Efficacy of laidlomycin propionate in low-protein diets fed to growing beef
steers: Effects on steer performance and ruminal nitrogen metabolism1,2
D. W. Bohnert*,3, D. L. Harmon*,4, K. A. Dawson*, B. T. Larson*,
C. J. Richards*, and M. N. Streeter†
*Department of Animal Sciences, University of Kentucky, Lexington 40546-0215
and †Roche Vitamins Inc., Parsippany, NJ 07054
> .11). However, propionate concentration was increased (P < .09) with 12.5% CP and LP, and acetate:propionate was lower (P = .02) with LP supplementation. In Exp. 2, six steers were used in a replicated
3 × 3 Latin square design to compare ruminal fermentation and protein degradation in steers without ionophore feeding or adapted to LP or monensin. In vitro
deamination of amino acids by adapted ruminal microbes was also assessed. Ionophore supplementation
decreased (P = .07) ruminal NH3 N concentration compared with control steers, and LP increased (P = .02)
ruminal NH3 N compared with monensin. Molar proportion of acetate was decreased (P = .02) and propionate increased (P = .01) with ionophore treatment. Consequently, ionophore supplementation depressed the
acetate:propionate ratio (P = .01). In situ degradation
rate of soybean meal (SBM) CP was greater (P = .09)
with ionophore treatment, but estimates of SBM undegradable intake protein were not altered by treatment
(P > .25). Microbial specific activity of net NH3 N release
and α-amino N degradation were decreased (P < .04)
with ionophores. Based on this study, LP and monensin
did not affect the extent of ruminal degradation of SBM
CP but decreased amino acid deamination.
ABSTRACT: We conducted two experiments to evaluate the effect of the ionophore laidlomycin propionate
(LP) on steer performance and ruminal N metabolism.
Experiment 1 was a 91-d growth study evaluating the
growth and ruminal characteristics of steer calves consuming supplemental LP. Steers (n = 96; 255 ± 3 kg;
four steers/pen; six pens/treatment) were used in a randomized complete block design with a 2 × 2 factorial
arrangement of treatments consisting of two levels of
dietary CP (formulated to be 10.5 and 12.5% of DM)
with and without LP (11 mg/kg diet DM). Ruminal fluid
was collected via stomach tube on d 91 from one steer
randomly selected from each pen. No CP × LP interactions were observed with performance data (P > .64).
Final weight and total gain were greater (P < .07) for
12.5% CP and LP compared with 10.5% CP and control
steers, respectively. Also, DMI was increased (P = .08)
with 12.5% CP but not with LP supplementation (P =
.36). In addition, ADG and gain:feed ratio were greater
(P < .03) for both 12.5% CP and supplemental LP. Ruminal NH3 N concentration was greater (P < .09) with
12.5% CP and LP. Total VFA concentration and molar
proportion of acetate were not affected by treatment (P
Key Words: Laidlomycin Propionate, Ionophores, Protein, Steers
2000 American Society of Animal Science. All rights reserved.
Introduction
J. Anim. Sci. 2000. 78:173–180
gested that monensin increased feed efficiency of ruminants by decreasing ruminal degradation of dietary protein. This protein-sparing effect was proposed following
studies indicating that monensin supplementation increased abomasal flow of dietary protein in steers (Poos
et al., 1979) and improved gain efficiency of steers on
lower-protein diets (10.5% CP) to a greater extent than
it improved that of steers consuming higher-protein
diets (12.5% CP; Hanson and Klopfenstein, 1979). Mo-
Dinius et al. (1976) provided the first evidence that
an ionophore, monensin, could affect N metabolism in
ruminants. They reported that monensin decreased ruminal NH3 N concentration in steers. Early studies sug-
1
Approved by the director of the Kentucky Agric. Exp. Sta. as
publication 98-07-183.
2
The authors are grateful to Roche Vitamins Inc., Parsippany, NJ
for provision of laidlomycin propionate; Grand Laboratories, Inc.,
Larchwood, IA, for provision of vaccines; and Merck and Company,
Rahway, NJ, for provision of anthelmintic.
Received January 11, 1999.
Accepted May 30, 1999.
3
Present Address: Eastern Oregon Agric. Res. Center, Oregon
State Univ., Burns 97720.
4
To whom correspondence should be addressed (phone: (606) 2577516; fax: (606) 257-3412; E-mail: [email protected]).
173
174
Bohnert et al.
nensin has subsequently been shown to decrease ruminal NH3 N concentration by decreasing degradation of
peptides and deamination of amino acids by ruminal
bacteria (Chen and Russell, 1991; Yang and Russell,
1993; Lana and Russell, 1997). However, monensin
does not seem to affect ruminal degradation of dietary
protein (Nagaraja, 1995).
Laidlomycin propionate (LP) may not affect N metabolism in the same manner as monensin. Galyean et al.
(1992) noted LP supplementation increased the ruminal NH3 N concentration of steers offered a concentrate
diet. In addition, Zinn et al. (1996) reported LP increased duodenal flow of NH3 N for steers, suggesting
an increased ruminal NH3 N concentration. Therefore,
we conducted two experiments to evaluate the effect of
LP on steer growth and ruminal N metabolism. In Exp.
1, growth and ruminal characteristics of steer calves
consuming low-protein diets supplemented with LP
were evaluated to determine whether LP elicited a protein-sparing effect. In Exp. 2, we compared ruminal
fermentation and CP degradation in steers adapted to
LP or monensin. In vitro deamination of amino acids
by mixed ruminal bacteria adapted to LP or monensin
was also evaluated.
Materials and Methods
Growth Experiment
Animals and Diets. Beef steers (n = 96; 255 ± 3 kg;
primarily of Angus influence) were obtained through
public auctions in central Kentucky. A 3-wk receiving
protocol for health and corn silage diet adaptation was
used. Steers were monitored for temperature (rectally;
>39°C) and respiratory problems and treated appropriately. Prior to initiation of the 91-d study, steers were
vaccinated with Clostri Shield 7 Way and Vira Shield 5
+ Somnus (Grand Laboratories, Larchwood, IA), treated
for elimination of internal and external parasites with
Ivomec (Merck and Company, Rahway, NJ), and implanted with Ralgro (Schering-Plough Animal Health,
Union, NJ).
Experimental diets (Table 1) consisted of 90% corn
silage (8.9% CP and 50% NDF) and 10% supplement
(nonpelleted; DM basis). The experimental design was
a randomized complete block with a 2 × 2 factorial arrangement of treatments consisting of two levels of dietary CP (formulated to 10.5 and 12.5% of DM) with
and without LP (11 mg/kg diet DM). Diets were formulated to provide adequate amounts of Ca, P, and vitamins A, D, and E (NRC, 1984). Steers were stratified by
weight and allotted randomly to one of four treatments.
They were then sorted by treatment and weight and
allotted randomly to one of 24 pens (3.0 × 3.6 m; four
steers/pen; six pens/treatment). Steers were weighed
before feeding (0800) on two consecutive days at the
beginning and end of the experiment. Intermediate
weights were taken approximately every 28 d. All steers
were offered diets at a common percentage of BW (calcu-
lated from the pen of steers previously consuming the
least daily DMI on a BW basis) for the final 5 d of
the study in order to minimize the effects of intake on
ruminal fill.
Ruminal fluid (approximately 40 mL) was collected
with a 60-mL catheter-tip syringe (product #309664,
Becton-Dickinson, Rutherford, NJ) and a stomach tube
(Rumen Fluid Suction Strainer, Precision Machine Co.,
Lincoln, NE; 90 cm of 6.4 mm i.d. × 9.6 mm o.d. Tygon
tubing, Norton Performance Plastics, Akron, OH) on d
91 from one steer randomly selected from each pen 4
h after feeding. The first aliquot of ruminal fluid was
discarded to minimize contamination by saliva. Ruminal fluid pH was measured immediately after collection
(Accumet Basic pH Meter, Fisher Scientific, Pittsburgh,
PA). Five milliliters was acidified with 1 mL of 25% (wt/
vol) meta-phosphoric acid, placed on ice for transport
to the laboratory, and stored (−20°C) for subsequent
analysis of VFA and NH3 N. Frozen (−20°C) ruminal
fluid samples were prepared for analysis by thawing,
centrifuging (15,000 × g for 10 min, 4°C), and collecting
supernatant. Volatile fatty acids were analyzed as described by Bock et al. (1991) and NH3 N with a modification (sodium salicylate was substituted for phenol) of
the procedure described by Broderick and Kang (1980).
Feed bunks were checked daily at 0730, and pen intake was adjusted to allow for 10% refusals. Steers were
offered 55% of the daily allotment of corn silage at 0800
and 45% at 1600. The daily allotment of supplement
was top-dressed at 0800 to ensure consumption. Fresh
water was available at all times. Supplements and corn
silage were collected and analyzed weekly for DM (55°C
for 48 h). Feed samples were ground through a 1-mm
screen (Cyclotech 1093 Sample Mill, Tecator, Hoganas,
Sweden) and analyzed for DM (AOAC, 1990) and N
(Leco FP-2000, Leco Corporation, St. Joseph, MI).
Ruminal Metabolism Experiment
Animals and Diets. Six ruminally cannulated Angus
steers (262 ± 6 kg initial BW) were used in a replicated
3 × 3 Latin square design. The steers were offered a
90% corn silage and 10% supplement diet (DM basis;
nonpelleted supplement; Table 1) at 2.0% of BW in
two equal portions daily (0700 and 1900). The diet was
formulated to contain 12.5% CP. Soybean meal (SBM)
and urea were used as sources of supplemental N. Dietary treatments consisted of a control (no ionophore)
and two ionophore treatments (LP or monensin). Laidlomycin propionate and monensin were individually
weighed and mixed into the supplement at each feeding
to provide 11 and 33 mg/kg of diet DM, respectively
(monensin was provided at 16.5 mg/kg d 1 through d 7
then at 33 mg/kg d 8 through d 28 to allow adaptation
and minimize intake depression often associated with
monensin; Goodrich et al., 1984).
Sample Collection. Experimental periods were 28 d.
Steers were dosed at 0700 on d 25 with 300 mL of CrEDTA (Binnerts et al., 1968). Ruminal fluid (≈ 100 mL)
175
Laidlomycin and ruminal nitrogen metabolism
Table 1. Ingredient composition of diets fed to steers
Growth study
Control
Item
Ingredient, % of DM
Corn silage
Soybean meal
Corn
Urea
Choice white grease
Limestone
Dicalcium phosphate
Trace mineral saltb
Vitamins A, D, and Ec
Cattlystd
Chemical CP, % of DM
Laidlomycin propionate
10.5% CP
12.5% CP
10.5% CP
12.5% CP
Metabolism
studya
90.00
2.39
5.61
.25
.12
.79
.51
.30
.03
—
10.8
90.00
7.04
.96
.25
.12
.79
.51
.30
.03
—
13.0
90.00
2.39
5.60
.25
.12
.79
.51
.30
.03
.01
10.7
90.00
7.04
.95
.25
.12
.79
.51
.30
.03
.01
13.0
90.00
7.75
—
.50
.12
.79
.51
.30
.03
—
13.0
a
Control treatment received basal diet, and the monensin and laidlomycin propionate treatments received
the basal diet and 33 and 11 mg/kg DM, respectively, of monensin and laidlomycin propionate.
b
98.5% NaCl, .35% Zn, .34% Fe, .20% Mn, 330 ppm Cu, 70 ppm I, 50 ppm Co, and 90 ppm Se.
c
8,800 IU/g vitamin A, 1,760 IU/g vitamin D, and 1.1 IU/g vitamin E.
d
11.02% laidlomycin propionate.
was collected at 0, 1, 3, 5, 7, 9, and 12 h after dosing
and immediately analyzed for pH (Accumet Basic pH
Meter, Fisher Scientific). Five milliliters was acidified
with 1 mL of 25% (wt/vol) meta-phosphoric acid and
stored (−20°C) for analysis of NH3 N and VFA. Fifteen
milliliters was stored (−20°C) for Cr analysis to determine ruminal fluid dilution rate and ruminal liquid
volume. The 15-mL and acidified samples were prepared for analysis by thawing, centrifuging (15,000 ×
g; 10 min, 4°C), and collecting supernatant. Samples
were analyzed for Cr with atomic absorption spectroscopy using a nitrous oxide/acetylene flame (Unicam
929 AA Spectrometer, ATI Unicam, Cambridge, U.K.),
NH3 N using a slight modification of the Sigma Diagnostics Procedure 171-UV using glutamate dehydrogenase
(Sigma Chemical Co., St. Louis, MO) and a centrifugal
analyzer (COBAS FARA II, Roche Diagnostic Systems),
and VFA as described by Bock et al. (1991).
In situ evaluation of SBM CP degradation was conducted on d 27. Dacron bags were labeled with a waterproof, permanent marker and weighed after drying at
55°C for 24 h. In situ bags (5 × 10 cm; Ankom Co.,
Fairport, NY) containing 1 g of SBM were prepared
in triplicate and analyzed for initial N content. Three
empty bags (blanks) were analyzed to account for any
N present in the bags themselves. Duplicate bags (containing 1 g of SBM) were heat-sealed and placed in a
bucket containing warm water (39°C) prior to incubation in the steers (approximately 5 min). Dacron bags
were placed in a weighted polyester mesh bag within
the rumen of each steer (0, 2, 4, 6, 8, 12, 16, and 24-h
incubations) in reverse order, allowing all bags to be
removed from the rumen simultaneously. Duplicate
bags were incubated for 24 h and used to correct for
microbial and feed contamination. Upon removal, in
situ bags were rinsed under warm tap water until the
effluent was clear. The bags were allowed to drip dry
for 24 h, dried at 55°C for 24 h, and weighed. The entire
bag and contents was analyzed for N (Leco FP-2000).
The in situ degradation of SBM N was expressed as a
percentage of the original N. Variables determined in
the in situ study were percentage N disappearance at
0 h (assumed to be soluble N), N degradation per hour
(calculated as the slope of the regression of the natural
log of the percentage N remaining vs time), and percentage of undegradable intake protein (UIP; determined
according to the equation of Mathers and Miller, 1981;
passage rate = .05/h).
Mixed Culture In Vitro Incubation and Sampling.
Whole ruminal contents obtained from all areas of the
rumen were collected at 0900 (2 h after feeding) on d 28
of each period. Contents were squeezed through eight
layers of cheesecloth and fluid was collected in a 1-L
Erlenmeyer flask. The flasks were immediately transported to the laboratory and allowed to incubate anaerobically at 39°C for 30 min to buoy feed particles to the
top of the flask and sediment protozoa to the bottom.
Mixed ruminal bacteria used in preparation of inoculum were harvested from the center of the flask using
a 60-mL catheter-tip syringe (product #309664; BectonDickinson) and Tygon tubing (60 cm; 4.8 mm i.d. and
8 mm o.d.) attached to a glass tube (22 cm; 4 mm i.d.
and 6 mm o.d.). The inoculum consisted of a 50:50 combination of ruminal fluid and the anaerobic dilution
solution described by Bryant and Robinson (1961; without resazurin and cysteine sulfide).
Fifty milliliters of anaerobic dilution solution (39°C)
containing 1.5 g of Amicase (casein acid hydrolysate
consisting of approximately 80% free amino acids and
20% di- and tri-peptides; Product #A2427, Sigma Chemical Co.) was added in duplicate to 125-mL Erlenmeyer
flasks and capped with #6 neoprene stoppers (product
#14-135J, Fisher Scientific) equipped with vacuum
check valves (product #15-339-2; Fisher Scientific) for
176
Bohnert et al.
release of gas resulting from fermentation. The flasks
were flushed with CO2 before and during inoculum addition. An equal volume (50 mL) of ruminal fluid was
added to each flask to bring the final concentration of
Amicase to 15 g/L. Treatments in vitro (control, LP, or
monensin) were the same as each donor animal received. Ionophores were dissolved in ethanol and included in the inoculum at 6 ␮g/mL and 2 ␮g/mL for
monensin (Sigma product #M-5273) and LP, respectively. The control treatment received an equal volume
of ethanol (500 ␮L). Ionophore solutions were prepared
fresh each period. Laidlomycin propionate was extracted from 1.824 g of Cattlyst 50 (11.02% LP; Roche
Vitamin Inc., Parsippany, NJ) by adding 10 mL of ethanol and grinding with a mortar and pestle for 5 min.
The mixture was quantitatively transferred into a 50mL tube and centrifuged (15,000 × g for 15 min, 4°C).
The resulting supernatant was transferred into a 500mL volumetric flask. The pellet was resuspended in 50
mL of ethanol and centrifuged, and the supernatant
was collected as before. This step was repeated twice.
The LP solution was brought to volume with ethanol
and stored (4°C).
Flasks were incubated for 8 h at 39°C with samples (2
mL) taken after 0, 1, 2, 3, 4, 5, 6, 7, and 8 h. Preliminary
experiments indicated NH3 N concentration was firstorder with respect to time for this incubation period.
Samples were placed in prechilled 2-mL microcentrifuge tubes and centrifuged (15,000 × g; 5 min) to terminate fermentation and isolate bacteria. An aliquot of
supernatant (750 ␮L) was acidified with 150 µL of 25%
meta-phosphoric acid (wt/vol) and stored (−20°C). An
additional 750-␮L aliquot was stored (−20°C) for analysis of α-amino N (AAN). The bacterial pellet was
washed once with 1 mL of .9% NaCl (wt/vol) and stored
(−20°C) for analysis of protein. Protein was determined,
following treatment of the pellet with 1.5 mL of .11 N
NaOH (100°C, 30 min), using the BCA procedure
(Smith et al., 1985). Acidified samples were centrifuged
as before, and supernatant was collected and stored
(−20°C) for analysis of NH3 N (as described above using
glutamate dehydrogenase) using a centrifugal analyzer
(COBAS FARA II, Roche Diagnostic Systems). Upon
thawing, a .5-mL aliquot of the non-acidified sample
and 2 mL of 7.5 N HCl were placed in a 30-mL serum
bottle, bubbled with N for 30 s, tightly sealed with a
rubber stopper (Bellco Glass, Vineland, NJ; product
#2048-11800), capped with an aluminum seal (Fisher
Scientific; product #06-406-14B), and placed in a 110°C
oven for 24 h. Upon cooling, 2 mL of 7.5 N NaOH was
added to neutralize excess HCl, and samples were analyzed for AAN (Palmer and Peters, 1969). Rates of net
NH3 N production (nmol NH3 Nⴢmg protein−1ⴢmin−1)
and AAN degradation (nmol AANⴢmg protein−1ⴢmin−1)
were calculated based on changes in concentration of
NH3 N and AAN.
Statistical Analysis
Growth Experiment. Dry matter intake, ADG,
gain:feed ratio, ruminal pH, NH3 N, and VFA were
analyzed as a randomized complete block design using
the GLM procedure of SAS (1995). The statistical model
included weight block, protein level, LP, and protein
level × LP. Pen was used as the experimental unit;
however, n was 4 for ruminal data associated with the
10.5% CP treatment that received LP because of sample
loss. Consequently, least squares means were used for
ruminal data. Treatment responses were considered
different when P < .10.
Ruminal Metabolism Experiment. Data were analyzed
as a replicated 3 × 3 Latin square design using the GLM
procedure of SAS (1995). The statistical model included
square, treatment, period within square, and steer
within square. Orthogonal contrasts were 1) control vs
LP and monensin and 2) LP vs monensin. Response
variables included percentage in situ SBM N degradation per hour, percentage of ruminal escape N, ruminal
volume, ruminal fluid dilution rate, and rates of net
NH3 N production and AAN degradation. Ruminal
VFA, NH3 N, and pH data collected at fixed times
throughout the sampling day were analyzed using the
REPEATED statement in the GLM procedure of SAS
(1995). The statistical model included square, period
within square, steer within square, and treatment. No
treatment × time interactions were detected (P > .10);
therefore, measurements were averaged across time,
and treatment means were compared as described
above. Treatment responses were considered different
when P < .10.
Results
Growth Experiment
No LP × CP interactions were observed for performance data (P > .64). Steer final weight and total gain
were greater (P < .07) for 12.5% CP and LP compared
with 10.5% CP and control, respectively (Table 2). In
addition, DMI increased (P = .08) with 12.5% CP but
not for steers supplemented with LP (P = .36). Average
daily gain and gain:feed ratio were increased (P < .03)
for 12.5% CP and LP compared with 10.5% CP and
control, respectively.
A LP × CP interaction was not observed with ruminal
pH or NH3 N (P > .47). Ruminal pH was not affected
by LP (P > .44), but it was lower (P = .01) in steers
supplemented with 12.5% CP than in those given 10.5%
CP (Table 3). Ruminal NH3 N (mM) was greater with
steers supplemented with both 12.5% CP (P = .01) and
LP (P = .08).
No LP × CP interactions (P > .35) were observed for
ruminal VFA, except for isobutyrate (P = .05) and isovalerate (P = .06). Protein level and LP did not affect total
VFA concentration (P > .11) or molar proportion of acetate (P > .23). However, propionate (concentration) was
greater in steers supplemented with 12.5% CP (P = .08)
and LP (P = .005). Molar proportion of butyrate was
not affected by protein or LP (P > .45). In addition,
protein did not affect (P > .13) proportions of valerate
177
Laidlomycin and ruminal nitrogen metabolism
Table 2. Effect of laidlomycin propionate (LP) and protein on steer dry matter intake,
average daily gain, and gain:feed ratio
Control
Item
10.5% CP
Initial weight, kg
Final weight, kg
Total gain, kg
12.5% CP
256
351
95
Days 0 to 91
DMI, kg/d
ADG, kg/d
Gain:feed ratio
LP
256
368
112
6.29
1.04
.167
10.5% CP
256
360
106
6.64
1.23
.185
P-value
12.5% CP
254
376
122
6.51
1.16
.179
SEMa
CP
LP
CP × LP
—
—
.001
.01
—
.06
.02
—
.96
.90
.15
.04
.005
.08
.01
.01
.36
.02
.01
.65
.90
.76
4
4
6.72
1.34
.200
n = 6.
a
or acetate:propionate ratio. Conversely, LP decreased
valerate and the acetate:propionate ratio (P < .03). As
dietary CP increased, isobutyrate molar proportion increased without LP but decreased with LP. Isovalerate
was not affected by dietary CP in control steers; however, it was decreased in LP-supplemented steers consuming 12.5 compared with those given 10.5% CP diets
(1.9 and 1.3 for 10.5 and 12.5% CP, respectively).
trations) were observed between LP and monensin. Molar proportions of isobutyrate, butyrate, isovalerate,
and valerate were not different (P > .10) for control
and ionophore-supplemented steers. In addition, molar
proportions of isobutyrate, isovalerate, and valerate
were similar (P > .26) for LP and monensin. Butyrate
(concentration) was decreased (P = .01) with monensin
compared with LP. Ionophore supplementation decreased (P = .01) acetate:propionate compared with control steers. No difference (P = .82) in acetate:propionate
was observed between LP and monensin.
In Situ Protein Degradation. Soybean meal CP degradation rate was lower (P = .09) for control than for
ionophore-supplemented steers (Table 4). No differences (P = .52) in SBM CP degradation rate were observed between LP and monensin. However, extent of
SBM CP degradation was not affected (P > .25) by ionophore addition.
In Vitro Deamination of Amino Acids. Microbial specific activity of net NH3 N production was greater (P =
.03) for control than for ionophore-adapted microbes
(Table 4). Laidlomycin propionate and monensin had
similar (P = .40) microbial specific activities of net NH3
N production. Also, microbial specific activity of net
AAN degradation was greater (P = .02) for microbes
Ruminal Metabolism Experiment
Ruminal Variables. Ruminal fluid dilution rate (percentage per hour) was greater (P = .01) for steers given
LP and monensin than for control steers (Table 4). No
difference (P = .13) was observed in dilution rate between LP and monensin. Also, ruminal volume and pH
were not affected (P > .28) by ionophore treatment.
However, ruminal NH3 N concentration was greater
(P = .07) for control than for ionophore-supplemented
steers. Addition of LP increased (P = .02) ruminal NH3
N concentration compared with monensin.
Total ruminal VFA concentration was not affected (P
> .15) by ionophore treatment. However, molar proportions of acetate were decreased (P = .02) and propionate
increased (P = .01) in ionophore-supplemented steers.
No differences (P > .60) in acetate or propionate (concen-
Table 3. Effect of laidlomycin propionate (LP) and protein on ruminal pH, NH3 N, and VFA in the growth study
Control
LP
P-value
10.5% CP
12.5% CP
10.5% CP
12.5% CP
SEMa
CP
LP
CP × LP
pH
NH3 N, mM
Total VFA, mM
6.79
.7
90.6
6.65
2.8
100.0
6.79
1.9
96.8
6.55
4.7
100.4
.08
.97
4.7
.01
.01
.12
.45
.08
.41
.48
.70
.48
VFA, mol/100 mol
Acetate
Propionate
Isobutyrate
Butyrate
Isovalerate
Valerate
65.8
17.3
1.7
12.5
1.2
1.3
66.0
18.5
2.0
11.2
1.3
1.7
65.3
19.6
2.1
11.0
1.9
.9
63.5
20.8
1.8
11.3
1.3
1.0
1.5
.8
.2
1.1
.2
.2
.52
.08
.76
.58
.26
.19
.24
.005
.37
.46
.06
.005
.44
.93
.05
.36
.06
.43
3.8
3.6
3.4
3.1
.2
.14
.02
.64
Item
Acetate:propionate ratio
n = 6 except for 10.5% CP with laidlomycin propionate, for which n = 4; therefore, the largest SEM is presented.
a
178
Bohnert et al.
Table 4. Effect of laidlomycin propionate (LP) and monensin (M) on rumen
characteristics, soybean meal (SBM) CP degradation rate, undegradable intake
protein, and in vitro net NH3 N production and α-amino N (AAN)
degradation in the ruminal metabolism study
Control
LP
M
SEMa
Control
vs LP & M
LP vs M
Ruminal dilution rate, %/h
Ruminal volume, L
pH
NH3 N, mM
Total VFA, mM
8.24
31.9
6.62
5.28
90.2
9.08
30.6
6.64
5.20
88.0
9.74
29.8
6.69
4.28
85.6
.27
1.2
.03
.20
1.7
.01
.29
.34
.07
.16
.13
.656
.31
.02
.36
VFA, mol/100 mol
Acetate
Propionate
Isobutyrate
Butyrate
Isovalerate
Valerate
65.8
16.9
2.7
11.3
2.0
1.3
63.3
19.0
2.8
11.4
2.3
1.2
63.5
19.4
2.9
10.4
2.4
1.3
.6
.5
.1
.2
.2
.04
.02
.01
.19
.10
.25
.59
.80
.61
.27
.01
.79
.42
4.0
8.73
32.6
3.4
9.81
29.8
3.4
10.34
30.9
.1
.55
1.5
.01
.09
.26
.82
.52
.61
40.1
30.8
29.3
21.4
24.3
16.0
3.8
3.0
.03
.02
.40
.25
Item
Acetate:propionate ratio
SBM CP degradation rateb, h−1
Undegradable intake protein, %
Microbial specific activity,
nmolⴢmg protein−1ⴢmin−1
Net NH3 N production
Net AAN degradation
n = 6.
In situ.
a
b
not adapted to ionophore, with no difference (P = .25)
between LP and monensin.
Discussion
Steer Performance
In the current study, LP did not alter DMI but improved ADG and gain:feed ratio (10 and 8%, respectively). This is similar to other studies that have used
LP. Zinn and Spires (1987) found that LP increased
ADG (11%) of steers consuming concentrate diets without affecting DMI. Consequently, gain:feed ratio was
improved (8%) with LP supplementation. Spires et al.
(1990) reviewed six experiments in which LP was used
in diets of feedlot cattle. They noted that LP improved
rate of gain and gain:feed ratio when included within
the range of 6 to 12 mg/kg of diet DM. In addition,
LP did not substantially affect DMI (one experiment
reported increased DMI due to LP). It was also suggested that improvements in performance with LP were
greater on lower-energy diets than on higher-energy
diets (ranging from 1.08 to 1.49 Mcal NEg/kg of DM).
Diets in the current study contained 1.05 Mcal NEg/kg
of DM (calculated from tabular values; NRC, 1984).
Lack of a LP effect on DMI is contrary to most results
observed with monensin. Raun et al. (1976) increased
monensin inclusion in steer diets from 0 to 88 mg/kg of
diet (air-dry basis). Dry matter intake decreased when
monensin was added to the diet at 22, 33, 44, and 88 mg/
kg. Average daily gain was not affected. Consequently,
gain:feed ratio increased with increasing monensin. In
a review evaluating the effects of monensin on the performance of approximately 16,000 feedlot cattle, Goodrich et al. (1984) reported cattle consuming diets containing monensin consumed 6.4% less feed, gained
weight 1.6% faster, and required 7.5% less feed/kg of
gain than cattle fed control diets.
Hanson and Klopfenstein (1979) conducted a series
of experiments to evaluate the protein-sparing effect of
monensin (200 mgⴢsteer−1ⴢd−1) with beef steers consuming corn silage-based diets. They used urea, brewers
dried grains, and SBM as supplemental N sources in
formulating diets either low (10.5 or 11.1%) or high
(12.5 or 13.1%) in CP (DM basis). As with the current
study, ADG and gain:feed ratio were improved by increasing dietary CP. Monensin did not improve ADG
or gain:feed ratio; however, it did tend to improve
gain:feed ratio to a greater extent for low- than for highprotein diets (16 vs 9% and 8 vs 3% for 10.5 vs 12.5%
CP and 11.1 vs 13.1% CP, respectively). Therefore, the
authors suggested that monensin had a protein-sparing
effect. In contrast, improvements in gain:feed ratio and
ADG due to LP in the current study were comparable
for the 10.5 and 12.5% CP diets (7 vs 8% and 12 vs 9%
for gain:feed ratio and ADG, respectively). Also, lack of
a CP × LP interaction for ADG suggests LP did not
elicit a protein-sparing response.
Ruminal Characteristics
Ionophore effects on ruminal fluid dilution rate, ruminal volume, and ruminal pH have been variable. Campbell et al. (1997) and Yang and Russell (1993) reported
Laidlomycin and ruminal nitrogen metabolism
results similar to those observed in the current study.
Campbell et al. (1997) supplemented corn-based steer
diets with free amino acids and LP or monensin. They
reported that LP and monensin had no effect on ruminal
fluid dilution rate, ruminal liquid volume, or ruminal
pH. In addition, Yang and Russell (1993) noted that
ruminal fluid dilution rate, ruminal volume, and ruminal pH were unaltered by monensin addition (350 mg/
d) to diets of nonlactating cows supplemented with 0,
1, or 2 kg/d of SBM. In contrast, Lemenager et al. (1978)
reported that steers consuming a low-quality forage
diet with 200 mg/d monensin had decreased ruminal
fluid dilution rates (44%) and ruminal liquid volumes
(36%) compared with controls not supplemented with
monensin. In addition, Burrin and Britton (1986; 150
or 300 mg monensin/d) and Galyean et al. (1992; 6 or
12 mg LP/kg diet DM) reported ionophore supplementation increased ruminal pH of steers consuming concentrate diets compared with unsupplemented controls.
Some ionophores have been shown to reduce ruminal
NH3 N concentration. Reviews by Bergen and Bates
(1984), Russell and Strobel (1989), and Nagaraja (1995)
describe mechanisms attributed to ionophore-induced
depression of ruminal NH3 N. These include decreased
degradation of peptides, decreased deamination of
amino acids, decreased numbers of amino acid-fermenting ruminal bacteria, and decreased ruminal urease activity.
Laidlomycin propionate has been reported to maintain or increase ruminal NH3 N concentration in steers,
as noted in the growth and ruminal metabolism experiments (Galyean et al., 1992; Campbell et al., 1997).
Galyean et al. (1992) adapted steers to a 75% concentrate diet with or without LP (12 mg/kg diet DM) for
21 d. They noted no difference in ruminal NH3 N concentration between LP and control steers for the first 14
d of adaptation. However, LP increased ruminal NH3
N on d 20 and 21 (97 and 159%, respectively). Campbell
et al. (1997) reported no difference in ruminal NH3 N
concentration of steers consuming an 86% dry-rolled
corn diet with or without LP (11 mg/kg diet DM; 13 vs
10 mM, respectively). However, ruminal NH3 N was
not affected by monensin (33 mg/kg diet DM) in their
study. Based on current data, differences in ruminal N
metabolism that increase the ruminal concentration of
NH3 N with LP compared with monensin supplementation are not clear.
Bergen and Bates (1984) reported that the most consistent observation with ionophore supplementation is
modification of ruminal fermentation. Typically, concentrations of total VFA are not affected, but molar
proportions of propionate are increased and acetate and
butyrate are decreased compared with unsupplemented
controls (Raun et al., 1976; Chalupa et al., 1980). Laidlomycin propionate has been reported to affect ruminal
VFA concentrations in a similar fashion, except for butyrate, which is not altered (Galyean et al., 1992; Zinn
et al., 1996; Campbell et al., 1997). Ionophore effects on
179
ruminal VFA concentrations in the growth and ruminal
metabolism experiments agree with these observations.
A minor shift was noted in the molar proportion of
valerate in the growth experiment but not in the ruminal metabolism experiment. Others (Zinn and Spires,
1987; Galyean et al., 1992; Campbell et al., 1997) have
noted that LP does not alter molar proportions of four
and five-carbon branched- and straight-chain VFA.
Steers in the ruminal metabolism experiment, in which
isovalerate and valerate were not affected by LP, were
consuming a 12.5% CP basal diet. The increased molar
proportion of isovalerate with LP-supplemented steers
in the growth experiment was due to an increase with
the 10.5% CP LP treatment, as indicated by a LP × CP
interaction. Therefore, dietary CP may have influenced
molar proportion of isovalerate. In contrast, LP decreased the molar proportion of valerate with both 10.5
and 12.5% CP. The procedures used to sample ruminal
fluid may have also affected molar proportions of these
minor VFA. Growth study steers were sampled with a
stomach tube at a single time, and ruminal metabolism
steers were sampled directly from the rumen at various
times throughout the day.
Ruminal degradation rate of SBM CP was greater
with LP and monensin supplementation compared with
the control, possibly due to the increased ruminal fluid
dilution rates observed with ionophore supplementation. The greater dilution rates may have increased
microbial activity (Russell and Hespell, 1981); however,
no differences were observed in UIP.
Monensin has been reported to decrease degradation
of peptides and deamination of amino acids to a greater
extent than protein degradation (Van Nevel and Demeyer, 1977). In addition, Chen and Russell (1991)
noted in vitro protein degradation by mixed ruminal
bacteria was not affected by monensin addition; however, NH3 N production was decreased. Consequently,
ionophores seem to decrease deamination of amino
acids and peptides without affecting proteolysis (Nagaraja, 1995). Results observed for extent of ruminal degradation of SBM CP in the current experiment support
these findings.
Rates of net NH3 N production reported here are
similar to rates reported by Yang and Russell (1993)
and Lana and Russell (1997) for mixed populations of
ruminal bacteria. In addition, they noted that monensin
decreased net NH3 N production rate from 22 to 62%
compared with controls. Similarly, monensin and LP
decreased microbial specific activity of net NH3 N production (37 and 67%, respectively) and AAN degradation (44 and 92%, respectively) compared with the control treatment in the current study. Also, Wampler et
al. (1998) evaluated the effects of LP (2 ␮g/mL) and
monensin (5 ␮g/mL) on serine uptake by Streptococcus
bovis. They noted that the specific activity of serine
uptake was decreased with monensin and LP (106 and
19%, respectively) compared with an ethanol-treated
control.
180
Bohnert et al.
Laidlomycin propionate increases ruminal NH3 N
concentration compared with monensin, even though
both ionophores decrease the capacity of ruminal bacteria to degrade peptides and amino acids without affecting proteolysis. However, with the dosages used in the
current study, monensin seems to be a more potent
inhibitor of amino acid deamination by mixed ruminal
bacteria (20 and 34% for net ammonia nitrogen production and α-amino nitrogen degradation, respectively).
Implications
Laidlomycin propionate does not seem to elicit the
protein-sparing effect observed with monensin. In addition, laidlomycin propionate and monensin do not seem
to affect overall ruminal nitrogen metabolism in a similar fashion, even though both ionophores decrease deamination of amino acids without affecting the extent of
protein degradation. However, laidlomycin propionate
seems to improve steer average daily gain and
gain:feed ratio.
Literature Cited
AOAC. 1990. Official Methods of Analysis (15th Ed.). Association of
Official Analytical Chemists, Arlington, VA.
Bergen, W. G., and D. B. Bates. 1984. Ionophores: Their effect on
production efficiency and mode of action. J. Anim. Sci.
58:1465–1483.
Binnerts, W. T., A. T. Van’t Klooster, and A. M. Frens. 1968. Soluble
chromium indicator measured by atomic absorption in digestion
experiments. Vet. Rec. 82:470.
Bock, B. J., D. L. Harmon, R. T. Brandt, Jr., and J. E. Schneider.
1991. Fat source and calcium level effects on finishing steer
performance, digestion, and metabolism. J. Anim. Sci.
69:2211–2224.
Broderick, G. A., and J. H. Kang. 1980. Automated simultaneous
determination of ammonia and total amino acids in ruminal
fluid and in vitro media. J. Dairy Sci. 63:64–75.
Bryant, M. P., and I. M. Robinson. 1961. An improved nonselective
culture medium for ruminal bacteria and its use in determining
diurnal variation in numbers of bacteria in the rumen. J. Dairy
Sci. 44:1446–1456.
Burrin, D. G., and R. A. Britton. 1986. Response to monensin in cattle
during subacute acidosis. J. Anim. Sci. 63:888–893.
Campbell, C. G., E. C. Titgemeyer, R. C. Cochran, T. G. Nagaraja,
and R. T. Brandt, Jr. 1997. Free amino acid supplementation
to steers: Effects on ruminal fermentation and performance. J.
Anim. Sci. 75:1167–1178.
Chalupa, W., W. Corbett, and J. R. Brethour. 1980. Effects of monensin and amicloral on rumen fermentation. J. Anim. Sci.
51:170–179.
Chen, G., and J. B. Russell. 1991. Effect of monensin and a protonophore on protein degradation, peptide accumulation, and deamination by mixed ruminal microorganisms in vitro. J. Anim. Sci.
69:2196–2203.
Dinius, D. A., M. E. Simpson, and P. B. Marsh. 1976. Effect of monensin fed with forage on digestion and the ruminal ecosystem of
steers. J. Anim. Sci. 42:229–234.
Galyean, M. L., K. J. Malcolm, and G. C. Duff. 1992. Performance
of feedlot steers fed diets containing laidlomycin propionate or
monensin plus tylosin, and effects of laidlomycin propionate concentration on intake patterns and ruminal fermentation in beef
steers during adaptation to a high-concentrate diet. J. Anim.
Sci. 70:2950–2958.
Goodrich, R. D., J. E. Garrett, D. R. Gast, M. A. Kirick, D. A. Larson,
and J. C. Meiske. 1984. Influence of monensin on the performance of cattle. J. Anim. Sci. 58:1484–1498.
Hanson, T. L., and T. Klopfenstein. 1979. Monensin, protein source
and protein levels for growing steers. J. Anim. Sci. 48:474–479.
Lana, R. P., and J. B. Russell. 1997. Effect of forage quality and
monensin on the ruminal fermentation of fistulated cows fed
continuously at a constant intake. J. Anim. Sci. 75:224–229.
Lemenager, R. P., F. N. Owens, B. J. Shockey, K. S. Lusby, and R.
Totusek. 1978. Monensin effects on rumen turnover rate, twentyfour hour VFA pattern, nitrogen components and cellulose disappearance. J. Anim. Sci. 47:255–261.
Mathers, J. C., and E. L. Miller. 1981. Quantitative studies of food
protein degradation and the energetic efficiency of microbial
protein synthesis in the rumen of sheep given chopped lucerne
and rolled barley. Br. J. Nutr. 45:587–604.
Nagaraja, T. G. 1995. Ionophores and antibiotics in ruminants. In:
R. J. Wallace and A. Chesson (Ed.) Biotechnology in Animal
Feeding. pp 173–204. VCH Publishers, New York.
NRC. 1984. Nutrient Requirements of Beef Cattle (6th Ed.). National
Academy Press, Washington, DC.
Palmer, D. W., and T. Peters, Jr. 1969. Automated determination of
free amino groups in serum and plasma using 2,4,6-trinitrobenzene sulfonate. Clin. Chem. 15:596.
Poos, M. I., T. L. Hanson, and T. J. Klopfenstein. 1979. Monensin
effects on diet digestibility, ruminal protein bypass and microbial
protein synthesis. J. Anim. Sci. 48:1516–1524.
Raun, A. P., C. O. Cooley, E. L. Potter, R. P. Rathmacher, and L. F.
Richardson. 1976. Effect of monensin on feed efficiency of feedlot
cattle. J. Anim. Sci. 43:670–677.
Russell, J. B., and R. B. Hespell. 1981. Microbial rumen fermentation.
J. Dairy Sci. 64:1153–1169.
Russell, J. B., and H. J. Strobel. 1989. Minireview: Effect of ionophores
on ruminal fermentation. Appl. Environ. Microbiol. 55:1–6.
SAS. 1995. SAS User’s Guide: Statistics (Release 6.10). SAS Inst.
Inc., Cary, NC.
Smith, P. K., R. I. Krohn, G. T. Hermanson, A. K. Mallia, F. H.
Gartner, M. D. Provenzano, E. K. Fujimoto, N. M. Goeke, B. J.
Olson, and D. C. Klenk. 1985. Measurement of protein using
bicinchoninic acid. Anal. Biochem. 150:76–85.
Spires, H. R., A. Olmsted, L. L. Berger, J. P. Fontenot, D. R. Gill, J.
G. Riley, M. I. Wray, and R. A. Zinn. 1990. Efficacy of laidlomycin
propionate for increasing rate and efficiency of gain by feedlot
cattle. J. Anim. Sci. 68:3382–3391.
Van Nevel, C. J., and D. I. Demeyer. 1977. Effect of monensin on
rumen metabolism in vitro. Appl. Environ. Microbiol. 34:251–
257.
Wampler, J. L., S. A. Martin, and G. M. Hill. 1998. Effects of laidlomycin propionate and monensin on glucose utilization and nutrient transport by Streptococcus bovis and Selenomonas ruminantium. J. Anim. Sci. 76:2730–2736.
Yang, C-M.J., and J. B. Russell. 1993. The effect of monensin supplementation on ruminal ammonia accumulation in vivo and the
numbers of amino acid-fermenting bacteria. J. Anim. Sci.
71:3470–3476.
Zinn, R. A., Y. Shen, C. F. Adam, M. Tamayo, and J. Rosalez. 1996.
Influence of dietary magnesium level on metabolic and growthperformance responses of feedlot cattle to laidlomycin propionate. J. Anim. Sci. 74:1462–1469.
Zinn, R. A., and H. R. Spires. 1987. Influence of laidlomycin supplementation on feedlot performance and digestive function in
steers. J. Anim. Sci. 65(Suppl. 1):457.