Trials were conducted to evaluate the effects of weaning calves at 150, 210 and 270 days of age (i.e. August, October and December, respectively). A total of 75 Angus x MARC II heifers calves were used in this study. Heifers were bled on the day of weaning and again at 2, 7, 14 and 28 days after weaning. Blood was analyzed for differential WBC, cortisol, T3 and glucose. Weight changes were recorded. The data suggests October weaned calves (210 days) had both greater blood cortisol and glucose at days 7, 14 and 28 post-weaning and greater weight gains when compared to calves weaned at 150 and 210 days of age

Bueno, Andrea

Cappel, Todd

Clemens, Edd

Dragastin, Mark

Rasby, Richard J.

Story, Chuck

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Nebraska Beef Cattle Reports Animal Science Department 
January 1998 
Evaluating Stress in Calves Weaned at Three Different Ages 
Andrea Bueno 
University of Nebraska-Lincoln 
Todd Cappel 
University of Nebraska-Lincoln 
Chuck Story 
University of Nebraska-Lincoln 
Richard J. Rasby 
University of Nebraska-Lincoln, rrasby1@unl.edu 
Edd Clemens 
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 
Bueno, Andrea; Cappel, Todd; Story, Chuck; Rasby, Richard J.; Clemens, Edd; and Dragastin, Mark, 
"Evaluating Stress in Calves Weaned at Three Different Ages" (1998). Nebraska Beef Cattle Reports. 326. 
https://digitalcommons.unl.edu/animalscinbcr/326 
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 
Andrea Bueno, Todd Cappel, Chuck Story, Richard J. Rasby, Edd Clemens, and Mark Dragastin 
This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/
animalscinbcr/326 
Page 23 — 1998 Nebraska Beef Report
for switchgrass over stages of growth
and years. Disappearance of Rubisco in
the lower tract indicates a significant
portion of ingested bundle sheath cells
escape the rumen to be degraded in the
lower tract. Bundle sheath cells enter-
ing the lower tract may be structurally
weakened due to rumen activity and
their contents, including Rubisco, may
become available to digestive enzymes
in the lower tract. Mean percentages of
Rubisco escaping the entire digestive
tract were above 10% for both species,
except for the 1996 vegetative samples.
A portion of bundle sheath cells appar-
ently escaped the entire digestive tract.
Our results indicate a significant part
of intake Rubisco escapes rumen degra-
dation via bundle sheath cells and dis-
appears in the lower tract. The Rubisco,
which we used as a marker of bundle
sheath cell integrity, represents only a
portion of the available protein in bundle
sheath cells. Because concentration of
Rubisco in bundle sheath cells has not
been determined for switchgrass and
big bluestem, we cannot accurately es-
timate amount of protein escaping the
rumen via these cells. Composition of
bundle sheath cells and total soluble
protein relative to Rubisco, however,
has been determined for such warm-
season, agronomic grasses as corn and
millets. For example, we used the
Rubisco concentrations in millet, along
with our values of rumen-escape
Rubisco, to determine if the amount of
rumen-escape protein via bundle sheath
cells was biologically significant. Esti-
mates of rumen-escape protein ranged
from 7% to 32% of the total crude
protein content for switchgrass and 7%
to 14% for big bluestem. Rumen-es-
cape protein estimates were lower for
the vegetative stage and higher for the
elongation/reproductive stages. Our
estimates of escape protein via bundle
sheath cells are about 50% less than
estimates of total rumen-escape protein
for big bluestem and switchgrass re-
ported in the literature. Our values are
low compared to other estimates par-
tially because we are not accounting for
the non-bundle sheath cell protein that
escapes. However, our example calcu-
lations indicate that the bundle sheath
cell mechanism may account for as
much as 50% of the rumen escape pro-
tein in big bluestem and switchgrass.
In conclusion, passage of bundle
sheath cells from the rumen appears to
provide a mechanism which allows pro-
tein escape from the rumen. Also, our
results indicate Rubisco and associated
proteins found in a portion of the escap-
ing bundle sheath cells disappear in the
lower tract. The amount of Rubisco and
associated proteins escaping the rumen
via bundle sheath cells could represent
a significant portion of rumen-escape
protein in big bluestem and switch-
grass. Understanding the mechanisms
involved in rumen escape protein should
improve the efficiency of livestock feed-
ing systems and assist in the selection of
improved forage species.
1Dan Vaughn, graduate student, Walter
Schacht, Assistant Professor, Lowell Moser,
Professor, Agronomy, Lincoln; Robert Graybosch,
Research Geneticist, USDA/ARS, Lincoln; Terry
Klopfenstein, Professor, Animal Science, Lincoln.
Table 2. Percentage intake Rubisco (+S.E.) disappearing in the rumen and lower tract, and escaping
the entire digestive tract of beef cattle grazing big bluestem or switchgrass in vegetative or
elongation/reproductive stages of growth.
Vegetative Elongation/Reproductive
Species 1995 1996 1995 1996
----------------------------------------- % ---------------------------------------------
Disappearing in rumen
Big bluestem 63.6 (3.4) 80.8 (6.8) 65.3 (13.3) 63.8 (9.0)
Switchgrass 49.6 (9.6) 84.1 (2.3) 39.3 (  8.9) 47.9 (9.4)
Disappearing in lower trace
Big bluestem 14.4 (.42) 10.6 (2.4) 14.7 (  5.7) 19.5 (5.3)
Switchgrass 21.7 (8.9) 13.3 (2.4) 27.1 (  3.8) 39.6 (.54)
Escaping entire trace
Big bluestem 22.2 (3.0) 9.1 (3.4) 19.9 (  7.6) 14.2 (2.3)
Switchgrass 28.7 (1.0) 4.8 (  .9) 33.5 (  6.0) 21.8 (3.2)
Evaluating
Stress in Calves
Weaned at
Three Different
Ages
Andrea Bueno
Todd G. Cappel
Chuck Story
Mark Dragastin
Rick Rasby
Edd Clemens1
Calves weaned in October
(210 days) exhibited less chronic
stress, more prolonged endocrine
responses, and greater weight gains
than calves weaned in August (150
days) and December (270 days).
Summary
Trials were conducted to evaluate
the effects of weaning calves at 150,
210 and 270 days of age (i.e. August,
October and December, respectively).
A total of 75 Angus x MARC II heifers
calves were used in this study. Heifers
were bled on the day of weaning and
again at 2, 7, 14 and 28 days after
weaning. Blood was analyzed for dif-
ferential WBC, cortisol, T3 and glu-
cose. Weight changes were recorded.
The data suggests October weaned
calves (210 days) had both greater
blood cortisol and glucose at days 7, 14
and 28 post-weaning and greater weight
gains when compared to calves weaned
at 150 and 210 days of age.
Introduction
Cattle, which are animals of habit,
become stressed when they experience
a novel or painful situation. Weaning
can be one such stressful change. Wean-
ing involves not only psychological
(Continued on next page)
1998 Nebraska Beef Report — Page 24
stress due to separation, but also abrupt
changes in the calf’s environment, nutri-
tion and social structure. Because of
these variables, weaning could result in
a considerable setback in a calf’s per-
formance.
Studies on cattle suggest the physi-
ological effects of separating a calf
from its mother may contribute to a
performance decrease several days af-
ter weaning. Physiological effects may
be classified into three general catego-
ries; gross clinical signs, blood compo-
sition changes and endocrine interposed
changes.
The initial response to stress is a
release of hormones from the adrenal
gland. The adrenal hormone cortisol
functions to increase gluconeogenesis
resulting in increased blood glucose,
decreased glucose uptake by the tis-
sues, decreased protein synthesis and
an increased immune-defense system
(increase in WBC count).
Triiodothyronine (T3) responds to
stress by calibrating the metabolic state
of the animal, which means body heat
production is altered, allowing the
stressed animal to adapt to the environ-
ment. Thus, both rapid defense systems
(cortisol) and long-term adaptation
mechanism (T3) are effected by stress.
In this study, cortisol, T3, glucose,
differential WBC and weight changes
were analyzed to determine the effects
of weaning at 150, 210 and 260 days of
age.
Procedure
Animals and management
This research was conducted using
75 Angus x MARC II crossbred heifer
calves. All animals were managed at
the University of Nebraska, Dalbey-
Halleck Farm near Virginia, Nebraska.
Calves were randomly allotted to one of
three weaning groups based on age (150,
210 and 260 days; August, October and
December weaning, respectively). In
addition, control groups of non-weaned
calves were assigned to August and
October weaning groups. At weaning,
all calves were separated from their
dams and taken to a post-weaning pen
with free access to grass hay and water.
After three days they were fed corn and
Figure 1. Plasma cortisol means observed in the calves at the day of weaning and at 2, 7, 14 and 28
days after weaning for August, October and December groups.
Figure 2. Plasma glucose means observed in the calves at day of weaning and at 2, 7, 14 and 28 days
after weaning for August, October and December groups.
a protein supplement to gain 1.25 to 1.5
pounds per day. The non-weaned calves
remained with their mother.
Blood sampling
Blood samples were collected via
jugular venipuncture on the day of wean-
ing (day 0) and days 2, 7, 14 and 28 after
weaning from both weaned and non-
weaned calves. Plasma samples were
analyzed for T3 and cortisol, using radio-
immunoassay and glucose, and using
automated, colorimetric determination
(Auto Analyser I). Blood smears were
7
6
5
4
3
2
1
0
Pl
as
m
a 
co
rti
so
l, 
ug
/d
l
0 2 7 14 28
Day
August October December
100
80
60
40
20
0
Pl
as
m
a 
gl
uc
os
e,
 m
g/
10
0m
l
0 2 7 14 28
Day
August October December
Page 25 — 1998 Nebraska Beef Report
December weaned calves at day 2 post-
weaning (P<0.001), but continued to
increase and remain high only in
October-weaned calves (P<0.01-
Figure 1). Plasma cortisol values
decreased at days 7 and 14 for the
August weaned calves (P<0.05). Plasma
glucose concentration changes were
not as dramatic as those of cortisol
(Figure 2). Blood glucose concentra-
tions for October calves continued to
increase and remain high throughout
the post-weaning period, while concen-
trations for August and most notice-
ably December weaning decreased.
Concentrations of plasma T3 were
highest in the August and lowest in the
December calves at the time of weaning
(P<0.05 - Figure 3). Plasma T3 de-
creased (P<0.05) in each age group, but
were similar at day 2 post-weaning.
Thereafter, post-weaning concentra-
tions of T3 were generally reflective of
the environmental temperature during
that post-weaning period. Calves
weaned in the warm August days main-
tained the lower T3; calves weaned in
December exhibited higher T3 concen-
trations.
Figure 4 presents the data for the
Neutrophil: Lymphocyte ratio (WBC
count). Calves weaned in August dem-
onstrated the most dramatic increase in
N: L ratio at day 2 post-weaning
(P<0.05), and continued to maintain the
higher ratio throughout the post-wean-
ing period. The October and December
weaned calves had similar, but lower,
N: L ratio’s during the post-weaning
period.
Figure 5 illustrates the weight gain
of the calves from weaning (day 0) to
the completion of the trial (day 28) for
each age group, as well as for the con-
trol (non-weaned) calves. Mean weight
gains were greater (P<0.05) for October
(67.5 lb) weaned calves compared to
August (52.2 lb - P<0.1) and December
(43.7 lb) weaned calves for the first 28
days post-weaning.
We know stress response increases
the animals resistance to stress. The
overall effects of stress can be favor-
able or not, depending on the animal’s
perceptions. In an acute stage, the stress
response is, in general, beneficial. On
made from each sample to determine
differential white blood cell counts.
Results and Discussion
Significant differences (P<0.01) ex-
isted for most blood parameters due to
age of weaning. Mean values for each
blood parameter are presented in Fig-
ures 1 through 4. Non-weaned calves
presented no significant changes in the
concentration of the blood parameters
analyzed over the 28-day trial. Plasma
cortisol increased for October and
Figure 3. Plasma T3 means observed in the calves at the day of weaning and at 2, 7, 14 and 28 days
after weaning for August, October and December groups.
Figure 4. Neutrophil:Lymphocyte ratio means observed in the calves at the day of weaning, and at
day 2, 7, 14 and 28 after weaning for August, October and December groups.
(Continued on next page)
180
160
140
120
100
80
60
40
20
0
Pl
as
m
a 
T 3
,
 n
g/
dl
0 2 7 14 28
Day
August October December
0.6
0.5
0.4
0.3
0.2
0.1
0
N
:L
 ra
tio
0 2 7 14 28
Day
August October December
1998 Nebraska Beef Report — Page 26
the other hand, if the stress is too in-
tense, it may be harmful to the calves. In
this study, calves weaned in October
(210 days) had higher concentrations of
cortisol and glucose on days 7, 14 and
28 after the weaning; however weight
gain was significantly greater in this
group of calves compared to calves
weaned in August (150 days) and
December (270 days). Therefore, for
October-weaned calves, the stress was
not severe enough to decrease animal
performance and actually induced a
favorable response increasing their
weight gains as compared with the other
two groups.
1Andrea Bueno, Todd Cappel and Chuck
Story, graduate students. Rick Rasby and Edd
Clemens, Professors, Animal Science, Lincoln;
Mark Dragastin, manager, Dalbey-Halleck Research
Farm, Virginia.
Figure 5. Changes in weight observed in weaned and non-weaned calves in August, October and
December groups.
70
60
50
40
30
20
10
0
W
ei
gh
t g
ai
n,
 lb
August October December
weaned non-weaned October x December weaned group (P<.05)
October weaned x non-weaned (P<.01)


Evaluating Stress in Calves Weaned at Three Different Ages

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department January 1998 Evaluating Stress in Calves Weaned at Three Different Ages Andrea Bueno University of Nebraska-Lincoln Todd Cappel University of Nebraska-Lincoln Chuck Story University of Nebraska-Lincoln Richard J. Rasby University of Nebraska-Lincoln, rrasby1@unl.edu Edd Clemens 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 Bueno, Andrea; Cappel, Todd; Story, Chuck; Rasby, Richard J.; Clemens, Edd; and Dragastin, Mark, "Evaluating Stress in Calves Weaned at Three Different Ages" (1998). Nebraska Beef Cattle Reports. 326. https://digitalcommons.unl.edu/animalscinbcr/326 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 Andrea Bueno, Todd Cappel, Chuck Story, Richard J. Rasby, Edd Clemens, and Mark Dragastin This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/animalscinbcr/326 Page 23 — 1998 Nebraska Beef Reportfor switchgrass over stages of growthand years. Disappearance of Rubisco inthe lower tract indicates a significantportion of ingested bundle sheath cellsescape the rumen to be degraded in thelower tract. Bundle sheath cells enter-ing the lower tract may be structurallyweakened due to rumen activity andtheir contents, including Rubisco, maybecome available to digestive enzymesin the lower tract. Mean percentages ofRubisco escaping the entire digestivetract were above 10% for both species,except for the 1996 vegetative samples.A portion of bundle sheath cells appar-ently escaped the entire digestive tract.Our results indicate a significant partof intake Rubisco escapes rumen degra-dation via bundle sheath cells and dis-appears in the lower tract. The Rubisco,which we used as a marker of bundlesheath cell integrity, represents only aportion of the available protein in bundlesheath cells. Because concentration ofRubisco in bundle sheath cells has notbeen determined for switchgrass andbig bluestem, we cannot accurately es-timate amount of protein escaping therumen via these cells. Composition ofbundle sheath cells and total solubleprotein relative to Rubisco, however,has been determined for such warm-season, agronomic grasses as corn andmillets. For example, we used theRubisco concentrations in millet, alongwith our values of rumen-escapeRubisco, to determine if the amount ofrumen-escape protein via bundle sheathcells was biologically significant. Esti-mates of rumen-escape protein rangedfrom 7% to 32% of the total crudeprotein content for switchgrass and 7%to 14% for big bluestem. Rumen-es-cape protein estimates were lower forthe vegetative stage and higher for theelongation/reproductive stages. Ourestimates of escape protein via bundlesheath cells are about 50% less thanestimates of total rumen-escape proteinfor big bluestem and switchgrass re-ported in the literature. Our values arelow compared to other estimates par-tially because we are not accounting forthe non-bundle sheath cell protein thatescapes. However, our example calcu-lations indicate that the bundle sheathcell mechanism may account for asmuch as 50% of the rumen escape pro-tein in big bluestem and switchgrass.In conclusion, passage of bundlesheath cells from the rumen appears toprovide a mechanism which allows pro-tein escape from the rumen. Also, ourresults indicate Rubisco and associatedproteins found in a portion of the escap-ing bundle sheath cells disappear in thelower tract. The amount of Rubisco andassociated proteins escaping the rumenvia bundle sheath cells could representa significant portion of rumen-escapeprotein in big bluestem and switch-grass. Understanding the mechanismsinvolved in rumen escape protein shouldimprove the efficiency of livestock feed-ing systems and assist in the selection ofimproved forage species.1Dan Vaughn, graduate student, WalterSchacht, Assistant Professor, Lowell Moser,Professor, Agronomy, Lincoln; Robert Graybosch,Research Geneticist, USDA/ARS, Lincoln; TerryKlopfenstein, Professor, Animal Science, Lincoln.Table 2. Percentage intake Rubisco (+S.E.) disappearing in the rumen and lower tract, and escapingthe entire digestive tract of beef cattle grazing big bluestem or switchgrass in vegetative orelongation/reproductive stages of growth.Vegetative Elongation/ReproductiveSpecies 1995 1996 1995 1996----------------------------------------- % ---------------------------------------------Disappearing in rumenBig bluestem 63.6 (3.4) 80.8 (6.8) 65.3 (13.3) 63.8 (9.0)Switchgrass 49.6 (9.6) 84.1 (2.3) 39.3 (  8.9) 47.9 (9.4)Disappearing in lower traceBig bluestem 14.4 (.42) 10.6 (2.4) 14.7 (  5.7) 19.5 (5.3)Switchgrass 21.7 (8.9) 13.3 (2.4) 27.1 (  3.8) 39.6 (.54)Escaping entire traceBig bluestem 22.2 (3.0) 9.1 (3.4) 19.9 (  7.6) 14.2 (2.3)Switchgrass 28.7 (1.0) 4.8 (  .9) 33.5 (  6.0) 21.8 (3.2)EvaluatingStress in CalvesWeaned atThree DifferentAgesAndrea BuenoTodd G. CappelChuck StoryMark DragastinRick RasbyEdd Clemens1Calves weaned in October(210 days) exhibited less chronicstress, more prolonged endocrineresponses, and greater weight gainsthan calves weaned in August (150days) and December (270 days).SummaryTrials were conducted to evaluatethe effects of weaning calves at 150,210 and 270 days of age (i.e. August,October and December, respectively).A total of 75 Angus x MARC II heiferscalves were used in this study. Heiferswere bled on the day of weaning andagain at 2, 7, 14 and 28 days afterweaning. Blood was analyzed for dif-ferential WBC, cortisol, T3 and glu-cose. Weight changes were recorded.The data suggests October weanedcalves (210 days) had both greaterblood cortisol and glucose at days 7, 14and 28 post-weaning and greater weightgains when compared to calves weanedat 150 and 210 days of age.IntroductionCattle, which are animals of habit,become stressed when they experiencea novel or painful situation. Weaningcan be one such stressful change. Wean-ing involves not only psychological(Continued on next page)1998 Nebraska Beef Report — Page 24stress due to separation, but also abruptchanges in the calf’s environment, nutri-tion and social structure. Because ofthese variables, weaning could result ina considerable setback in a calf’s per-formance.Studies on cattle suggest the physi-ological effects of separating a calffrom its mother may contribute to aperformance decrease several days af-ter weaning. Physiological effects maybe classified into three general catego-ries; gross clinical signs, blood compo-sition changes and endocrine interposedchanges.The initial response to stress is arelease of hormones from the adrenalgland. The adrenal hormone cortisolfunctions to increase gluconeogenesisresulting in increased blood glucose,decreased glucose uptake by the tis-sues, decreased protein synthesis andan increased immune-defense system(increase in WBC count).Triiodothyronine (T3) responds tostress by calibrating the metabolic stateof the animal, which means body heatproduction is altered, allowing thestressed animal to adapt to the environ-ment. Thus, both rapid defense systems(cortisol) and long-term adaptationmechanism (T3) are effected by stress.In this study, cortisol, T3, glucose,differential WBC and weight changeswere analyzed to determine the effectsof weaning at 150, 210 and 260 days ofage.ProcedureAnimals and managementThis research was conducted using75 Angus x MARC II crossbred heifercalves. All animals were managed atthe University of Nebraska, Dalbey-Halleck Farm near Virginia, Nebraska.Calves were randomly allotted to one ofthree weaning groups based on age (150,210 and 260 days; August, October andDecember weaning, respectively). Inaddition, control groups of non-weanedcalves were assigned to August andOctober weaning groups. At weaning,all calves were separated from theirdams and taken to a post-weaning penwith free access to grass hay and water.After three days they were fed corn andFigure 1. Plasma cortisol means observed in the calves at the day of weaning and at 2, 7, 14 and 28days after weaning for August, October and December groups.Figure 2. Plasma glucose means observed in the calves at day of weaning and at 2, 7, 14 and 28 daysafter weaning for August, October and December groups.a protein supplement to gain 1.25 to 1.5pounds per day. The non-weaned calvesremained with their mother.Blood samplingBlood samples were collected viajugular venipuncture on the day of wean-ing (day 0) and days 2, 7, 14 and 28 afterweaning from both weaned and non-weaned calves. Plasma samples wereanalyzed for T3 and cortisol, using radio-immunoassay and glucose, and usingautomated, colorimetric determination(Auto Analyser I). Blood smears were76543210Plasma cortisol, ug/dl0 2 7 14 28DayAugust October December100806040200Plasma glucose, mg/100ml0 2 7 14 28DayAugust October DecemberPage 25 — 1998 Nebraska Beef ReportDecember weaned calves at day 2 post-weaning (P<0.001), but continued toincrease and remain high only inOctober-weaned calves (P<0.01-Figure 1). Plasma cortisol valuesdecreased at days 7 and 14 for theAugust weaned calves (P<0.05). Plasmaglucose concentration changes werenot as dramatic as those of cortisol(Figure 2). Blood glucose concentra-tions for October calves continued toincrease and remain high throughoutthe post-weaning period, while concen-trations for August and most notice-ably December weaning decreased.Concentrations of plasma T3 werehighest in the August and lowest in theDecember calves at the time of weaning(P<0.05 - Figure 3). Plasma T3 de-creased (P<0.05) in each age group, butwere similar at day 2 post-weaning.Thereafter, post-weaning concentra-tions of T3 were generally reflective ofthe environmental temperature duringthat post-weaning period. Calvesweaned in the warm August days main-tained the lower T3; calves weaned inDecember exhibited higher T3 concen-trations.Figure 4 presents the data for theNeutrophil: Lymphocyte ratio (WBCcount). Calves weaned in August dem-onstrated the most dramatic increase inN: L ratio at day 2 post-weaning(P<0.05), and continued to maintain thehigher ratio throughout the post-wean-ing period. The October and Decemberweaned calves had similar, but lower,N: L ratio’s during the post-weaningperiod.Figure 5 illustrates the weight gainof the calves from weaning (day 0) tothe completion of the trial (day 28) foreach age group, as well as for the con-trol (non-weaned) calves. Mean weightgains were greater (P<0.05) for October(67.5 lb) weaned calves compared toAugust (52.2 lb - P<0.1) and December(43.7 lb) weaned calves for the first 28days post-weaning.We know stress response increasesthe animals resistance to stress. Theoverall effects of stress can be favor-able or not, depending on the animal’sperceptions. In an acute stage, the stressresponse is, in general, beneficial. Onmade from each sample to determinedifferential white blood cell counts.Results and DiscussionSignificant differences (P<0.01) ex-isted for most blood parameters due toage of weaning. Mean values for eachblood parameter are presented in Fig-ures 1 through 4. Non-weaned calvespresented no significant changes in theconcentration of the blood parametersanalyzed over the 28-day trial. Plasmacortisol increased for October andFigure 3. Plasma T3 means observed in the calves at the day of weaning and at 2, 7, 14 and 28 daysafter weaning for August, October and December groups.Figure 4. Neutrophil:Lymphocyte ratio means observed in the calves at the day of weaning, and atday 2, 7, 14 and 28 after weaning for August, October and December groups.(Continued on next page)180160140120100806040200Plasma T 3, ng/dl0 2 7 14 28DayAugust October December0.60.50.40.30.20.10N:L ratio0 2 7 14 28DayAugust October December1998 Nebraska Beef Report — Page 26the other hand, if the stress is too in-tense, it may be harmful to the calves. Inthis study, calves weaned in October(210 days) had higher concentrations ofcortisol and glucose on days 7, 14 and28 after the weaning; however weightgain was significantly greater in thisgroup of calves compared to calvesweaned in August (150 days) andDecember (270 days). Therefore, forOctober-weaned calves, the stress wasnot severe enough to decrease animalperformance and actually induced afavorable response increasing theirweight gains as compared with the othertwo groups.1Andrea Bueno, Todd Cappel and ChuckStory, graduate students. Rick Rasby and EddClemens, Professors, Animal Science, Lincoln;Mark Dragastin, manager, Dalbey-Halleck ResearchFarm, Virginia.Figure 5. Changes in weight observed in weaned and non-weaned calves in August, October andDecember groups.706050403020100Weight gain, lbAugust October Decemberweaned non-weaned October x December weaned group (P<.05)October weaned x non-weaned (P<.01)

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Evaluating Stress in Calves Weaned at Three Different Ages

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