Influence of Chromium Tripicolinate on Growth and Glucose
Metabolism in Yearling Horses1,2
Edgar A. Ott3 and Jan Kivipelto
Animal Science Department, University of Florida, Gainesville 32611-0910
ABSTRACT: Thoroughbred and Quarter Horse yearlings (n = 24; 335 ± 7 d of age) were used in a 112d feeding trial to determine whether chromium (Cr)
supplementation would alter growth, development, and
energy metabolism of growing horses on high-concentrate diets. The horses were assigned at random within
breed and gender subgroups to one of four treatment
groups: A) basal concentrate; B) basal plus 175 µg of
Cr/kg concentrate; C) basal plus 350 µg of Cr/kg concentrate; and D) basal plus 700 µg of Cr/kg concentrate.
Chromium was provided via Cr tripicolinate (Prince
Agri Products, Quincy, IL). The horses were weighed,
measured for withers and hip height, heart girth, and
body length and underwent ultrasound evaluation for
croup fat thickness. The concentrate was fed for ad
libitum consumption for two, 1.5-hr feeding periods
daily. Coastal bermudagrass (Cynodon dactylon) hay
was group-fed (six animals/group) at 1% of BW daily.
Feed intake was 60% concentrate and 40% hay, resulting in a supplemental Cr intake of 0, 105, 210, and
420 µg/kg diet for groups A, B, C, and D, respectively.
Colts consumed more concentrate and total feed than
did fillies (P < .05), but no dietary effect on feed intake
was detected. Colts weighed more than fillies at the
completion of the experiment (P = .0754), but no dietary
effects on weight, body measurements, or croup fat were
detected. An i.v. glucose tolerance test (.2 g of glucose/
kg BW) and an i.v. insulin sensitivity test (.1 IU of
insulin/kg BW) were conducted on each animal during
the third 28-d period of the experiment. Plasma glucose
peaked immediately following injection and decreased
more rapidly in animals consuming the high-Cr diet
than in those consuming the control diet (P < .01). Mean
glucose fractional turnover rate values increased (P =
.0369) and mean half-life of glucose decreased (P =
.0634) in response to the high Cr supplementation.
Plasma glucose depletions in animals fed the other two
diets were between and not different from (P > .10) the
depletions in control animals or in those fed high-Cr
diets. No difference in insulin sensitivity was detected
(P > .10). Results indicate that Cr tripicolinate supplementation of yearling horses increases the rate at which
glucose is metabolized and may lower the plasma glucose concentration. No effect of Cr supplementation on
development of the animals was detected.
Key Words: Horses, Glucose Tolerance, Growth, Chromium
1999 American Society of Animal Science. All rights reserved.
Introduction
Chromium (Cr) can influence carbohydrate metabolism (Steel et al., 1977; Mertz, 1993; Bunting et al.,
1994), lipid metabolism (Steel and Rosebrough, 1981;
Abraham et al., 1991), and protein absorption and me-
1
Florida Agric. Exp. Sta. Journal Series no. R- 06425.
Our thanks to Eric Reller, Huisheng Xie, Naomi Katzowitz, and
Erica Lacher for assistance in collecting blood samples, Roger West for
performing the ultrasound croup fat determinations, and the Horse
Research Center staff for caring for the animals. This research was
supported in part by a gift from Prince Agri Products Inc., Quincy, IL.
3
To whom correspondence should be addressed: P. O. Box 110910
(phone: 352-392-2454; fax: 352-392-7652; E-mail: ott@animal.
ufl.edu).
Received November 30, 1998.
Accepted May 12, 1999.
2
J. Anim. Sci. 1999. 77:3022–3030
tabolism (Okada et al., 1983; Kornegay et al., 1997) in
various species. Chromium seems to be essential for
optimal insulin sensitivity and glucose uptake by insulin-sensitive cells (Anderson, 1985). Chromium tripicolinate is a readily available source of Cr and has influenced the carcass composition of pigs (Lindemann et
al., 1993; Mooney and Cromwell, 1993) and lambs (Kitchalong et al., 1993). Chromium from enriched yeast
has also been shown to influence carbohydrate metabolism in working horses (Pagan et al., 1995).
Young growing horses are often fed high-energy diets
to maximize rate of gain so animals will develop adequately to compete with animals of similar age in sales,
shows, or racing competition. Most of the energy in
these diets is provided by starch. These high-starch
diets have been implicated in a variety of metabolic
problems, including skeletal abnormalities (Glade et
al., 1984). Davidson et al. (1991) demonstrated that
3022
3023
CHROMIUM SUPPLEMENTATION OF YEARLING HORSES
Table 1. Concentrate formulation and nutrient content of concentrate and hay
Concentrate
Item
Formulation
Ground corn
Ground oats
Soybean meal (48% CP)
Wheat middlings
Alfalfa, dehy. 17%
Calcium carbonate
Bio Fosb
Salt
Molasses
Luprosilc
Vitamin premixd
Trace mineral premixe
Analysis
Dry matter, %
DE, Mcal/kgfg
CP, %f
Calcium, %f
Phosphorus, %f
Zinc, mg/kgf
Manganese, mg/kgf
Copper, mg/kgf
Chromium, mg/kgfh
A
B
C
D
33.45
35.00
9.50
10.00
5.00
1.25
1.00
.70
3.00
.075
.035
1.00
33.45
35.00
9.50
10.00
5.00
1.25
1.00
.70
3.00
.075
.035
1.00
33.45
35.00
9.50
10.00
5.00
1.25
1.00
.70
3.00
.075
.035
1.00
33.45
35.00
9.50
10.00
5.00
1.25
1.00
.70
3.00
.075
.035
1.00
87.9
3.37
15.63
.88
.67
118
124
42.0
2.5
87.5
3.37
15.87
.87
.62
119
134
35.8
2.5
87.7
3.37
15.20
.91
.63
120
139
46.8
3.0
87.3
3.37
14.80
1.05
.58
139
150
36.7
2.9
Haya
89.9
2.02
8.10
0.22
0.17
24
49
5.0
—
a
Coastal bermudagrass.
International Minerals and Chemical Corp., Mundelein, IL. This product contains 18% Ca and 21% P.
BASF Corp., Mount Olive, NJ. Active ingredient: calcium propionate.
d
Vitamin premix provided per kg concentrate: 13,229 IU vitamin A, 1,322 IU vitamin D, 88 IU vitamin
E, .26 mg biotin, 1.32 mg folic acid, 52.8 mg niacin, 5.3 mg pantothenic acid, 10.6 mg riboflavin, 13.2 mg
thiamin, 2.6 mg B6, and .05 mg B12.
e
Trace mineral premix provided per kg concentrate: 50 mg Fe, 80 mg Mn, 80 mg Zn, 30 mg Cu, .2 mg
Co, .2 mg I, and .2 mg Se. For concentrates B, C, and D chromium was added as chromium tripicolinate to
provide 175, 350, and 700 µ/kg concentrates, respectively.
f
Dry matter basis.
g
Calculated values based on NRC (1989).
h
Includes the ingredient Cr and supplemental Cr.
b
c
high starch feeding programs increased blood glucose
and insulin values in weanling Quarter Horses, but
they did not detect any adverse effects of the high starch
feeding program on skeletal development. High-starch
diets may also be a primary cause of obesity when nutrients that should be used for growth and muscle development are stored as fat. If Cr supplementation could
enhance insulin efficiency and lower blood glucose concentrations in growing horses, these animals might experience fewer metabolic and developmental problems.
This project was designed to determine the influence
of varying concentrations of supplemental Cr from Cr
tripicolinate on growth, development, and energy metabolism in growing horses.
Materials and Methods
Yearling Thoroughbreds (n = 11) and Quarter Horses
(n = 13) that were 335 ± 7 d of age were assigned at
random within breed and gender subgroups to one of
four treatment groups. Each group was assigned to a
diet consisting of ad libitum intake of a specified pelleted concentrate (Table 1) for two 1.5-h feeding periods
each day. The animals were fed at 0730 and 1430.
Coastal bermudagrass (Cynodon dactylon) hay was
group-fed in each paddock at 1.0 kg/100 kg BW daily.
The concentrates assigned to each of the groups were
identified as follows: A) basal, B) basal plus 175 µg
of Cr/kg concentrate, C) basal plus 350 µg of Cr/kg
concentrate, and D) basal plus 700 µg of Cr/kg concentrate. Chromium was provided as Cr tripicolinate
(Prince Agri Products, Quincy, IL). The diets were designed to provide the following concentrations of supplemental Cr in the total diet: A) 0, B) 105, C) 210, and
D) 420 g/kg, assuming the horses consumed 60% concentrate and 40% hay.
The animals were housed in drylot paddocks with
six animals in a 9.1- × 34.9-m paddock. The paddock
provided 44.6 m2 of open area and 8.6 m2 of covered
area per animal. The yearlings were fed their assigned
concentrate in 1.3- × 3.0-m individual feeding stalls.
The yearlings were weighed and measured for height
at withers and hip, heart girth, and body length at the
start of the experiment and at 28-d intervals for 112 d.
Radiographs of the third metacarpal were taken at the
start and completion of the experiment for estimation
of bone mineral content according to the procedure of
Meakim et al. (1981) as modified by Ott et al. (1987).
3024
OTT AND KIVIPELTO
Fat thickness over the croup was determined by ultrasound on d 0, 56, and 112 for estimation of body composition.
Feed samples taken periodically during the experiment were analyzed for N, Ca, P, Zn, Mn, and Cu.
The samples were analyzed for N with the automated
procedure of Noel and Hambleton (1976) using the
Technicon autoanalyzer (Technicon Industrial Systems, Terrytown, NY). Phosphorus was determined using a colorimetric procedure (Harris and Popat, 1954)
on the automated Technicon system. Samples were prepared for Ca, Zn, Mn, and Cu analyses as described by
Fick et al. (1979) and analyzed with atomic absorption
spectrophotometry using a Perkin-Elmer (Norwalk,
CT) Model 5000 with an AS-50 autosampler. Chromium
content of pooled feed samples was analyzed with inductively coupled plasma spectrometry (Prince Agri Products). Chromium values of the hay were too low to
detect.
Glucose Tolerance and Insulin Sensitivity Tests
During the third period of the experiment, glucose
tolerance and insulin sensitivity tests were conducted
on each animal according to the procedure of Kaneko
(1989). Following the afternoon feeding on the day
before the tests were to be conducted, animals were
moved to individual 3.4- × 3.4-m stalls for an overnight
period without feed (16 h). The animals were fitted
with jugular catheters (Angiocath [14 gauge, 2.1 mm
× 13.3 cm), Becton Dickinson Vascular Access, Sandy,
UT) with a 12.7-cm extension at 0700 the next morning. Pretreatment blood samples were collected at
0730 and 0745. Each animal was infused via the catheter with a 50% dextrose solution providing .20 g of
glucose /kg BW at 0800. The catheter was flushed with
heparinized saline following the infusion. Blood was
collected at 5, 15, 30, 45, 60, 90, 120, and 180 min
following completion of the infusion. Insulin was then
infused (185 min after the glucose injection) via the
catheter at .1 IU/kg BW, and the catheters were
flushed with heparinized saline. Blood samples were
collected at 5, 15, 30, 45, 60, 90, and 120 min following
the completion of the infusion. Blood samples were
collected in 20-mL syringes, and 10-mL aliquots were
transferred to one tube containing potassium oxalate
and sodium fluoride and one containing sodium heparin. The blood samples were immediately placed on
ice. All samples were centrifuged, and the plasma was
separated within 30 min and transferred to the freezer,
where samples were stored at –20°C until they were
analyzed.
Plasma glucose was determined with the Trinder
procedure (Sigma Chemical Co., St. Louis, MO) using
the sodium fluoride treated plasma. Plasma insulin
was analyzed with the Coat-A-Count Insulin procedure (Diagnostic Products Corp., Los Angeles, CA) using the heparinized plasma. Glucose fractional turnover, k (percentage/min), and the time required for the
glucose to fall by half, t¹⁄₂, were calculated as described
by Kaneko (1989).
Statistical Analyses
Growth and blood data were analyzed with ANOVA
procedures (Steel and Torrie, 1980) using the GLM
procedure of SAS (1989). Diet, breed, gender, and period or time were included in the model. When breed
and(or) gender effects were not significant, they were
dropped from the model. Due to unequal treatment
group sizes, the standard error of the mean for diet
groups was calculated using the harmonic mean of the
sample size (5.45). The Mixed Model procedure of SAS
was used to test the equal slope hypothesis for the
glucose curves and the glucose k and t¹⁄₂ values.
Animal Care
This experiment was reviewed and approved by the
University of Florida’s Institutional Animal Care and
Use Committee (IACUC). Animals were managed and
cared for according to the guidelines of the IACUC.
Results
One colt receiving 105 µg/kg Cr experienced a colic
problem early in the trial and underwent surgery for
a blockage and was removed from the data set. A filly
receiving 420 µg/kg Cr developed enteritis late in the
trial; its growth data were deleted from the data set
but its glucose and insulin data were included because
there was no evidence that the filly was ill during
the sensitivity trial and its data were compatible with
those of the other animals in that treatment group.
Analysis of the feed samples revealed that nutrient
compositions of the four concentrates were similar and
consistent with formulation expectations (Table 1).
The hay composition was similar to that of other samples from this station. Chromium concentrations of 2.5
to 3.0 mg/kg DM were at the lower limit of our ability to
analyze them, and the values for the four concentrates
were considered not different. The hay value was too
low to detect with this procedure. We did not expect to
be able to detect the Cr additions with this procedure.
Feed Intake and Growth Response
Mean daily as-fed concentrate, hay, and total intake
were 1.46, .96, and 2.42 kg/100 kg BW, respectively
(Table 2). The mean diet was 60% concentrate and
40% hay. No differences in intake were detected between diets (P > .10), but colts consumed more concentrate (5.11 vs 4.65 kg) and more total feed (8.47 vs
7.73 kg) daily than fillies (P < .05). Feed efficiency was
not influenced by gender or diet (P > .10). Average
daily gain (Table 3) varied from .42 kg on the 420 µg/
kg Cr diet to .56 on the control diet, but no differences
(P > .10) were detected due to diet. Final weight of the
colts was greater than that of the fillies (376.0 vs 349.4
3025
CHROMIUM SUPPLEMENTATION OF YEARLING HORSES
Table 2. Influence of chromium supplementation on daily
feed intake and feed efficiency
Sex
Item
Colts
No. of observations
Intake, dry matter, kg
Concentrate
Hayc
Total
Nutrient intake
DE, Mcal/kg
CP, g
Calcium, g
Phosphorus, g
Zinc, mg
Manganese, mg
Copper, mg
11
4.48a
3.02
7.50d
Feed efficiency,
g gain/kg intake
Fillies
Supplemental Cr, µg/kg diet
SEM
11
4.07b
2.77
6.84e
21.2
933
48
33
628
761
196
19.3
850
44
30
571
692
178
62.5
62.1
.13
.13
6.7
0
105
210
420
6
5
6
5
4.58
2.88
7.46
4.16
2.86
7.02
4.23
2.89
7.12
4.13
2.94
7.07
21.2
949
47
36
610
709
207
19.8
892
42
31
564
698
163
20.1
877
45
32
577
730
212
18.8
849
50
29
645
764
166
67.5
60.7
69.4
51.6
SEM
.20
.24
9.5
Sex difference (P = .0105).
Coastal bermudagrass hay was provided at 1 kg/100 kg BW each day.
Sex difference (P = .0005).
a,b
c
d,e
Table 3. Influence of chromium intake on growth and development of yearling horses
Sex
Item
Colts
0
105
210
420
SEM
No. of observations
Weight, kg
Initial
Final
Gain
ADG
Withers height, cm
Initial
Final
Gain
Heart girth, cm
Initial
Final
Gain
Body length, cm
Initial
Final
Gain
Hip height, cm
Initial
Final
Gain
Croup fat, cm
Initial
Final
Gain
Bone mineral, g/2 cm
Initial
Final
Gain
11
11
6
5
6
5
—
316.9
376.0a
59.1
.53
295.9
349.4b
53.6
.48
11.4
10.4
5.9
.05
325.5
388.5
63.0
.56
292.6
346.5
53.8
.48
290.7
352.7
62.0
.55
316.7
363.2
46.5
.42
16.3
15.0
8.4
.08
139.9
144.8
4.9
141.0
146.6
5.5
1.8
1.4
.6
142.3
147.3
4.8
139.5
147.3
5.4
138.2
144.0
5.8
141.8
146.6
4.8
2.6
2.1
0.9
151.7
161.2
9.5
149.2
159.1
9.9
1.9
1.4
1.1
153.6
163.3
9.7
149.5
160.2
10.7
146.6
157.6
11.0
152.1
159.4
7.3
2.6
2.0
1.5
138.1
146.6
8.5
135.6
143.5
7.9
1.8
1.7
.8
139.3
149.4
10.2
134.1
142.3
8.2
135.6
143.2
7.6
138.3
145.1
6.8
2.6
2.2
1.1
144.2
148.9
4.7
144.5
150.3
5.8
1.8
1.4
.7
146.3
151.2
5.0
143.6
148.5
4.9
141.6
148.0
6.4
146.1
150.9
4.8
2.5
2.0
1.0
Sex effect (P = .0754).
Sex effect (P = .0145).
a,b
c,d
.25c
.42
.17
26.0
27.2
1.1
Fillies
Supplemental Cr, µg/kg diet
.21d
.51
.30
25.8
26.0
.2
SEM
.01
.06
.07
.4
.4
.4
.25
.42
.17
26.8
27.5
.7
.21
.46
.25
25.3
26.3
1.0
.25
.48
.23
25.5
26.4
.9
.21
.51
.30
26.1
26.1
.0
.02
.10
.10
.6
.5
.7
3026
OTT AND KIVIPELTO
Figure 1. Influence of chromium supplementation on plasma glucose during glucose tolerance and insulin sensitivity
tests. Glucose was administered at .2 g/kg BW. Insulin was administered at .1 IU/kg BW.
kg; P = .0754). No differences in wither heights, heart
girth, body length, hip height, or bone mineral deposition were detected (P >.10). Croup fat was greater for
the colts than for the fillies at the start of the experiment (.25 vs .20 cm; P = 0.0145), but subsequent data
were not different (P > .10). Diet did not influence
croup fat thickness (P > .10).
Glucose Tolerance Test
Fasting plasma glucose concentrations were numerically higher for the animals consuming the unsupplemented diet than for the animals receiving chromium
supplementation (Figure 1). Administration of .2 g glucose/kg BW resulted in a mean increase in plasma
glucose of 104.3 ± 5.0 mg/dL by 5 min after injection
and a return to baseline by 120 min after injection.
There were no differences among the mean glucose
values at any of the postinjection times (P > .10), but
the control group was numerically higher than the Crsupplemented groups at all times except immediately
following the glucose injection (5 min), at which time
the highest Cr group was the highest. Because there
was a sizable variation in the peak glucose values at
5 min after injection, the data were adjusted to a common mean peak height (229.1 mg/dL) by subtracting
the smaller value from the mean or the mean from the
larger value for each 5-min treatment group mean and
then adjusting each of the other subsequent glucose
values at 15, 30, and 45 min after injection by that
number. A regression line was fitted to each data set,
and the slope of the clearance curves from 5 to 45 min
after injection was compared (Figure 2). The regression lines for the four treatments were as follows:
Control: Plasma glucose
(r2 = .41)
105 µg/kg: Plasma glucose
(r2 = .76)
210 µg/kg: Plasma glucose
(r2 = .67)
420 µg/kg: Plasma glucose
(r2 = .56)
(mg/dL) = 225.3 – 1.35x
(mg/dL) = 222.4 – 1.63x
(mg/dL) = 222.8 – 1.49x
(mg/dL) = 220.3 – 2.18x
The intercept is at 5 min after the glucose injection
and x = minutes following the 5-min sample.
The glucose clearance curve for the animals consuming the control diet was different (P = .008) from that
of animals consuming the highest Cr diet, and animals
consuming intermediate levels of Cr were not different
from the animals consuming the highest or lowest
amounts of Cr (P > .10). Because of the variation in
the baseline for the groups, the data for calculating
the k and t¹⁄₂ were adjusted to the mean of the baseline
values at –15, –5, 120, and 180 min, which was 124.85
mg/dL. Mean k values increased (P = .0369) and mean
t¹⁄₂ values decreased (P = .0634) in response to the high
chromium supplementation (Table 4). No gender differences were detected (P > .10).
Fasting plasma insulin concentrations indicate that
insulin was lower for the animals consuming the basal
diet than for those consuming the diets providing sup-
3027
CHROMIUM SUPPLEMENTATION OF YEARLING HORSES
Figure 2. Influence of chromium supplementation on glucose depletion following administration of .2 g glucose/
kg BW after data were adjusted to a mean peak height of 229.1 mg/dL at 5 min after injection.
plemental Cr, but differences were not significant (P
> .10). This relationship continued throughout the glucose tolerance test (Figure 3). Insulin values peaked
5 min following glucose injection and gradually declined to baseline values by 180 min after injection.
No differences were detected due to diet (P > .10). The
insulin:glucose ratio increased following the glucose
injection (Figure 4) and returned to near preinjection
levels by 120 min. Although dietary differences were
not significant (P > .10), the control diet was low, the
high-Cr diet was high, and the other diets were intermediate throughout the test.
Insulin Sensitivity Test
Plasma insulin concentrations at 5 min after insulin
injection were highly variable, suggesting that we did
not get an adequate mix in the circulatory system of
some animals by min 5 or that some residual insulin
was retained in some of the catheters following the
insulin injection, even though the catheters were
flushed following injection. From 30 min after injection
to 60 min after injection, the insulin depletion curves
for the four diets were almost identical (Figure 5).
No difference in glucose clearance following insulin
injection was detected between diets (P > .10).
Discussion
Concentrate and hay intakes were slightly less than
those reported in other experiments in which the management and feeding systems were similar (Ott and
Asquith, 1989; Graham et al., 1994; Ott and Asquith,
1995). This may have been due to the inclusion of some
Table 4. Influence of chromium picolinate supplementation
on glucose kinetics in yearling horses
Supplemental Cr, µg/kg diet
Item
Glucose tolerance test
Half-life (t¹⁄₂), min
Clearance (k), %/min
0
105
210
420
45.7 ± 5.7
1.74 ± .39
31.9 ± 6.3
2.36 ± .43
35.8 ± 5.7
2.00 ± .39
25.9 ± 5.7a
3.22 ± .39b
Different from the control (P = .0634).
Different from the control (P = .0369).
a
b
3028
OTT AND KIVIPELTO
Figure 3. Influence of chromium supplementation on
plasma insulin response to glucose infusion at .2 g/kg
BW.
borrowed horses that were genetically more diverse
and had less experience eating this type of diet than
the animals raised at the Horse Research Center. Nutrient intake met or exceeded NRC (1989) recommendations for all groups, except that the daily protein
intake was below recommendations for the control and
210 µg/kg Cr groups by 3 and 20 g, respectively. Lysine
intake was calculated to meet NRC (1989) recommendations even though the protein intake was slightly
below recommendations. Weight gain was similar to,
though slightly less than, that in earlier reports, but
the two groups with protein intake below recommendations had the greatest rate of gain, suggesting that
protein was not a limiting factor for these animals.
Wither heights, heart girth, body length, hip height,
and croup fat gains were similar for the four dietary
Figure 4. Influence of chromium supplementation on
plasma insulin:glucose ratio following glucose injection
at .2 g/kg BW.
Figure 5. Influence of chromium supplementation on
plasma insulin following insulin injection at .1 IU/kg BW.
treatments and similar to other reports on yearlings
(Ott and Asquith, 1989; Graham et al., 1994; Ott and
Asquith, 1995).
Basal plasma glucose concentrations were higher
than previously reported for yearlings at this station
(Ott and Kivipelto, 1998) but similar to the reports of
Glade et al. (1984) for weanlings and well within normal range (Kaneko, 1989). Mean plasma glucose concentrations were lower for the Cr-supplemented animals throughout the glucose tolerance and insulin sensitivity tests, but differences were not significant due
to animal variability. This is consistent with the report
of Amoikon et al. (1995) on swine and Pagan et al.
(1995) with mature horses. Following the glucose challenge, the glucose peaks were similar to those of Garcia
and Beech (1986). The chromium-supplemented animals returned to baseline more rapidly than those fed
the basal diet (Figure 2), and this is consistent with
previous reports (Amoikin et al., 1995). The k and t¹⁄₂
values were consistent with the above changes. Amoikon et al. (1995) reported that adding Cr to the diet
increased k and decreased t¹⁄₂ in swine, and Bunting
et al. (1994) reported that Cr increased glucose k in
cattle. It is not clear why the glucose depletion rate,
k, and t¹⁄₂ values for the two intermediate levels of Cr
supplementation fed in this study were not consistent
with the differences detected between the control and
the high-Cr diet.
This study suggests that chromium supplementation in the form of Cr tripicolinate reduces blood glucose and the time required for blood glucose to return
to baseline following a glucose peak in yearling horses
much as it does in working horses (Pagan et al., 1995).
This alteration in glucose metabolism could be beneficial for growing horses, because high blood glucose
concentrations are typical in animals consuming diets
with concentrate:roughage ratios of 50:50 or higher
CHROMIUM SUPPLEMENTATION OF YEARLING HORSES
(Stull and Rodiek, 1988; Davidson et al., 1991). Such
diets are commonly used for growing horses. High
blood glucose is accompanied by high insulin, which
may suppress thyroxine release after meals (Glade
et al., 1984; Davidson et al., 1991). This transitory
hypothyroidism may be the cause of some of the bone
cartilage problems seen in young growing foals (Glade
et al., 1984). Although direct evidence of this relationship in horses is minimal, in other species hypothyroidism causes a decrease in the growth plate cartilage
by not supplying enough thyroid hormone to cause
differentiation of the chondrocytes, reduced vascularization of the cartilage, and delayed mineralization
(Silberberg and Hasler, 1969; Lewinson et al., 1989).
Horses with osteochondrosis dissecans have been
shown to have higher postprandial plasma glucose
(155 ± 5 mg/dL, P = .0001) and insulin (46.4 ± 4 IU/
dL, P = .007) than controls (glucose, 127 ± 2 mg/dL;
insulin 30.0 ± 3 IU/dL) when fed diets providing 50%
grain and 50% hay (Ralston, 1995), thus providing
evidence that abnormal glucose metabolism may be
related to osteochondrosis dissecans. The diets tested
in the present study had no effect on bone mineral
deposition, suggesting that the lower blood glucose
in the horses on the high-Cr diet did not provide a
difference that was large enough to cause detectable
changes in this age of foal.
Implications
Chromium supplementation as chromium tripicolinate increases the rate at which glucose is metabolized
by growing horses following a glucose challenge. Chromium may also lower blood glucose concentrations
throughout the day. Although the effects of chromium
on growth and development of horses may not be measurable, a reduction in plasma glucose and an increase
in the rate at which glucose is removed from the circulation could be beneficial in reducing the effect of high
concentrate diets on hormone balance, and perhaps
metabolic bone disease, in growing horses.
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