composition and Quality
There are several published reports claiming positive effects of dietary supplemen-
tation with exogenous enzymes on the composition of cow milk. Beauchemin etal.
(2000) reported a 2% increase in protein content of milk after feed supplementation
with an enzyme product containing endoglucanase, β-glucanase, and xylanase.
There are other reports of an increase in milk protein or fat content (Bowman etal.
2002; Sutton etal. 2003; Eun and Beauchemin 2005). There are also some pub-
lished cases of improvements in milk yield because of enzyme supplementation.
Yang etal. (1999) observed an additional milk yield of 1.9kg/d when an exogenous
enzyme product, comprising predominantly of xylanase and cellulase, was used to
supplement hay at a relatively high enzyme inclusion rate (2g/kg hay). The result
was interpreted as being due to a 4% increase in total tract organic matter
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

56
digestibility. However, there are different research reports showing conicting
responses to enzyme supplementation of feed for dairy cows. Some studies reported
no effect of enzyme treatment of diets on milk yield (DeFrain etal. 2005; Bernard
etal. 2010; Peters etal. 2010; Ferraretto etal. 2011) or milk composition (Bernard
etal. 2010; Arriola etal. 2011). Holtshausen etal. (2011) investigated the effective-
ness of an exogenous enzyme preparation (Econase RDE), containing endogluca-
nase and xylanase as a supplement to dairy cow diets. Enzyme supplementation of
diets fed to lactating Holstein cattle increased fat-corrected milk yield in a dosage-
dependent manner. Holtshausen etal. (2011) tentatively attributed these results to
an improvement in ber digestibility of dietary forages, since, in the same study,
invitro measurements indicated that enzyme supplementation increased ber deg-
radation in one of the component dietary forages (alfalfa hay), but ber degradation
measured using the in sacco method was unaffected. Likewise, Arriola etal. (2011)
observed no effects of exogenous enzyme supplementation for high and low con-
centrate cattle diets in terms ofruminal ber degradation measured in sacco, despite
increases in total-tract digestibility and in efciency of milk production.The enzyme
preparation investigated in the study by Arriola etal. (2011), which contained cel-
lulose, xylanase, and esterase, was obtained from a strain of Trichoderma longibra-
chiatum. Diverse published data on production responses to exogenous enzyme
supplementation suggest that it is important for the type and dosage of enzyme
preparations to be standardized before adding them into the diets for dairy cattle.
The adoption of invitro screening techniques could aid determination of appro-
priate application rates for exogenous enzyme preparations and prediction of pro-
duction responses when used to supplement specic ruminant feeds. However, it is
not easy to evaluate the consistency of animal responses to each enzyme product, as
most of the enzymes preparations are atexperimental stageand their activities could
vary over time. Gado etal. (2009) investigated the inuence of the commercial
brolytic mixed enzyme product, ZADO® addition to a total mixed ration, based on
maize silage and concentrate fed to dairy cows, on the production and composition
of milk. Milk yield and milk energy were greater for cows fed with the diet supple-
mented with the exogenous enzyme product (Table4). However, exogenous enzyme
supplementation had no effect on the fat, protein, or lactose concentrations in milk,
although daily yield of milk protein was increased.
Rojo et al. (2015) examined the effects of cellulase addition to a diet fed to
French Alpine goats on the production and composition of their milk. Goats receiv-
ing the cellulase supplement yielded more milk with higher energydensity, and
higher concentrations of fat, protein, and lactose compared with that of goats receiv-
ing the unsupplemented ration. Therefore, milk energy yield, energy-corrected
yield, milk energy, and total solids contents were also increased (Table5).
Milk fat from the goats fed with the cellulase-supplemented diet had higher con-
centrations of mono-unsaturated acidssuch as palmitoleic acid (C16:1) and cis- 10-
heptadecanoic acid (C17:1), with lower levels of saturated fatty acids, and the
polyunsaturated fatty acids, linolenic acid (C18:2), and linoleic acid (C18:3).
A. Z. M. Salem et al.

57
Table 4 Milk production and composition from dairy cows fed with a total mixed ration with or
without a supplement of a commercial mixed enzyme product (ZADO®)-(Gado etal. 2009)
Treatmenta
TMRbTMR+ZADO®cSEM P value
Milk yield
Total production (kg/d) 12.8 15.7 0.85 0.046
Fat (kg/d) 0.50 0.60 0.041 0.126
Protein (kg/d) 0.45 0.57 0.022 0.047
Lactose (kg/d) 0.58 0.71 0.054 0.141
Total energy (MJ/d) 58.2 70.7 8.15 0.041
Milk composition (g/kg)
Fat 39 38 2.4 0.163
Protein 35 36 1.7 0.242
Lactose 45 45 2.2 0.361
aTreatment: Ten animals per treatment group
bTMR Total mixed ration, based on maize silage (70%, dry matter basis) and concentrate (30%, dry
matter basis); concentrate contained mainly ground maize grain and cottonseed cake
cZADO®: A commercial product obtained from Ruminococcus avefaciens comprising cellulase,
xylanase, protease, and α-amylase enzymes at a rate of 40g/h/d
5.6 Growth Performance andMeat Quality
Several studies have shown that the use of exogenous enzyme preparations added to
diets in varying compositions and doses increased the dry matter intake and growth
of a range of young ruminants, including beef steers, goat kids, and lambs
(McAllister etal. 1999; Titi 2003; Cruywagen and Van Zyl 2008). Conversely, other
published studies have reported no effects of exogenous enzyme supplementation
on intake or growth of beef steers or lambs (Mora-Jaimes etal. 2002; Miller etal.
2008a; b; Awawdeh and Obeidat 2011).
Rivero etal. (2012) investigated the effect of daily addition to a maize silage/
maize-based concentrate diet, of a mixture of 10g of the exogenous enzyme prepa-
ration, ZADO®, and 30mL of an extract from Salix babylonica leaves on the growth
of Suffolk lambs. Results showed that S. babylonica and ZADO® individually or in
combination in feeds did not affect growth or dietary intake. Blood chemistry, cel-
lular immune response, and animal health were unaffected by the plant extract and
the enzyme treatments. Even though 59 compounds were found in S. babylonica,
none of these compounds were examined individually for any effects on animal
nutrition.
However, several studies have shown that the addition of crude S. babylonica
extracts to feeds, without exogenous enzyme supplementation, resulted in enhanced
nutrient digestion and animal growth in lambs (Salem etal. 2011, 2014). Such dif-
ferences in results among separate studies could perhaps be attributed to variation
inplant secondary metabolites from S. babylonica extracts and their impacton the
activity of ruminal microorganisms (Salem et al. 2012, 2014; Jiménez-Peralta
etal. 2011).
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

58
Table 5 Milk production and composition during the rst third of the lactation period (60days)
from French Alpine dairy goats fed with a total mixed ration with or without a supplement of a
cellulase enzyme product (Celluase Plus®) -(Rojo etal. 2015)
Treatmenta
TMRbTMR+Cellulase Plus®c SEM P value
Milk yield
Total production (kg/d) 3.1 3.4 0.13 0.042
Energy-corrected milk (ECM, kg/d) 2.6 3.3 0.12 0.001
Milk energy output (MJ/day) 8.3 10.5 0.37 0.001
Total solids (kg/d) 315 392 13.3 0.001
Fat (kg/d) 103 136 5.9 0.001
Protein (kg/d) 87 105 3.4 0.001
Lactose (kg/d) 125 151 5.1 0.002
Milk composition
Milk energy content (MJ/kg) 2.8 3.1 0.18 0.008
Total solids (g/kg) 104 114 2.6 0.008
Fat (g/kg) 34 40 1.5 0.016
Protein (g/kg) 29 31 1.4 0.003
Lactose (g/kg) 41 44 2.0 0.050
Density (g/mL) 1.026 1.028 0.0012 0.003
Feed efciency
Milk (milk yield/DMId) 0.99 1.01 0.053 0.772
Energy corrected milk (ECM/DMI) 0.84 0.96 0.044 0.066
aTreatment: Twelve animals per treatment group
bTMR Total mixed ration, based on alfalfa hay, sorghum grain, and maize grain
cCellulase Plus®: Commercial cellulase preparation added to the TMR (2mL/kg dry matter)
dDMI Dry matter intake (kg/d)
Buendía etal. (2014) reported that the intake and growth performance of lambs
was not affected by the addition of phytase to the diet, although diet digestibility
was enhanced. The application of exogenous phytase also reduced the fecal excre-
tion of phosphorus, which could thus contribute to a reduction in environmental
pollution.
6 Conclusions
Application of exogenous enzymes as dietary additivesfor ruminants on brous
tropical forages and crop residues diets is an evolving technology. This is encour-
aged by the wide availability of potentially appropriate roughage feedstuffs, the
development of better techniques for assessing enzyme activity, and recent advances
in biotechnology that have provided more enzymes for cost-effective applications in
animal feeding. Exogenous enzymes can play an important role in enhancing ani-
mal feed utilization and potentially improve fodder and tree foliage quality in
A. Z. M. Salem et al.

59
ruminant diets. They can also stimulate the growth of useful bacteria, increase ber
digestion, and improve the capability of rumen bacteria to better degrade diets and
secondary metabolites. Enzymes may also reduce fecal nitrogen excretion and cre-
atinine production. Through their effects on diet digestion and rumen functioning,
exogenous enzymes added to ruminant diets can lead to improvements in produc-
tion efciency and the quality of both meat and milk.
References
Arriola K, Kim S, Staples C, Adesogan A (2011) Effect of brolytic enzyme application to low-
and high-concentrate diets on the performance of lactating dairy cattle. J Dairy Sci 94:832–841
Awawdeh M, Obeidat B (2011) Effect of supplemental exogenous enzymes on performance of
nishing Awassi lambs fed olive cake-containing diets. Livestock Sci 138:20–24
Beauchemin K, Holtshausen L (2010) Developments in enzyme usage in ruminants. In: Enzymes
in farm animal nutrition. CABI, pp206–230
Beauchemin K, Yang W, Rode L (1999) Effects of grain source and enzyme additive on site and
extent of nutrient digestion in dairy cows. J Dairy Sci 82:378–390
Beauchemin K, Rode L, Maekawa M etal (2000) Evaluation of a nonstarch polysaccharidase feed
enzyme in dairy cow diets. J Dairy Sci 83:543–553
Beauchemin K, Colombatto D, Morgavi D etal (2003) Use of exogenous brolytic enzymes to
improve feed utilization by ruminants. J Anim Sci 81:E37–E47
Beauchemin K, Kreuzer M, O’Mara F, McAllister T (2008) Nutritional management for enteric
methane abatement: a review. Aust J Exp Agric 48:21–27
Bedford M, Cowieson A (2012) Exogenous enzymes and their effects on intestinal microbiology.
Anim Feed Sci Technol 173:76–85
Bernard J, Castro J, Mullis N etal (2010) Effect of feeding alfalfa hay or Tifton 85 bermudagrass
haylage with or without a cellulase enzyme on performance of Holstein cows. J Dairy Sci
93:5280–5285
Bowman G, Beauchemin K, Shelford J (2002) The proportion of the diet to which brolytic
enzymes are added affects nutrient digestion by lactating dairy cows. J Dairy Sci 85:3420–3429
Buendía R, González M, Mendoza M etal (2014) Effects of exogenous phytase on growth perfor-
mance of weaned Dorper x Pelibuey lambs. Anim Nutr Feed Technol 14:183–188
Cheng K-J, McAllister T (1997) Compartmentation in the rumen. In: The rumen microbial eco-
system. Springer, pp492–522
Chung Y-H, Zhou M, Holtshausen L etal (2012) A brolytic enzyme additive for lactating
Holstein cow diets: ruminal fermentation, rumen microbial populations, and enteric methane
emissions. J Dairy Sci 95:1419–1427
Cruywagen C, Van Zyl W (2008) Effects of a fungal enzyme cocktail treatment of high and low
forage diets on lamb growth. Anim Feed Sci Technol 145:151–158
DeFrain J, Hippen A, Kalscheur K etal (2005) Effects of dietary α-amylase on metabolism and
performance of transition dairy cows. J Dairy Sci 88:4405–4413
Elghandour MMY, Salem AZM, Gonzalez-Ronquillo M etal (2013) Effects of exogenous enzymes
on invitro gas production kinetics and ruminal fermentation of four brous feeds. Anim Feed
Sci Technol 179:46–53
Eun J-S, Beauchemin K (2005) Effects of a proteolytic feed enzyme on intake, digestion, ruminal
fermentation, and milk production. J Dairy Sci 88:2140–2153
Eun J-S, Beauchemin K, Schulze H (2007) Use of exogenous brolytic enzymes to enhance
invitro fermentation of alfalfa hay and corn silage. J Dairy Sci 90:1440–1451
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

60
Faniyi TO, Adegbeye MJ, Elghandour MMY etal (2019) Role of diverse fermentative factors
towards microbial community shift in ruminants. J Appl Microbiol 30:1–10
Ferraretto L, Shaver R, Espineira M etal (2011) Inuence of a reduced-starch diet with or without
exogenous amylase on lactation performance by dairy cows. J Dairy Sci 94:1490–1499
Gado H, Salem A, Robinson P, Hassan M (2009) Inuence of exogenous enzymes on nutrient
digestibility, extent of ruminal fermentation as well as milk production and composition in
dairy cows. Anim Feed Sci Technol 154:36–46
Gado H, Salem A, Odongo N etal (2011) Inuence of exogenous enzymes ensiled with orange
pulp on digestion and growth performance in lambs. Anim Feed Sci Technol 165:131–136
Gado H, Salem A, Camacho L etal (2013) Inuence of exogenous enzymes on invitro ruminal
degradation of ensiled rice straw with DDGS.Anim Nutr Feed Technol 13:569–574
Holtshausen L, Chaves A, Beauchemin K etal (2009) Feeding saponin-containing Yucca schidig-
era and Quillaja saponaria to decrease enteric methane production in dairy cows. J Dairy Sci
92:2809–2821
Holtshausen L, Chung Y-H, Gerardo-Cuervo H etal (2011) Improved milk production efciency in
early lactation dairy cattle with dietary addition of a developmental brolytic enzyme additive.
J Dairy Sci 94:899–907
Jalilvand G, Naserian A, Kebreab E etal (2008) Rumen degradation kinetics of alfalfa hay, maize
silage and wheat straw treated with brolytic enzymes. Arch Zootec 57:155–164
Jiménez-Peralta F, Salem A, Mejia-Hernández P et al (2011) Inuence of individual and mixed
extracts of two tree species on invitro gas production kinetics of a high concentrate diet fed to
growing lambs. Livestock Sci 136:192–200
Kamble RD, Jadhav AR (2012) Isolation, identication and screening of potential cellulase-free
xylanase producing fungi and its production. Afr J Biotechnol 11:14175–14181
Krause DO, Denman SE, Mackie RI etal (2003) Opportunities to improve ber degradation in the
rumen: microbiology, ecology, and genomics. FEMS Microbiol Rev 27:663–693
Lee B, Pometto AL, Demirci A etal (1998) Media evaluation to produce microbial enzymes. J
Agric Food Chem 46:4775–4778
López-Aguirre D, Hernández-Meléndez J, Rojo R etal (2016a) Effects of exogenous enzymes
and application method on nutrient intake, digestibility, and growth performance of Pelibuey
lambs. Springerplus 5:1399
López-Aguirre D, Hernández-Meléndez J, Rojo R etal (2016b) In vitro gas production kinetics
and degradability of a diet for growing lambs: effect of brolytic enzyme products at different
dose levels. J Anim Sci 15:453–460
McAllister T, Oosting S, Popp J etal (1999) Effect of exogenous enzymes on digestibility of barley
silage and growth performance of feedlot cattle. Can J Anim Sci 79:353–360
McAllister T, Hristov A, Beauchemin K etal (2001) Enzymes in ruminant diets. In: Enzymes in
farm animal nutrition. CABI, pp273–298
McGinn S, Beauchemin K, Coates T etal (2004) Methane emissions from beef cattle: effects of
monensin, sunower oil, enzymes, yeast, and fumaric acid. J Anim Sci 82:3346–3356
Meale SJ, Beauchemin KA, Hristov A etal (2014) Board-invited review: opportunities and chal-
lenges in using exogenous enzymes to improve ruminant production. J Anim Sci 92:427–442
Mendoza GD, Loera-Corral O, Plata-Pérez FX etal (2014) Considerations on the use of exogenous
brolytic enzymes to improve forage utilization. Sci World J Art 2014:1
Miller D, Elliott R, Norton B (2008a) Effects of an exogenous enzyme, Roxazyme® G2, on intake,
digestion and utilisation of sorghum and barley grain-based diets by beef steers. Anim Feed Sci
Technol 145:159–181
Miller D, Granzin B, Elliott R etal (2008b) Effects of an exogenous enzyme, Roxazyme® G2
liquid, on milk production in pasture fed dairy cows. Anim Feed Sci Technol 145:194–208
Mora-Jaimes G, Bárcena-Gama R, Mendoza-Martínez G etal (2002) Performance and ruminal
fermentation in lambs fed sorghum grain treated with amylases. Agrociencia (Montecillo)
36:31–39
A. Z. M. Salem et al.

61
Morgavi D, Beauchemin K, Nsereko V etal (2001) Resistance of feed enzymes to proteolytic inac-
tivation by rumen microorganisms and gastrointestinal proteases. J Anim Sci 79:1621–1630
Morgavi DP, Kelly W, Janssen P etal (2013) Rumen microbial (meta) genomics and its application
to ruminant production. Animal 7:184–201
Nozière P, Besle JM, Martin C etal (1996) Effect of barley supplement on microbial brolytic
enzyme activities and cell wall degradation rate in the rumen. J Sci Food Agric 72:235–242
Peters A, Lebzien P, Meyer U etal (2010) Effect of exogenous brolytic enzymes on ruminal fer-
mentation and nutrient digestion in dairy cows. Arch Anim Nutr 64:221–237
Polderman L, Dillon C, Steele A (1955) Why monoethanolamine solution breaks down in gas-
treating service. Oil Gas J 54:180–183
Rivero N, Salem A, Gado H et al (2012) Effect of exogenous enzymes and Salix babylonica
extract or their combination on haematological parameters in growing lambs. J Anim Feed Sci
21:577–586
Rojo R, Kholif A, Salem A etal (2015) Inuence of cellulase addition to dairy goat diets on diges-
tion and fermentation, milk production and fatty acid content. J Agric Sci 153:1514–1523
Salem AZM, EL-adawy M, Gado H etal (2011) Effect of exogenous enzymes on nutrient digest-
ibility and growth performance in sheep and goat. Trop Subtrop Agroecosystem 14:867–874
Salem A, Hassan A, Khalil M etal (2012) Effects of sun-drying and exogenous enzymes on nutri-
ents intake, digestibility and nitrogen utilization in sheep fed Atriplex halimus foliages. Anim
Feed Sci Technol 171:128–135
Salem AZ, Gado H, Colobatto D etal (2013) Effects of exogenous enzymes on nutrient digest-
ibility, ruminal fermentation, and growth performance in beef steers. Livest Sci 154:69–73
Salem AZ, Kholif AE, Olivares M etal (2014) Inuence of S. babylonica extract on feed intake,
growth performance and diet invitro gas production prole in young lambs. Trop Anim Health
Prod 46:213–219
Salem AZM, Alsersy H, Camacho LM etal (2015a) Feed intake, nutrient digestibility, nitrogen
utilization, and ruminal fermentation activities in sheep fed Atriplex halimus ensiled with three
developed enzyme cocktails. Czech J Anim Sci 60:185–194
Salem A, Ammar H, Kholif A etal (2015b) Effect of glucoamylase enzyme extract on invitro gas
production and degradability of two diets with 25% of corn or sorghum grains. Ind J Anim Sci
85:183–188
Salem AZ, Elghandour MM, Kholif AE etal (2015c) The effect of feeding horses a high ber diet
with or without exogenous brolytic enzymes supplementation on nutrient digestion, blood
chemistry, fecal coliform count, and invitro fecal fermentation. J Equine Vet Sci 35:735–743
Stella A, Paratte R, Valnegri L etal (2007) Effect of administration of live Saccharomyces cerevi-
siae on milk production, milk composition, blood metabolites, and faecal ora in early lactat-
ing dairy goats. Small Ruminant Res 67:7–13
Sujani S, Seresinhe R (2015) Exogenous enzymes in ruminant nutrition: a review. Asian J Anim
Sci 9:85–99
Sutton J, Phipps R, Beever D etal (2003) Effect of method of application of a brolytic enzyme
product on digestive processes and milk production in Holstein-Friesian cows. J Dairy Sci
86:546–556
Titi H (2003) Replacing soybean meal with sunower meal with or without brolytic enzymes in
fattening diets of goat kids. Small Ruminant Res 48:45–50
Titi H, Lubbadeh W (2004) Effect of feeding cellulase enzyme on productive responses of preg-
nant and lactating ewes and goats. Small Ruminant Res 52:137–143
Togtokhbayar N, Cerrillo MA, Rodríguez GB etal (2015) Effect of exogenous xylanase on rumen
invitro gas production and degradability of wheat straw. Anim Sci J 86:765–771
Valdes K, Salem A, Lopez S etal (2015) Inuence of exogenous enzymes in presence of Salix
babylonica extract on digestibility, microbial protein synthesis and performance of lambs fed
maize silage. J Agric Sci 153:732–742
Vallejo L, Salem A, Camacho L etal (2016) Effects of xylanase supplementation on feed intake,
digestibility, and ruminal fermentation in Rambouillet sheep. J Agric Sci 154:1110–1117
Effects of Exogenous Enzymes on the Nutritive Value of Some Fibrous...

62
Wang Y, McAllister T, Rode L etal (2001) Effects of an exogenous enzyme preparation on micro-
bial protein synthesis, enzyme activity and attachment to feed in the rumen simulation tech-
nique (Rusitec). Brit J Nutr 85:325–332
Yang W, Beauchemin K, Rode L (1999) Effects of an enzyme feed additive on extent of digestion
and milk production of lactating dairy cows. J Dairy Sci 82:391–403
Zhang YHP, Lynd LR (2004) Toward an aggregated understanding of enzymatic hydrolysis of cel-
lulose: noncomplexed cellulase systems. Biotechnol Bioeng 88:797–824
Zhou M, Chung YH, Beauchemin K etal (2011) Relationship between rumen methanogens and
methane production in dairy cows fed diets supplemented with a feed enzyme additive. J Appl
Microbiol 111:1148–1158
A. Z. M. Salem et al.