Eight ruminally fistulated, yearling steers (two concurrent 4x4 Latin squares) were used to evaluate dietary Rumensin level (0, 30, 30/40 or 40 g/t), and bunk management strategy (ad libitum or clean bunk: 24- or 14-hour feed access).  Rumensin decreased meal size and increased meal frequency without compromising intake. Clean bunk management increased consumption rate, meal size and ruminal pH change and pH variance. Steers with limited feed exposure are at greater risk for subacute acidosis; Rumensin effects consumption favorably for controlling acidosis, especially for cattle with limited feed exposure

Cooper, Rob

Fanning, Ki

Jordon, D. J.

Klopfenstein, Terry J.

Milton, Todd

Parrott, Cal

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department January 1999 Effects of Rumensin Level and Bunk Management Strategy on Finishing Steers Ki Fanning University of Nebraska-Lincoln Todd Milton University of Nebraska-Lincoln Terry J. Klopfenstein University of Nebraska-Lincoln, tklopfenstein1@unl.edu D. J. Jordon University of Nebraska-Lincoln Rob Cooper University of Nebraska-Lincoln See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Animal Sciences Commons Fanning, Ki; Milton, Todd; Klopfenstein, Terry J.; Jordon, D. J.; Cooper, Rob; and Parrott, Cal, "Effects of Rumensin Level and Bunk Management Strategy on Finishing Steers" (1999). Nebraska Beef Cattle Reports. 404. https://digitalcommons.unl.edu/animalscinbcr/404 This Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Ki Fanning, Todd Milton, Terry J. Klopfenstein, D. J. Jordon, Rob Cooper, and Cal Parrott This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/animalscinbcr/404 Page 41 — 1999 Nebraska Beef ReportEffects of Rumensin Level and Bunk    Management Strategy on Finishing Steersfeed intake. Clean bunk management strategies can reduce input costs, feed wastage and human error; however, an increase in management intensity may be required to prevent over-consump-tion resulting in acidosis. University of Nebraska research suggests Rumensin reduces the area of ruminal pH below 5.6, ruminal pH change, and variance, without affecting feed intake when cattle are fed ad-libitum (1997 Nebraska Beef Report, pp. 49). This may result in reduced incidence of acidosis in high-grain diets. Effects of Rumensin and different bunk management strategies on cattle fed high-grain diets have not been documented. The objective of this trial was to determine if an interaction exists between feeding management strategy and Rumensin supplementation strategies in feedlot steers.Procedureused in two concurrent 4 x 4 Latin squares to determine if an interaction exists be-tween Rumensin level and bunk manage-ment strategy. Steers were assigned to one of two bunk management strategies and one of four Rumensin levels. Over a 21-day period, steers were stepped up with four diets decreasing in roughage level (45, 35, 25 and 15 percent). Steers consisted of 42.3 percent dry-rolled corn, 42.3 percent high moisture corn, 7.5 percent chopped alfalfa hay, 3 percent molasses and 5 percent supplement, on a dry matter basis.Levels of Rumensin fed were 0 g/t (CON), 30 g/t (30), 30 changing to 40 g/t the day of the challenge (30/40) and 40 g/t (40). Bunk management strategies employed were ad-libitum (24-hour feed access) and clean bunk management (ap-proximately 14-hour feed access). Steers were fed at 8 a.m. each morning. Steers on the ad-libitum bunk management strategy (ADLIB) were fed to have .25 to .5 pounds of feed left in the bunk at 7 a.m., while steers on the clean bunk management strategy (CLEAN) were fed to have consumed all their feed between 9 p.m. and 10 p.m. The following day’s intake was adjusted accordingly. Steers remained on their original assigned bunk management strategy during the step-up Individual feed bunks were suspended from load cells. Submersible pH probes, running through the ruminal cannula, were suspended in the rumen. Both load cells and pH probes were directly linked to a computer allowing intake and ruminal pH to be collected at two-minute intervals. Amount of feed offered to the CLEAN steers was determined from feed weights at 8, 9, and 10 p.m. retrieved from the computer.Each of the four periods were 35 days in length, during which feed in-take was monitored each day. Day 1-14 was a diet adaptation period with steers housed in free stalls. On day 15, steers were moved to tie stalls and tethered. Submersible pH probes were placed in the rumen through the ruminal cannula. Ruminal pH was monitored from day 15-35. On day 31, steers were challenged by feeding 125 percent of the previous day’s intake, four hours late (12 p.m.). During days 32-35, an intake recovery phase was allowed. On day 32, steers were fed the same amount of feed as day 30. During days 33-35, steers were fed to appetite as previously described. On the fourth day of every period, steers moved from the 40 g/t diet to the 0 g/t Ki FanningTodd MiltonTerry KlopfensteinD. J. JordonRob CooperCal Parrott1Rumensin increased meal fre-quency and decreased meal size without affecting intake. Clean bunk management decreased meal frequency, increased consumption rate, meal size, and ruminal pH change and pH variance.Summarywere used to evaluate dietary Rumensin level (0, 30, 30/40 or 40 g/t), and bunk management strategy (ad libitum or Rumensin decreased meal size and in-creased meal frequency without compro-mising intake. Clean bunk management increased consumption rate, meal size and ruminal pH change and pH vari-ance. Steers with limited feed exposure are at greater risk for subacute acidosis; Rumensin effects consumption favorably for controlling acidosis, especially for cattle with limited feed exposure.Introductionas well as digestive disorders, greatly these reductions are so subtle they may go undetected until an adverse feeding condition poses itself. Changes in intake can cause subacute acidosis; likewise subacute acidosis can cause changes in (Continued on next page)1999 Nebraska Beef Report — Page 42from a donor steer being fed a similar diet without Rumensin.Statistical analysis of the data was conducted by the use of the Mixed model procedure in SAS. Results were divided into three phases: pre-challenge (days 24-30, seven days previous to the challenge), challenge (day 31, the day of the challenge), and post-challenge (days 32-35, four days post challenge). Contrasts used in the pre-challenge phase were CON compared with the average of diets containing Rumensin and 30 compared with 40 g/t Rumensin. Con-trasts used in the challenge phase were CON compared with the average of diets containing Rumensin, 30 compared with 30/40 g/t Rumensin and 40 compared with 30/40 g/t Rumensin. Contrasts used in the post-challenge phase were CON compared with the average of diets containing Rumensin, 30 compared with 40 g/t Rumensin and 30 compared with 30/40 g/ton Rumensin.ResultsDry matter intakes (lb/day) were similar among Rumensin levels (CON = 21.4, 30 = 21.7, 30/40 = 21 and 40 = 21.5) and bunk management strategies Table 2. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH in steers fed a high-grain diet during the challenge phase.Rumensin levela Bunk managementbItem CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-ValueIntakeDM/dayc,d,lb 33.4 31.5 33.9 31.3 2.2 .20 33.9 31.1 2.9 .52Rate, %/hr 22.6 22.4 20.2 24.6 2.4 .66 27.1 17.9 1.7 <.01MealsNumber/day 7.13 6.88 7.00 6.33 .66 .81 6.19 7.48 .62 .20Avg, lb 5.25 5.31 5.20 5.19 .89 .99 6.08 4.39 1.05 .30Eating timeTotal, min/day 502 510 537 523 28.6 .80 521 515 20.2 .86Avg. meal, min 76 82 81 88 10.4 .81 90 73 10.7 .29Ruminal pHAverage 5.69 5.62 5.68 5.70 .13 .93 5.67 5.67 .15 .98Changee 1.53 1.51 1.47 1.64 .07 .24 1.65 1.42 .08 .10Variance .210 .181 .181 .220 .025 .48 .269 .127 .025 <.01Area < 5.6f 131 139 151 119 42.5 .89 135 134 48.9 .99aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.c30 versus 30/40 g/t Rumensin (P = .10).d40 versus 30/40 g/t Rumensin (P = .09).e40 versus 30/40 g/t Rumensin (P = .05).fArea = magnitude of ruminal pH below 5.6 by min.Table 1. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH on steers fed a high-grain diet during the pre-challenge phase.Rumensin levela Bunk managementbItem CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-ValueIntakeDM/day, lb 27.9 27.3 28.1 26.2 1.6 .47 27.1 27.7 2.1 .85Rate, %/hr 26.7 23.3 25.4 26.3 2.1 .69 32.3 18.5 1.5 <.01MealsNumber/day 5.9 6.8 6.5 6.3 .5 .50 4.5 8.2 .57 <.01Avgc, lb 7.4 5.0 4.9 5.0 1.1 .13 7.6 3.5 1.2 .05Eating timeTotal, min/day 502 519 505 530 28.5 .90 475 553 20.1 .04Avg. mealc, min 124 91 87 99 14.3 .10 130 70 15.7 .03Ruminal pHAverage 5.69 5.64 5.81 5.73 .11 .37 5.75 5.69 .14 .77Change 1.47 1.39 1.36 1.34 .09 .61 1.46 1.31 .08 .23Variancec .161 .120 .125 .127 .02 .15 .186 .080 .018 <.01Area < 5.6d 104 115 106 98 33 .87 95 116 43.7 .75aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.cRumensin versus Control (P < .05).dArea = magnitude of ruminal pH below 5.6 by min.Page 43 — 1999 Nebraska Beef Report(CLEAN = 21.1, ADLIB = 22.2) for the combined averages of the four, 35-day periods.Pre-challengeResults of the pre-challenge phase are presented in Table 1. No interactions were observed during the pre-challenge phase; therefore, main effects of Rumen-sin level and bunk management strategy are reported. During the pre-challenge phase, Rumensin reduced (P < .05) aver-age meal size and average meal length compared with the CON. Rumensin tended to reduce (P = .11) the largest meal consumed per day compared with CON (10.0 versus 11.9 pounds). Feed intake, intake rate, number of meals and total time spent eating were unaffected by Rumensin level. Rumensin reduced (P < .05) the variance in ruminal pH; however, average ruminal pH, ruminal pH change and the area below pH 5.6 were unaffected by Rumensin level.Intake was similar between bunk management strategies; however, steers on the CLEAN had a faster (P < .01) rate of intake and consumed fewer (P < .01) meals than steers on the ADLIB (Table 1). Average meal size was more than twice as large (P = .05) for steers on the CLEAN compared with the ADLIB. Average time spent eating a meal was longer (P = .03) for steers on the CLEAN; however, steers Table 3. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH in steers fed a high-grain diet during the post-challenge phase.Rumensin levela Bunk managementbItem CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-ValueIntakeDM/day, lb 27.7 26.1 27.4 26.3 1.6 .55 26.4 27.3 1.9 .75Ratec, %/hr 27.0 24.6 21.0 24.3 1.9 .22 30.2 18.2 1.9 <.01MealsNumber/dayd 6.2 7.3 7.4 6.5 .50 .09 5.5 8.3 .44 <.01Eating timeTotal, min/day 516 545 538 516 32.0 .84 492 565 28.9 .13Avg. meale, min 114 78 79 89 14.6 .31 107 73 10.3 .07Ruminal pHAverage 5.80 5.61 5.75 5.72 .15 .50 5.77 5.67 .18 .71Area < 5.6f 91 130 117 106 46.8 .51 83 140 62.3 .54aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.cRumensin versus Control (P = .12).dRumensin versus Control (P = .06).eRumensin versus Control (P= .08)fArea = magnitude of ruminal pH below 5.6 by min.on the ADLIB spent a greater (P = .04) portion of their day eating. Ruminal pH variance was greater (P < .01) for the CLEAN compared with ADLIB. Aver-age ruminal pH, ruminal pH change and area below a pH 5.6 were unaffected by bunk management strategy.ChallengeResults from the day of the challenge are presented in Table 2. No interac-tions were observed during the chal-lenge phase; therefore, main effects of Rumensin level and bunk management strategy are reported. Steers fed 30/40 had a higher (P < .10) feed intake than steers fed either 30 or 40 g/t Rumensin. Intake rate, number of meals, average meal size and total and average time spent eating were similar among Rumensin levels. Ruminal pH change was reduced (P = .05) by steers fed 30/40 compared with those fed 40 g/t Rumensin. Average ruminal pH, pH variance and the area below a pH of 5.6 were unaffected by Rumensin level.Steers on the CLEAN had a faster (P < .01) rate of intake than steers on the ADLIB. Number of meals, meal size and time spent eating were unaffected by bunk management strategy. Ruminal pH variance (P < .01) and change (P = .10) were greater for steers on the CLEAN compared with ADLIB. Average ruminal pH and area below pH 5.6 were unaf-fected by bunk management strategy.Post-challengeResults of the post-challenge phase are reported in Table 3. Steers fed CON tended to have a faster (P = .12) rate of intake than steers fed Rumensin; however, intake was unaffected by Ru-mensin level. Steers fed Rumensin had a greater (P = .06) number of meals than steers fed CON. An interaction (P = .10) was observed for Rumensin level and bunk management strategy for average meal size. Steers on the CLEAN fed Rumensin consumed smaller (P < .05) meals compared with steers fed CON (Table 4). For steers in the ADLIB, average meal size was similar across Rumensin levels. While total eating time was similar across Rumensin levels, steers fed the CON spent 30 minutes longer (P = .08) eating per meal than steers fed Rumensin (Table 3). Average ruminal pH and the area below pH 5.6 were similar across Rumensin levels. Interactions were observed between Rumensin level and bunk management strategy for ruminal pH change (P= .08) and pH variance (P = .04). Steers on the CLEAN fed CON or 40 g/t Rumensin experienced a larger ruminal pH change (P < .10) and greater ruminal pH vari-(Continued on next page)1999 Nebraska Beef Report — Page 44Table 4. Interactions of Rumensin level and bunk management strategy on intake behavior and ruminal pH in steers fed a high-grain diet during the post-challenge phase.Rumensin levelaItem CON 30 30/40 40 SEMAverage meal sizeb, lb DMCLEANc 8.2d 4.4e 4.5e 5.4e .78ADLIBc 3.5 3.3 3.5 4.0 .78Ruminal pH changefCLEANc 1.53g 1.21h 1.24h 1.51g .13ADLIBc 1.08 1.27 1.22 1.28 .13Ruminal pH varianceiCLEANc .213d .119e .116e .194d .021ADLIBc .055 .080 .066 .094 .021aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.bRumensin x bunk management interaction (P = .10).cCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.d,eMeans in a row not bearing a common superscript differ (P < .05).fRumensin x bunk management interaction (P = .08).g,hMeans in a row not bearing a common superscript differ (P < .10).iRumensin x bunk management interaction (P = .04).than steers on ADLIB. Average ruminal pH and area below pH 5.6 were unaf-fected by bunk management strategy.Rumensin was effective at decreasing meal size and increasing number of meals consumed per day without affecting feed intake. These changes in consumption patterns should be effective in manag-ing acidosis, especially for feedlot cattle with limited exposure to feed. Effects of Rumensin during the post-challenge phase were greater for steers on the CLEAN compared with ADLIB. It is unclear why differences exist between feeding 40 g/t Rumensin continuously compared with 30 g/t or 30/40 g/t for steers having limited access to feed. Steers on the CLEAN had an increased rate of intake and meal size as well as ruminal pH change and variance. Steers with limited exposure to feed are at a greater risk for subacute acidosis.1Ki Fanning, graduate student; Todd Milton, assistant professor; Terry Klopfenstein, professor Animal Science, Lincoln; D. J. Jordon and Rob Cooper, research technicians; Cal Parrott, Elanco ance (P < .05) than steers fed 30 or 30/40 g/t Rumensin. Ruminal pH change and variance were similar across Rumensin levels for steers on the ADLIB.Intake was similar across bunk man-agement strategies; however, intake rate was faster (P < .01) for steers on the CLEAN than those on the ADLIB (Table 3). The total number of meals was greater (P < .01) for steers fed on the ADLIB compared with CLEAN. Steers on the CLEAN tended to spend a smaller (P = .13) portion of the day eating, but their average meal length was longer (P = .07) Dietary Management for Starting Finishing Yearling Steers on FeedBurt WeichenthalIvan RushBrad Van Pelt1Limit-feeding of high-grain yearlings with minimal problems from acidosis and intake variation, resulting in less roughage needed SummaryAngus crossbred yearling steers were stepped-up in grain over 23 days or with dressing percentage and fat thickness, but did not affect daily gain or carcass quality and yield grades. In this small pen research trial, steers reached ad libitum this diet during start-up without major problems from acidosis or related intake variation.IntroductionTraditionally, starting cattle on a with increasing grain levels to allow the rumen microorganisms to gradually adjust to higher grain levels, attempting to minimize acidosis and intake varia-tion that can occur with overeating of grain. Limit-feeding of high-grain diets but little research has been done on start-up period. Use of limit-feeding in the start-up period could eliminate higher roughage diets and get cattle adjusted to acidosis which can lead to severe intake variation or death.The objective of our study was to 

Effects of Rumensin Level and Bunk Management Strategy on Finishing Steers

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Nebraska Beef Cattle Reports Animal Science Department 
January 1999 
Effects of Rumensin Level and Bunk Management Strategy on 
Finishing Steers 
Ki Fanning 
University of Nebraska-Lincoln 
Todd Milton 
University of Nebraska-Lincoln 
Terry J. Klopfenstein 
University of Nebraska-Lincoln, tklopfenstein1@unl.edu 
D. J. Jordon 
University of Nebraska-Lincoln 
Rob Cooper 
University of Nebraska-Lincoln 
See next page for additional authors 
Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr 
 Part of the Animal Sciences Commons 
Fanning, Ki; Milton, Todd; Klopfenstein, Terry J.; Jordon, D. J.; Cooper, Rob; and Parrott, Cal, "Effects of 
Rumensin Level and Bunk Management Strategy on Finishing Steers" (1999). Nebraska Beef Cattle 
Reports. 404. 
https://digitalcommons.unl.edu/animalscinbcr/404 
This Article is brought to you for free and open access by the Animal Science Department at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Beef Cattle 
Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
Authors 
Ki Fanning, Todd Milton, Terry J. Klopfenstein, D. J. Jordon, Rob Cooper, and Cal Parrott 
This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/
animalscinbcr/404 
Page 41 — 1999 Nebraska Beef Report
Effects of Rumensin Level and Bunk
    Management Strategy on Finishing Steers
feed intake. Clean bunk management 
strategies can reduce input costs, feed 
wastage and human error; however, an 
increase in management intensity may 
be required to prevent over-consump-
tion resulting in acidosis. University of 
Nebraska research suggests Rumensin 
reduces the area of ruminal pH below 
5.6, ruminal pH change, and variance, 
without affecting feed intake when 
cattle are fed ad-libitum (1997 Nebraska 
Beef Report, pp. 49). This may result in 
reduced incidence of acidosis in high-
grain diets. Effects of Rumensin and 
different bunk management strategies 
on cattle fed high-grain diets have not 
been documented. The objective of this 
trial was to determine if an interaction 
exists between feeding management 
strategy and Rumensin supplementation 
strategies in feedlot steers.
Procedure
used in two concurrent 4 x 4 Latin squares 
to determine if an interaction exists be-
tween Rumensin level and bunk manage-
ment strategy. Steers were assigned to 
one of two bunk management strategies 
and one of four Rumensin levels. Over 
a 21-day period, steers were stepped up 
with four diets decreasing in roughage 
level (45, 35, 25 and 15 percent). Steers 
consisted of 42.3 percent dry-rolled corn, 
42.3 percent high moisture corn, 7.5 
percent chopped alfalfa hay, 3 percent 
molasses and 5 percent supplement, on 
a dry matter basis.
Levels of Rumensin fed were 0 g/t 
(CON), 30 g/t (30), 30 changing to 40 
g/t the day of the challenge (30/40) and 
40 g/t (40). Bunk management strategies 
employed were ad-libitum (24-hour feed 
access) and clean bunk management (ap-
proximately 14-hour feed access). Steers 
were fed at 8 a.m. each morning. Steers 
on the ad-libitum bunk management 
strategy (ADLIB) were fed to have .25 
to .5 pounds of feed left in the bunk at 
7 a.m., while steers on the clean bunk 
management strategy (CLEAN) were fed 
to have consumed all their feed between 
9 p.m. and 10 p.m. The following day’s 
intake was adjusted accordingly. Steers 
remained on their original assigned bunk 
management strategy during the step-up 
Individual feed bunks were suspended 
from load cells. Submersible pH probes, 
running through the ruminal cannula, 
were suspended in the rumen. Both 
load cells and pH probes were directly 
linked to a computer allowing intake and 
ruminal pH to be collected at two-minute 
intervals. Amount of feed offered to the 
CLEAN steers was determined from feed 
weights at 8, 9, and 10 p.m. retrieved 
from the computer.
Each of the four periods were 35 
days in length, during which feed in-
take was monitored each day. Day 1-14 
was a diet adaptation period with steers 
housed in free stalls. On day 15, steers 
were moved to tie stalls and tethered. 
Submersible pH probes were placed in 
the rumen through the ruminal cannula. 
Ruminal pH was monitored from day 
15-35. On day 31, steers were challenged 
by feeding 125 percent of the previous 
day’s intake, four hours late (12 p.m.). 
During days 32-35, an intake recovery 
phase was allowed. On day 32, steers 
were fed the same amount of feed as 
day 30. During days 33-35, steers were 
fed to appetite as previously described. 
On the fourth day of every period, steers 
moved from the 40 g/t diet to the 0 g/t 
Ki Fanning
Todd Milton
Terry Klopfenstein
D. J. Jordon
Rob Cooper
Cal Parrott1
Rumensin increased meal fre-
quency and decreased meal size 
without affecting intake. Clean 
bunk management decreased meal 
frequency, increased consumption 
rate, meal size, and ruminal pH 
change and pH variance.
Summary
were used to evaluate dietary Rumensin 
level (0, 30, 30/40 or 40 g/t), and bunk 
management strategy (ad libitum or 
Rumensin decreased meal size and in-
creased meal frequency without compro-
mising intake. Clean bunk management 
increased consumption rate, meal size 
and ruminal pH change and pH vari-
ance. Steers with limited feed exposure 
are at greater risk for subacute acidosis; 
Rumensin effects consumption favorably 
for controlling acidosis, especially for 
cattle with limited feed exposure.
Introduction
as well as digestive disorders, greatly 
these reductions are so subtle they may 
go undetected until an adverse feeding 
condition poses itself. Changes in intake 
can cause subacute acidosis; likewise 
subacute acidosis can cause changes in (Continued on next page)
1999 Nebraska Beef Report — Page 42
from a donor steer being fed a similar 
diet without Rumensin.
Statistical analysis of the data was 
conducted by the use of the Mixed 
model procedure in SAS. Results were 
divided into three phases: pre-challenge 
(days 24-30, seven days previous to the 
challenge), challenge (day 31, the day 
of the challenge), and post-challenge 
(days 32-35, four days post challenge). 
Contrasts used in the pre-challenge phase 
were CON compared with the average 
of diets containing Rumensin and 30 
compared with 40 g/t Rumensin. Con-
trasts used in the challenge phase were 
CON compared with the average of diets 
containing Rumensin, 30 compared with 
30/40 g/t Rumensin and 40 compared 
with 30/40 g/t Rumensin. Contrasts 
used in the post-challenge phase were 
CON compared with the average of diets 
containing Rumensin, 30 compared with 
40 g/t Rumensin and 30 compared with 
30/40 g/ton Rumensin.
Results
Dry matter intakes (lb/day) were 
similar among Rumensin levels (CON 
= 21.4, 30 = 21.7, 30/40 = 21 and 40 = 
21.5) and bunk management strategies 
Table 2. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH in steers fed a high-grain diet during the 
challenge phase.
Rumensin levela Bunk managementb
Item CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-Value
Intake
DM/dayc,d,lb 33.4 31.5 33.9 31.3 2.2 .20 33.9 31.1 2.9 .52
Rate, %/hr 22.6 22.4 20.2 24.6 2.4 .66 27.1 17.9 1.7 <.01
Meals
Number/day 7.13 6.88 7.00 6.33 .66 .81 6.19 7.48 .62 .20
Avg, lb 5.25 5.31 5.20 5.19 .89 .99 6.08 4.39 1.05 .30
Eating time
Total, min/day 502 510 537 523 28.6 .80 521 515 20.2 .86
Avg. meal, min 76 82 81 88 10.4 .81 90 73 10.7 .29
Ruminal pH
Average 5.69 5.62 5.68 5.70 .13 .93 5.67 5.67 .15 .98
Changee 1.53 1.51 1.47 1.64 .07 .24 1.65 1.42 .08 .10
Variance .210 .181 .181 .220 .025 .48 .269 .127 .025 <.01
Area < 5.6f 131 139 151 119 42.5 .89 135 134 48.9 .99
aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.
bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.
c30 versus 30/40 g/t Rumensin (P = .10).
d40 versus 30/40 g/t Rumensin (P = .09).
e40 versus 30/40 g/t Rumensin (P = .05).
fArea = magnitude of ruminal pH below 5.6 by min.
Table 1. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH on steers fed a high-grain diet during the 
pre-challenge phase.
Rumensin levela Bunk managementb
Item CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-Value
Intake
DM/day, lb 27.9 27.3 28.1 26.2 1.6 .47 27.1 27.7 2.1 .85
Rate, %/hr 26.7 23.3 25.4 26.3 2.1 .69 32.3 18.5 1.5 <.01
Meals
Number/day 5.9 6.8 6.5 6.3 .5 .50 4.5 8.2 .57 <.01
Avgc, lb 7.4 5.0 4.9 5.0 1.1 .13 7.6 3.5 1.2 .05
Eating time
Total, min/day 502 519 505 530 28.5 .90 475 553 20.1 .04
Avg. mealc, min 124 91 87 99 14.3 .10 130 70 15.7 .03
Ruminal pH
Average 5.69 5.64 5.81 5.73 .11 .37 5.75 5.69 .14 .77
Change 1.47 1.39 1.36 1.34 .09 .61 1.46 1.31 .08 .23
Variancec .161 .120 .125 .127 .02 .15 .186 .080 .018 <.01
Area < 5.6d 104 115 106 98 33 .87 95 116 43.7 .75
aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.
bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.
cRumensin versus Control (P < .05).
dArea = magnitude of ruminal pH below 5.6 by min.
Page 43 — 1999 Nebraska Beef Report
(CLEAN = 21.1, ADLIB = 22.2) for the 
combined averages of the four, 35-day 
periods.
Pre-challenge
Results of the pre-challenge phase 
are presented in Table 1. No interactions 
were observed during the pre-challenge 
phase; therefore, main effects of Rumen-
sin level and bunk management strategy 
are reported. During the pre-challenge 
phase, Rumensin reduced (P < .05) aver-
age meal size and average meal length 
compared with the CON. Rumensin 
tended to reduce (P = .11) the largest 
meal consumed per day compared with 
CON (10.0 versus 11.9 pounds). Feed 
intake, intake rate, number of meals and 
total time spent eating were unaffected 
by Rumensin level. Rumensin reduced 
(P < .05) the variance in ruminal pH; 
however, average ruminal pH, ruminal 
pH change and the area below pH 5.6 
were unaffected by Rumensin level.
Intake was similar between bunk 
management strategies; however, steers 
on the CLEAN had a faster (P < .01) rate 
of intake and consumed fewer (P < .01) 
meals than steers on the ADLIB (Table 1). 
Average meal size was more than twice as 
large (P = .05) for steers on the CLEAN 
compared with the ADLIB. Average time 
spent eating a meal was longer (P = .03) 
for steers on the CLEAN; however, steers 
Table 3. Effects of Rumensin level and bunk management strategy on intake behavior and ruminal pH in steers fed a high-grain diet during the 
post-challenge phase.
Rumensin levela Bunk managementb
Item CON 30 30/40 40 SEM P-Value CLEAN ADLIB SEM P-Value
Intake
DM/day, lb 27.7 26.1 27.4 26.3 1.6 .55 26.4 27.3 1.9 .75
Ratec, %/hr 27.0 24.6 21.0 24.3 1.9 .22 30.2 18.2 1.9 <.01
Meals
Number/dayd 6.2 7.3 7.4 6.5 .50 .09 5.5 8.3 .44 <.01
Eating time
Total, min/day 516 545 538 516 32.0 .84 492 565 28.9 .13
Avg. meale, min 114 78 79 89 14.6 .31 107 73 10.3 .07
Ruminal pH
Average 5.80 5.61 5.75 5.72 .15 .50 5.77 5.67 .18 .71
Area < 5.6f 91 130 117 106 46.8 .51 83 140 62.3 .54
aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the challenge, 40 = 40 g/t Rumensin.
bCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.
cRumensin versus Control (P = .12).
dRumensin versus Control (P = .06).
eRumensin versus Control (P= .08)
fArea = magnitude of ruminal pH below 5.6 by min.
on the ADLIB spent a greater (P = .04) 
portion of their day eating. Ruminal pH 
variance was greater (P < .01) for the 
CLEAN compared with ADLIB. Aver-
age ruminal pH, ruminal pH change and 
area below a pH 5.6 were unaffected by 
bunk management strategy.
Challenge
Results from the day of the challenge 
are presented in Table 2. No interac-
tions were observed during the chal-
lenge phase; therefore, main effects of 
Rumensin level and bunk management 
strategy are reported. Steers fed 30/40 
had a higher (P < .10) feed intake than 
steers fed either 30 or 40 g/t Rumensin. 
Intake rate, number of meals, average 
meal size and total and average time spent 
eating were similar among Rumensin 
levels. Ruminal pH change was reduced 
(P = .05) by steers fed 30/40 compared 
with those fed 40 g/t Rumensin. Average 
ruminal pH, pH variance and the area 
below a pH of 5.6 were unaffected by 
Rumensin level.
Steers on the CLEAN had a faster (P 
< .01) rate of intake than steers on the 
ADLIB. Number of meals, meal size 
and time spent eating were unaffected by 
bunk management strategy. Ruminal pH 
variance (P < .01) and change (P = .10) 
were greater for steers on the CLEAN 
compared with ADLIB. Average ruminal 
pH and area below pH 5.6 were unaf-
fected by bunk management strategy.
Post-challenge
Results of the post-challenge phase 
are reported in Table 3. Steers fed CON 
tended to have a faster (P = .12) rate 
of intake than steers fed Rumensin; 
however, intake was unaffected by Ru-
mensin level. Steers fed Rumensin had 
a greater (P = .06) number of meals than 
steers fed CON. An interaction (P = .10) 
was observed for Rumensin level and 
bunk management strategy for average 
meal size. Steers on the CLEAN fed 
Rumensin consumed smaller (P < .05) 
meals compared with steers fed CON 
(Table 4). For steers in the ADLIB, 
average meal size was similar across 
Rumensin levels. While total eating time 
was similar across Rumensin levels, 
steers fed the CON spent 30 minutes 
longer (P = .08) eating per meal than 
steers fed Rumensin (Table 3). Average 
ruminal pH and the area below pH 5.6 
were similar across Rumensin levels. 
Interactions were observed between 
Rumensin level and bunk management 
strategy for ruminal pH change (P= .08) 
and pH variance (P = .04). Steers on the 
CLEAN fed CON or 40 g/t Rumensin 
experienced a larger ruminal pH change 
(P < .10) and greater ruminal pH vari-
(Continued on next page)
1999 Nebraska Beef Report — Page 44
Table 4. Interactions of Rumensin level and bunk management strategy on intake behavior and 
ruminal pH in steers fed a high-grain diet during the post-challenge phase.
Rumensin levela
Item CON 30 30/40 40 SEM
Average meal sizeb, lb DM
CLEANc 8.2d 4.4e 4.5e 5.4e .78
ADLIBc 3.5 3.3 3.5 4.0 .78
Ruminal pH changef
CLEANc 1.53g 1.21h 1.24h 1.51g .13
ADLIBc 1.08 1.27 1.22 1.28 .13
Ruminal pH variancei
CLEANc .213d .119e .116e .194d .021
ADLIBc .055 .080 .066 .094 .021
aCON = 0 g/t Rumensin, 30 = 30 g/t Rumensin, 30/40 = 30 changing to 40 g/t Rumensin the day of the 
challenge, 40 = 40 g/t Rumensin.
bRumensin x bunk management interaction (P = .10).
cCLEAN = Clean bunk management strategy, ADLIB = Ad-libitum bunk management strategy.
d,eMeans in a row not bearing a common superscript differ (P < .05).
fRumensin x bunk management interaction (P = .08).
g,hMeans in a row not bearing a common superscript differ (P < .10).
iRumensin x bunk management interaction (P = .04).
than steers on ADLIB. Average ruminal 
pH and area below pH 5.6 were unaf-
fected by bunk management strategy.
Rumensin was effective at decreasing 
meal size and increasing number of meals 
consumed per day without affecting feed 
intake. These changes in consumption 
patterns should be effective in manag-
ing acidosis, especially for feedlot cattle 
with limited exposure to feed. Effects 
of Rumensin during the post-challenge 
phase were greater for steers on the 
CLEAN compared with ADLIB. It is 
unclear why differences exist between 
feeding 40 g/t Rumensin continuously 
compared with 30 g/t or 30/40 g/t for 
steers having limited access to feed. 
Steers on the CLEAN had an increased 
rate of intake and meal size as well as 
ruminal pH change and variance. Steers 
with limited exposure to feed are at a 
greater risk for subacute acidosis.
1Ki Fanning, graduate student; Todd Milton, 
assistant professor; Terry Klopfenstein, professor 
Animal Science, Lincoln; D. J. Jordon and Rob 
Cooper, research technicians; Cal Parrott, Elanco 
ance (P < .05) than steers fed 30 or 30/40 
g/t Rumensin. Ruminal pH change and 
variance were similar across Rumensin 
levels for steers on the ADLIB.
Intake was similar across bunk man-
agement strategies; however, intake rate 
was faster (P < .01) for steers on the 
CLEAN than those on the ADLIB (Table 
3). The total number of meals was greater 
(P < .01) for steers fed on the ADLIB 
compared with CLEAN. Steers on the 
CLEAN tended to spend a smaller (P = 
.13) portion of the day eating, but their 
average meal length was longer (P = .07) 
Dietary Management for Starting Finishing 
Yearling Steers on Feed
Burt Weichenthal
Ivan Rush
Brad Van Pelt1
Limit-feeding of high-grain 
yearlings with minimal problems 
from acidosis and intake variation, 
resulting in less roughage needed 
Summary
Angus crossbred yearling steers were 
stepped-up in grain over 23 days or with 
dressing percentage and fat thickness, 
but did not affect daily gain or carcass 
quality and yield grades. In this small pen 
research trial, steers reached ad libitum 
this diet during start-up without major 
problems from acidosis or related intake 
variation.
Introduction
Traditionally, starting cattle on a 
with increasing grain levels to allow 
the rumen microorganisms to gradually 
adjust to higher grain levels, attempting 
to minimize acidosis and intake varia-
tion that can occur with overeating of 
grain. Limit-feeding of high-grain diets 
but little research has been done on 
start-up period. Use of limit-feeding in 
the start-up period could eliminate higher 
roughage diets and get cattle adjusted to 
acidosis which can lead to severe intake 
variation or death.
The objective of our study was to 


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Effects of Rumensin Level and Bunk Management Strategy on Finishing Steers

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