Published December 11, 2014
BloodSerumConcentrations
of Selenium inFemaleLlamas
(Lama gIama) in Relationship to Feeding
Practices,
Region
of
United States, Reproductive
Stage,
and
Health
of Offspring'12r3
Thomas H. Herdt
College of Veterinary Medicine, Michigan StateUniversity,EastLansing
and at both sampling times in the females ( P .01).
In adult females, mean serum Se was actually higher
duringgestation ( P = . 0 6 ) and at parturition ( P <
.O 1) for the low-Se region than for the high-Se region,
but this effect was removed by covariate adjustment
for intake of supplemental Se. Serum Se in females
was correlated ( P < .05) to supplemental Se consumption. Vigor and(or) viability of thecria were not
affected by the Se status of the dams ( P> . 3 or cria
( P > . 2 ) . However, there were very few weak or
stillborncriainthisstudy.The
data suggest that
for
serumSein
excess of 85 ng/mL isadequate
newborn cria and that dams with serum Se in excess
of 160 ng/mLcan be predicted t o give birth to cria
withadequateSestatus.
ABSTRACT:
SerumSeandvitamin
E concentrations weredetermined twice ineach of 35 female
llamas from a high-Se region and 96 female llamas
from a low-Se region of the United States. The first
determination was taken at a randomtimeduring
gestation and the second shortly after parturition. At
the time of postpartum sampling, a sample was also
taken from the cria. Dietary information was collected
from each llama owner and a subjective estimate of
strength and vigor was assigned by the owner to each
cria studied. The mean blood serum concentrations of
Se in llamas during gestation andat parturition were
213 and 203 ng/mL, respectively. The mean serum Se
concentration was 113 ng/mL in neonatal cria. Among
herds, serum Se means varied for the cria ( P < .05)
Key
Words:
48824
Llamas,Selenium,Vitamin
E, Diet,Health,
Blood Serum
J. h i m . Sci. 1995.
73:337-344
Introduction
Deficiency of Se is known or suspected to cause or
contribute to abortion, stillbirth, and neonatal mortality in a number of animal species includingcattle
(Taylor et al., 1979; Hutchinson et al., 1982; Ohba et
al., 1992; Smyth et al., 19921, sheep (Kott et al.,1983;
SchmitzandSonn,
1984; Langlandsetal.,
19911,
rabbits (Yamini and Stein, 19891, horses (Ohike et
al., 1992), pigs (Smythetal.,
19921, andperhaps
humans (Dolamore et al.,
1990). The effects of dietary
Se on gestationandneonatalhealthinllamas,
however, seem to be unknown. Recently, it hasbecome
popular to raise llamas in areas of North America in
which indigenous forages have low Se concentrations.
Therefore, it is important to determine the relationship of Se status to fetal health and neonatal survival
in llamas. The objectives of the study reported here
were to determine the blood serum concentrations of
Se in pregnant female llamas in different
regions of
North America. A further objective was to relate these
serumnutrientconcentrations
to feeding practices
within herds and to cria viability. Serum vitamin E
concentrationswere also measuredandthevalues
used as covariates in assessing the effects of serum Se
on criahealth.
Materials and Methods
Animals, Cooperating farms were identified in two
'Research supported in part
by a grant from the International
LlamaAssociation.
'Acknowledgment is made to the Michigan Agric. Exp. Sta. for
additionalsupportof
this research.
3TheauthorthanksAnne
House, DavidBrigham,Kathleen
O'Hare,andToniThiel
for technical assistance and Dale Persing
and
Keith
Nelson for clerical assistance.
Received
March
23,
1994.
Accepted
September
24,
1994.
regions of the United States. The Great Lakes region
( GLR) consisted of Ohio, Michigan, Wisconsin, and
Indiana, and the mountainregion ( MTR) of Colorado
and Montana. The distributionof herds and numberof
females
sampled
per herd
is
given in
Table
1.
Cooperators
were
selected from
members
of the
InternationalLlama
Association. Individualllamas
337
HERDT
338
Table 1. Distribution of herds andnumber of
females sampled/herd for serum selenium
and vitamin E concentrations
N of females
sampled per
State
herda
N of herds
Colorado
Montana
Ohio
Michigan
Indiana
Wisconsin
5
3
4
10
2
5
Region
5.2 ( 3 - 9 )
3 (1-7)
6 (3-7)
3.9 ( 2 - 6 )
6.5 ( 5-8)
4 (1-7) .
MTR
MTR
GLR
GLR
GLR
GLR
aMean and range.
selected for study were confirmed pregnant before
March1989butotherwisewereinallstages
of
gestation.
Blood Sampling. Single, 10-mL blood samples were
taken from allfemalesduringthespring
of 1989.
Samples were collected intoevacuatedcontainers
withoutpreservativeandmailedtoMichiganState
University’s Animal Health Diagnostic Laboratory for
analysis. A second sample was taken from the dam
shortly after parturition. At that time, a sample was
also taken from the cria. Theaim was to takeall
paired dam-cria samples on the day of birth. When
this was not possible, the exact age of the cria in days
was recorded. In all, at least
one blood sample was
received from 168 females and dam-cria samples were
obtainedfrom
73 pairs.
FarmInformation.
Two types of questionnaires
were used to collect farm information. The first was
feed
used to gathergeneralinformation,including
of roughagesand
concenformulations,quantities
trates fed, andthemannerin
whichSe-containing
mineral supplementswere supplied (i.e., ad libitum or
mixed in concentrates). This farm-background questionnairewassubmitted
onceby
eachcooperating
of theanalysis,herds
were
herd owner. Forpart
divided retrospectively into one of three groups: those
at less
not supplementingSe,thosesupplementing
than 1 mg/d, or thosesupplementingSe
at greater
than 1 mg/d t o individualfemales.
A second questionnaire was supplied with the kits
for blood collection and included a section for recording
a graded assessment of cria vigor (cria vigor score:
Table 2. Criavigor
CVS). The criteria for scoring are shown in Table 2.
Telephone calls were made
to assess the survival of
the cria to 2 wk and to assure that no cria included in
thestudyhad
received aSe injection before blood
sampling.
Sample Analysis. Serum samples were analyzed for
Se by wet ashing and flourometeric detection of the
2,3-diaminonaphthalene
derivative.
The
procedure
was essentially the same asdescribed by Whetter and
Ullrey ( 19781, except that phosphoric and nitric acids,
instead of perchloric acid, were used in the digestion
step(Reamerand
Veillon, 1983).VitaminEwas
extracted from l-mL serum samples using one times
thesample volume of ethanoland two timesthe
sample volume of hexane. Vitamin E was measured as
alpha-tocopherol by high-pressure liquid chromatography using a 3.9-mm x 150-mm silica column (Waters
Porasil)and UV detection at 292 nm.Themobile
phase was hexane:chloroform (85: 15) with isocratic
elution(WidicusandKirk,1979).
Statistical
Analysis.
Comparisons
among
means
weredone usinglinear models appropriate for use
with unbalanced sample sizes (GLM; SAS, 1988) The
dependent variable was serum Se concentration and
main effects were time of sampling, region, herd of
origin, and cria vigor score. Specific, one-way interactions wereexamined
as indicatedintheResults
section. The cria-vigor-score effect was also analyzed
E concentration asa
singly usingserumvitamin
covariate.
This
was
done
because the effects of
selenium deficiency can, in some cases, be masked by
high tissue concentrations of vitamin E. For the above
analyses, individual animal was the unit of observation.The effect of region was also examined at the
herd level, using
herd
mean
serum
Se
as
the
as estidependent variable. Supplemental Se intake,
mated from owner reports, was used as a covariate in
this analysis. In both the individual- and herd-level
models, specific contrasts betweenindividualmeans
were performed using the Bonferroni t-statistic. Correlationparametersare
Pearson’s correlation coefficients.Correlationsandregressionswerecalculated
usingthe CORR and REG procedures, respectively
(SAS, 1988). Multiple regressionmodels were used to
examine the relationship of diet to serum selenium
concentration at the herd level. Herd mean serum Se
concentration was the dependent variable and dietary
score criteria
Characteristic
seems birth,
30 min after
very vigorous
withinStanding
stands
First
within
withinand
30 min
seems1 h
normally vigorous
First
stands
between 1 andbirth,
after
seems
3 h
slightly less vigorous than normal
Cannot
stand
a t after
3birth,
seems
h generally
weak makes
and
little
attmept
nurse
to
Very weak, seems
stupid
unaware
and
of surroundings,
makes
no attempt to rise or nurse
2
Abortion or stillbirth
Score
6
5
4
3
1
339
SERUM SELENIUM IN LLAMAS
nutrientconcentrations,ascalculated
fromowner
reports, were the independent variables. The models
wereconstructed by addingindependentvariables,
one at a time, in the order of diminishing F-statistics
for the univariate regressions. With the addition
of
each new variable, previously included variables were
dropped if the P-valueof their multivariate F-statistic
waslessthan
.5 (Stepwise; SAS, 1988).
parturition and this decline was greater in the MTR
than in theGLR, resulting in a sampling time x region
interaction ( P = .05). Serum vitamin E concentrations
did not differ between region, either during gestation
( P = . 5 5 ) or at parturition ( P = .54, data not shown).
Diet Effects. Feed intakes and diet composition of
gestating llamas, as reported by owners, are given in
Table 4. Relationshipsbetweenestimateddietary
nutrient concentrations and serum Se concentrations
wereexamined
attheherd
level usingmultiple
regression. When herd mean serum Se concentration
wasthedependentvariable,
daily supplementalSe
intake was the first independent variable to enter the
regression, with r2 values of .34 and .35 ( P < .O 1)
during
gestation
and
at parturition, respectively.
Additional variablesenteringthegestation
model
were, in order of entry, TDN, ADF, phosphorus, and
E. The overall r2 for the
supplemental
vitamin
gestation model was .77 ( P < .01). Similarly, for the
parturition model, independent dietary variables entering after supplemental Se were, in order of entry,
phosphorus, TDN, and supplemental vitamin E. The
overall r2 for the parturition model was .54 ( P < .O 1).
Regression parameters and partial r2 values for the
models are given inTables
5 and 6.
The effect of Se supplementation at less than or
greater than 1 mg/d to individual animals is shown in
Table 7. Mean serum Seof llamas from herds in which
Se was supplemented to individuals at less than 1 mg/
d were not different ( P > .05) from those in which no
supplemental Se was given. Conversely, those herds
supplementing Seto individuals at greater than1 mg/
d had serum Se means higher ( P < . 0 5 ) than either
those with no supplementation or supplementation at
less than 1 mg/d.
Results
Dam
Values
GestationEffects. Mean serumSeintheadult
females was 213 ng/mL during gestation, which
did
not differ ( P = .45) from the mean of 203 ng/mL at
parturition.Frequencydistributions
for serum Se
duringgestationand
atparturitionare
shown in
Figure 1. Mean serum Se concentrations within herds
ranged from 162 to 264 ng/mL during gestation and
139 to 317 ng/dL at parturition. These values differed
among herds ( P < .O 1) at both sampling times;54 and
48% of the variation was attributable to herd effects
during
gestation
and
atparturition,
respectively.
Individual animal values during gestation
were correlated to values at parturition ( P < .01, r2 =.2).
Meanserumvitamin
E concentrationinadult
females during gestation was 1.63 pg/mL, which was
not different ( P = .23) from the value of 1.85 pg/mL at
parturition.Meanserumvitamin
E concentrations
differed amongherdsduringgestation
( P < .05),
ranging from .05 to 2.79 pg/mL. At parturition, herd
serum vitamin E means vaned between .53 and 2.86
pg/mL but were not significantly different ( P = .45).
As with
Se,
serum
vitamin
E concentrations of
individualsduringgestation
werecorrelatedwith
those atparturition
( P < .01, r2 =.11).
Region Effects. Regional means and least squares
regional means for serum Se during gestation and at
parturition are given in Table 3. Least squares means
werecalculatedusingsupplementalSeintake
asa
covariate. The general pattern was for serum Se to be
higher in theGLR and for this effect to be removed by
adjustment for supplemental Se consumption. Serum
Se concentrations tended to decline from gestation to
Cria
Values
Blood samples wereobtainedfrom 73 cria. In all
but five cases,criaserumSeconcentrationswere
lower than those in samples taken from the dam at
the same time. It is very unusual to find serum Se
concentrations in neonates to be higher than those in
their dams, and this finding suggested that, in spite
of
our requests that theynot receive Se supplementation
before blood sampling, these cria had. Therefore, these
Table 3. Serum selenium concentrations by region (Great Lakesregion [GLR] andmountain
and within reproductive stage in female llamas
region [MTR])
Gestation
GLR
Item
Raw means, nglmLa
Least squares means,
ng/mLb
217
214
t
*
4.4
3.9
Parturi
MTR
P
*
.06
.68
202
211
t
6.1
6.6
GLR
213
209
2
t
6.9
6.2
MTR
181
189
t
2
7.0
1.1
~~~
aMeans 2 SE.
bLeast squares means
t
SE with covariate adjustment for calculated individual daily intake of supplemental Se.
P
,006
.07
HERDT
340
16
t
l4
12 10
I
p
4
$
-
8 6 4-
2
0
t
L
J
Figure 1. Frequency distribution of serum Se concentrations in female llamas. Values on the abscissa indicate the
minimum serum Se concentration for each bar group. Lighter bars indicate values measured at random times during
gestation. Dark bars indicate values measured within 25 d after parturition. Note that, overall, the distribution near
parturition
seems
to be shifted to
the
left,
compared
with
the
distribution
during
gestation.
five cases were deleted from all analysesin which cria
valueswereused.
It was intended that blood samples fromcriabe
taken on theday of birth,butduetotheon-farm
nature of this experiment the actual timeof sampling
of
ranged from 0 to 25 d from parturition, with a mean
6.5 d. By regression analysis, cria serum Se concentrations were estimated to decrease by .7 ng.mL-l.d-l ( P
= .09). The overall mean of cria serum Se concentrations was 113 ng/mL. Individual herd means ranged
from 66 to 186 ng/mL and varied significantly among
herds ( P < . O l ) , with or without covariate adjustment
for age at sampling. Herd meansof cria serum Sewere
not affected by region ( P = .88). Supplemental Se in
the diet of the dam tended to increase cria serum Se
( r 2 = .13; P = .067). Cria serum Se was correlated
positively withtheserumSe
of thedamduring
gestation ( r 2 = .28, P < .01) and at parturition ( r 2 =
.26, P < .01). Scatter plots and regression parameters
relating cria serum Se to dam serum Se are shown in
Figures 2 and 3.
Criaserumvitamin
E concentrationvariedfrom
undetectable to 5.4 pg/mL, with a mean value of 1.1
pg/mL. The values were not affected ( P = .37) by age
of cria a t samplingandherdmeans
did notvary
E
significantly ( P = .35).Thecriaserumvitamin
concentration
was
correlated
positively with
dam
serum vitamin E a t parturition ( r 2 = .12, P < .Ol), but
notduringgestation
( P = .57).
Table 4. Nutrient composition of individual female llama dietsas calculated from
owner-submittedsurveyforms
Maximum
Nutrienta
Minimum
Dry matter, kg/d
TDN, 9
6
'
ADF, %
Crude protein, 'X
Calcium, %
Phosphorus, 7i
Supplemental Se, mgid
Supplemental vitamin E, UVd
Meanb
3.84
64.1
37.2
12.9
.85
.28
.74
69.3
*
.35
22
.l3
.05
.005
,001
.28
*
f
*
*
*
*
f
26
1.64
52.2
26.3
9.0
.26
.l4
0
0
9.65
92.5
46.3
17.7
2.0
.38
5.4
480
aFeed composition values for TDN, ADF, calcium and phosphorus were calculated from NRC ( 1982).
bMean SE.
CTotaldigestible nutrient values are those expressed in the tables (NRC,
1982) for ruminants.
0
341
IN LLAMAS
SELENIUM SERUM
Table 5 . Parameters for the regression of herd-mean blood serum selenium concentration during gestation on
calculated dietary nutrient concentrations for llamas
Step at which
Parameter
Partial
entered
variable
regression
Variable
Intercept, ng/mL
Supplemental Se, mg.anima1-l.d-l
TDN, 56 DM
ADF, % DM
Phosphorus, 56 DM
Supplemental vitamin E, mg.anirnal-l&'
.005
1
2
3
5
Discussion
Serum orblood concentrations of nutrients, especially vitamins and minerals, are commonly used to
judge the nutritional statusof animals. The validityof
this practice withrespect to each specific nutrient
seems to depend on the physiological factors affecting
its serum concentration. With respect to Se, these are
incompletely understood.
However,
recent
pharmacokinetic studiesinhumanssuggestthatSeis
0
2
A
y=43+.33x,
pc.01
-3
_-
.34
4
Cria were observed at all vigor scores except
category 3. The distribution of cria among vigor-score
categories and the mean valuesfor serum Se in dams
and cria are shown in Table 8. Cria Se means among
vigor scores were compared using age at sampling and
vitamin E concentration as covariates; no differences
were observed ( P > .2). Moreover, there wereno
differences across vigor scores indamserumSe
concentrations, either during gestation( P = .86) or a t
parturition ( P = .38).
-G 220
Model
estimate
R2
R2
P
113.6
5.5
1.5
-2.6
339.0
-.OS
.34
.l6
.06
.l4
.07
-
,006
50
.02
.56
.70
.77
.l1
.01
.05
absorbed from the gastrointestinal tract in an unregulatedmannerand
avidly takenup
by the liver
(Pattersonetal.,
1989; Pattersonand Zech, 1992;
Kat0 et al., 1992). Excess Se is then transported to
the kidneys for excretion. Flux of Se from liver to
kidneysseems to be animportantdeterminant
of
serum
Se
concentration
(Patterson
et
al., 1989;
Patterson and Zech, 1992) and the rate of this flux
can be expected to be related to dietary Se availability.
Thisexpectationissupported
by alarge
body of
empirical evidence indicating that serum Se concento dietarySeintakeinmany
trationsarerelated
animal species (Ammerman et al., 1980; Byersand
Moxon, 1980;Maus et al., 1980; Stowe et al., 1988;
Braunetal.,1991;
Stowe andHerdt,1992).
Several results from this study suggest that serum
Se is a valuable measureof Se status in llamas. First,
therewas a significant effect of herd on serumSe
concentrations.Thissuggests
that some factor associated with
herd,
most
likely nutrition, affects
serum Seconcentrations. Moreover, the significant
correlationbetweendamserumSeconcentrations
during gestation and at parturition further indicates
A
A
Q
g
140g 120E 1002
Q)
80-
6
50100150200250
300 350 400
A
A
v)
!r
6
60.
A
,
50100150200250300350400
i
Dam's serum Se during gestation, ng/ml
Dam's serum Se after parturition, nglml
Figure 2 . Regression of cria serum Se concentrations
within 25 d of birth on dam's serum Se at random times
during gestation.
Figure 3. Regression of cria serum Se on dam serum
Se within 25 d after birth of the cria.
342
HERDT
Table 6. Parameters for the regression of herd-mean blood serum selenium concentration at parturition on
calculated dietary nutrient concentrations for llamas
Variable
estimate
Step at which
Parameter
Partial
entered
variable
regression
1
Intercept, ngimL
Supplemental Se, mg-animal-'&l
Phosphorus, 5% DM
TDN, % DM
Supplemental vitamin E, IU.animal-l&l
2
3
4
that serum Se concentrations were not random, but
were influenced by theanimal or itsenvironment.
Most importantly, however, estimated intake of supplementaldietary
Se had
relatively
a
largeand
positive influence on serum Se concentration, further
indicating that diet playsa large role in determination
of serum Seconcentrationinllamas.
The effect of region, as measured in this study, was
unexpected; the mean serum Se concentration of the
llamas in the GLR was higher than that of llamas in
the MTR. This was surprising because the GLR were
selected because forages produced in those states are
known to have low Se concentrations, compared with
MTR (NRC, 1983).However, it seems that this result
might have occurred because of greater usage of Se
supplements in the GLR. Indeed, the effect of region
was removed when supplemental Se was included as a
covariate in the model. It seems that llama producers
inthe
GLR
of
thisexperimentareaware
of the
potential for Se deficiency and commonly useSe
supplements, resulting in higher serum Se concentrations thaninthe
MTR.
In most species, Se seems to be concentrated into
of the
the fetus and mammary gland at the expense
dam's body stores (McConnell and Roth,1964; Jacobsson and Oksanen, 1966; Koller et al., 19841, presumably accounting for the peripartum decline in serum Se
concentration that has been observed (Van Saun et
al.,1989).Inthisstudy,meanmaternalserumSe
concentration at parturition was not different ( P =
.45) from the
mean
measured
during
gestation.
Initially, this appears in contrast
to observations in
other species. However, when the frequency distribu-
Model
R2
P
-
-
.34
.OB
.09
.34
.42
51
.53
,030
,002
R2
144
24.7
-245.2
1.8
-.07
.02
tions (Figure 1) are examined, it can be noted that
there is greater
dispersion of values at parturition
than during gestation. This suggests that, at least in
some individuals, serum Se diminishes at parturition
and that this
effect might be overridden by factors
such as dietary supplementation. This speculation is
supported by thestatistical
( P = . 0 5 ) interaction
between region and sampling time. This interaction
was characterized by a greater periparturient decline
inserumSe
in the MTR thaninthe
GLR. The
interactionmight be attributed to thegreater frequency of Se supplementation in the GLR than in the
MTR. Thus, the data presented here may
be viewed t o
be consistent with placental concentration
of Se into
the llama fetus, potentiallyat theexpense of maternal
reserves. The lower concentration of serum Se in cria
than in their dams is consistent with observations in
other species (Van Saun et al., 1989) and has
been
suggested to occur due to agreaterhepaticSe
clearance rate in the fetus than in the adult (Shariff
etal.,1984).
An important objective of this investigation was t o
relatedamandcriaSestatus
to criahealthand
viability. Unfortunately,due to the low numbers of
weak or nonviable cria, it is impossible t o determine
from these data a dam or cria serum Se concentration
that isclearly associated with deficiency and increased
diseaserisk.However,someimportant
conclusions
can be reached.First,serum
Seconcentrations associated with healthy cria under North
American farm
conditions have been determined. Of 39 cria withvigor
scores of 6, the median serum Se concentration was
111 ng/mL witharangefromthe10th
to 90th
Table 7. Serum selenium concentrations (ng/mLJ of llamas receiving
different levels of dietary selenium supplementation
Daily amount of supplemental Se per animal
Item
Gestationb
Parturitiond
< 1 mga
0
205'
191
f
*
26
43
.l0
,067
.36
206
195
f
*
23
36
1 mg
P
*
.03
248
269
*
20
38
aIncludes those animals with dailyaccess to trace-mineralized salt containingSe.
bValues measured a t random times during gestation.
CMean * SE.
dValues measured between 1 and 25 d postpartum.
,006
SELENIUM
343
IN LLAMAS
SERUM
Table 8. Serum selenium concentrations for damsand cria within each cria vigor-score category"Jb
Vigor score
3
Sample
Cria
Dam (gestation)d
Dam (parturition)c
1
-
n
X
NAC
213
171
2
2
2
10
8
5
5
5
-
5
4
X
n
1172 3
214 2 45
240 2 50
2
2
3
x
-
-
-
n
X
n
0
0
0
103 2 2
199 -c 21
191 2 29
2
3
3
-
6
X
n
115 2 8
219 * 9
200 2 11
25
24
29
-
X
n
121 2 6
207 -c 7
212 47
2 7
39
37
aVigor scorecategories are described in Table 2.
bMean -c SE.
CCria incategory 1 were stillborn and, thus, no serum samples were available.
dValues measured a t random times during gestation.
eValues measured between 1 and 25 d postpartum.
percentiles of 85 to 143 ng/mL. Although we may not
conclude that values in this range are necessary
for
healthy cria, they are clearly
sufficient for healthy cria
over a wide range of farm conditions. Furthermore,
theserumSevalues
of the cria at birthcan
be
predicted from the serum concentrations of the dams
measured at randomtimesduringgestation.The
on dam Se duringgestation
regression of criaSe
predicts that females with serum Seof 160 ng/mL will
give birth to cria with serum Se between 87 and 106
ng/mL (95%, confidence interval of theestimate).
Thus,damswithserum
Se of 160ng/mL or above
couldbe expected to have cria with serum Se above
the lowest decile of thenormalpopulation.
This information can be applied in the development
of sampling strategies for testing llama herds for the
risk of Se deficiency-associated health problems. In
small herds (fewer than fiveor six individuals), all
female llamas should be tested and Se supplementation instituted if serum Se concentrations are consistently below 160 ng/mL. Larger herds can be evaluated from themean of a representativenumber of
animals. I suggest that 190ng/mL
be used asa
reference value for herd serum Se means. Herds with
means in excess of 190ng/mL couldbe expected to
have no more than 16% of animals with values less
than 160 ng/mL, based on a normal probability profile
and the average within-herd standard deviation of 27
ng/mL. If seven is chosen as a representative number
of animals to test per herd, then the 68% confidence
interval of themean willbe approximately 24ng/
mL. Thus,increasingthe
reference value for herd
means to 214 ng/mL, an increase of 24 over 190 ngl
mL, would increase theconfidence one could have that
the true herd mean wasmore than 190 ng/mL. Of the
five herds in this experiment in which seven females
in gestation were tested, none had means below 190
ng/mL, and only onemeanwas
below 214ng/mL,
suggesting that these reference values are conservative and realistic.
Someinferencesaboutthe
levels of dietary Se
supplementation
appropriate
for llamas or llama
herds with serum values below the suggested reference ranges can be made from the data of this study.
From Table 7 it seems that, when supplementation is
required, amounts of Se in the rangeof 1 mg/d to each
adult may be necessary to substantially raise serum
Seconcentrations.Suchamounts
are unlikely to be
consumedwhen
the only sources of supplemental
dietary Se are selenized trace-mineral salt (consumed
ad libitum) or concentrates containing . l ppm or less
of supplemental Se.To provide 1 mg/d of supplemental
Se,theSeconcentrationinthetotaldietarydry
matter would need to be intherange
of .24ppm,
based on theaverage of the individualdaily feed
intakeestimates provided by llamaownersinthis
study.Thisamountis
above the . l ppmmaximum
dietary Se concentration currentlyallowed by the U.S.
government for food-producing animals.Whether or
not llamasfallunderthisregulationis
not clear.
Some
care
needs
to be takeninjudgingthe
implications of Table 7 for dietary Se supplementation
inllamas. Note that all of the serum Se means in
Table 7 are in excess of the suggested reference value
of 190ng/mL.Therefore,
it seems that both the
supplemented and unsupplemented animals had,
on
average, serum Se concentrations that are consistent
withnutritional sufficiency. Thus, we cannotinfer
from thesedatawhat
effect Sesupplementation at
levels below 1 mg/d might have had on animals that
were initially Se-deficient.
Implications
Cria with serum Se concentrations in excess of 85
ng/mL are unlikely to be suffering from Se deficiency.
When there
is
a herd-health concern about
Se
deficiency in cria, female llamas may reasonably
be
tested atanytimeduringgestation
to predict the
possibility of their giving birth to Se-deficient cria.
When individual, pregnant llama serum Se concentrations are less than 160 ng/mL, or when herd means
are less than 190 ng/mL, dietary Se supplementation
should be considered.
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