Six ruminally-fistulated steers were used to evaluate the effect of Rumensin and feed intake variation on ruminal pH. Steers were adapted to a 92.5 percent concentrate diet and then subjected to three levels of intake variation: ad libitum, intake variation of 2 lb/day, and intake variation of 4 lb/day. Feed intakes and ruminal pH were monitored continuously throughout the entire trial. Results indicate that Rumensin reduced acidosis by elevating average ruminal pH and decreasing are of ruminal pH below 5.6. In addition, Rumensin stabilized rate of intake and daily ruminal pH fluctuation at the high level of intake variation

Cooper, Rob

Herold, Dan

Klopfenstein, Terry J.

Parrott, Cal

Stock, Rick

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Nebraska Beef Cattle Reports Animal Science Department 
January 1997 
Effect of Rumensin and Feed Intake Variation on Ruminal pH 
Rob Cooper 
University of Nebraska-Lincoln 
Terry J. Klopfenstein 
University of Nebraska-Lincoln, tklopfenstein1@unl.edu 
Rick Stock 
University of Nebraska-Lincoln, rstock3@Unl.edu 
Cal Parrott 
Lilly Research Laboratories, Greenfield, IN 
Dan Herold 
University of Nebraska-Lincoln 
Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr 
 Part of the Animal Sciences Commons 
Cooper, Rob; Klopfenstein, Terry J.; Stock, Rick; Parrott, Cal; and Herold, Dan, "Effect of Rumensin and 
Feed Intake Variation on Ruminal pH" (1997). Nebraska Beef Cattle Reports. 430. 
https://digitalcommons.unl.edu/animalscinbcr/430 
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. 
Effect of Rumensin and Feed Intake Variation on 
Rob Cooper 
Terry Klopfenstein 
Rick Stock 
Cal Parrott 
Dan Herold' 
Steers receiving Rumensin had 
reduced acidosis as indicated by 
elevated ruminal pH and reduced 
area of ruminal pH below 5.6. 
Therefore. Ruinensin can be used 
as a management tool to aid in 
reducing acidosis and thereby in- 
creasing feedlot perfoimance. 
Summary 
Six runzinallj~-Jistz~luted steers I iwe 
used to evaluate the ejject of Rzlmensin 
and feed intake variation on rz~minal 
pH. Steers Ii.ere adapted to a 92.5 
percent concentrate diet and then szlb- 
jected to three levels of intake varia- 
tion: ad libitunz, intake variation o f 2  
lb/daj; and intake variation of 4 1b/ 
daj,. Feed intakes andrunzinalpH Iiwe 
nzonitored continz~ously throughout the 
entire trial. Results indicate that 
Rzlnzensin redz~ced acidosis by elevat- 
ing average runzinal pH and decreas- 
ing area ofrunzinal pH belo~t, 5.6. In 
addition, Rzlmensin stabilized rate of 
intake and daily rz~minal pH Jluctz~a- 
tion at the high level of intake varia- 
tion. 
Introduction 
Changes in dry matter intalie by cattle 
fed high-concentrate diets can nega- 
tively influence feedlot gain and effi- 
ciency as well as predispose digestive 
disorders such as acidosis. Subacute 
acidosis increases variation in feed in- 
take and decreases dry matter intalie of 
cattle consuming high-grain diets. Dur- 
ing acidosis, cattle will reduce feed 
Ruminal pH 
intake until ruminal pH increases to 
approxiinately 5.6. Thus, ruininal pH 
must affect feed intake. On the other 
hand. it is not totally clear whether 
ruminal pH causes feed intake variation 
orwhether feed intake variation changes 
ruminal pH, and how these factors are 
controlled in cattle. Rumensin is an 
ionophore widely used in the feedlot 
industry to increase feed efficiency. It 
has been widely observed and recently 
shown that Rumensin reduces feed in- 
take variation and may reduce digestive 
disturbances and death loss. This effect 
of Rumensin and its mechanism have 
been difficult to measure and explain. 
Therefore, a system of continuous ac- 
quisition of feed intake and ruininal pH 
data was developed so that a inore coin- 
plete understanding of the interactions 
between ruminal pH and feed intake 
variation would be possible. The objec- 
tives of this trial were to evaluate the 
effects of Rumensin and feed intake 
variation on iuminal pH through con- 
tinuous data acquisition. 
Procedure 
Six iuminally-fistulated steers (860 
Ib) were used in a 1 1  I-day inetabolism 
finishing trial. To have the steers used 
in this trial respond in intake and perfor- 
mance similar to yearling cattle coining 
off grass and going to the feedlot in 
early fall. the steers were cannulated in 
the spring at approxiinately one year of 
age and then summered on grass until 
the start of the trial in mid-October. 
Table 1. Composition of finishing diet. 
l tem % of DM 
Dr) -rolled corn 81 95 
Alfalfa ha) 7 50 
Molasses-~~rea supplement 6 36 
Dr) supplementa 1 1 9  
"Contamed m~nerals  \ ~tamlns. and T) Ian. \ \ ~ t h  or 
T\ ithout Rurne~lsi~l 
Steers were then allotted randomly to 
one of two dietary treatments, a 92.5 
percent concentrate diet with or with- 
out Ruinensin at 25 glton (Table 1). 
Steers were adapted to the finishing diet 
through a 20-day, four step grain adap- 
tation period. Each step was fed for a 5- 
day period and consisted of 45. 35. 25. 
and 15% (DM basis) alfalfa hay in place 
of diy-rolled corn for steps one through 
4. respectively. All steers were then 
subjected to three levels of intake varia- 
tion: ad libituin intake with no con- 
trolled intake variation on days 21-47 
and 60-98 (NV). low daily intake varia- 
tion of 2 Iblday of diy matter on days 
48-53 and 99-104 (LV). and high daily 
intake variation of 4 Iblday of dry mat- 
ter on days 54-59 and 106-1 1 1  (HV). 
Dietaiy treatments were switched on 
day 78. with the three steers receiving 
Ruinensin going to the control diet and 
the three steers already on the control 
diet going to the Ruinensin treatment. 
Throughout the entire trial, steers 
were tethered in individual inetabolism 
stalls. Feed intakes were monitored 
continuously with individual feed bunks 
that were suspended from load cells. 
Ruininal pH was also monitored con- 
tinuously with submersible pH elec- 
trodes suspended through the plugs of 
the rumen cannulas of each steer. Each 
pH electrode was encased in a weighted 
four-wire metal shroud to keep the elec- 
trode in a stationaiy position approxi- 
mately five to ten inches above the 
ventral floor of the rumen, while allow- 
ing rumen contents to flow freely 
through it. Load cells and pH electrodes 
were linked directly to a computer al- 
lowing data acquisition software to 
record both feed weight and ruminal pH 
every minute for each steer over the 
entire feeding period. 
Analysis included DM intake, rate 
of DM intake, average ruminal pH, area 
of ruminal pH below 5.6, daily magni- 
(Continued on next page) 
Page 49 - 1997 Nebruska Beef Report 
Table2. Effect of Rumensin during grain 
adaptation period. 
Item Control R u m e ~ l s ~ ~ l  
DM i~ltahe lbldax a 25 9 1  23 81 
Rate ot  Intake % of 
dall) ~ntal,e/m~n 77 79 
Ruminal pH i 79 i 78 
Area belo\\ 5 bb 13121 98 16 
pHDIFFC I I6  1 1 1  
~ H V A R ~  093 072 
a M e a ~ s  differ (P < 10) 
b ~ r e a =  rumlnal pH unlts belo\\ 5 6 b) mlnute 
CMag~litude of dad) r u ~ l l ~ ~ l a l  pH change 
dVar~ance ot da~l)  rumlnal pH 
tude of ruminal pH change (pHDIFF). 
and daily variance of ruininal pH 
(pHVAR). Rate of intake was calcu- 
lated as a first-order reaction with units 
of percent of daily intake per minute. 
Area of ruininal pH below 5.6 was 
calculated as time (minutes) by the 
units of ruininal pH below 5.6. Since it 
has been shown that on average cattle 
will reduce intakes at a ruininal pH 
below 5.6, the area of the ruininal pH 
curve below 5.6 should provide a mea- 
surement of subacute acidosis. Both 
pHDlFF and pHVAR indicate the de- 
-.- Control 
-a- Ru~l le~ l s i~ l  
20 1 I I 1 I I 
Stepl Step2 Step3 Step4 Finl Fin2 
Vont ro l  \ s R~~mensin (P<.01). 
" Control vs Ru~lle~lsin ( E l i ) .  
" T o ~ o o l  \-s Runlensin (P<.lO). 
Step 1 th ro~~gh  Step 1 are the 5 da) aberage of each respectibe step-up diet 
Finl and Fin2 are the first and second i days of finisher. respectively. 
Figure 1. Dry matter intakes during grain adaptation period. 
Table 3. Effect of step-up diet during grain adaptation period. 
Diet" 
l tem Steo l Steo2 Steo3 Steo4 Finl Fin2 
DM intake. lblday 21.1i"276c 2i.09d 2i .21d 27.0r 28.04e 
Rate of intake. 
% o f  dail) intal;e/min .72hc . 5  0" .8lkd .82"d .9ICd .91* 
Ruminal pH 5.89" 5 .80"~  5.88" 5.92" 5.73C 5 . 5 0 ~  
Area belo\\ 5.6' 64.8Sh 93.41"3.23"4.40h 1 3 9 . 5 0 ~ 6 1 . 6 6 ~  
pHDIFF2 .99" 1.08" 11.36d 1.2lc  1.18C 1.0" 
~ H V A R ~  .OiSbc , 0 7 3 " ~ ~  .130e .094d , 0 8 8 ~ ~  .050b 
Ttep1 through Step4 are the i da) a\ erage of each respectlr e step-up d ~ e t  F ~ n l  and Fin2 are the first and 
second 5 da) s of fin~sher respect11 el) 
eMean~ d~ffer (P < 10) 
fArea = r u ~ l l ~ ~ l a l  pH u~lits belon i 6 b! llllnute 
SMagn~t~lde of dall) rumlnal pH change 
"var~ance of dad) ruminal pH 
gree to which the ruminal pH is chang- 
ing or fluctuating within a day. where 
pHDlFF is calculated as the difference 
between the inaximuin and the inini- 
muin ruininal pH for a steer in a day. 
Results 
Dry inatter intakes and daily gains 
were typical of yearling feedlot cattle. 
Dry inatter intakes during the finishing 
period averaged 28.0 Ib per day and 
ADG for the six steers during the trial 
was 4.0 Ib. 
Grain Adaptation Period 
Analysis of the grain adaptation pe- 
riod included the 5-day average for 
each step-up diet (I through 4) plus the 
average ofthe first and second five days 
on the f inisher.  Steers receiving 
Ruinensin consumed less feed over the 
grain adaptation period (P < .05) (Table 
2). reaching the level of the controls by 
the second five days on finisher (Figure 
1). Diy matter intakes on step one were 
similar for the steers on the control and 
Ruinensin treatments. On steps two and 
three, steers receiving Rumensin con- 
sumed approximately 16 percent less 
feed than the controls (P < .0 1). During 
step four and the first five days on 
finisher, steers on the Rumensin treat- 
ment tended to consume eight percent 
less feed than the controls (P < .16). By 
the second five days on finisher. DM 
intakes were not different. During the 
grain adaptation period. rate of DM 
intake was not affected by dietaiy treat- 
ment or step-up diet. 
Average daily ruininal pH was not 
affected by Rumensin, although it was 
affected by step-up diet (Table 3). Ru- 
minal pH was relatively constant from 
step one through step four, averaging 
5.87. During the first five days on fin- 
isher, average ruminal pH dropped to 
5.73 (P < .05, from step 4). During the 
second five days on finisher, average 
ruminal pH dropped to 5.50 (P < .05, 
from first 5 days on finisher). Area of 
ruminal pH below 5.6 followed the 
same pattern as average ruminal pH. 
Steps one through four were not differ- 
ent from each other and averaged 73.90 
across dietary treatments. Area of rumi- 
1997 Nebraska Beef Report - Page 50 
Table 1. Effect of Rumensin during finishing period. 
Item Control Rumensin 
DM Intake Iblda) 
Rate of ~ntake % of dad) intahe/~ll~n 
Rumlnal pHa 
Area belo\\ 5 bbc 
~ H D I F F ~  
pHVARe 
aMeans dlffer (P  = 11) 
bArea= rumlnal pH unlts belo\\ 5 6 b) mlnute 
C M e a ~ s  differ (P < 10) 
* ~ a g n ~ t ~ l d e  of d a ~ l )  rumlnal pH change 
5 0 
0 
Step1 Step2 Step3 Step1 Fin1 Fin2 
- 
- 
+ Control 
- - R ~ ~ m e n s i n  
- 
I I I I 
Tontrol  \-s Runlensin (P=.2i). 
"Control 1 s  Rumensin (P=.08). 
Stepl through Stepl  are the 5 da) merage of each respectibe step-up diet. 
Finl and Fin2 are the first and second i days of finisher. respectively. 
nal pH below 5.6 tended (P = .16. from 
step 4) to increase during the first five 
days on finisherto an average of 139.50. 
Area again increased during the second 
five days of finisher to an average of 
261.66 (P < .05, fi-om first 5 days on 
finisher). For steers on the Ruinensin 
treatment, area ofruminal pH below 5.6 
was numerically lower (P = .25) during 
the first five days on finisher and was 
significantly lower (P = .08) during the 
second five days on finisher compared 
to the controls (Figure 2). 
Daily magnitude of ruminal pH 
change was not affected by Ruinensin. 
However, pHVAR tended (P = .14) to 
be lower for the Rumensin treatment 
compared to the control (Table 2). Both 
pHDlFF and pHVAR had significant (P 
< .01) quadratic responses to step-up 
diet (Table 3). Both started low on step 
one, were highest on step three, and 
returned to levels similar to step one by 
the second five days on finisher. 
Therefore, results of the grain adap- 
tation period indicate that Rumensin 
caused steers to move on feed more 
gradually, but did not affect DM intake 
by the second five days on finisher. In 
addition. Rumensin reduced area of 
ruminal pH below 5.6 for the first and 
second five days on finisher. indicating 
less acidosis while adapting to the final 
diet. 
Figure 2. Area of rnmi~ial pH beloll 5.6 during grain adaptation period. Finishing period 
Analysis of the finishing period in- 
cluded the average of the last two days 
on each level of intake variation. Diy 
250 matter intake was not affected by di- 
etaiy treatment or level of intake varia- 
Control Ru~l le~ l s i~ l  
Figure 3. Area of ruminal pH below 5.6 during finishing period. 
tion and averaged 28.0 Ib per day forthe 
finishing period. Rate of intake in- 
creased linearly (P < .05) with level of 
intake variation on the control diet, but 
was not affected by level of intalie 
variation on the Rumensin diet (data 
not shown). 
Average daily ruminal pH tended 
(P = . I  1) to be higher for the steers on 
Rumensin than the controls across 
all three levels of intake variation 
(Table 4). Average daily ruminal pH 
increased (P < .05, linear) with 
increasing level of intalie variation 
(Continued on next page) 
Page 5 1 - 1997 Nebruska Beef Report 
Table 5. Effect of level of intake variation during finishing period. 
Item No \ ariation Lo\\ \ ariation High ariation 
DM intake. lblday 28.16 27.85 27.92 
Rate of intake. % of dail) intalte/minh .52 .62 .59 
Ruminal pH 5.52' 5.69d 5.76d 
Area belo\\ 5.6e 231.03C 112.72d 91.67d 
~ H D I F F '  1 .03C 1 .07Cd 1 . 1 9  
pHVAR3 .050C .O5sc .072d 
aNo Variation = Ad libitum. Lon- Variation = 2 lblday intake variation. High Variation = 4 lblday intake 
variation (DM basis). 
bSignifi cant interaction detected (P = .08). Olerall means presented but not statisticall) a11al)zed. 
dMea~ls differ (P < . lo) .  
rArea= r~~minal  pH ~lnits belo\\ 5.6 b) minute. 
f ~ a g n i t u d e  of daily ruminal pH change. 
%Variance of daily ruminal pH. 
8 0.04 
5 0.03 t Control 
> 
0.02 & Rumensin 
Tontrol  \ s R~~mensin (P<.O5). 
NV = A d  libitum. no co~ltrolled intake variation. 
LV = Lon- intake variation. 
HV = High intake \ ariation. 
Figure 4. \ arialice of dailj ruminal pH during finishing period. 
(Table 5). Area of ruminal pH below 
5.6 was significantly greater (P = .07) 
for the steers on control than on 
Rumensin, indicating more subacute 
acidosis with the controls (Figure 3). 
Area of ruininal pH below 5.6 linearly 
decreased (P < .05) with increasing 
level of intake variation (Table 5). The 
reason average ruminal pH increased 
and area below 5.6 decreased with in- 
creasing level of intake variation is 
unclear. 
Daily magnitude of ruminal pH 
change (pHDIFF) and pHVAR were 
relatively constant and not affected by 
dietary treatment across NV and LV. 
However. with high intake variation. 
both pHDlFF and pHVAR significantly 
increased (P < .05) for the control, 
while remaining constant for the 
Ruinensin treatment (Figure 4). 
Therefore, results of the finishing 
period indicate that the use of Ruinensin 
elevates average ruininal pH and de- 
creases area of ruininal pH below 5.6. 
while stabilizing rate of intake and daily 
ruminal pH fluctuation at high levels of 
feed intake variation. 
'Rob Cooper. graduate student: Terry 
IClopfenstein. Professor. Animal Science. Lincoln: 
Rick Stock. Former Professor. Animal Science. 
Lincoln: Cal Parrott. Lilly Research Laboratories. 
Greenfield. IN.: Dan Herold. research technician. 
Animal Science.Lincoln. 
Evaluating Breakeven for Various Management 
Systems for Different Breed Types from Weaning 
to Slaughter 
Maximizing summer pasture 
gain after utilizing cornstalk graz- 
ing resulted in lower overall cost of 
production. 
Cynthia Hayden Summary 
Ivan Rush 
Burt Weichenthal Two hundred hventql-four n7ediunz 
Brad Van Pelt' fi.un?ed, weuned British-breed ateer 
culvea (509 16) und 139 11,eaned conti- 
nentul-breedateer caltjes (542 16) 11,ere 
ztaed rn ht'o conseczttive j'eura (1994, 
1995; 2 frnrahrngpena/treut~?zent/j~~*) to 
evulzlute the effects of wrnter gain und 
length of sun7n7er gruring seuson on 
a zlbseqztent frnrshing perfornzance und 
overall sjlstenz breukeven wrt/7in hvo 
different breed tjpes 
Calves were 11,zntered ut hvo rates of 
gazn < 75 lb/duy (Slolt? and uppro~z- 
n7utelj' 2 Ib/duy (Faat) Culvea fi.onz 
euch wrnterrng treutnzent groztp grazed 
erther nutrve runge or created 11,heat 
grusa The grazmg perrod ~ t u s  fi.onz 
Majl to Jztlj~ (61 duja, Slqort) or Sep- 
tenzber (120 duj's, Long) All ateers 
11,ere finrshed on a 90% concentrate 
finrshzng dret for 131 d (S/7ort) und 118 
d (Long) Wrnter gazn and breed tqpe 
1997 Nebrasku Beef Report - Page 52 


Effect of Rumensin and Feed Intake Variation on Ruminal pH

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department January 1997 Effect of Rumensin and Feed Intake Variation on Ruminal pH Rob Cooper University of Nebraska-Lincoln Terry J. Klopfenstein University of Nebraska-Lincoln, tklopfenstein1@unl.edu Rick Stock University of Nebraska-Lincoln, rstock3@Unl.edu Cal Parrott Lilly Research Laboratories, Greenfield, IN Dan Herold University of Nebraska-Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Animal Sciences Commons Cooper, Rob; Klopfenstein, Terry J.; Stock, Rick; Parrott, Cal; and Herold, Dan, "Effect of Rumensin and Feed Intake Variation on Ruminal pH" (1997). Nebraska Beef Cattle Reports. 430. https://digitalcommons.unl.edu/animalscinbcr/430 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. Effect of Rumensin and Feed Intake Variation on Rob Cooper Terry Klopfenstein Rick Stock Cal Parrott Dan Herold' Steers receiving Rumensin had reduced acidosis as indicated by elevated ruminal pH and reduced area of ruminal pH below 5.6. Therefore. Ruinensin can be used as a management tool to aid in reducing acidosis and thereby in- creasing feedlot perfoimance. Summary Six runzinallj~-Jistz~luted steers I iwe used to evaluate the ejject of Rzlmensin and feed intake variation on rz~minal pH. Steers Ii.ere adapted to a 92.5 percent concentrate diet and then szlb- jected to three levels of intake varia- tion: ad libitunz, intake variation o f 2  lb/daj; and intake variation of 4 1b/ daj,. Feed intakes andrunzinalpH Iiwe nzonitored continz~ously throughout the entire trial. Results indicate that Rzlnzensin redz~ced acidosis by elevat- ing average runzinal pH and decreas- ing area ofrunzinal pH belo~t, 5.6. In addition, Rzlmensin stabilized rate of intake and daily rz~minal pH Jluctz~a- tion at the high level of intake varia- tion. Introduction Changes in dry matter intalie by cattle fed high-concentrate diets can nega- tively influence feedlot gain and effi- ciency as well as predispose digestive disorders such as acidosis. Subacute acidosis increases variation in feed in- take and decreases dry matter intalie of cattle consuming high-grain diets. Dur- ing acidosis, cattle will reduce feed Ruminal pH intake until ruminal pH increases to approxiinately 5.6. Thus, ruininal pH must affect feed intake. On the other hand. it is not totally clear whether ruminal pH causes feed intake variation orwhether feed intake variation changes ruminal pH, and how these factors are controlled in cattle. Rumensin is an ionophore widely used in the feedlot industry to increase feed efficiency. It has been widely observed and recently shown that Rumensin reduces feed in- take variation and may reduce digestive disturbances and death loss. This effect of Rumensin and its mechanism have been difficult to measure and explain. Therefore, a system of continuous ac- quisition of feed intake and ruininal pH data was developed so that a inore coin- plete understanding of the interactions between ruminal pH and feed intake variation would be possible. The objec- tives of this trial were to evaluate the effects of Rumensin and feed intake variation on iuminal pH through con- tinuous data acquisition. Procedure Six iuminally-fistulated steers (860 Ib) were used in a 1 1  I-day inetabolism finishing trial. To have the steers used in this trial respond in intake and perfor- mance similar to yearling cattle coining off grass and going to the feedlot in early fall. the steers were cannulated in the spring at approxiinately one year of age and then summered on grass until the start of the trial in mid-October. Table 1. Composition of finishing diet. l tem % of DM Dr) -rolled corn 81 95 Alfalfa ha) 7 50 Molasses-~~rea supplement 6 36 Dr) supplementa 1 1 9  "Contamed m~nerals  \ ~tamlns. and T) Ian. \ \ ~ t h  or T\ ithout Rurne~lsi~l Steers were then allotted randomly to one of two dietary treatments, a 92.5 percent concentrate diet with or with- out Ruinensin at 25 glton (Table 1). Steers were adapted to the finishing diet through a 20-day, four step grain adap- tation period. Each step was fed for a 5- day period and consisted of 45. 35. 25. and 15% (DM basis) alfalfa hay in place of diy-rolled corn for steps one through 4. respectively. All steers were then subjected to three levels of intake varia- tion: ad libituin intake with no con- trolled intake variation on days 21-47 and 60-98 (NV). low daily intake varia- tion of 2 Iblday of diy matter on days 48-53 and 99-104 (LV). and high daily intake variation of 4 Iblday of dry mat- ter on days 54-59 and 106-1 1 1  (HV). Dietaiy treatments were switched on day 78. with the three steers receiving Ruinensin going to the control diet and the three steers already on the control diet going to the Ruinensin treatment. Throughout the entire trial, steers were tethered in individual inetabolism stalls. Feed intakes were monitored continuously with individual feed bunks that were suspended from load cells. Ruininal pH was also monitored con- tinuously with submersible pH elec- trodes suspended through the plugs of the rumen cannulas of each steer. Each pH electrode was encased in a weighted four-wire metal shroud to keep the elec- trode in a stationaiy position approxi- mately five to ten inches above the ventral floor of the rumen, while allow- ing rumen contents to flow freely through it. Load cells and pH electrodes were linked directly to a computer al- lowing data acquisition software to record both feed weight and ruminal pH every minute for each steer over the entire feeding period. Analysis included DM intake, rate of DM intake, average ruminal pH, area of ruminal pH below 5.6, daily magni- (Continued on next page) Page 49 - 1997 Nebruska Beef Report Table2. Effect of Rumensin during grain adaptation period. Item Control R u m e ~ l s ~ ~ l  DM i~ltahe lbldax a 25 9 1  23 81 Rate ot  Intake % of dall) ~ntal,e/m~n 77 79 Ruminal pH i 79 i 78 Area belo\\ 5 bb 13121 98 16 pHDIFFC I I6  1 1 1  ~ H V A R ~  093 072 a M e a ~ s  differ (P < 10) b ~ r e a =  rumlnal pH unlts belo\\ 5 6 b) mlnute CMag~litude of dad) r u ~ l l ~ ~ l a l  pH change dVar~ance ot da~l)  rumlnal pH tude of ruminal pH change (pHDIFF). and daily variance of ruininal pH (pHVAR). Rate of intake was calcu- lated as a first-order reaction with units of percent of daily intake per minute. Area of ruininal pH below 5.6 was calculated as time (minutes) by the units of ruininal pH below 5.6. Since it has been shown that on average cattle will reduce intakes at a ruininal pH below 5.6, the area of the ruininal pH curve below 5.6 should provide a mea- surement of subacute acidosis. Both pHDlFF and pHVAR indicate the de- -.- Control -a- Ru~l le~ l s i~ l  20 1 I I 1 I I Stepl Step2 Step3 Step4 Finl Fin2 Vont ro l  \ s R~~mensin (P<.01). " Control vs Ru~lle~lsin ( E l i ) .  " T o ~ o o l  \-s Runlensin (P<.lO). Step 1 th ro~~gh  Step 1 are the 5 da) aberage of each respectibe step-up diet Finl and Fin2 are the first and second i days of finisher. respectively. Figure 1. Dry matter intakes during grain adaptation period. Table 3. Effect of step-up diet during grain adaptation period. Diet" l tem Steo l Steo2 Steo3 Steo4 Finl Fin2 DM intake. lblday 21.1i"276c 2i.09d 2i .21d 27.0r 28.04e Rate of intake. % o f  dail) intal;e/min .72hc . 5  0" .8lkd .82"d .9ICd .91* Ruminal pH 5.89" 5 .80"~  5.88" 5.92" 5.73C 5 . 5 0 ~  Area belo\\ 5.6' 64.8Sh 93.41"3.23"4.40h 1 3 9 . 5 0 ~ 6 1 . 6 6 ~  pHDIFF2 .99" 1.08" 11.36d 1.2lc  1.18C 1.0" ~ H V A R ~  .OiSbc , 0 7 3 " ~ ~  .130e .094d , 0 8 8 ~ ~  .050b Ttep1 through Step4 are the i da) a\ erage of each respectlr e step-up d ~ e t  F ~ n l  and Fin2 are the first and second 5 da) s of fin~sher respect11 el) eMean~ d~ffer (P < 10) fArea = r u ~ l l ~ ~ l a l  pH u~lits belon i 6 b! llllnute SMagn~t~lde of dall) rumlnal pH change "var~ance of dad) ruminal pH gree to which the ruminal pH is chang- ing or fluctuating within a day. where pHDlFF is calculated as the difference between the inaximuin and the inini- muin ruininal pH for a steer in a day. Results Dry inatter intakes and daily gains were typical of yearling feedlot cattle. Dry inatter intakes during the finishing period averaged 28.0 Ib per day and ADG for the six steers during the trial was 4.0 Ib. Grain Adaptation Period Analysis of the grain adaptation pe- riod included the 5-day average for each step-up diet (I through 4) plus the average ofthe first and second five days on the f inisher.  Steers receiving Ruinensin consumed less feed over the grain adaptation period (P < .05) (Table 2). reaching the level of the controls by the second five days on finisher (Figure 1). Diy matter intakes on step one were similar for the steers on the control and Ruinensin treatments. On steps two and three, steers receiving Rumensin con- sumed approximately 16 percent less feed than the controls (P < .0 1). During step four and the first five days on finisher, steers on the Rumensin treat- ment tended to consume eight percent less feed than the controls (P < .16). By the second five days on finisher. DM intakes were not different. During the grain adaptation period. rate of DM intake was not affected by dietaiy treat- ment or step-up diet. Average daily ruininal pH was not affected by Rumensin, although it was affected by step-up diet (Table 3). Ru- minal pH was relatively constant from step one through step four, averaging 5.87. During the first five days on fin- isher, average ruminal pH dropped to 5.73 (P < .05, from step 4). During the second five days on finisher, average ruminal pH dropped to 5.50 (P < .05, from first 5 days on finisher). Area of ruminal pH below 5.6 followed the same pattern as average ruminal pH. Steps one through four were not differ- ent from each other and averaged 73.90 across dietary treatments. Area of rumi- 1997 Nebraska Beef Report - Page 50 Table 1. Effect of Rumensin during finishing period. Item Control Rumensin DM Intake Iblda) Rate of ~ntake % of dad) intahe/~ll~n Rumlnal pHa Area belo\\ 5 bbc ~ H D I F F ~  pHVARe aMeans dlffer (P  = 11) bArea= rumlnal pH unlts belo\\ 5 6 b) mlnute C M e a ~ s  differ (P < 10) * ~ a g n ~ t ~ l d e  of d a ~ l )  rumlnal pH change 5 0 0 Step1 Step2 Step3 Step1 Fin1 Fin2 - - + Control - - R ~ ~ m e n s i n  - I I I I Tontrol  \-s Runlensin (P=.2i). "Control 1 s  Rumensin (P=.08). Stepl through Stepl  are the 5 da) merage of each respectibe step-up diet. Finl and Fin2 are the first and second i days of finisher. respectively. nal pH below 5.6 tended (P = .16. from step 4) to increase during the first five days on finisherto an average of 139.50. Area again increased during the second five days of finisher to an average of 261.66 (P < .05, fi-om first 5 days on finisher). For steers on the Ruinensin treatment, area ofruminal pH below 5.6 was numerically lower (P = .25) during the first five days on finisher and was significantly lower (P = .08) during the second five days on finisher compared to the controls (Figure 2). Daily magnitude of ruminal pH change was not affected by Ruinensin. However, pHVAR tended (P = .14) to be lower for the Rumensin treatment compared to the control (Table 2). Both pHDlFF and pHVAR had significant (P < .01) quadratic responses to step-up diet (Table 3). Both started low on step one, were highest on step three, and returned to levels similar to step one by the second five days on finisher. Therefore, results of the grain adap- tation period indicate that Rumensin caused steers to move on feed more gradually, but did not affect DM intake by the second five days on finisher. In addition. Rumensin reduced area of ruminal pH below 5.6 for the first and second five days on finisher. indicating less acidosis while adapting to the final diet. Figure 2. Area of rnmi~ial pH beloll 5.6 during grain adaptation period. Finishing period Analysis of the finishing period in- cluded the average of the last two days on each level of intake variation. Diy 250 matter intake was not affected by di- etaiy treatment or level of intake varia- Control Ru~l le~ l s i~ l  Figure 3. Area of ruminal pH below 5.6 during finishing period. tion and averaged 28.0 Ib per day forthe finishing period. Rate of intake in- creased linearly (P < .05) with level of intake variation on the control diet, but was not affected by level of intalie variation on the Rumensin diet (data not shown). Average daily ruminal pH tended (P = . I  1) to be higher for the steers on Rumensin than the controls across all three levels of intake variation (Table 4). Average daily ruminal pH increased (P < .05, linear) with increasing level of intalie variation (Continued on next page) Page 5 1 - 1997 Nebruska Beef Report Table 5. Effect of level of intake variation during finishing period. Item No \ ariation Lo\\ \ ariation High ariation DM intake. lblday 28.16 27.85 27.92 Rate of intake. % of dail) intalte/minh .52 .62 .59 Ruminal pH 5.52' 5.69d 5.76d Area belo\\ 5.6e 231.03C 112.72d 91.67d ~ H D I F F '  1 .03C 1 .07Cd 1 . 1 9  pHVAR3 .050C .O5sc .072d aNo Variation = Ad libitum. Lon- Variation = 2 lblday intake variation. High Variation = 4 lblday intake variation (DM basis). bSignifi cant interaction detected (P = .08). Olerall means presented but not statisticall) a11al)zed. dMea~ls differ (P < . lo) .  rArea= r~~minal  pH ~lnits belo\\ 5.6 b) minute. f ~ a g n i t u d e  of daily ruminal pH change. %Variance of daily ruminal pH. 8 0.04 5 0.03 t Control > 0.02 & Rumensin Tontrol  \ s R~~mensin (P<.O5). NV = A d  libitum. no co~ltrolled intake variation. LV = Lon- intake variation. HV = High intake \ ariation. Figure 4. \ arialice of dailj ruminal pH during finishing period. (Table 5). Area of ruminal pH below 5.6 was significantly greater (P = .07) for the steers on control than on Rumensin, indicating more subacute acidosis with the controls (Figure 3). Area of ruininal pH below 5.6 linearly decreased (P < .05) with increasing level of intake variation (Table 5). The reason average ruminal pH increased and area below 5.6 decreased with in- creasing level of intake variation is unclear. Daily magnitude of ruminal pH change (pHDIFF) and pHVAR were relatively constant and not affected by dietary treatment across NV and LV. However. with high intake variation. both pHDlFF and pHVAR significantly increased (P < .05) for the control, while remaining constant for the Ruinensin treatment (Figure 4). Therefore, results of the finishing period indicate that the use of Ruinensin elevates average ruininal pH and de- creases area of ruininal pH below 5.6. while stabilizing rate of intake and daily ruminal pH fluctuation at high levels of feed intake variation. 'Rob Cooper. graduate student: Terry IClopfenstein. Professor. Animal Science. Lincoln: Rick Stock. Former Professor. Animal Science. Lincoln: Cal Parrott. Lilly Research Laboratories. Greenfield. IN.: Dan Herold. research technician. Animal Science.Lincoln. Evaluating Breakeven for Various Management Systems for Different Breed Types from Weaning to Slaughter Maximizing summer pasture gain after utilizing cornstalk graz- ing resulted in lower overall cost of production. Cynthia Hayden Summary Ivan Rush Burt Weichenthal Two hundred hventql-four n7ediunz Brad Van Pelt' fi.un?ed, weuned British-breed ateer culvea (509 16) und 139 11,eaned conti- nentul-breedateer caltjes (542 16) 11,ere ztaed rn ht'o conseczttive j'eura (1994, 1995; 2 frnrahrngpena/treut~?zent/j~~*) to evulzlute the effects of wrnter gain und length of sun7n7er gruring seuson on a zlbseqztent frnrshing perfornzance und overall sjlstenz breukeven wrt/7in hvo different breed tjpes Calves were 11,zntered ut hvo rates of gazn < 75 lb/duy (Slolt? and uppro~z- n7utelj' 2 Ib/duy (Faat) Culvea fi.onz euch wrnterrng treutnzent groztp grazed erther nutrve runge or created 11,heat grusa The grazmg perrod ~ t u s  fi.onz Majl to Jztlj~ (61 duja, Slqort) or Sep- tenzber (120 duj's, Long) All ateers 11,ere finrshed on a 90% concentrate finrshzng dret for 131 d (S/7ort) und 118 d (Long) Wrnter gazn and breed tqpe 1997 Nebrasku Beef Report - Page 52 

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Effect of Rumensin and Feed Intake Variation on Ruminal pH

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