Serum Zinc Concentrations in Spring-Born Missouri
W. Tyler, DVM, PhD*†
Ronald K. Tessman, DVM*†
Stan Casteel, DVM, PhD†
Robert Larson, DVM, PhD*
Richard F. Randle, DVM,
*Departments of Veterinary Medicine and Surgery and
†Veterinary Pathobiology, University
of Missouri, Columbia,
KEY WORDS: cattle, zinc deficiency, risk factors
This study determined
the prevalence of zinc deficiency in Missouri feeder calves. Additionally, this study identified
factors related to zinc status and determined whether serum zinc concentrations
were related to owner perceptions of disease. Serum samples and survey
data were collected from calves throughout Missouri. Regression models were developed predicting serum
zinc concentrations and zinc status. Associations between zinc status
and owner perceptions of disease were examined using Chi-squared tests.
The statewide zinc deficiency rate was 2.1%. An additional (24.4%) of
the calves had marginal serum zinc concentrations. Low serum zinc concentrations
were associated with owner perceptions that adult cow diarrhea, poor
hair coats, and reproductive failure were problems in the herd of origin.
The Northwest, Northeast, Central, Southwest, and South Central regions
were associated with increased serum zinc concentrations. Commercial
fertilizer was associated with increased serum zinc concentrations and
pasture application of lime was associated with decreased serum zinc
concentrations. Red clover and orchard grass were associated with increased
serum zinc concentrations and fescue, white clover, ladino clover, and
birdsfoot trefoil were associated with decreased serum zinc concentrations.
Provision of trace mineralized salt was associated with increased serum
zinc concentrations. Logistic regression models revealed that application
of a commercial fertilizer, orchard grass, and trace mineralized salt
were associated with a decreased probability of serum zinc concentrations
<0.8 ppm, and lespedeza and calf age over 7 months were associated
with an increased probability of serum zinc concentrations ≥0.8
is an essential micronutrient in cattle diets. Clinical signs and abnormalities
present in cattle with zinc deficiency include decreased growth rate,
diarrhea, poor appetite, salivation, abnormal hooves, swollen joints
and coronary bands, stiff gait, hair loss, parakeratosis, thymic atrophy,
lymphoid depletion, decreased disease resistance with specific depression
of cell-mediated responses, and decreased reproductive performance.1–10
These clinical signs are not pathognomonic and zinc deficiency could
readily be overlooked. Although experimental zinc deficiency readily
induces clinical disease, the diagnosis of zinc deficiency is rarely
made by veterinarians.
Cattle have a small, labile zinc storage pool. Clinical
signs and laboratory abnormalities associated with zinc deficiency occur
rapidly after removal of zinc from diets and rapidly return to normal
after supplementation.10,11 Consequently, optimal zinc nutrition requires
ongoing, adequate, and continuous intakes. Zinc deficiency can be induced
either by low dietary zinc concentrations or excess dietary calcium,
sulfates, iron, or molybdenum.
deficiency is usually diagnosed on the basis of serum or plasma zinc
concentrations; however, liver and hair concentrations have been used.12,13
None of these measures is optimal or consistently accurate. Serum and
plasma concentrations appear accurate, but inflammatory conditions cause
decreased serum and plasma zinc concentrations, creating the potential
for the spurious diagnosis of zinc deficiency.14 Cattle with serum concentrations
of zinc ≥0.8 ppm wet weight are zinc replete, cattle with serum
zinc concentrations ≥0.4 ppm and <0.8 ppm have marginal zinc
status, and cattle with serum zinc concentrations <0.4 ppm are deficient.12,13
purpose of this study was to determine the prevalence of zinc deficiency
in Missouri feeder calves. A secondary goal of this study was to identify
management and husbandry factors related to zinc status and serum zinc
concentrations. Finally, we determined whether serum zinc concentrations
were related to owner perceptions of disease.
MATERIALS AND METHODS
Sample and Survey Data Collection
The sampling strategy was premised on geographic localities
(counties) rather than random sampling. Private veterinary practitioner-collaborators
having a large beef cattle component in their practices were identified
throughout the state. Collaborator veterinarians collected blood samples
from 3 calves in each enrolled herd and obtained samples from no more
than 3 herds in each county. Sampling was performed at the time of routine
fall processing of calves and was restricted to calves between the ages
of 4 and 10 months. Practitioners were cautioned that sampled calves
should be representative of herd. Calves that were overtly ill were
not sampled. Approximately half of the samples were collected in the
fall of 1998 and the remainder in the fall of 1999. Whole blood samples
were collected into tubes specifically designed to limit zinc contamination
(Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ). Collaborating
practitioners shipped samples to a central laboratory using postage-prepaid
mailers. Blood centrifugation and serum collection was performed at
the central laboratory. Practitioners completed a questionnaire summarizing
exposure to potential risk factors for zinc deficiency. The survey included
the questions regarding region, calf age in months, pasture type, soil
amendment practices, including commercial fertilizer use, lime application,
and cattle, swine, and poultry manure application, and mineral supplementation
practices. Information regarding whether calves were weaned was not
available. Potential risk factors that were present in less than 5%
of study population were removed from further consideration. Owners
also were asked whether diarrhea of mature cows, calf diarrhea, pneumonia,
fractures, abnormal hair coats, lameness, and cow fertility were perceived
as ongoing health problems in their herd.
Serum Zinc Determinations
Briefly, serum zinc was analyzed by atomic absorption
spectrophotometry at 213.9 nm. The method used was identical to the
published method for the assessment of serum copper with the exception
of the substitution of 0.5% Triton X-100 for the glycerol in preparation
of standard solutions (2, 1, 0.5, and 0.2 ppm) and the selection of
an appropriate detection wavelength.15 Plastic tubes were used throughout
the procedure to limit the binding of zinc to glassware. The external
control contained 2.86 ppm zinc. Five percent of samples were processed
in duplicate to verify analytic quality. Sample sets were reanalyzed
if more than 10% variation occurred in duplicate samples.
For the purpose of this study, low serum zinc concentration
was defined as a serum zinc concentration <0.4 ppm wet weight. Marginal
serum concentration was defined as greater than or equal to 0.4 ppm
wet weight and <0.8 ppm wet weight. Adequate serum zinc concentrations
were defined ≥0.8 ppm wet weight. Only calves for which blood
zinc concentration and complete survey data were obtained were included.
The proportion of calves with low, marginal, and replete serum zinc
concentrations was reported for each of the 9 agricultural districts:
Northeast, North Central, Northwest, West Central, Central, East Central,
Southeast, South Central, and Southwest, defined by the Missouri Agriculture
Statistics Service (2001 Missouri Farm Facts, Missouri Department of
Agriculture, Jefferson City, MO). Initially, low and marginal serum
zinc concentration groups were combined to eliminate cells with less
than 5 observations. These proportions were compared among districts
using a 2-¥-9 Chi-squared test
(Triton X-100, Fisher Scientific Co., Fair Lawn, NJ).19 Patterns of
deficiency were deemed to differ significantly when the calculated
P value <0.05. The statewide proportions of calves with deficient,
marginal, and replete zinc status were calculated as follows. The proportion
of calves with low blood zinc concentrations in each region was multiplied
times the number of calves in the respective region to calculate the
number of calves in each region with less-than-optimal zinc status.
These numbers then were summed and divided by the total state beef calf
population, yielding statewide weighted results.
between owner perceptions of herd health and calf serum zinc concentrations
were explored using a series of Chi-squared tests. Observations were
cross-classified using 2-¥-2
tables defined by disease status (0, 1) and serum zinc concentrations
(<0.4 ppm). Disease status variables included the presence of diarrhea
in mature cows, calf diarrhea, pneumonia, fractures, abnormal hair coats,
lameness, and cow fertility. These analyses were repeated using serum
zinc <0.8 ppm as a threshold for marginal zinc status as a cut point.
For all significant associations (P <0.05), odds ratios were calculated.
Stepwise, multivariate, backward-stepping design-variable
regression models were developed to predict blood zinc concentration
as a function of district, calf age in months, husbandry and animal
health practices, pasture type, soil amendment practices, and mineral
supplementation practices. Initially, all variables were forced to enter
the model. Thereafter, the variable with the largest P-to-enter was removed at each
step. The process was repeated until no variable had a
P-to-enter greater than 0.10.
stepwise logistic regression models were developed predicting the incidence
of low or marginal serum zinc status (<0.80 ppm) as a function of
district, calf age, animal health and husbandry practices, pasture type,
soil amendment practices, and mineral supplementation practices. In
each regression model, the independent variable with the smallest P-to-enter was added to the model
at each step until no remaining variable had a
P-to-enter >0.10. Logistic regression models were not developed
to predict serum zinc concentrations <0.4 ppm because only 11 of
the 529 calves had serum zinc concentrations <0.4 ppm.
Five hundred twenty-nine calves drawn from 177 farms were
enrolled. At least 3 calves were sampled in 74 of Missouri’s 114 counties.
Of the 529 calves studied, 34% had access to creep feed and 71% of the
calves had access to trace mineralized salt. Twelve percent of the calves
originated from herds that were provided with supplemental hay and 17%
of the calves originated from herds that were provided with supplemental
concentrates. The predominant pasture plant was fescue (94% of pastures);
however, orchard grass (31%) and red clover (44%) also were common.
The presence of reed canary grass, coastal Bermuda grass, and timothy
in pasture and the use of poultry or swine manure as soil amendments
were all very infrequent (<5%). Consequently, these variables were
removed from further consideration.
The proportion of zinc deficient calves varied from 0%
to 5.9% by agricultural district (Table 1). No deficient calves were
observed in 5 districts, and the highest proportion of deficient calves
was observed in the Northwest district. The regional proportion of calves
with marginal serum zinc status varied from 0.138 to 0.458. The regional
proportion of calves with adequate serum zinc status varied from 0.542
to 0.862. Of the 529 calves enrolled in the study, only 11 had serum
zinc concentrations less than 0.4 ppm. The calculated statewide zinc
deficiency rate was 2.1% and an additional 24.4% of calves had marginal
serum zinc concentrations, ≥0.4 ppm and <0.8 ppm. The patterns
of zinc status varied among the 9 agricultural districts (P
Low serum zinc concentrations (<0.4 ppm) were associated
with owner perception that adult cow diarrhea was a problem in the herd
of origin (P = 0.013, odds ratio [OR] = 6.82).
Low serum zinc concentrations were associated with owner perception
that poor hair coats were common in the herd (P = 0.019, OR = 6.33). Low serum
zinc concentrations were associated with owner perception that infertility
was common in the herd of origin (P <0.0001, OR = 12.35). Low
serum zinc concentrations were not significantly associated with owner
perceptions that calf diarrhea, pneumonia, fractures, or lameness were
problems in the herd. Marginal or low serum zinc concentrations (<0.8
ppm) were not significantly associated with any of the surveyed owner
perceptions of disease.
The developed regression model revealed a number of significant
associations between independent variables and serum zinc concentrations.
The Northwest, Northeast, Central, Southwest, and South Central districts
were associated with increased serum zinc concentrations (Table 2).
Pasture fertilization, red clover or orchard grass pastures, and access
to trace mineralized salt were associated with increased serum zinc
concentrations. Pasture application of lime, fescue, white clover, ladino
or trefoil pastures, thin cows, feeding of supplemental hay, and increased
age were associated with decreased serum zinc concentrations (Table
Logistic models predicting
the presence of marginal to deficient serum zinc concentrations (<0.8
ppm) reveal similar patterns (Table 3). Fertilization, orchard grass
pastures, and access to trace mineralized salt were associated with
a decreased probability of serum zinc <0.8 ppm. Lespedeza pastures
and increased calf age were associated an increased probability of serum
zinc <0.8 ppm.
Overt zinc deficiency (serum zinc <0.4 ppm) was rare
in the study population. Only 11 of 529 calves (2%) had serum zinc concentrations
<0.4 ppm. An additional 24% of the population had marginal serum
zinc concentrations, and the majority of calves had replete serum zinc
concentrations. However, the frequency of marginal zinc status, serum
zinc concentrations less than 0.8 ppm, is cause for concern. Deficient
and marginal zinc status (serum zinc <0.8 ppm) has been associated
with suboptimal growth in cattle and sheep.16,17 Impaired reproductive
performance has been associated with zinc deficiency in cattle, sheep,
and laboratory animals.17,18
In the present study, zinc deficiency was significantly
associated with owner perceptions regarding 3 clinical observations:
adult cow diarrhea, poor hair coats, and infertility. The association
between low serum zinc and perceived infertility (OR = 12.35) raises
serious concerns. The limited number of deficient calves supports the
possibility that this association was spurious. However, the strength
of this association (OR = 12.35) and the degree of statistical significance
<0.0001) suggest this association is representative of a biologically
meaningful relationship. Marginal serum zinc concentrations (<0.8
ppm) were not significantly associated with any owner-perceived disease
problem. Consequently, if low serum zinc concentrations are associated
with overtly impaired health, this relationship appears to be restricted
to cattle with profound deficiency and is less closely associated with
marginal zinc status. Previous experimental studies support the possibility
that zinc deficiency could be a cause of reproductive failure.18–20
Increased prostaglandin F2a synthesis has
observed in zinc-deficient females.20–22 This increased production of
PGF2a could either
result in an increased potential for luteolysis or increased myometrial
activity. Either could potential have an impact on fertility. Additional
manifestations of reproductive failure that have been associated with
zinc deficiency include decreased spermatogenesis, abortion, fetal mummification,
decreased birth weight, uterine inertia, and delayed testicular development.10,18–23
However, it should be noted that owner perception of disease, in this
case reproductive failure, is an imprecise end point.
Models predicting serum zinc concentration and models
predicting serum zinc status were consistent. The majority of factors
that were associated with decreased serum zinc concentrations also were
associated with an increased risk of serum zinc concentrations less
than 0.8 ppm.
Provision of a trace mineralized salt was associated with
a small but significant increase in serum zinc concentration (Table
2). Similarly, the probability of low zinc concentrations (<0.8 ppm)
was decreased in calves that were provided access to trace mineralized
salt (OR <1). A cautionary note regarding the potential impact of
trace mineralized salt on calf zinc status is appropriate. A mineral
source with a high concentration of highly bioavailable zinc would likely
increase serum zinc concentration and decrease the probability of zinc
deficiency. However, a mineral source with low zinc concentrations or
unavailable zinc sources might actually increase the probability of
zinc deficiency if the mineral contains high concentrations of calcium,
iron, sulfur, and molybdenum.3,10,11 The composition of mineral sources
and intake were not documented in this study.
Pasture amendment practices were associated with serum
zinc concentrations and calf zinc status. Use of commercial fertilizer
was associated with increased serum zinc concentrations and a decreased
probability of serum zinc concentrations less than 0.80 ppm. This contradicts
previous reports in which commercial fertilizers containing either nitrogen
or phosphorous predisposed zinc deficiency.10,11 The negative relationship
between pasture application of lime and serum zinc concentrations was
anticipated. Soil pH greater than 6.5 has been associated with decreased
serum zinc concentrations.10,11 Consequently, the increased pasture
pH caused by lime application could cause decreased serum zinc concentrations.
Furthermore, commercial lime application could increase the pasture
concentrations of calcium impairing absorption of zinc.13
The decreased serum concentrations of zinc in calves on
white clover, ladino clover, and birdsfoot trefoil pastures and the
increased probability of serum zinc concentrations <0.8 ppm in calves
on lespedeza pastures were in agreement with previous studies. Previous
studies have substantiated the presence of lower serum zinc concentrations
in cattle grazed on legume pastures than cattle grazing on grasses.10,11
This generalization was not consistent. Red clover was associated with
increased serum zinc concentrations and fescue pastures were associated
with decreased serum zinc concentrations.
Increasing calf age
was associated with both lower serum zinc concentrations and an increased
probability of lower serum zinc concentrations. This could reflect an
actual age effect or, alternatively, an effect caused by the shift from
a dam’s milk-based diet to pasture or supplemental forage and concentrates.
In conclusion, marginal
serum zinc concentrations were common in the study population, but overt,
frank deficiency (<0.4 ppm) was rare. In the present study, sampling
was restricted to feeder calves. Consequently, this study only provides
an indirect measure of whole-herd zinc status and not a direct measure
of either cow or bull zinc status. It should be noted that the impact
of zinc deficiency on reproductive performance has been documented best
in laboratory animals, and evidence supporting a direct association
between zinc status and reproductive performance in cattle is less compelling.
The described research was supported in part by United
States Department of Agriculture Formula Funds, the University of Missouri,
Agriculture Experiment Station and the Department of Veterinary Medicine
and Surgery, Committee on Research. The authors acknowledge the technical
assistance of private practitioners throughout Missouri in sample and
survey data collection.
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Numbers and Proportions of Calves With Deficient, Marginal and Replete
Serum Zinc Concentrations by Agricultural District in a Survey of 529
Missouri Feeder Calves*
Deficient Proportion Marginal Proportion Replete Proportion
at Risk† Calves Deficient Calves
Marginal Calves Replete
223,000 85 5 0.059 16 0.188 64
Central 222,000 48
0 0.000 22 0.458 26 0.542
121,000 102 1 0.010 30 0.294 71
Central 240,000 36
0 0.000 12 0.333 24 0.667
460,000 80 3 0.038 16 0.200 61
Central 136,000 55
0 0.000 14 0.255 41 0.745
312,000 50 2 0.040 10 0.200 38
Central 320,000 58
0 0.000 8 0.138 50 0.862
39,000 15 0 0.000 5 0.333 10
estimates 2,073,000 529 11
0.021 133 0.244 385
estimates are weighted on the basis of calf numbers in each of the districts.
X-100, Fisher Scientific Co., Fair Lawn, NJ.
Results of a Forward-Stepping Stepwise
Regression Model Predicting Serum Zinc Concentration (ppm) in 529 Spring-Born
Missouri Beef Calves as a Function of Agricultural District, Cow Condition,
Calf Age, Pasture Fertilization Practices, and Predominant Pasture Forage
Analysis of variance
Source of Variation F Value P
Intercept 0.894 0.082
Northwest 0.085 0.050
Northeast 0.135 0.048
Central 0.040 0.049
Southwest 0.115 0.057
Central 0.242 0.055
cows -0.098 0.086
Fertilizer 0.050 0.039
Lime -0.088 0.045
Fescue -0.051 0.066
grass 0.032 0.034
clover 0.061 0.032
clover -0.082 0.061
clover 0.038 0.037
trefoil -0.119 0.067
hay -0.035 0.050
mineralized salt 0.034 0.035
(>7 months) calves -0.070 0.038
Results of a Forward Stepwise Logistic
Regression Model Predicting the Occurrence of
Serum Zinc Concentrations <0.80 ppm in 529 Feeder Calves as
a Function of Geographic, Management, and Nutritional Risk Factors
Coefficient SE P
Odds Ratio (95% CI)
Intercept -0.247 0.265 NA NA
Fertilizer -0.690 0.237 0.004 0.502
grass -0.475 0.230 0.039 0.622
Lespedeza 0.839 0.294 0.004 2.315
mineralized salt -0.435 0.213 0.041 0.647
calves (>7 months) 0.874 0.225 <0.001 2.396