Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol86.Issue1-2.Jul2000:

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Ef®cacy of chromium-yeast supplementation

for growing beef steers

$

K.C. Swanson

a

, D.L. Harmon

a,*

, K.A. Jacques

b

, B.T. Larson

a

,

C.J. Richards

a,1

, D.W. Bohnert

a,2

, S.J. Paton

a

a_{Department of Animal Sciences, University of Kentucky, Lexington, KY 40546-0215, USA} b_{Alltech Inc., Nicholasville, KY 40356, USA}

Received 17 September 1999; received in revised form 7 March 2000; accepted 21 March 2000

Abstract

This experiment was conducted to determine the ef®cacy of feeding chromium yeast to growing beef steers. Animal growth, gain ef®ciency, and blood glucose kinetics were determined in 24 beef steers (initial body weight2534 kg) fed a corn silage-based diet supplemented with 0 (control), 100, 200, or 400mg chromium from high-chromium yeast/kg of diet dry matter. Intravenous glucose tolerance tests (IVGTT) and intravenous insulin challenge tests (IVICT) were conducted at 3 and 6 weeks of chromium-yeast supplementation. There were minimal effects on plasma glucose kinetics during IVGTT and IVICT. There were tendencies for glucose clearance rate to increase (p0.16) and half-life to decrease (p0.14) during IVICT. However, chromium-yeast supple-mentation had no effect (p>0.24) on ADG and gain ef®ciency, suggesting that chromium-yeast supplementation to unstressed growing calves may not be bene®cial.#2000 Elsevier Science B.V. All rights reserved.

Keywords:Beef cattle; Chromium; Glucose tolerance; Growth

1. Introduction

Chromium has been implicated as an essential nutrient for humans and lab animals (Mertz, 1993). Chromium increases glucose tolerance by potentiating the action of

86 (2000) 95±105

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Approved by the Director of the Kentucky Agricultural Experimental Station as publication 99-07-106.

*_{Corresponding author. Tel.:}_{1-859-257-7516; fax:}_{1-859-257-3412.}

E-mail address: dharmon@ca.uky.edu (D.L. Harmon)

1_{Present address: University of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071.}

2_{Present address: Eastern Oregon Agricultural Research Center, Oregon State University, Burns Station, HC}

71, 4.51 Highway 205, Burns, OR 97720-9399.

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insulin in clearing postprandial glucose from the blood (Mertz, 1993). This could lead to improved glucose utilization and increased growth and ef®ciency. However, inorganic forms of chromium are relatively unavailable for absorption (Mordenti et al., 1997). Organic forms of chromium, such as high-chromium yeast, are usually more available for absorption (Mordenti et al., 1997). High-chromium yeast has been grown in the presence of high chromium concentrations. Yeast has the ability to accumulate ions, such as chromium, in high concentrations (Ingledew, 1999) and, therefore, can be useful as a source of supplemental minerals. Research with ruminants has suggested that organic chromium supplementation may have the greatest in¯uence on stressed animals (Chang and Mowat, 1992; Moonsie-Shageer and Mowat, 1993; Burton, 1995; Kegley and Spears, 1995). Research regarding the biological effects of organic chromium supplementation on non-stressed ruminants have been variable (Chang and Mowat, 1992; Bunting et al., 1994; Kitchalong et al., 1995; Gentry et al., 1999) and different levels of supplementation have rarely been examined (Moonsie-Shageer and Mowat, 1993). Therefore, our objectives were to examine the in¯uence of increasing amounts of chromium yeast supplementation to non-stressed growing beef steers on (1) growth and gain ef®ciency, and (2) blood glucose kinetics during intravenous glucose tolerance and intravenous insulin challenge tests.

2. Materials and methods

Thirty steers were purchased from public auction through a local order buyer. They were predominantly British crosses with little or no Charolais or Brahman in¯uence. Upon receiving, steers were vaccinated (IBR and PI3) and treated for external and internal parasites (Ivomec1

). Rectal temperatures were checked and any exceeding 408C were treated with Tilmicosin and re-examined after 2 days. Steers were fed hay and a medicated receiving diet until adjusted to their new environment and outbreaks of respiratory disease and/or shipping fever had passed. Steers were trained to tie by halter and were accustomed to handling. This enabled collection of blood samples without the animals being overly excited. Based on temperament and ease of handling, 24 of the 30 steers were selected for use in the experiment. The time interval between arrival and the initiation of the experiment was 30 days.

Experimental steers (initial body weight2534 kg) were fed individually twice daily (0800 and 1600) a diet containing 90% corn silage and 10% soybean meal-based supplement (dry matter basis; Table 1) at 2.2% body weight/day (DM basis) and were housed in concrete-¯oored pens in an open-sided barn. The diet was selected because corn silage diets are commonly fed to growing cattle in Kentucky. Steers were limit-fed at 2.2% of body weight so that differences in intake would not confound the results obtained due to chromium-yeast supplementation. Steers were supplemented with 0 (control), 100, 200, or 400mg Cr from chromium-yeast/kg of diet dry matter (Alltech, Nicholasville, KY). Chromium yeast was mixed with the soybean meal supplement and top-dressed at the 0800 feeding. Steers would rapidly and completely consume the supplement. Feed samples were collected and analyzed weekly for DM (558C for 48 h) and as-fed dietary intakes were adjusted accordingly so that dry matter intake was 2.2% of body weight

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throughout the experiment. Steers consumed all of the feed offered. Body weights were taken prior to assignment to experimental treatment before the 0800 feeding. Three days prior to assignment to treatment, steers were placed in individual pens and fed a corn silage-based diet at equal intakes to minimize the effects of intake on ruminal ®ll. Body weights also were taken at 3 and 6 weeks of chromium-yeast supplementation prior to the 0800 feeding. Average daily gain (ADG) and gain ef®ciency for the 6-week feeding period were calculated for each steer.

Intravenous glucose tolerance tests (IVGTT) and intravenous insulin challenge tests (IVICT) were conducted at 3 and 6 weeks of chromium-yeast supplementation at 0800 and 1300, respectively. Procedures were similar to those described by Bunting et al. (1994) and Kitchalong et al. (1995). Tests were done on two consecutive days with half of the steers from each treatment tested each day.

Steers were ®tted with sterile indwelling jugular catheters the day prior to IVGTT and IVICT. At 3 weeks of chromium supplementation, a 14-gage thin-wall needle was inserted into the jugular vein and a 30-cm piece of 18-gage thin-wall Te¯on tubing introduced into the jugular vein through the needle. The needle was removed and a 19-gage luer-lock tubing adapter with a 50-cm extension was attached. The catheter was sutured to the skin. The catheter was ¯ushed with 100 U/ml heparin in saline, capped, and the steers' necks wrapped with elastic tape to secure catheters. Due to problems with the catheters becoming non-functional and the dif®culty of infusing large volumes rapidly, larger catheters (Abocath-T, 14-gage14 cm; Butler; Columbus, OH) were used for the collection after 6 weeks of supplementation. A 38-cm extension was connected to the

Table 1

Components and composition of basal dieta

Diet components

Ingredient Diet dry matter (%)

Corn silage 90.0

Soybean meal 7.61

Fine ground corn 0.57

Urea 0.23

Choice white grease 0.11

Vitamin A, D, & E premixb _0.02

Trace mineral salt with Sec _0.27

Dicalcium phosphate 0.47

Limestone 0.72

Diet composition

Item Diet dry matter (%)

Ash 6.0

Crude protein 12.5

NDF 42.3

ADF 21.4

a_{Diet contained 0 (control), 100, 200, or 400}_m_{g Cr/kg diet dry matter from chromium yeast.} b_{8800 IU/g vitamin A, 1760 IU/g vitamin D, and 1.1 IU/g vitamin E.}

c_{98.5% NaCl, 0.35% Zn, 0.34% Fe, 0.20% Mn, 330 ppm Cu, 70 ppm I, 50 ppm Co, and 90 ppm Se.}

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catheter and the catheter was sutured to the skin. Catheters were then ¯ushed with 100 U/ ml heparin in saline, capped, and the steers' necks wrapped with elastic tape. The IVGTT and IVICT were initiated after an overnight fast by intravenously dosing each steer via the jugular catheter with glucose (0.5 g/kg BW as a 50% solution) or insulin (0.1 unit/kg as a 1.3 U/ml solution containing, respectively, 0.2% BSA and 0.9% NaCl; Sigma, St. Louis, MO). Glucose and insulin solutions were ®ltered through 0.45 and 0.2mm membranes, respectively, into sterile bottles prior to intravenous administration. Blood samples (10 ml) were collected using a heparinized syringe atÿ10, 0, 5, 10, 15, 20, 25, 30, 45, 90, 120, 150, and 180 min relative to dosing. Blood was transferred to a tube containing sodium ¯uoride (20 mg), mixed by inversion, and placed on ice. Catheters were ¯ushed with 20 U/ml heparin in saline after each collection time. Plasma was harvested by centrifugation (2500g, 48C, 15 min) and stored at ÿ308C until analyzed for glucose using the hexokinase method (Slein, 1963; Sigma Procedure 16-UV) with modi®cations for use on a Cobas Fara II (Roche Diagnostic Systems, Montclair, NJ). Blood glucose clearance rate (k) and half-life (T1/2) were calculated according to Kaneko (1989), using the following equations: k (%/min){(ln [glucosetime1]ÿln [glucosetime2 ])/(time2-ÿtime1)}100 and T1/2 (min)(0.693/k)100. For the IVGTT, k and T1/2 were calculated using the interval from 15 to 45 min. For the IVICT,kandT1/2were calculated using the interval from 0 to 30 min. The time points used for the calculation ofkandT1/2 during the IVGTT and IVICT were selected because they were in a linear range of glucose clearance and also because similar time points have been used previously (Kitchalong et al., 1995). The area under the curve and that above the curve from 0 to 180 min for the IVGTT and IVICT, respectively, were calculated using trigonometric geometry (Swokowski, 1988). Calculations of areas under, and above, the curve were calculated relative to basal levels (i.e. Time 0 values were subtracted from others).

Data were analyzed using GLM procedures of SAS (1988). The IVGTT and IVICT data were analyzed as a completely randomized design within period. The IVGTT and IVICT were also subjected to split-plot analysis testing the effects of treatment, animal within treatment, period, and treatment by period using animal within treatment as the error term. Growth data were analyzed as a completely randomized design. Contrast statements were used to compare treatments for linear and quadratic effects due to chromium-yeast supplementation using the appropriate coef®cients for unequal spacing of treatments. Contrasts with p<0.10 were considered to be statistically signi®cant. Contrasts with probability values between 0.10 and 0.16 were considered to indicate a trend toward statistical signi®cance. Data for plasma glucose kinetics for two animals from the 200mg/kg treatment and one animal from the 400mg/kg treatment were not included for period 1 because of failed catheters. In the case of means with unequal numbers of observations, the standard errors of the mean for the treatment with the lowest number of observations are reported.

3. Results

There were no effects of chromium supplementation on Week 3 body weight, Week 6 body weight, average daily gain, or gain ef®ciency (Table 2). No differences were

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observed among treatments for basal glucose concentration and glucose concentration at 15 and 45 min after dosing during the IVGTT after 3 or 6 weeks of supplemental treatment (Tables 3 and 4). Subsequently, no differences were observed in glucose clearance rate, half-life from 15 to 45 min, and in glucose area under the curve from 0 to 180 min.

When combining the IVGTT results from weeks 3 and 6, basal glucose concentration was not in¯uenced by treatment (Table 5; Fig. 1A). Plasma glucose concentration 15 min after dosing was greater in steers supplemented with 200mg/kg chromium than other treatment groups (quadratic effect,p0.09). Glucose concentration 45 min after glucose dosing and glucose clearance rate from 15 to 45 min was not in¯uenced by treatment. Glucose half-life tended to increase linearly (p_{0.11) with increasing supplemental} chromium yeast. Glucose area under the curve was not in¯uenced by treatment.

Table 2

In¯uence of chromium yeast supplementation on body weight (BW), average daily gain (ADG), and gain ef®ciency

Item Treatment SEMa Contrast p-value Chromium supplied from yeast (mg/kg dry matter) Linear Quadratic 0 (Control) 100 200 400

Initial BW (kg) 250 252 255 255 8.34 0.65 0.85 Week 3 BW (kg) 271 272 273 277 9.39 0.60 0.94 Week 6 BW (kg) 293 294 295 299 9.81 0.64 0.95 ADG (kg/day) 1.04 1.03 0.98 1.07 0.06 0.77 0.37 Gain:Feed 0.19 0.19 0.18 0.20 0.01 0.74 0.25

a_{Standard error of the mean,}_n_{6 for all treatments.}

Table 3

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous glucose tolerance test (Week 3)

Item Treatment SEMa _Contrast_p_-value

Chromium supplied from yeast (mg/kg dry matter) Linear Quadratic 0 (Control) 100 200 400

Glucose concentration(mM)

Basal (Time 0 min) 4.29 4.10 4.63 4.12 0.22 0.78 0.29 15 min 14.59 13.57 15.30 12.91 0.84 0.20 0.30 45 min 9.79 9.29 10.19 9.20 0.91 0.61 0.65 Clearance rate

(k; %/min)

1.32 1.27 1.43 1.14 0.30 0.52 0.52 Half-life (T1/2; min) 54.0 63.1 48.6 82.0 26.3 0.27 0.27

Area under the curve (0 to 180 min; min mM)

1033 1030 1044 1016 77.8 0.87 0.85

a_{Standard error of the mean,}_n_{6, 6, 4, and 5 for control, 100, 200, and 400}_m_{g/kg treatments, respectively.}

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For the IVICT at 3 weeks, basal glucose concentration was not in¯uenced by treatment (Table 6). Glucose concentration 30 min after dosing was not in¯uenced by treatment. In addition, glucose clearance rate, half-life, and area under the curve were not in¯uenced by treatment.

At 6 weeks, basal glucose concentrations were not in¯uenced by treatment during the IVICT (Table 7). Also, glucose concentration 30 min after dosing was not in¯uenced by chromium-yeast supplementation. However, glucose clearance rate from 0 to 30 min tended to increase linearly (p0.11) with increasing chromium-yeast supplementation.

Table 4

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous glucose tolerance test (Week 6)

Item Treatment SEMa Contrastp-value Chromium supplied from yeast (mg/kg dry matter) Linear Quadratic 0 (Control) 100 200 400

(k; %/min)

1.32 1.32 1.39 1.45 0.11 0.36 0.94 Half-life (T1/2; min) 52.7 54.6 51.6 48.3 4.40 0.37 0.67

Area under the curve (0±180 min; min mM)

1146 1149 1193 1204 51.3 0.32 0.87

Table 5

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous glucose tolerance test (combined data from Week 3 and Week 6 blood collection periods)

(k; %/min)

1.32 1.40 1.52 1.17 0.20 0.46 0.23 Half-life (T1/2; min) 53.2 53.9 46.2 79.5 16.6 0.11 0.29

Area under the curve (0±180 min; min mM)

1089 1080 1123 1107 38.2 0.58 0.75

a_{Standard error of the mean,}_n_{12, 11, 10, and 11 for control, 100, 200, and 400}_m_{g/kg treatments,}

respectively.

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There was a quadratic response (p0.05) for glucose half-life with the control and 400mg/kg treatments greater than the 100 and 200mg/kg treatments. Glucose area above the curve from 0 to 180 min was not in¯uenced by treatment.

When combining IVICT results from periods 3 and 6, basal glucose concentration and glucose concentration 30 min after dosing were not in¯uenced by supplemental treatment (Table 8; Fig. 1B). Glucose clearance rate from 0 to 30 min after insulin dosing tended to

Fig. 1. Plasma glucose concentration during an intravenous glucose tolerance test (A) or intravenous insulin challenge test (B). Combined data from Week 3 and Week 6 blood collection periods.

Table 6

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous insulin challenge test (Week 3)

Basal (Time 0 min) 4.11 3.78 4.58 3.56 0.27 0.30 0.14 30 min 2.63 2.50 3.06 2.25 0.29 0.40 0.16 Clearance rate

(k; %/min)

1.37 1.41 1.41 1.59 0.25 0.46 0.80 Half-life (T1/2; min) 54.9 54.7 59.6 47.1 10.6 0.56 0.54

Area above the curve (0±180 min; min mM)

90.3 98.6 137.1 112.3 22.5 0.35 0.26

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increase linearly (p0.16) and half-life tended to decrease linearly (p0.14) with increasing chromium supplementation. Glucose area above the curve was not in¯uenced by treatment.

4. Discussion

The present study indicates that chromium-yeast supplementation to growing non-stressed steers does not in¯uence growth and gain ef®ciency. However, our experimental design may not have been sensitive enough to detect differences in growth and gain

Table 7

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous insulin challenge test (Week 6)

(k; %/min)

1.04 1.28 1.31 1.26 0.13 0.11 0.33 Half-life (T1/2; min) 74.3 55.1 54.0 58.2 6.2 0.15 0.05

Area Above the Curve (0±180 min; min mM)

71.1 107.8 97.0 76.6 18.1 0.87 0.16

a_{Standard error of the mean,}_n_{6 for all treatments.}

Table 8

In¯uence of chromium yeast supplementation on plasma glucose kinetics during an intravenous insulin challenge test (combined data from Week 3 and Week 6 blood collection periods)

(k; %/min)

1.21 1.34 1.37 1.48 0.15 0.16 0.80 Half-life (T1/2; min) 64.6 54.9 56.6 50.5 6.7 0.14 0.67

Area above the Curve (0±180 min; min mM)

80.7 103.2 110.6 100.5 16.7 0.42 0.24

a_{Standard error of the mean,}_n_{12, 12, 10, and 11 for control, 100, 200, and 400}_m_{g/kg treatments,}

respectively.

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ef®ciency because only 24 individually-fed steers were used in a 42-day experiment. A larger number of steers fed in groups over a longer period of time would allow for more experimental power. However, our results agree with other researchers (Bunting et al., 1994; Kitchalong et al., 1995) who have supplemented calves or lambs with other forms of organic chromium.

Chromium-yeast supplementation had minimal effects on glucose kinetics during the IVGTT and IVICT. However, there were tendencies for glucose clearance rate to increase and glucose half-life to decrease with increasing chromium-yeast supplementation during the IVICT (Table 8). Supplementation of non-stressed ruminants with other forms of organic chromium has had variable effects on glucose kinetics during IVGTT and IVICT (Bunting et al., 1994; Kitchalong et al., 1995). The tendency of glucose half-life to increase with increasing chromium-yeast supplementation for the combined IVGTT data is dif®cult to explain (Table 5). This response was largely because of the elevated value observed for the 400mg/kg treatment during the Week 3 collection (Table 3). However, the effect did not occur at Week 6, thus this response is either short-lived (the biological effect is lost by Week 6) or occurred by chance.

The biological relevance of subtle changes in blood glucose kinetics and insulin sensitivity in ruminants is unclear. The minor changes observed in this experiment may have little biological signi®cance because growth and gain ef®ciency seem to be unin¯uenced by organic chromium supplementation. This would suggest that chromium's major effect in ruminants is not mediated through differences in glucose tolerance. The major in¯uence is likely through the immune system in stressed animals as others have suggested (Chang and Mowat, 1992; Moonsie-Shageer and Mowat, 1993; Burton, 1995; Kegley and Spears, 1995) . The reason that no differences in growth and gain ef®ciency were observed in this experiment may be because the chromium status was adequate without additional supplementation. It also could be related to differences in insulin sensitivity between ruminant and monogastric species. Ruminants have been considered less sensitive to insulin than monogastric species (Brockman and Laarveld, 1986). This can clearly be seen if we compare the IVGTT and IVICT curves from our experiment with those of Amoikon et al. (1995) using pigs. For example, the plasma glucose concentrations during the IVGTT returned to basal levels20 min after dosing in pigs, whereas it took 180 min in our experiment. The differences in the magnitude of response to a IVGTT and IVICT between ruminants and monogastrics may partly explain why organic chromium supplementation often increases gain ef®ciency and carcass characteristics in pigs (Page et al., 1993; Lindemann et al., 1995; Kornegay et al., 1997) yet has little in¯uence in ruminants.

Although growth and gain ef®ciency were not in¯uenced by chromium-yeast supplementation in this experiment, carcass characteristics may be altered with chromium supplementation. Reports of decreased fat over the 10th rib and lower yield grades have been reported in lambs supplemented with chromium tripicolinate (Kitchalong et al., 1995). However, Chang et al. (1992) reported supplementing high chromium yeast to beef growing±®nishing steers had no in¯uence on carcass characteristics. Although organic chromium supplementation may have minor effects on blood glucose kinetics when fed to non-stressed growing calves, organic chromium supplementation may not be bene®cial.

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5. Conclusion

Increasing the ability to clear glucose from the circulation could lead to improved glucose utilization and increased ADG and gain ef®ciency. However, since blood glucose kinetics were minimally in¯uenced and ADG and gain ef®ciency were not in¯uenced, the use of chromium yeast in diets for non-stressed growing steers fed a corn silage-based diet may not be bene®cial.

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