Administration of triiodothyronine and dopamine to broiler chicks increases growth, feed conversion and visceral organ mass

Administration of Triiodothyronine and Dopamine to Broiler Chicks Increases Growth, Feed Conversion and Visceral Organ Mass1 S. C. Chang,*,† M. J. Lin,*,† J. Croom,‡,1 and Y. K. Fan†,2 *Kaohsiung Breeding Animal Propagation Station, Taiwan Livestock Research Institute, Council of Agriculture, Pingtung, Taiwan 912; †Department of Animal Science, National Chung Hsing University, Taichung, Taiwan 402; and ‡Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695

(Key words: triiodothyronine, dopamine, broiler, visceral organs, growth) 2003 Poultry Science 82:285–293

tion. Any alteration in gastrointestinal function in terms of energy or protein requirements should alter wholebird growth and performance (Croom et al., 1999). Coles et al. (1999, 2001) demonstrated that the in ovo administration of peptide YY, a known enhancer of jejunal glucose transport (Croom et al., 1998), to broiler chicks and turkey poults resulted in increased posthatch growth. In order to elucidate further, the impact of potential alterations on gastrointestinal function on whole-broiler growth, we have investigated the effects of exogenous administration of two neurohormonal agents known to alter metabolism in the whole body and gastrointestinal tract, triiodothyronine (T3) and dopamine (DA).

INTRODUCTION The gastrointestinal tract comprises only 4 to 7% of body weight (Croom et al., 1993; Kelly and McBride, 1990), yet accounts for 20% and 25 to 40% of the energy (Croom et al., 1993) and protein requirements of the body (Lobley et al., 1980), respectively. These disproportional requirements for energy and protein by the gastrointestinal tract have profound implications for poultry produc-

2003 Poultry Science Association, Inc. Received for publication April 30, 2002. Accepted for publication September 18, 2002. 1 The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service, nor criticism of similar products not mentioned. 2 To whom correspondence should be addressed: ykfan@dragon. nchu.edu.tw.

Abbreviation Key: DA = dopamine; T3 = 3,3′,5-triiodo-L-thyronine; FDBW = feed-deprived body weight.

285

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were carried out with 216 chicks. The results in Trial 2 showed that the effects of T3 (X, µmol/kg diet) on body weight gain (Y1, g) and feed consumption (Y2, g) were linear (Y1 = 310 − 21.5X, R2 = 0.868, P < 0.001 and Y2 = 398 − 22.3X, R2 = 0.765, P < 0.001, respectively). The feed conversion ratio, the weight of liver, the weights of various intestinal segments, the lengths of the duodenum, jejunum and the ileum, as well as weight per centimeter jejunal length, gizzard weight as percentage of FDBW, and the duodenal length per kilogram FDBW all had linear responses (P < 0.05) to the level of dietary supplementation of T3. The effect of dietary supplementation of T3 on the heart weight was quadratic (Y16 = 2.58 + 0.89X − 0.17 X2, R2 = 0.526, P < 0.01). Similarly, the weights of pancreas and gizzard, the heart weight as a percentage of FDBW and the pancreas weight as a percentage of FDBW all had second-order curve responses. Dietary DA supplementation exerted no effect on the variables measured except that the regression of the heart weight as a percentage of FDBW on dietary DA supplementation (X1, µmol/kg diet) existed, namely, Z1 = 0.64 + 0.24 X1 − 0.23 X12 + 0.05 X13 (R2 = 0.868, P < 0.05).

ABSTRACT The influences of triiodothyronine (T3) or dopamine (DA) administration on growth, feed conversion, and visceral weights in broiler chicks between the ages of 6 and 12 d posthatch were investigated. In Trial 1, six chicks at age 6 d were randomly administered one of the following treatments: 0.37, 0.74, 1.48, and 2.96 µmol T3/kg BW or 0.07, 0.14, 0.28, and 0.56 µmol DA/kg BW. Both T3 and DA were administered via intraperitoneal injections between the end of sternum and the ends of os pubis, with 0.9% saline as the excepient. In addition, two groups of six birds each were either not injected or injected with excepient only, as controls. Four replications were carried out with a total of 264 chicks. Heart weight as a percentage of feed-deprived body weight (FDBW) of the chicks injected with 2.96 µmol T3/kg BW was heavier than that of controls. Other variables measured were not significantly different between treatments. In trial 2, six chicks at age 6 d were randomly administered, one of the following treatments: 0.56, 1.12, 2.24, and 4.48 µmol T3/kg diet or 0.40, 0.80, 1.60, and 3.20 µmol DA/kg diet as well as a nonsupplemented control. Four replications

286

CHANG ET AL.

MATERIALS AND METHODS Animals All procedures involving animals were according to the Regulations of Laboratory Animals, National Chung Hsing University, Taiwan. Hubbard broiler chicks of mixed sex used were wing-banded immediately after hatch. A ration suitable for broilers (23% CP) during 0 to 3 wk of age was offered ad libitum (Table 1). Drinking water supplemented with vitamins was freely accessible during age of 0 to 6 d. The birds were randomly allotted to treatment groups at 6 d of age. The chicks were raised in wire-floor cages with dimensions of 45 cm in width and 90 cm in length. Lighting and heat were supplied with an incandescent 40-watt bulb at a height that would

3

T3, Sigma Chemical Co., St. Louis, MO. Dopamine, Sigma Chemical Co., St. Louis, MO.

4

TABLE 1. The components and composition of the ration for broilers in Trials 1 and 2 Ingredients Yellow corn Sorghum Soybean meal Heat-processed whole soybean Corn gluten meal Fish meal Meat-bone meal Tallow Limestone Dicalcium phosphate Salt DL-Met Premix1 Total Calculated value Crude protein, % AME, kcal/kg Crude fat, % Calcium, % Available phosphorus, % Total phosphorus, % Lys, % Met, % Met + Cys, % Trp, % Thr, %

% 55.1 2.0 23.6 3.4 3.0 6.0 2.0 2.5 0.66 0.5 0.2 0.04 1.0 100.0 23.0 3,133 6.47 0.87 0.49 0.63 1.25 0.71 1.04 0.26 0.85

1 Each kilogram of premix contained: vitamin A, 1,000,000 IU; vitamin D3, 100,000 IU; vitamin E, 2,000 mg; vitamin B1, 200 mg; vitamin B2, 400 mg; vitamin B6, 300 mg; vitamin B12, 1.5 mg; biotin, 6 mg; vitamin K3, 150 mg; D-calcium pantothenate, 1,500 mg; folic acid, 100 mg; nicotinic acid, 3,500 mg; Cu, 0.5 g; Fe, 4 g; Zn, 6 g; Mn, 8 g; Co, 10 mg; Se, 30 mg; I, 40 mg.

maintain ambient temperature at 32 C during 0 to 7 d and 29 C during 8 to 14 d and 27 C, thereafter.

Experimental Design A randomized complete block design was utilized for both Trials 1 and 2 and replicate was regarded as block. In Trial 1, 3,3′,5-triiodo-L-thyronine3 at 0 (5% alcohol containing saline as solvent for T3), 0.37, 0.74, 1.48, and 2.96 µmol/kg BW or 3,4- dihydroxyphenethylamine4 at 0 (saline as solvent for DA), 0.07, 0.14, 0.28, and 0.56 µmol/ kg BW were injected intraperitoneally at 6, 9, and 12 d of ages, as well as a sham-injected control group, for a total of 11 treatments. There were 264 chicks used in Trial 1 with 6 chicks for each treatment replicate and 4 replicates for each treatment. The chicks had ad libitum access to a starter ration (Table 1) and drinking water. In Trial 2, the experimental treatments were the basal ration, as listed in Table 1, supplemented with either T3 at 0.56, 1.12, 2.24, and 4.48 µmol/kg diet or DA at 0.40, 0.80, 1.60, and 3.20 µmol/kg diet as well as nonsupplemented controls for a total of 9 treatments. The oral dosages of the two chemicals used in Trial 2 were designed in parallel with the amounts of T3 and DA administered in the intraperitoneal dosages used in Trial 1 by using the predicted feed intakes of the broilers. Two hundred and sixteen chicks were used in Trial 2 with 6 chicks in each treatment replicate and 4 replicates for each treatment. The birds in Trial 2 were fed the supplemented

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Thyroid hormones are known to have a variety of effects on growth and feed efficiency (Rosebrough, 1999), intestinal and whole-body metabolism, such as increased oxygen consumption (Levin and Syme, 1975; Hwang-Bo et al., 1990), intestinal nutrient absorption (Debiec et al., 1989; Szabo et al., 1989), dietary-induced thermogenesis (Gabarrou et al., 1997), intestinal enterocyte proliferation (Uni et al., 2001), body composition (Rosebrough et al., 1996; Rosebrough, 1999; Rosebrough and McMurtry, 2000), molting (Queen et al., 1997), immune function (Marsh et al., 1992), cardiac muscle synthesis (Kardami, 1990), and steroidogenesis (Carsia et al., 1997). In contrast to thyroid hormones, dopamine generally decreases physiological and metabolic processes in the whole animal and the gastrointestinal tract. Dopamine administration has been reported to decrease intestinal contractions and motility in both the chick (Lot 1993) and in the duodenum of critically ill humans (Dive et al., 2000). Pawlik et al. (1976) demonstrated that infusing 20 µg DA/kg BW per minute via artery to hybrid dogs for 10 min inhibited 45% of their intestinal oxygen uptake. Dopamine decreases Na+/K+ ATPase in rat jejunal enterocytes (Lucas-Teixeira et al., 2000). Hens selected for low group productivity and survivability have lower circulating concentrations of dopamine than those selected for greater productivity and survival (Cheng et al., 2001). It is unknown if any of these effects are mediated by the central nervous system. Dopamine receptors have been identified in the chick brain (Sun and Reiner, 2000), although the intestinal dopaminergic system is believed to be a localized nonneuronal system (Lucas-Teixeira et al., 2000). The following study describes the effects of intraperitoneal injection and oral administration of various dosages of T3 and dopamine on growth, feed efficiency, visceral organ weight, and intestinal length and weight in broiler chicks.

TRIIODOTHYRONINE, DOPAMINE, AND BROILERS

diets between 6 to 15 d. The experimental diets and drinking water were offered ad libitum, and their daily consumption recorded. Body weights were recorded at ages 9, 12, and 15 d, and feed conversion ratios were calculated.

Tissue Preparation and Analyses

Calculation and Statistical Analyses The data collected were statistically analyzed using general linear models procedure (GLM) of SAS software (1988). The differences between treatments were tested using the least square means procedure. The independent variables were treatment. All other variables, such as BW, feed intake, feed conversion, and visceral organ weights were considered dependent variables. If the variables were significantly influenced by the treatments (P < 0.05) according to ANOVA, we further proceeded to develop the regression of the variable of interest on the level of T3 or DA. Multivariate ANOVA was carried out also to understand the partial correlations between the variables measured.

RESULTS In Trial 1, the initial BW of the chicks at 6 d of age were not different among the treatments. After peritoneal injection of T3 or DA to the chicks at 6 d, there were no significant differences in body weight gain, feed consumption, and feed conversion between 7 to 15 d (Table 2). Chicks injected with 0.28 µmol DA/kg BW consumed less drinking water during 7 to 15 d than controls (P < 0.05). Chicks injected with 2.96 µmol T3/kg BW had greater (P < 0.001) heart weight as a percentage FDBW comparing to controls (Table 3). No treatment differences were noted in adjusted heart weights at 16 d. No differences were observed in all other variables (Table 3) amongst the 11 treatments. In Trial 2, chicks fed with diets supplemented with various levels of T3 had less body weight gain (P < 0.001) compared to control chicks (Table 4). Similarly, chicks fed with diets supplemented with 1.12 µmol T3/kg diet consumed less feed and had a greater feed conversion ratio (P < 0.001) between 7 to 15 d (Table 4). In contrast,

chicks fed diets supplemented with various levels of dopaminie demonstrated no differences in growth, feed and water consumption, and feed conversion ratio. Dietary supplementation of T3 increased (P < 0.001) heart weight at all levels of T3, increased liver weight as a percentage FDBW, and decreased pancreatic weight as percentage FDBW (Table 5) at 2.24 µmol/kg diet as compared to nonsupplemented controls. Gizzard weight as a percentage FDBW decreased at the 0.56, 2.24, and the 4.48 µmol/kg diet. Dopamine supplementation had no effect on visceral organ mass adjusted for FDBW (Table 5). Diets supplemented with various levels of T3 or DA from 7 to 15 d did not result in differences in the weights of the duodenum, jejunum, and ileum adjusted for FDBW at 16 d (Table 6). Chicks fed with diets supplemented with 2.24 and 4.48 µmol T3/kg diet had less cecal weight adjusted for FDBW (P < 0.05) compared to those in control. The lengths of duodenum, jejunum, and ileum per kilogram of FDBW were longer (P < 0.05) in chicks fed a diet supplemented with 4.48 µmol T3/kg diet than those fed the control diet (Table 7). Jejunal density was less (mg weight/mm length; P < 0.05) in chicks fed the diet supplemented with 2.24 and 4.48 µmol T3/kg in comparison with those fed the control diet (Table 8). Feeding diets supplemented with various levels of DA during 7 to 15 d had no significant effects on the weights of visceral organs, intestinal density, small intestinal and cecal weights, and small intestinal and cecal lengths adjusted for FDBW. Regressions for those variables, which significantly responded to varying levels of T3 in the diet, were calculated. If dietary supplementation of T3 is defined as X (µmol/kg diet) and body weight gain and feed consumption is defined as Y1 (g) and Y2 (g), respectively, then Y1 = 310 − 21.5X (R2 = 0.868, P < 0.001) and Y2 = 398 − 22.3X (R2 = 0.765, P < 0.001). Similar linear responses to various levels of T3 in diets were also observed with feed conversion ratio, liver weight, gizzard weight as a percentage of FDBW, small intestinal weight, cecal weight, duodenal length, cecal length, and lengths of duodenum, jejunum, and ileum per kilogram FDBW as well as densities of duodenum, jejunum, and ileum (Table 9). Curvilinear regression of heart weight (Y16, g) on dietary supplementation of T3 was observed as Y16 = 2.58 + 0.89X − 0.17X2 (R2 = 0.526, P < 0.01). Similar curvilinear responses of pancreas weight, gizzard weight, heart weight as a percentage of FDBW, and pancreas weight as a percentage of FDBW on dietary supplementation of T3 were also observed. There were no differences between the 9 dietary treatments in spleen weight adjusted for FDBW. The regression calculations are helpful in calculating at which levels of T3 or dopa would be expected to obtain a maximal response. If the equation in this study was quadratic, a response for the variable of interest can be estimated by differentiating the equation, setting the derivative equal to 0. For instance, with heart weight, (Y16 = 2.58 + 0.89X − 0.17X2), as shown above, setting the first

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The chicks were sacrificed by cervical dislocation at age 15 d after 18 h of feed deprivation. The weights of heart, liver, pancreas, spleen, gizzard, duodenum, jejunum, ileum, and ceca for each chick were determined and the lengths of duodenum, jejunum, ileum, and cecum were measured. According to Mitchell and Smith (1991), the duodenum is defined as beginning at the attachment of the gizzard and ending at the conjunction of the bile and pancreatic ducts. The jejunum and ileum comprise the remainder of the small intestine. The jejunum is defined as the proximal 4/5 of the jejuno-ileum and ileum as the distal 1/5 according to Fan (1995). The breast muscle was separated at the crista sternum into left and right sides, and their weights recorded.

287

288

CHANG ET AL. TABLE 2. The effect of intraperitoneal injection of T3 or dopamine to broiler chicks on growth performance from 7 to 15 d of age; Trial 11 Dopamine (µmol/kg BW) C

0

120

122

0.07 117

0.14

0.28

119

123

T3 (µmol/kg BW) 0.56

0

0.37

0.74

Initial BW at 6 d of age (g/bird) 121 122 121 120

1.48

2.96

SE

P-value

122

122

1.70

0.5646

288 298 292 287 300 284 Water consumption of 7- to 15-d-old birds (g/bird)

290

5.30

0.3121

BW gain of 7- to 15-d-old birds (g/bird) 301

288

295

291

769a

767a

783a

796a

697b

747ab

743ab

780a

762a

791a

789a

19.3

0.0449

Feed consumption of 7- to 15-d-old birds (g/bird) 410

389

1.36

1.35

399

398

399

404

400

395

402

398

Feed conversion ratio of 7- to 15-d-old birds (g feed/g gain) 1.36 1.37 1.39 1.35 1.37 1.38 1.34 1.40

392 1.35

7.15

0.7617

0.019

0.4934

Means within the same row without a common superscript differ (P < 0.05). 1 C = No injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. a,b

for the equation equal to 0, the following variable estimates are generated: heart weight as a percentage of FDBW (Z1, %) with dietary supplementation of DA (X1, µmol/kg diet), Z1 = 0.64 + 0.24 X1 − 0.23 X12 + 0.05 X13 for instance, setting the first derivative Z1′ = 0.24 − 0.46 X1 + 0.15 X12 = 0, we obtain two levels of DA, 0.67 and 2.4 µmol DA/kg diet, and their corresponding heart weight as a percentage of FDBW, 0.71 and 0.58, respectively. These represent levels of dopamine supplementa-

TABLE 3. The effect of intraperitoneal injection of T3 or dopamine on the visceral organs and intestinal weight percentage of feed-deprived body weight in 16-d-old broiler chicks; Trial 11 Dopamine (µmol/kg BW) C

2

0

0.07

0.14

0.28

T3 (µmol/kg BW) 0.56

0

0.37

0.74

1.48

2.96

SE

P-value

0.429

0.0534

Feed-deprived BW (% of BW) 91.8

92.5

91.6

90.9

92.1

92.0

91.7

91.4

91.8

92.8

90.7

Heart weight (% of FDBW2) 0.80bcde

0.73e

0.79cde

0.82bcd

0.76cde

0.78cde

0.75de

0.80bcde

0.86abc

0.87ab

0.93a

0.028

0.0007

3.33

3.35

3.37

0.099

0.6549

0.40

0.39

0.40

0.011

0.1940

3.37

3.19

3.01

0.112

0.4929

0.094

0.090

0.093

0.006

0.8842

1.13

1.06

1.03

0.045

0.3223

2.63

2.56

2.57

0.084

0.9625

0.50

0.50

0.51

0.024

0.7040

0.87

0.74

0.76

0.048

0.6152

Liver weight (% of FDBW) 3.25

3.15

3.23

3.42

3.29

3.18

3.37

3.24

Pancreas weight (% of FDBW) 0.40

0.37

0.39

0.41

0.41

0.37

0.38

0.39

Gizzard weight (% of FDBW) 3.19

3.04

3.22

3.32

3.20

3.14

3.31

3.21

Spleen weight (% of FDBW) 0.089

0.085

0.095

0.095

0.091

0.094

0.094

0.100

Duodenal weight (% of FDBW) 1.05

1.00

1.06

1.16

1.00

1.06

1.10

1.05

Jejunal weight (% of FDBW) 2.54

2.46

2.54

2.61

2.63

2.55

2.60

2.58

Ileal weight (% of FDBW) 0.48

0.51

0.50

0.49

0.56

0.50

0.51

0.50

Cecal weight (% of FDBW) 0.77

0.78

0.72

0.77

0.80

0.75

0.83

0.81

Means within the same row without a common superscript differ (P < 0.05). C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. 2 Eighteen-h feed-deprived body weight. a–e 1

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derivative of the equation Y16′ = 0.89 − 0.34X = 0, an estimate for X = 2.62 µmol T3/kg diet and maximal heart weight Y16 = 3.75 g of chicks. Cubic order regression of heart weight as a percentage of FDBW (Z1, %) on dietary supplementation of DA (X1, µmol/kg diet) was observed as Z1 = 0.64 + 0.24 X1 − 0.23 X12 + 0.05 X13 (R2 = 0.868; P < 0.05). If a cubic order regression is used to estimate the relative maximal and minimal response points by setting the first derivative

289

TRIIODOTHYRONINE, DOPAMINE, AND BROILERS TABLE 4. The effect of T3 or dopamine supplementation in diet on growth and performance of broiler chicks from 6 to 15 d of age; Trial 21 Dopamine (µmol/kg diet) C

0.40

125

0.80

126

122

1.60

T3 (µmol/kg diet) 3.20

0.56

1.12

2.24

Initial BW at 6 d of age (g/bird) 122 120 126 126

120

4.48 119

SE

P-value

4.46

0.9062

3.42

0.0001

BW gain of 7- to 15-d-old birds (g/bird) 317a

316a

317a

787

780

778

307ab 313ab 299b 277c 263c 216d Water consumption of 7- to 15-d-old birds (g/bird) 750

771

818

845

941

790

42.6

0.1176

Feed consumption of 7- to 15-d-old birds (g/bird) 402a

399a

1.27c

406a

1.26c

388a

399a

386ab

365bc

351c

299d

Feed conversion ratio of 7- to 15-d-old birds (g feed/g gain) 1.28c 1.26c 1.27c 1.29bc 1.33ab 1.34a 1.38a

7.75

0.0001

0.018

0.0004

Means within the same row without a common superscript differ (P < 0.05). 1 C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. a–d

Dopamine (µmol/kg diet) C

0.40

0.80

1.60

92.6a

91.6a

91.6a

T3 (µmol/kg diet) 3.20

0.56

1.12

2.24

4.48

91.7a

90.0b

SE

P-value

0.464

0.0242

Feed-deprived BW (% of BW) 92.0a 0.64d

0.71cd

0.72cd

92.6a 91.8a 92.0a Heart weight (% of FDBW2)

0.66d

0.70d

0.80bc

0.88b

1.07a

1.07a

0.033

0.0001

3.37a

3.25ab

0.087

0.0345

0.31bc

0.30c

0.011

0.0001

2.66d

2.63d

0.092

0.0001

0.083

0.077

0.004

0.1645

Liver weight (% of FDBW) 3.04bc

3.07bc

2.93c

2.98c

3.17abc

3.02bc

3.11bc

Pancreas weight (% of FDBW) 0.40a

0.41a

0.38a

0.39a

0.40a

0.39a

0.33b

Gizzard weight (% of FDBW) 3.22ab

3.11b

3.26ab

3.22ab

3.40a

2.81cd

3.01bc

Spleen weight (% of FDBW) 0.091

0.089

0.079

0.080

0.088

0.080

0.086

Means within the same row without a common superscript differ (P < 0.05). C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. 2 Eighteen-h feed-deprived body weight. a–d 1

TABLE 6. The effect of T3 or dopamine supplementation in diet on the intestinal weight as a percentage of feed-deprived body weight in 16-d-old broiler chicks; Trial 21 Dopamine (µmol/kg diet) C

0.40

0.99

0.98

0.80

1.60

T3, (µmol/kg diet) 3.20

0.56

1.12

2.24

4.48

SE

P-value

1.01

1.01

0.039

0.8193

2.44

2.38

0.707

0.5614

0.48

0.51

0.035

0.5976

0.55bc

0.49c

0.043

0.0108

Duodenal weight (% of FDBW2) 0.97

0.98

1.03

0.94

1.00

Jejunal weight (% of FDBW) 2.46

2.44

2.40

2.49

2.56

2.44

2.57

Ileal weight (% of FDBW) 0.53

0.54

0.54

0.46

0.55

0.52

0.49

Cecal weight (% of FDBW) 0.73a

0.67a

0.62ab

0.68a

0.72a

0.67a

0.66ab

Means within the same row without a common superscript differ (P < 0.05). C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. 2 Eighteen-h feed-deprived body weight. a–c 1

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TABLE 5. The effect of dietary supplementation of T3 or dopamine on visceral organ weights as a percentage of feed-deprived body weight in 16-d-old broiler chicks; Trial 21

290

CHANG ET AL. TABLE 7. The effect of T3 or dopamine supplementation in diet on the intestinal length per kilogram of feed-deprived body weight in 16-d-old broiler chicks; Trial 21 Dopamine (µmol/kg diet) C

0.40

0.80

1.60

T3 (µmol/kg diet) 3.20

0.56

1.12

2.24

4.48

SE

P-value

50.6a

13.1

0.0371

72.5

0.0116

18.1

0.0116

2

44.5b

45.4b

43.9b

45.7b

Duodenal length (cm/kg of FDBW ) 46.0b 44.4b 47.2ab 47.2ab Jejunal length (cm/kg of FDBW)

164b 41.1b

172b

166b

43.0b

41.5b

175b

173b 174b 184b 183b Ileal length (cm/kg of FDBW)

43.9b

43.0b

43.4b

46.0b

207a

45.7b

51.8a

34.3

46.4

Cecal length (cm/kg of FDBW) 34.1

35.2

39.1

40.4

35.2

41.8

35.3

4.07

0.4023

Means within the same row without a common superscript differ (P < 0.05). C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. 2 Eighteen-h feed-deprived body weight. a,b 1

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TABLE 8. The effect of T3 or dopamine supplementation in the diet on the intestinal density (mg/mm) in 16-d-old broiler chicks; Trial 21 Dopamine (µmol/kg diet) C

0.40

0.80

1.60

T3 (µmol/kg diet) 3.20

0.56

1.12

2.24

4.48

SE

P-value

21.7

20.3

0.875

0.8432

13.5b

11.7c

0.481

0.0015

10.9

10.3

0.812

0.0535

18.9

12.4

2.83

0.1451

Duodenal density, mg/mm 21.7

21.9

22.2

21.5

22.5

21.3

21.3

Jejunal density, mg/mm 15.1a

14.4ab

14.8ab

14.4ab

15.0a

14.2ab

14.2ab

Ileal density, mg/mm 13.2

12.7

13.2

10.6

13.0

12.1

10.7

Cecal density, mg/mm 24.6

23.3

17.8

18.6

22.9

18.4

21.2

Means within the same row without a common superscript differ (P < 0.05). C = no injection; dopamine = 3,4-dihydroxyphenethylamine; T3 = 3,3′,5-triiodo-L-thyronine. Means presented represent an average of four replicate pens of six birds per pen. a–c 1

TABLE 9. The regressions of various variables measured in broiler chicks on dietary supplementation levels of T3 (X, µmol/kg diet); Trial 21 SE Item BW gain of 7- to 15-d-old birds, Y1 g/bird Feed consumption of 7- to 15-d-old birds, Y2 g/bird Feed conversion ratio of 7- to 15-d-old birds, Y3 g feed/g gain Liver weight, Y4 g Gizzard weight, Y5 % of FDBW Duodenal weight, Y6 g Jejunal weight, Y7 g Ileal weight, Y8 g Cecal weight, Y9 g Duodenal length, Y10 cm Cecal weight, Y11 % of FDBW Duodenal length, Y12 cm/kg of FDBW Jejunal length, Y13 cm/kg of FDBW Ileal length, Y14 cm/kg of FDBW Jejunal weight per unit length, Y15 mg/mm Heart weight, Y16 g Pancreas weight, Y17 g Gizzard weight, Y18 g Heart weight, Y19 % of FDBW Pancreas weight, Y20 % of FDBW

Regression equation

R2

Y1 = 310 − 21.5X Y2 = 398 − 22.3X Y3 = 1.28 + 0.024X Y4 = 12.2 − 0.43X Y5 = 3.052 − 0.11X Y6 = 3.82 − 0.15X Y7 = 9.92 − 0.59X Y8 = 2.05 − 0.12X Y9 = 2.81 − 0.31X Y10 = 17.7 − 0.52X Y11 = 0.706 − 0.05X Y12 = 44.4 + 1.39X Y13 = 167 + 8.78X Y14 = 41.9 + 2.20X Y15 = 14.9 − 0.71X Y16 = 2.58 + 0.89X − 0.17X2 Y17 = 1.63 − 0.33X + 0.04X2 Y18 = 12.6 − 1.87X + 0.19X2 Y19 = 0.644 + 0.28X − 0.04X2 Y20 = 0.408 − 0.07X + 0.01X2

0.868 0.765 0.493 0.306 0.273 0.290 0.746 0.402 0.702 0.549 0.249 0.249 0.278 0.278 0.599 0.526 0.773 0.850 0.853 0.779

T3 = 3,3′,5-triiodo-L-thyronine; FDBW = feed-deprived body weight.

1

Second order

First order

Intercept

P-value

0.045 0.075 0.086 0.008 0.003

1.98 2.91 0.006 0.154 0.043 0.055 0.080 0.035 0.048 0.112 0.011 0.570 3.332 0.833 0.138 0.214 0.065 0.398 0.040 0.013

4.55 6.69 0.013 0.354 0.098 0.126 0.184 0.080 0.110 0.256 0.025 1.309 7.655 2.635 0.316 0.168 0.051 0.313 0.031 0.102

0.0001 0.0001 0.0006 0.0115 0.0181 0.0145 0.0001 0.0027 0.0001 0.0002 0.0001 0.0251 0.0168 0.0168 0.0001 0.0018 0.0001 0.0001 0.0001 0.0001

TRIIODOTHYRONINE, DOPAMINE, AND BROILERS

tion needed to induce maximal and minimal heart weights adjusted for FDBW.

DISCUSSION

have less energy for BW gain with a concomitant decrease in the efficiency of feed conversion. These effects, in conjunction with decreased feed consumption, likely account for the decreased body weights observed with T3 supplementation. Similar to the birds in Trial 1, that were supplemented with intraperitoneal injections of T3, the orally supplemented birds in Trial 2 had increased heart weights compared to controls and dopamine-treated birds. Scanes et al. (1986) reported that T3 supplementation, via injection or the diet, increased heart weight in hypophysectomized chicks. Decuypere et al. (1994) fed chickens diets supplemented with 0.5 mg T3/kg diet and found hypertrophy of the right ventricles of the heart. Similarly, Rosebrough (1994) fed chickens between the ages of 7 d and 28 d with a diet supplemented with 1 mg T3/kg BW and observed increased heart weight and decreased pancreatic weight as a percentage of body weight. We have no explanation for the effects of T3 administration on in vivo heart growth since in vitro studies by Kardami (1990) has shown that culture of cardiac myocytes in the presence of T3 results in a decreased in mitogenic stimulation by basic fibroblast growth factor in developing chicken cardiomyocytes. Our data suggest that T3 hypertrophic effects on the cardiomyocytes of older birds may be via a different mechanism. The effects of T3 on heart size is of special interest since it is known that T3 is likely involved in the etiology of ascites in broilers and that increased levels of T3 in lines of birds selected for high and low susceptibility for ascites results in increased heart rate and pronounced increases in mortality in the ascites susceptible line (Decuypere et al., 1994). Our calculations indicate that the optimal dosage of T3 for increased heart rate is 2.62 µmol T3/kg of diet. This is very close to the treatment level in the present study (2.2 µmol T3/kg diet) where maximal heart weights occurred with T3 supplementation. The practical implications of this observation makes obvious the need for minimizing stress of broilers in production systems as well as the careful selection of breeding paradigms to ensure circulating levels of T3 remain in an optimal range for bird health. The effects of exogenous administration of dopamine on the growth, performance, and physiology of the chicken has not been extensively investigated. Dopamine receptors D1A and D1B have been identified in the forebrain and midbrain of the chick (Sun and Reiner, 2000). This suggests that, in addition to any localized regulation within the gastrointestinal tract, DA may play a role in “gut-brain” axis regulation. Pawlik et al. (1976) reported that hybrid dogs administered dopa at 20 µg/kg BW, intrarterially, exhibited a 45% decrease in intestinal oxygen uptake. Dopa is converted to dopamine within the intestinal mucosal cells and, hence, may act locally as a regulator of intestinal function (Lucas-Teixeira et al., 2000). Lucas-Teixeira et al. (2000) report that dopamine inhibited intestinal mucosal Na+/K+ ATPase from cells isolated from young, milk-fed rat pups; however, this inhibition was not noted in older rats fed solid food. Cheng et al. (2001) found that laying hens selected for low

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In the present study, broiler chicks injected with various levels of T3 or dopamine, intraperitoneally, at 6, 9, and 12 d of age exhibited very limited responses to either compound. A possible explanation for this lack of response is that the half-life of T3 is too short to evoke a broad range of measurable biological responses in just 3 d. Tata and Shellabarger (1959) found that the half-life of intramuscularly administered T3 and T4 was 22.5 ± 1 h in Light Sussex × Rhode Island 21-d-old males. May et al. (1974) estimated the half-life of plasma T4 in commercial broilers was 34.1 to 52.6 min. Hutchins and Newcomer (1966) reported that T3, in comparison to T4, was metabolized and excreted more rapidly in chickens 4 h postadministration. Birds administered 2.96 µmol T3/kg BW did have greater heart weight as a percentage of fasted BW. Similar increases in heart weight as the result of exogenous administration of T3 have been reported by Scanes et al. (1986) and Decuypere et al. (1994). This increase in heart weight may be due to right ventricular hypertrophy (Decuypere et al., 1994). In Trial 2, administration of T3 via the diet resulted in a threefold increase in serum T3 concentrations. This was associated with lower BW, feed consumption, and less efficient feed conversion. May (1980) reported that chickens fed a diet containing 1 ppm T3 had poor weight gain and feed efficiency as compared to nonsupplemented controls. Rosebrough (1994) fed chickens, between the ages of 7 to 28 d, with diets containing various levels of crude protein with 0 or 1 mg T3/kg diet and reported that the T3 supplemented birds gained less compared to controls. The net energy obtained from the gross energy of the diet, after accounting for the energetic costs of digestion, absorption, and metabolism, is used to supply energy for growth and work (Klasing, 1998). The fundamental regulatory role of thyroxine is the regulation of metabolic processes, including diet-induced thermogenesis as well as physiological reactions to stress. Uni et al. (2001) have proposed that hatchling chicks exposed to thermal stress had decreased circulating levels of T3, and 48 h after the return to a normal thermal environment, T3 levels rebounded with a concomitant increase in intestinal development. The supraphysiological levels of circulating T3 in the treated birds during the present study may have increased thermogenesis and mimicked environmental stress. Gabarrou et al. (1997) found that high circulating postprandial levels of T3 increased in chickens selected for poor feed efficiency. Jepson et al. (1988) reported that T3 increased skeletal muscle protein degradation in the rat. In addition, T3 likely increases the basal metabolic rate and increases the metabolizable energy requirement for whole-body maintenance and intestinal function and, subsequently, adversely affects the efficiency of nutrient utilization. This results in less energy available for production. Hence, chickens fed diets supplemented with T3

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ACKNOWLEDGMENTS The authors thank National Scientific Council, Taiwan, for the financial support (NSC87-2313-B-005-053) that made this study possible.

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