Effects of Monensin Fed to Replacement Dairy Heifers During the Growing and
Gestation Period upon Growth, Reproduction, and Subsequent Lactation
CLIFTON A. BAILE, CAROL L. M c L A U G H L I N , and W. V. C H A L U P A
School of Veterinary Medicine
University of Pennsylvania
Kennett Square 19348
D. L. S N Y D E R , L. C. P E N D L U M , and E. L. POTTER
Lilly Research Laboratories
Greenfield, IN 46140
ABSTRACT produced by a strain of Streptornyces cin-
Sixty Holstein heifers initially weighing namonensis (3). The compound improves
feed efficiency of feedlot cattle by less feed
196 kg were assigned by weight to
treatments of 0, 200, and 600 mg of being required per unit of growth (1, 9).
Improved feed efficiency is associated with
monensin. These treatments were fed
increased concentration of propionic acid and
daily until calving to determine effects of
decreased concentrations of acetic and butyric
monensin on growth rate, feed con-
acid in the rumen when monensin is fed (2, 9).
sumption, feed efficiency, reproductive
In pasture-fed cattle, monensin improved feed
performance, and subsequent lactation.
efficiency by increasing weight gains without
Throughout the :feeding period the
affecting feed intake (5, 7, 10). In growing
control (0 rag) heifers received sufficient
feed to allow a calculated growth rate of steers and heifers grazing pastures, monen-
sin at 200 mg/day provided maximum response
.68 kg/day. Monensin treatment groups
were fed the same amount of the identical (8).
ration over the 448-day experiment. Monensin also has been evaluated in mature
Daily gain, feed intake, and feed efficiency beef cows for decreasing feed costs during
for the 0, 200, and 600 mg treatments gestation. In mature brood cows fed meadow
were .60, .69, .69 kg, 7.47, 7.46, hay ad libitum, monensin (200 rag) improved
7.43 kg, and 12.411, 10.81, 10.81. Al- feed efficiency, increased weight gain, and
though days on tri~J to first estrus were decreased interval to first estrus following
not different among treatment groups, calving (11). Feeding of monensin to beef cows
heifers fed monensin at 200 and 600 being fed approximately 10% less feed than
rag/day conceived 38 and 34 days sooner untreated animals resulted in similar cow
than 0 mg heifers. Percent conception, weight, calf birth weight, weaning weight, and
number of calves born, calf birth weight, conception rate. Thus, monensin improved feed
and calving difficulty were not affected efficiency (12, 13).
by treatment. Milk production was Most monensin work has been with beef
measured for 120 days subsequent to the cattle with interest in improving growth rate
experimental feeding of monensm. During and feed efficiency of growing and finishing
this period heifers were fed a common cattle and in improving feed efficiency and
ration ad libitum. Milk production of production in the mature beef cow. In dairy
17.1, 16.9, and 17.0 kg/day for 0, 200, replacement heifers improved feed efficiency
and 600 mg was not affected by prior would reduce the cost of growing heifers, and
treatment. increased growth rate would allow for earlier
breeding. This experiment was designed to
INTRODUCTION measure the effects of feeding 200 mg of
monensin daily to Holstein heifers upon growth
Monensin is a biologically active compound
rate, feed efficiency, reproductive performance,
and milk production. In addition, 600 mg of
monensin were included as a treatment to
Received November 17:. 1981. determine consequences (safety) of feeding
1982 J Dairy Sci 65:1941--1944 1941
1942 BAILE ET AL.
three times more monensin upon growth, bull was allotted to each pen of heifers for
reproduction performance, and milk production. observation of standing heat. Bulls were rotated
among pens each day, and date of each estrus
EXPERIMENTAL PROCEDURE was recorded. Heifers weighing 340 kg or more
were bred at each estrus according to the
Experimental Design following routine. Heifers exhibiting estrus in
Sixty Holstein heifers weighing approxi- the morning observation period were artifically
mately 195 kg were selected from a group of 66 inseminated in the afternoon. Those detected in
purchased heifers, divided into heavy and heat in the afternoon were serviced the following
light weight groups blocked by weight into sets morning. The same ejaculate from an Angus
of 3 and assigned by blocks to three pens of 10 bull was used to breed all heifers. If conception
animals per group Treatments of 0, 200, and did not occur after three services, the heifer was
600 mg of monensin per animal per day were considered a nonbreeder and was deleted
assigned randomly to the three pens in each from the experiment. Heifers were palpated for
weight group. confirmation of pregnancy at 45 days post-
breeding. Birth date, weight, and sex of calves
Housing born were recorded.
Heifers were confined in six 4.6 × 9.1 m Lactation and Rebreeding
concrete floored pens which had a gutter
cleaner. The building in which the heifers were Approximately 3 days before calving heifers
housed was open sided but had a roof. Feed were relocated in a milking facility and were no
bunk space was adequate for all animals to ~at longer fed monensin. After calving cows were
at the same time, and water was provided fed ad libitum a common ration, and milk
by an automatic waterer in each pen. Six young production was recorded for two daily milkings
mature (18 month old) vasectomized bulls used on 5 consecutive days for each of 19 wk
for detection of heifer estrus were housed in postpartum. Biweekly milk samples taken every
separate pens in the same building. 2 wk were analyzed for fat and protein content.
Cows were observed for standing heat and were
F~eeding rebred starting 45 days postpartum.
Each group of heifers was fed a ration of
62% haylage, 24% corn silage, and 15% ground RESULTS AND DISCUSSION
shelled corn (dry matter) in quantities sufficient
to permit daily gain of .68 kg per day for Growth Performance
The 448-day growth performance data are
summarized in Table 1. Feeding monensin at
Estrus and Breeding
both 200 and 600 mg/head per day resulted in
Each morning and evening one vasectomized .09 kg/day additional weight gain (P<.05) as
TABLE 1. Performance of growing Holstein heifers fed monensin for 448 days.
Item 0 200 600
Number of heifers 20 20 20
Initial weight (kg) 197 195 195
Average weight gain (kg/day) .60a .69b .69b
Average dry feed intake (kg/day) 7.47 a 7.46 a 7.43b
Feed efficiency (intake/gain) 12.41 10.85 10.75
a'bMeans with a common superscript are not different, Duncan's multiple range test (P<.05).
Journal of Dairy Science Vol. 65, No. 10, 1982
MONENSIN FOR REPLACEMENT DAIRY HEIFERS 1943
TABLE 2. Breeding performance of growing Holstein heifers fed monensin.
Item 0 200 600
Number of heifers bred 19 19 19
Days on trial to first estrus 150 153 154
Days on trial to conception 280 242 246
Percent total conception a 95 100 100
Number of heifers calved 18b 18 c 19 d
Number of male calves 12 7 13
Number of female calves 6 8 6
Number of live calves 16 15 17
Calf birth weight (kg) 36.7 33.3 35.4
Cow weight at calving (kg) 454.5 482.6 495.3
Calving ease scoree 1.4 1.1 1.4
aFor all services.
bl calf stillborn and 1 calf died through torsion of uterus.
c3 calves were aborted; sex unknown.
dl calf stillborn and 1 calf died as a result of traumatic delivery.
el = no assistance; 2 = easily assisted; 3 = difficult assist; 4 = very difficult; 5 = Caesarean; 6 = abnormal
presentation (does not include data from aborted heifers).
c o m p a r e d to control heifers. This additional m o n e n s i n resulted in beef heifers reaching
weight gain was achieved on dry m a t t e r intakes estrus earlier and that this was n o t related
of 7.47, 7.46, and 7.43 kg/day for the 0, 200, strictly to increased b o d y weight. Percent
and 600 mg treatments. Thus, heifers fed 200 c o n c e p t i o n measured by palpation after breeding
and 600 mg o f m o n e n s i n were 12.6 and 13.4% indicated t h a t all heifers b u t one (0 m g treat-
m o r e efficient in converting feed to gain than m e n t ) were bred.
control heifers. These results are similar to All heifers calved with the e x c e p t i o n o f
those by Oliver (5), Potter et al. (7), R o u q u e t t three heifers in the 200 mg t r e a t m e n t t h a t
(10), and Potter and Muller (8) in which there aborted. Causes of these abortions are u n k n o w n
were faster growth, little effect on feed intake, but do n o t appear related to m o n e n s i n treat-
and i m p r o v e d feed efficiency w h e n m o n e n s i n m e n t as a no abortions were observed in the
was fed to b e e f cattle with high roughage rations. 600 mg treatment. Calf birth weights were
n o t affected by treatment. These data agree
with those of T u r n e r et al. (11) and Walker et
Breeding Performance al. (13), w h o r e p o r t e d no effects of m o n e n s i n
Of the 20 heifers initially assigned to each u p o n calf birth weight, n u m b e r of calves born,
t r e a t m e n t group, one heifer was r e m o v e d f r o m or calving difficulty.
each t r e a t m e n t because no signs o f estrus were Heifer weights at calving indicate that the
observed. Estrus and breeding p e r f o r m a n c e are 200 and 600 m g heifers were a p p r o x i m a t e l y 30
in Table 2. First estrus was observed in all and 4 0 kg heavier than the 0 mg heifers. The
groups at a b o u t 150 days on trial. Days on trial a p p r o x i m a t e l y 40 days earlier calving in the
to c o n c e p t i o n were 280, 242, and 246 for the 200 and 600 mg m o n e n s i n t r e a t m e n t groups
0, 200, and 600 m g / h e a d per day treatments. was n o t a c c o m p a n i e d by an increase in calving
The earlier c o n c e p t i o n with the m o n e n s i n difficulty.
t r e a t m e n t s appears to be related to heifers
Lactation and Rebreeding
grown faster and reaching weight desirable for
breeding earlier. However, Moseley et al. (4), There were no differences a m o n g t r e a t m e n t
and Pendlum et al. (6) r e p o r t e d that feeding groups in daily milk p r o d u c t i o n or p e r c e n t fat
Journal of Dairy Science Vol. 65, No. 10, 1982
1944 BAILE ET AL.
TABLE 3. Performance of heifers subsequent to feeding monensin.
Item 0 200 600
Number of heifers lactating 16 a 15 18
Milk production/day (kg) 17.1 16.9 17.0
Milk fat % 3.39 3.59 3.40
Milk protein % 3.24 3.15 3.24
Interval to first estrus (days) 53.9 46.6 39.6
Interval to conception (days) 66.9 70.4 71.6
Services/conception 1.54 1.69 1.47
Percent conceptionb 64.7 66.7 94.4
aone heifer removed from lactation phase for severe mastitis but was evaluated for rebreeding.
bFor all services.
or p r o t e i n o f milk during t h e 120 days (Table 5 Oliver, W. N. 1975. Effect of monensin on gains of
3). T r e a t m e n t o f heifers with m o n e n s i n at steers grazed on coastal Bermuda grass. J. Anim.
p r o p o s e d a m o u n t s during growing, breeding,
6 Pendlum, L. C., L. H. Carroll, W. J. Dunn, H. P.
and g e s t a t i o n p e r i o d s did n o t a f f e c t s u b s e q u e n t Grueter, J. W. McAskill, R. M. Meyer, D. L. Snyder,
days t o first estrus, c o n c e p t i o n postcalving, o r and A. J. Stewart. 1981. Effect of monensin on
p e r c e n t c o n c e p t i o n for all services (Table 3). rate of weight gain and time to first estrus of
growing beef and dairy cattle. Proc. Western Sect.
Thus, m o n e n s i n at 600 m g / h e a d per d a y (3
Am. Soc. Anita. Sci. 32:15.
times the r e c o m m e n d e d d o s e ) is safe and 7 Potter, E. L., C. O. Cooley, A. P. Raun, L. F.
effective in i m p r o v i n g g r o w i n g p e r f o r m a n c e Richardson, and R. P. Rathmacher. 1974. Effect of
and s h o r t e n i n g t i m e to calving o f Holstein monensin on daily gain of cattle on pasture. Proc.
heifers w i t h o u t increasing calving d i f f i c u l t y o r Western Sec. Am. Soc. Anim. Sci. 25:343.
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Richardson, and E. L. Potter. 1974. Effect of
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Journal of Dairy Science Vol. 65, No. 10, 1982