DIRECT FED MICROBIALS AND ENZYMES FOR RUMINANTS
Kung, Jr., Ph.D.
Department of Animal & Food Sciences
University of Delaware
Newark, Delaware 19717-1303
fed microbial additives that contain lactobacilli are common but
significant data to support claims of increased growth and decreased
mortality are lacking. Of
the various fungal products have been tested, additives containing yeast
have consistently improved milk production.
Several other bacteria have been used experimentally to improve
the performance of ruminant animals but are not commercially available.
A significant amount of research has recently shown that adding
fibrolytic enzymes to diets improves milk production. Direct fed
microbials and other nontraditional feed additives may be viable
alternatives to traditional antibiotic-based growth promoters.
In some countries, use of traditional growth promoting substances
for livestock has met with much resistance.
For example, in much of Europe, only a few growth-promoting
additives are approved and the tide against such products and those
associated with genetically modified organisms (GMO) continues to grow.
The use of direct fed microbial and other nontraditional feed
additives has increased in response to demands for using more
“natural” growth promoting substances. The objective of this paper
is to briefly discuss the applications of direct fed microbial and
nontraditional feed additives in ruminant nutrition.
birth, developing animals are sterile in the womb of their mothers. Upon
birth, the digestive tracts of all animals are naturally colonized by a
variety of microorganisms (Savage, 1987).
Under healthy and non-stressful conditions,
“beneficial” microflora colonize the rumen and lower gut in a
symbiotic relationship with the host.
Beneficial rumen and gut microorganisms supply nutrients to the
host, aid in digestion of dietary nutrients, and compete with potential
pathogens. In contrast,
when young animals are removed and raised under sterile conditions,
microorganisms from the environment are prevented from colonizing their
digestive tracts. These
animals often have increased nutritional needs (e.g., requiring more
vitamin K in the diet) and abnormal immune responses.
Sterile animals also are more susceptible to bacterial
infections, presumably due to rapid establishment of pathogens.
original concept of administering direct fed microbial to animals was to
feed large amounts of "beneficial" microbes to livestock when
they were “stressed.” This
practice would prevent the establishment of pathogenic microorganisms
and could help re-establish normal gut microflora.
This practice was termed "probiotic", or “for
life.” The term “probiotic” implied a curative nature of these
products that would require government approval in order to make legal
product claims (e.g., decreased mortality, fewer sick days, and
increased production). Thus,
in conjunction with the FDA and USDA, the feed industry in the US has
since accepted the term direct-fed microbial (DFM) to describe
microbial-based feed additives and these products may be sold without
reviewed efficacy data as long as health or production claims are not
the most common hypotheses that may explain how DFM improve animal
performance suggests that the addition of beneficial bacteria exclude
the establishment of pathogens (competitive exclusion).
Production of antimicrobial end products such as acids and
antibiotics are also commonly discussed.
Some of the major hypothesis are listed in Table 1 and can be
found in an excellent discussion by Fuller (1989).
general, most would agree that DFM based on bacteria must be “live.”
Thus, they must survive processing, storage and the gut
future research may prove that end products such as bacteriocins (narrow
spectrum antimicrobial substances) and not the actual organism itself
may be beneficial. A list of some common bacteria that have potential as DFM
additives is shown in Table 2.
acidophilus (and other Lactobacillus species),
L. casei, Enterococcus diacetylactis, and
Bacillus subtilis are commonly used as DFM products for ruminants.
These organisms appear to have little effect on ruminal
fermentation (Ware et. al., 1988) and the site of action from these
organisms appears to be in the lower gut but solid and repeatable data
is lacking. Initial
research with these organisms in ruminants was first centered around
“stressed” animals with the general assumption that feeding
beneficial organisms would decrease or prevent intestinal establishment
of pathogenic microorganisms (Vandevoorde et al., 1991).
In addition, it was hypothesized that massive doses of beneficial
organisms would re-colonize a “stressed” intestinal environment and
return gut function to normal more quickly. In ruminants, much of this research involved feeding lactobacillus-based
DFM to young calves fed milk, calves being weaned, or shipped cattle
(Jenny et al., 1991; Hutcheson et al., 1980) because these conditions
were often classified as times of high stress.
Calves fed L. acidophilus have been reported to have reduced incidence of
diarrhea (Beecham et al., 1977) and reduced counts of intestinal
coliform bacteria (Bruce et al., 1979).
Data summarizing more than 30 trials with incoming feedlot cattle
showed an advantage of 10.7 and 5.4% in average daily gain and feed
efficiency, respectively, for cattle fed a DFM (Pioneer Hi-Bred
Only a few studies have documented positive effects of feeding
bacterial DFM to lactating dairy cows.
High producing cows in early lactation would be the best
candidates for such products because these cows are in negative energy
balance and have diets that contain highly fermentable carbohydrates
that sometimes leads to acidosis. Jaquette et al. (1988) and Ware et al.
(1988) reported increased milk production from cows fed L.
acidophilus (1 x 109
colony-forming units per head per day).
More recently, Block et al., (1999, unpublished data) reported
improvements in milk production when cows were fed a DFM containing
yeast and 2 strains of bacteria. Supplementation
of lactobacilli may be useful in the close-up dry period of lactation
when intake is depressed and animals are stressed.
However, there is limited data to support this use.
some extent, the practice of using DFM on farm is already being used on
many dairies. Specifically,
producers and veterinarians have been inoculating sick ruminants with
rumen fluid from healthy animals in hopes of stimulating normal rumen
function for improving dry matter intakes has been practiced for
decades. Several attempts
have been made to use bacteria to alter rumen metabolism but only a few
have been successful on a practical scale.
detoxification of the 3-hydroxy-4(1H)-pyridone (DHP) by Synergistes
jonesii, isolated from Hawaiian cattle, is probably one of the most
cited successes of manipulating ruminal fermentation with bacteria.
The tropical forage Leucaena leucocephala contains mimosine, a non-protein amino acid.
When consumed by ruminants in Australia and some parts of India,
DHP causes goitrogenic effects. Jones
and Megarrity (1986) showed that rumen microbes, from cattle in Hawaii,
were able to detoxify DHP. The
specific organism responsible for detoxification, S.
jonesii (Allison et al., 1990), was inoculated and established
itself in the rumen of Australian cattle thus conferring protection from
DHP toxicity. Another problem in feeding ruminants, identified in
Australia, is monofluroacetate. This
compound is found in some Australian plants and can be toxic to
ruminants at doses of about 0.3 mg/kg of body weight.
Gregg et al. (1998) reported that they successfully inserted the
gene encoding for fluoroacetate dehalogenase into several strains of Butyrivibrio fibrisolvens and when sheep were inoculated with the
altered microbes, they showed reduced toxicological symptoms.
However, use of the genetically modified rumen bacteria in the
field is not currently approved.
is the major lactate-utilizing organism in the rumen of adapted
cattle fed high grain diets. However, when cattle are abruptly shifted from a high-forage
to high-concentrate diet, the numbers of ME are often insufficient to
prevent lactic acidosis. We
have shown that during a challenge with highly fermentable
carbohydrates, addition of Megasphaera
elsdenii B159 prevented an accumulation of lactic acid and shifted
ruminal fermentation away from acetate and propionate towards butyrate
and valerate (Kung and Hession, 1995).
Addition of ME has also experimentally prevented acidosis in
steers (Robinson et al., 1992). Development of this organism for feedlot cattle, and perhaps
high producing dairy cows, should be continued with emphasis on
optimizing dose and timing of administration.
Success with such an organism could allow feedlot producers to
decrease the time it takes to adapt cattle to a high concentrate diet.
It could also be useful by reducing chronic acidosis in lactating
Propionibacteria are naturally
found in high numbers in the rumen of animals fed forage and medium
concentrate diets. These
organisms convert lactate and glucose to acetate and propionate.
Propionibacteria may be
beneficial if inoculated into the rumen (Kung et al., 1991) because
higher concentrations of ruminal propionate would be absorbed into the
blood and converted to glucose by the liver of the host animal.
can metabolize lactic acid, they are probably too slow growing and acid
intolerant to prevent a challenge that would lead to acidosis (Kung et
al., unpublished data, University of Delaware).
A commercially available product based on a strain of Propionibacteria
that naturally occurs in the rumen has been claimed to reduce the
chance of nitrate toxicity but definitive data is lacking.
Recently, Swinney-Flyod et al. (1999) reported that feedlot
cattle fed a diet containing Propionibacteria, strain P-63 (1 ´ 109 cfu/head/day) and L. acidophilus,
strain 5345, (1 ´
108 cfu/head/day) had better feed efficiencies during
adaptation to a high concentrate diet and during a 120-d feeding period.
Similarly, Huck et al. (1999) reported that cattle fed L.
acidophilus (5 ´
108 cfu/head/day) strain BG2F04, and P. freudenrechii (1 ´ 109 cfu/head/day) had better feed
efficiencies than those fed a control diet.
More research in these areas is warranted.
variety of mechanisms have been put forth to explain changes in ruminal
fermentations and improvements in performance when ruminants are fed
fungal-based DFM. For example, yeast may have a buffering effect in the rumen
by mediating the sharp drops in rumen pH, which follows feeding.
Martin and Streeter (1995) suggested that fungal cultures improve
the use of lactate by the ruminal organism Selenomonas
ruminantium by providing a source of dicarboxcylic acids (e.g.,
malic acid) and other growth factors.
Thus, yeast may help to buffer excess lactic acid production when
ruminants are fed high concentrate diets.
The effects on buffering are subtle; as added yeast cannot
prevent lactic acidosis if the rumen is challenged with a diet rich in
fermentable carbohydrates (Aslan et al., 1995; Dawson and Hopkins,
1991). However, a higher pH
may be one reason for the finding of increased numbers of rumen
cellulolytic bacteria and improvements in fiber digestion with fungal
cultures (Arambel et al., 1987). Newbold
et al. (1995b) reported that the stimulation of rumen bacteria by Saccharomyces
cerevisiae different with specific strains. Some fungal extracts have been suggested to contain esterase
enzymes that may improve fiber digestion (Varel et al., 1993).
Yeast may also stimulate rumen fermentation by scavenging excess
oxygen from the rumen (Newbold et al., 1996).
They have also been shown to stimulate acetogenic bacteria in the
presence of methanogens (Chaucheryas et al., 1995).
The effect of fungal cultures on ruminal VFA has been
(1995a) summarized the literature and reported that fungal extracts had
no effect or tended to increase the rumen acetate:propionate ratios
while active yeast either had no effect or decreased the
acetate:propionate ratio. Arizona
researchers reported that feeding AO to cows in hot environments
decreased rectal temperatures in some but not all studies (Huber et al.,
1994). There is no direct
evidence that yeast or fungal extracts affect digestion or metabolism in
the lower gut. However, the
potential for such effects have not been well studied.
need for high numbers of live fungal organisms in fungal DFM additives
has been the subject of many debates.
Some products guarantee live yeast cells (e.g., 1 x 109
cfu per g) and are fed at low inclusion rates (only 10-20 grams per day)
but other products suggest that live organisms are not required for
beneficial effects because end products present in the additives are the
“active” ingredients. Newbold
et al. (1991) reported that autoclaving, but not irradiation, decreased
the ability of an AO extract to stimulate rumen bacterial growth and
activity. Dawson et al.
(1990) reported that the stimulatory effect of yeast on numbers of rumen
cellulolytic bacteria was negated when yeasts were autoclaved.
Martin and Nibs (1992) reported that unpublished data
from their lab showed enhanced uptake of D-lactate by S.
ruminantium was enhanced by a filtrate from AO but not from SC.
Although there have been implications that suggests yeasts were able to
grow in continuous rumen cultures (Dawson et al., 1990) others have
observed that live yeasts are essentially washed out of ruminal
fermentations. We reported
that Saccharomyces cerevisiae
did not multiply in sterile ruminal fluid, but they did survive and were
metabolically active (Kung et al., 1996).
In contrast to research with bacterial DFM, there is much data on
the effect of feeding fungal DFM to lactating cows. In
a review of 32 lactation comparisons conducted with yeast between 1986
and 1997, these supplements increased milk production on average by more
than 1.13 kg (2.49 lb.) per day with the response being greater for cows
in early lactation (Figure 1). Response
appeared to be consistent over the years. In a summary of 26 comparisons
where fungal extracts (from Aspergillus
oryzae) were fed to lactating ruminants, we found an average
increase in milk production of only 0.45 kg (1.01 lb.) of milk per day
(Figure 2). Unexplainably,
since 1991, milk production responses from fungal extracts (AO) have
been relatively poor. Fungal
cultures have also been fed to calves, sheep, and steers but
applications with these species have been less researched than with
lactating cows. For
example, Beharka et al. (1991) reported that young calves fed an AO
fermentation extract were weaned one wk earlier than untreated calves
and that supplementation increased the numbers of rumen bacteria and VFA
From a practical point, fungal additives appear to be more useful
when fed to cows in early lactation that are consuming high quantities
Considerations for DFM
Direct-fed microbial products are available in a variety of forms
including powders, pastes, boluses, and capsules.
In some applications, DFM may be mixed with feed or administered
in the drinking water. However,
use of DFM in the latter manner must be managed closely since
interactions with chlorine, water temperature, minerals, flow rate, and
antibiotics can affect the viability of many organisms.
Non-hydroscopic whey is often used as a carrier for bacterial DFM
and is a good medium to initiate growth.
Bacterial DFM pastes are formulated with vegetable oil and inert
gelling ingredients. Some
fungal products are formulated with grain by-products as carriers. Some
DFM are designed for one-time dosing while other products are designed
for feeding on a daily basis. However,
there is little information comparing the efficacy of administering a
DFM in a single massive dose compared to continuous daily dosing.
Lee and Botts (1988) reported that pulse dosing alone or pulse
dosing with daily feeding of Streptococcus
faecium M74 resulted in improved performance of incoming feedlot
cattle. The need for a bacterial DFM to actually attach and colonize
gut surfaces in order to have a beneficial effect is also questionable.
However, in certain applications, the argument could be made that
a DFM organism need only produce its active component (without
colonization) to be beneficial. Dose levels of bacterial DFM have varied.
Studies can be found where L.
acidophilus have been fed at levels ranging from 106 to
1010 cfu per animal per day.
Hutchenson et al. (1980) suggested that feeding more than 107
cfu per head per day may cause lower nutrient absorption due to
overpopulation of the gut. Orr
et al. (1988) reported that feeding a continuous high dose of L.
acidophilus to feeder calves (1010 cfu per head/day) had no effect on gain and actually reduced feed
efficiency when compared to feeding a lower dose (106).
Tolerance of DFM microorganisms to heat is important since many
feeds are pelleted. In
general, most yeast, Lactobacillus, Bifidobacterium,
and Streptococcus are
destroyed by heat during pelleting.
In contrast, bacilli form
stable endospores when conditions for growth are unfavorable and are
very resistant to heat, pH, moisture and disinfectants.
Thus, bacilli are currently used in many applications that
require pelleting. Over-blending
can sometimes compensate for microbial loss during pelleting, but this
is not an acceptable routine practice.
Future improvements in strain development may allow use of heat
sensitive organisms in pelleted feeds.
Bacterial products may or may not be compatible with use of
traditional antibiotics and thus care should be taken when formulations
contain both types of additives. Information on DFM and antibiotic compatibility should be
available from the manufacturer. For
example, some species of bacilli are sensitive to virginiamycin, and
lactobacilli are sensitive to chlortetracycline and penicillin.
Viability of DFM products has improved over the past several
years but it is highly advisable to adhere to storage recommendations.
For example, products should be kept away from moisture, excess
heat, and light.
National Feed Ingredient Association along with the Food and Drug
Administration have set forth guidelines to regulate sales and claims of
DFM products. Producers and
sellers of DFM products, by law, cannot make therapeutic claims, cannot
claim to establish viable bacterial colonies in the gut, and cannot
claim to affect structure or function of the animal.
At this time, DFM products cannot claim to decrease morbidity,
reduce sick days, or increase milk production, affect growth or feed
intake without a new animal drug application.
Enzymes are protein molecules that catalyze specific chemical
digestive enzymes have been studied for use as additives to enhance
animal performance with success in poultry and
swine diets. However, feeding enzyme preparations to improve ruminal
digestion has been a questionable practice in the past.
The reasoning behind this thought came from the fact that enzymes
are proteins and they would be subject to degradation by microbial
proteases in the rumen and/or inactivated by proteases in the small
Adding Enzymes (dry) to Feed
et al. (1987) reported that a cellulase enzyme complex was rapidly
degraded by rumen bacterial proteases and addition to ruminal fluid had
no effect on in vitro fiber
digestion. Some have suggested that feeding unprotected enzymes may be
more useful in immature ruminants where rumen microbial populations are
not fully developed. For
example, Baran and Kmet (1987) reported that a pectinase-cellulase
enzyme additive improved ruminal fermentation in newly weaned lambs but
not in adult sheep (with established rumen microflora).
Recently, there has been renewed interest in the use of enzymes
in ruminant diets because some fibrolytic enzymes have been shown to be
stable when incubated with protease enzymes.
Fontes et al. (1995) reported that several xylanases were
resistant to several proteases but only one cellulase from a mesophilic
organism was resistant to proteolytic attack.
Posttranslational glycosylation has also been reported to protect
enzymes from deactivation caused by high temperatures and proteinases
(Olsen and Thomsen, 1991). Hirstov
et al. (1998) reported that when added to the rumen, fibrolytic enzymes
maintained partial activity. However,
integrity of the enzyme is not the only criteria that should be used
when evaluating enzymes for ruminant diets, because in order for them to
be effective, they must bind to their substrate and catalyze reactions.
Tricarico and Dawson (1999) reported that the addition of
xylanase and cellulase enzyme preparations improved the in vitro ruminal
digestion of fescue hay. Zinn
and Salinas (1999) reported that a rumen-stable fibrolytic enzyme
supplement increased the ruminal digestion of NDF and Feed N by 23 and
5%, respectively. They also
reported an improvement in dry matter intake and average daily gain in
steers supplemented with this additive. These data suggest that adding enzymes directly (in a dry
form) to the diets of ruminants may improve digestion and production.
Enzymes (liquid) Directly onto Feeds
the past use of enzymes was restricted to their application on to
forages at the time of ensiling. However,
this mode of application has met with variable results.
One method to protect or minimize enzyme degradation by ruminal
proteases is to treat feeds with enzymes just prior to feeding.
When enzymes are applied to feed in this fashion, binding with
substrates cause conformational changes that may help to protect these
exogenous enzymes from ruminal degradation. Treacher and Hunt (1996)
reviewed the use of spraying enzymes directly onto feeds, rather than
adding at the time of ensiling, to enhance their nutritive values. This approach offers exciting possibilities for using enzymes
to improve nutrient digestion, utilization, and productivity in
ruminants and at the same time reduce animal fecal material and
pollution. Spraying enzymes
onto feeds just before feeding provides increased management flexibility
for feeding and bypasses any negative interactions that the ensiling
process may have on enzyme performance. A number of different mechanisms
have been theorized as reasons for positive effects including, direct
hydrolysis, improvements in palatability, changes in gut viscosity,
complementary actions with ruminal enzymes, and changes in the site of
digestion (Beauchemin and Rode, 1996; Treacher and Hunt, 1997).
Feng et al. (1992) reported that pretreatment of dry grass with
fibrolytic enzymes improved in vitro ruminal fiber digestion.
Lewis et al. (1996) reported that enzymes sprayed onto a grass
hay:barley diet increased VFA production and NDF digestion.
Spraying enzymes on silage has increased the release of residual
sugars and rate of NDF digestion. A
growing body of evidence exists that supports improvements in animal
productivity when feeds are treated with enzymes prior to feeding.
In some instances, enzymes have been applied directly to the
grain but in some studies enzymes were applied only to the forage
component of the diets prior to mixing into a TMR.
In 1999, six research papers were published documenting positive
effects on milk production (Table 3).
Interestingly, several, but not all, publications have reported
that high levels of enzymes resulted in lower milk yields than moderate
levels of enzyme treatment (Lewis et al, 1999; Beauchemin et al., 1995,
Kung et al., 1999). Over-treatment
of feeds with enzymes may result in blocking sites that may otherwise be
available for microbial enzymatic digestion or may prevent attachment by
rumen microbes. More
research will be needed in this area.
the activity of enzyme additives and predicting improvement in animal
performance will be a challenge for future research because temperature,
time, substrate concentration, enzyme concentration, product reactions,
cofactors, and pH, among other factors, have profound effects on enzyme
activity. In addition,
sources (bacterial versus fungal) and activity of enzymes differs
markedly. The purity of enzyme products must also be ascertained
because many commercial enzymes are actually complexes of various
enzymes that must work in concert to hydrolyze a substrate to monomer
units. For example, crude preparations of a cellulase enzyme complex
actually contain endo- and exo-beta-1,4 glucanases, beta-glucosidases,
and cellobiase. Hemicellulase
preparations are even more complex.
Determining the proper ratio of individual enzyme activities
relative to the targeted feed must be determined in order to optimize
their effects on feeds. No
universally accepted methods exist for determining enzyme activity but
they are usually based on release of a monomer under optimal and
standardized conditions. Certainly,
newer methods that evaluate enzymes should consider their optimum
activities at rumen temperature and pH.
We know very little about the stability of added enzymes
and interactions of enzymes with components of feeds.
If added during processing, enzymes must be able to withstand
temperatures during pelleting. Several
practical problems must be addressed before liquid enzymes will find
acceptance on the farm. First,
liquid enzymes will probably require refrigeration for prolonged storage
and thus bulk storage space will be needed.
In addition, sprayer mechanisms must be mounted on to TMR wagons.
The cost of transporting liquid enzymes to farms will also be
high because of the weight of the liquid.
Regulatory Status of Enzyme Feed Additives
All enzyme feed additives are considered either food additives or
GRAS substances and are under regulation by the FDA.
As of January 1, 1998, the AAFCO Enzyme and Microbial Task Force
that includes members of the AAFCO, FDA, and Agriculture and Food Canada
have put forth guidelines for the use of enzymes in animal feeds. Producers of enzymes must provide the source of the enzyme
(organism) along with information on enzyme activity, substrates,
reaction products and site of enzymatic activity.
Enzymes must come from non-pathogenic organisms.
Enzymes from genetically altered organisms are acceptable if the
amino acid sequence of the enzyme has not been significantly altered and
if no altered organisms are in the formulation and no transformable
antibiotic resistant DNA is present. Products must also be safe relative to animal, human and
environmental concerns. Functionality
must be proven via in vitro tests.
Importantly, as with DFM, therapeutic and production claims are
FUTURE OF DIRECT
FED MICROBIALS AND ENZYMES
understanding of how and when DFM improve animal production is in its
infancy. Many improvements
in strain selection and stability have resulted from research in the
past 10 years but more information is needed.
In the future, rumen and traditional DFM organisms may be
genetically modified through recombinant DNA technology.
For example, organisms may be engineered to secrete essential
amino acids or secrete high levels of growth factors. Genetic
modification of bacteria to improve fiber digestion in the rumen has
also been studied. However,
the likelihood that such organisms could establish themselves in a rumen
environment and compete with fibrolytic bacteria is quite low.
In addition, release of such organisms is currently banned by
regulatory agencies. In the
immediate future, approaches that identify naturally occurring microbes
capable of filling niches within the rumen such as detoxification of
compounds such as alkaloids, oxalates, tannins, or mycotoxins may be
better. However commercial
development of these organisms will not occur if they cannot be
economically grown and stabilized, especially if daily feeding is not
on treating feeds with enzymes also continues.
Many questions relative to choice of enzymes, doses, and
interactions with maturity and moisture need answering.
Improvements in technology that will help to reduce production
costs and will have a major effect on product development. Herbs and plant extracts may also have potentials as feed
additives but information on their use for ruminants is lacking.
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V. S., M. Thamsborg, R. J. Jorgensen, and A. Basse. 1995. Induced acute
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1. Proposed mechanisms for
improvements in animal performance when fed a DFM.
antibacterial compounds (acids, bacteriocins, antibiotics)
undesirable organisms for colonization space and/or nutrient
other beneficial microorganisms
stimulation of enzymes
detoxification of undesirable compounds
immune response in host animal
Table 2. Some bacteria that
have potential uses as direct-fed microbials.
End Products or Potential Use
acid, acidophilin, glycosidases
amylase, hydrogen peroxide, proteases
ureases, lactic acid, formic acid
Megasphaera elsdenii ruminal
Ruminal lactate utilizer, propionate producer
3. Effect of spraying
enzymes onto feeds prior to feeding on milk production in studies
published or accepted for publication in 1999.
in milk production1,
in fat corrected milk
Beauchemin et al., 1999
Kung et al., 1999
1. +2.5 (P < 0.10), -0.8
2.5 (P < 0.10)
1. +2.9 (P
< 0.10), -2.0
Lewis et a., 1999
+1.2, +6.3 (P
< 0.05), +1.6
-0.1, +6.3 (P
< 0.05), +0.1
Rode et al., 1999
+3.6 (P < 0.11)
Schingoethe et al., 1999
2. +1.3 (P < 0.01)
2. +1.9 (P < 0.05)
Yang et al., 1999
+0.9, +1.9, +1.6
+0.5, +2.2 (P
< 0.05), + 1.8 (P
Mean for all treatments
1When more than 1 value is listed ,
several enzyme treatments were tested.
Increase in milk is relative to milk production by control cows.
FCM was 3.5 or 4.0%.
1. Effect of supplementing
diets for lactating ruminants with yeast.
N = 32. Average
response to yeast was + 1.13 kg (2.4 lb./day).
Effect of supplementing diets for lactating ruminants with fungal
extracts. N = 26. Average
response to yeast was + 0.46 kg (1.01 lb./day).