Effects of Lighting Pattern and Dietary Tryptophan Supplementation on Growth and Mortality in Broilers

Effects of Lighting Pattern and Dietary Tryptophan Supplementation on Growth and Mortality in Broilers R. BLAIR Department of Animal Science, University of British Columbia, 248-2357 Main Mall, Vancouver, British Columbia, Canada, VST 1Z4 R. C. NEWBERRY and E. E. GARDINER

ABSTRACT The effect of lighting pattern and supplementation of the diet with Trp on growth and mortality of male broiler chickens was evaluated in three experiments using 2,392, 2,608, and 2,400 chickens, respectively. There were two lighting treatments, either a constant 23 h of continuous light/ 24-h period or an increasing photoperiod lighting system, i.e., 0 to 3 days, 23 h light (L):l h dark (D); 4 to 14 days, 6L:18D; 15 to 21 days, 10L:14D; 22 to 28 days, 14L:10D; 29 to 35 days, 18L:6D; 36 to 42 days, 23L:1D. The design was a completely randomized 2x2 factorial, with four replicates per treatment. In the first two experiments, a starter diet with or without .2% supplemental L-Trp (feed grade) was fed from 0 to 3 wk of age and a finisher diet with or without .2% supplemental Trp was fed from 3 to 6 wk of age. In the third experiment, the level of supplemental Trp was .4% in the starter and finisher diet. Birds raised on the increasing light pattern consumed less feed during the first 3 wk, were lighter in weight at 3 wk, and had lower feed:gain ratios (P < .001) than their counterparts on constant light. By market age (6 wk) they had similar body weight but feed intake was significantly (P < .05) lower in all experiments, and feed:gain ratio was significantly lower in these birds in Experiment 3 (P < .05) than in their counterparts on constant light. The increasing light pattern was associated with reduced total mortality and mortality from Sudden Death Syndrome (SDS) (P < .05 in Experiments 1 and 2, and P < .01 in Experiment 3). There was also reduced mortality from ascites with increasing light (P < .001) in Experiments 1 and 2, although the overall incidence of ascites was low (<1%). The incidence of varus leg abnormalities was reduced with increasing light (P < .05), and the birds appeared to be more mobile than those on constant light as judged by their ability to jump up onto a raised platform to feed. Supplementing the diet with Trp had no significant effect on growth performance, total mortality, SDS mortality, or ascites mortality. The blood heterophiklymphocyte ratio was higher at 5 than at 2 wk (P < .001) but was not affected by lighting pattern or diet. The overall incidence of SDS was approximately 9%, suggesting that the basal diets used in this study may be of interest to other researchers studying the etiology of this condition. (Key words: broiler, light, tryptophan, Sudden Death Syndrome, ascites) 1993 Poultry Science 72:495-502

INTRODUCTION

Received for publication May 5, 1992. Accepted for publication October 30, 1992.

Currently, there is interest in discontinuous lighting patterns for broilers because the altered growth pattern may be 495

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Agriculture Canada, Research Station, P.O. Box 1000, Agassiz, British Columbia, Canada, VOM 1A0

496

BLAIR ET AL.

'Heartland Lysine Inc., Chicago, IL 60631.

Nockels (1989), who showed that Trp in combination with discontinuous light enhanced immunity in broilers, possibly through an effect on melatonin, which is considered to be immunostimulatory and is inhibited by light. The objective of the work described in this paper was to investigate the influence of lighting pattern and supplementation of the diet with Trp on growth and mortality in broilers. MATERIALS AND METHODS In each of three experiments male broiler chickens (Peterson x Arbor Acres), vaccinated against Marek's disease, were obtained at day-old from a commercial hatchery, and raised to 42 days of age in light-proofed floor pens measuring 24 m 2 , in groups of approximately 150 (Experiments 1 and 3) or 163 (Experiment 2) birds per pen. At 43 days of age they were slaughtered at a commercial processing plant. All experiments were approved by the institutional Animal Care Committees. Experiments 1 and 2 A starter diet with or without .2% supplemental feed grade L-Trp 1 (Table 1) was fed from 0 to 3 wk of age and a finisher diet with or without .2% supplemental Trp was fed from 3 to 6 wk of age. The Trp was added at the expense of corn. There were two lighting treatments, either a constant 23 h of continuous light/24-h period or an increasing photoperiod lighting system, i.e., 0 to 3 days, 23 h light (L):l h dark (D); 4 to 14 days, 6L:18D; 15 to 21 days, 10L:14D; 22 to 28 days, 14L:10D; 29 to 35 days, 18L: 6D; 36 to 42 days, 23L:1D. Light intensity on the constant lighting treatment (measured 23 cm above the litter and directly below one incandescent light bulb per pen), was maintained throughout at 20 lx in Experiment 1, and was 20 lx during Days 0 to 6 and 5 lx during Days 7 to 42 in Experiment 2. On the increasing photoperiod lighting treatment it was 20 lx during Days 0 to 6 and 5 lx j — :

T-\

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«:

„i.~

uumig, L
The statistical design of each experiment was a 2 x 2 factorial arrangement of treatments, completely randomized, and with four replicate pens per treatment. Each pen contained four hanging tube feeders,

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associated with a reduction in the incidence of skeletal abnormalities and mortality from Sudden Death Syndrome (SDS) (Classen et al, 1991). The syndrome is an important cause of mortality in Canadian broiler flocks with reported incidences of .71 to 4.07% (Riddell and Springer, 1985) and 1.31 to 9.62% (Gardiner el al, 1988). There is a higher incidence in males (Riddell and Springer, 1985; Gardiner el al, 1988). The etiology of the condition is unknown and SDS is currently assumed to be a metabolic disease influenced by genetics, environment, physiology, and nutrition (Guenter, 1991). Sudden death in broilers may also be due to ascites, which can occur secondarily to right ventricular failure, and is a significant cause of mortality in many flocks (Calnek el al, 1991). The reported incidence of ascites is around 1% in many broiler flocks and occasionally 15 to 20% in roaster flocks (Calnek el al, 1991). The exact etiology of the condition is unknown, although it is known that growth rate (Luis el al, 1991; Vega et al, 1991) is a contributory factor. Scheele et al (1991) have suggested that continued improvement in growth rate may result in an increased incidence of ascites. Bowes et al (1988) reported that a feed restriction of 25%, which resulted in a 40% reduction in body weight, eliminated mortality due to SDS. It is possible that the lighting effects on SDS, which were reported by Classen and Riddell (1989) and Classen et al (1991), might be mediated through an effect on early growth restriction or a reduction in stress associated with continuous lighting (Freeman et al, 1981). Further data in this area might help to explain the etiology of the SDS condition, and further work needs to be done on growth rate and its relationship to ascites. Tryptophan has been found to reduce aggressive behavior in chickens (Shea et al, 1990), and this amino acid is being used as a dietary supplement by humans to induce sleep (Leathwood, 1987). An interaction between light and Trp has been suggested by the work of Bowman and

497

PHOTOPERIOD, DIETARY TRYPTOPHAN, AND BROILER PERFORMANCE TABLE 1. Compositions of basal diets Ingredients and analyses

Finisher (3 to 6 wk)

31.91 25.00 35.37 2.82 1.54 1.54 .24 .08 1.00 .15 100

35.84 30.00 28.05 1.29 1.59 1.43 .21 .09 1.00 .15 100

Finisher Experiments 1 and 2 OTrp +Trp

(%) Trp Dry matter CP Ether extract Crude fiber Ash Calcium Phosphorus

.28 88.8 23.5 5.18 2.31 5.84 .96 .79

.45 88.5 23.7 5.15 2.35 5.87 .96 .78

.27 87.1 23.2 5.24 2.54 5.75 .92 .79

Experiment 3 OTrp +Trp

(%) .60 87.1 22.7 5.11 2.47 5.8 .95 .76

.24 87.3 21.5 3.90 2.32 5.55 .91 .75

.37 88.4 21.5 3.90 2.36 5.57 .92 .73

.26 87.6 20.7 3.79 2.44 5.35 .85 .75

.60 87.2 21.5 3.67 2.51 5.41 .91 .77

Provided per kilogram of diet: vitamin A, 9,000 IU; cholecalciferol, 1,500 IU; vitamin E, 10IU; vitamin K, .5 mg; vitamin Bj2, -007 mg; thiamin, .4 mg; riboflavin, 6 mg; folic acid, 1 mg; biotin, .15 mg; pantothenic acid, .12 mg; niacin, 35 mg; pyridoxine, 4 mg; choline, 1,000 mg; Mn, 60 mg; Cu, 5 mg; Zn, 50 mg; Se, .1 mg; I, .35 mg; ethoxyquin, 1.25 mg; sodium chloride, 1 g; salinomycin, 60 mg; zinc bacitracin, 4.4 mg. ^Pellet binder; ITT Rayonier, Inc., Seattle, WA 98188. 3 0Trp = no supplemental Trp; +Trp = with supplemental Trp.

two water troughs, and a gas brooder. Temperature under the brooder was reduced by 2.2 C/wk, from 33 C at day-old to 22 C at 5 wk, and kept at 21 C from 5 to 6 wk. Fresh kiln-dried softwood shavings were used as litter. Feed and water were supplied for ad libitum consumption. Mortality was recorded daily and all chickens found dead were necropsied. Records of mean body weight at 3 and 6 wk of age, feed consumption, and feed:gain ratio were obtained. Feed:gain ratio was calculated taking into account the weights of chickens that died. Experiment 3 In this experiment, the level of supplementary Trp in the starter and finisher

diets was .4%. In other respects, the treatments and experimental conditions were similar to those described for Experiment 2. Blood samples were obtained 1 to 2 h following lights on from the cutaneous ulnar vein of three chickens per pen at 2 wk, and from three different chickens per pen at 5 wk, for determination of the heterophil: lymphocyte ratio. Two stained slides per bird were prepared (Lillie and Fillmer, 1976) and counts made of 100 leucocytes per slide. Data on leg deformities were obtained at 3 and 6 wk of age by clinical examination of birds during weighing. The incidence of varus twisting (legs bowed inward) and valgus twisting (legs twisted outwards) was recorded. Mobility of birds at 43 days was assessed by requiring birds to jump up

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Corn Wheat Soybean meal (47% CP) Fat (animal and vegetable mixture) Dicalcium phosphate (16% Ca, 20% P) Limestone Salt, iodized DL-methionine Vitamin-mineral premix1 Supplement2 Total Determined analyses (air-dry basis) Starter Experiments Experiment 3 1 and 2 0Trp3 +Trp3 OTrp +Trp

Starter (0 to 3 wk)

498

BLAIR ET Ah.

still lower in this group (P < .05). The lighting pattern had a significant effect on total mortality and mortality due to SDS (P < .05), both being reduced- at 3 and 6 wk with the increasing photoperiod. Ascites mortality at 6 wk was reduced from .8 to .3% with the increasing photoperiod (P < .001): there was no similar effect at 3 wk. There were no significant effects of dietary Trp supplementation on growth performance or mortality. No significant interactions involving diet and lighting pattern were observed.

Experiment 3 Analyses The diets were analyzed for dry matter, crude protein, ash, ether extract, and crude fiber by conventional methods of the Association of Official Analytical Chemists (AOAC, 1984). Calcium and phosphorus were analyzed by initial digestion using the method of Zazoski and Burau (1977), followed by colorimetric assay for phosphorus using the Parks and Dunn (1963) method. Calcium was assayed by atomic absorption spectrophotometry (AOAC, 1984). Tryptophan was analyzed by column chromatography following alkaline hydrolysis (Jones et ah, 1981). The data from all three experiments were analyzed by ANOVA using a 2 x 2 factorial arrangement of treatments to determine the effects of lighting treatment and dietary Tip supplementation and their interaction, with the pen used as the experimental unit. Mortality data were converted by arc sine transformation before analysis, but for interpretation purposes the data are presented as untransformed values.

RESULTS Experiments 1 and 2 The performance and mortality data were combined and are set out in Table 2. At 3 wk of age, birds reared on the increasing lighter in weight, had lower feed intakes, and had lower feed:gain ratios (P < .001) than those reared on the constant light treatment. The live weight effect had disappeared by 6 wk of age, but feed intake was

The performance and mortality data are shown in Table 3. As in Experiments 1 and 2, the birds on the increasing photoperiod were lighter in weight and had lower feed: gain ratios at 3 wk than their counterparts on the constant lighting program. By 6 wk they had similar body weights and lower feed:gain ratios (P < .05). No significant effects due to Trp supplementation of the diet were recorded. Total mortality and mortality due to SDS were significantly lower with the increasing photoperiod treatment at 3 wk (P < .05) and at 6 wk (P < .01). Although average ascites mortality was lower at 6 wk under the increasing photoperiod, the effect of lighting was not significant (P = .25). The heterophil: lymphocyte ratio was higher at 5 than at 2 wk (P < .001), but was not affected by lighting pattern or diet (Table 4). The increase with age was due to an increase in heterophils (P < .001) and a decrease in lymphocytes (P < .001). At 6 wk of age, 4.4% of the birds on the increasing photoperiod had varus twisting of the legs as compared with 8.6% of the birds on the 23 h lighting program (P < .05). The incidence of valgus twisting was not affected significantly by lighting program (average 21.0% of chickens affected at 6 wk). Birds on the increasing photoperiod were more mobile than those on the constant lighting program, as judged by their higher intake of feed over a 2-h period from feeders accessible only by jumping onto a 30-cm-high platform (Table 4). Feed intake over a 1-h period following return of the feeders to their regular positions did not differ significantly between treatments. No significant interactions were observed. Electricity consumption per pen from 0 to 6 wk was reduced

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onto a i m 2 wooden platform set at 30 cm above the floor (placed in each pen 1 wk earlier), and measuring feed intake from a tube feeder hanging over the center of the platform over a 2-h period, following removal of all the feeders for a period of 20 h. After the 2-h mobility test, the platforms were removed, all four feeders were returned to their regular positions, and feed intake was recorded over a further 1-h period. Electricity consumption for lighting and ventilation and gas consumption for brooding were monitored in this experiment.

PHOTOPERIOD, DIETARY TRYPTOPHAN, AND BROILER PERFORMANCE

499

TABLE 2. Effects of lighting pattern (photoperiod) and dietary tryptophan supplementation on the growth and mortality of broilers from 0 to 42 days of age, Experiments 1 and 2 combined

Treatment

Feed intake 1

Live weight

-(g)

Feed: gain 2

Mortality Total

SDS3

Ascites

("<,}

(ffg) 3 wk -

Lighting Constant Increasing Significance Diet 4 OTrp +Trp Significance SEM

1,087 1,006

1.33 1.30

***

*+*

»*•*

*

*

.1 0 NS

806 802 NS 5.5

1,046 1,048 NS 8.0

1.31 1.32 NS .006 6 wk -

5.4 4.6 NS .32

4.2 4.1 NS .28

.2 0 NS .05

2,398 2,400 NS

4,195 4,160

11.5 9.5

9.7 7.8

.8 .3

*

1.78 1.77 NS

*

*

*

2,405 2,393 NS 4.9

4,190 4,165 NS 10.9

1.78 1.77 NS .005

10.8 10.3 NS .45

8.6 8.8 NS .42

.7 .4 NS .11

827 781

5.6 4.4

4.8 3.5

'Calculated on bird-day basis. Calculated as [pen feed consumption:(live weight + mortality weight)]. 3 Sudden Death Syndrome. 4 0Trp = no supplemental Trp; +Trp = with supplemental Trp. *P < .05. **P < .01. ***P < .001.

from 269 to 214 kWh under the increasing photoperiod, and gas consumption was reduced from 171 to 123 m 3 (P < .05).

DISCUSSION The overall results of the present study suggest that an increasing light pattern is beneficial in broiler flocks in reducing overall mortality, SDS mortality, the incidence of leg deformities, and improving feed efficiency, with no reduction in body weight at market age. These results confirm the findings of Bowes et al. (1988), Gardiner et al. (1988), Classen and Riddell (1989), Chung (1990), and Classen et al. (1991) that a growth restriction in broilers results in reduced mortality. There was evidence of reduced mortality from ascites in the present study, although ascites was

not found to be a major cause of death. The incidence of varus leg abnormalities was reduced with the increasing light pattern, and the birds appeared to be more mobile than those on constant light as judged by their ability to jump u p onto a raised platform to feed. Because chickens on both light treatments made obvious attempts to jump onto the platform during the 2-h test, and because feed intake over the 1 h following the test did not differ significantly between treatments, it is reasonable to conclude that the test indicated a difference in bird mobility between treatments rather than a difference in feeding motivation. Thus the altered growth pattern seems to be generally beneficial for market broilers, with no evidence of an increased stress response as judged by blood heterophiblymphocyte

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Lighting Constant Increasing Significance Diet 4 OTrp +Trp Significance SEM

500

BLAIR ET AL.

TABLE 3. Effects of lighting patterns (photoperiod) and dietary tryptophan supplementation on the growth and mortality of broilers from 0 to 42 days, Experiment 3

Treatment

Live weight

Feed intake 1 M

(&

Lighting Constant Increasing Significance Diet4 OTrp +Trp Significance SEM

Mortality Total

SDS3

Ascites

C°<,1

teg) 3 wk -

1,162 979

1.31 1.24

***

***

***

*

*

.1 .1 NS

850 851 NS 14.3

1,072 1,069 NS 24.3

1.28 1.27 NS .010 6 wk -

7.2 7.8 NS .80

3.6 3.9 NS .50

.1 .1 NS .06

2,434 2,463 NS

4,298 4,215

1.81 1.75

15.3 9.8

8.6 4.7

*

*

**

**

1.3 .7 NS

2,459 2,440 NS 15.9

4,270 4,243 NS 17.6

1.78 1.78 NS .012

11.3 13.3 NS 1.11

6.2 7.1 NS .74

.9 1.0 NS .27

904 797

9.5 5.5

4.9 2.6

Calculated on a bird-day basis. Calculated as [pen feed consumption:(liveweight + mortality weight)]. 3 Sudden Death Syndrome. 4 0Trp = no supplemental Trp; +Trp = with supplemental Trp. *P < .05. **P < .01. *»*P < .001.

ratio (Gross and Siegel, 1983). The benefits plementation. In addition, no significant may stem from the reduced feed intake interactions between diet and lighting and resultant reduction in growth rate program were detected. Thus, it is conduring the early phase of growth, coupled cluded that Trp supplementation of the with physiological benefits associated with diet, although previously found to reduce the light-dark cycle (Classen and Riddell, aggressive behavior in broiler breeders 1990). A reduced consumption of electric- (Shea et ah, 1990) and in combination with ity was an additional benefit expected, discontinuous light to enhance the immuand observed, with the increasing pho- nity of broilers (Bowman and Nockels, toperiod treatment. The reduced gas con- 1989), was not beneficial in reducing sumption was unexpected and might be mortality in broilers at the Trp levels used related to increased heat production by in this study. the birds due to higher activity and lower The study of SDS is made difficult by mortality (i.e., more birds present). the relatively low incidence of the condiThere was no significant effect of sup- tion and by an inability to identify affected plementary Trp on growth, SDS mortality, birds prior to the onset of death (Newascites mortality, blood heterophil: berry et ah, 1987). Thus, large experiments lymphocyte ratio, incidence of leg defor- are required and results are often difficult mities, or mobility. In two of the experi- to confirm. Identification of a rearing ments there was a trend for the incidence regimen that promoted a high incidence of of ascites to be reduced with Trp sup- SDS would be of distinct benefit to

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Lighting Constant Increasing Significance Diet4 OTrp +Trp Significance SEM

Feed: gain 2

PHOTOPERIOD, DIETARY TRYPTOPHAN, AND BROILER PERFORMANCE

501

TABLE 4. Effects of lighting pattern (photoperiod) and dietary tryptophan supplementation on heterophihlymphocyte ratio (H:L), incidence of varus and valgus leg deformities, and feed intake at 43 days from a raised platform over 2 h following a 20-h fast, and from lowered feeders over next 1 h, Experiment 3 Feed intake 1 from: 2 wk

5 wk

Valgus

Varus

H:L Treatment

3 wk

3 wk

6 wk

6 wk

Platform feeders

„. (%i

.43 .42 NS

.57 .63 NS

4.9 6.5 NS

8.6 4.4

.38 .48 NS .029

.60 .61 NS .030

4.5 6.9 NS .76

7.7 5.1 NS .82

4-

(c)

\£>)

18.8 17.7 NS

20.7 21.3 NS

7.1 15.6

76.0 82.5 NS

19.3 17.2 NS 1.27

18.8 23.2 NS 1.37

10.4 12.3 NS 1.19

79.2 79.2 NS 1.98

1

Based on (pen feed consumption:number of birds present). 0Trp = no supplemental Trp; +Trp = with supplemental Trp. *P < .05. **P < .01. ***P < .001. 2

researchers studying the condition. The basal diets used in the present study may be useful in this regard, because an incidence of SDS mortality of around 9% was reported with these diets. This incidence is much higher than that usually experienced in commercial and research flocks (Riddell and Springer, 1985; Gardiner et al, 1988). Various dietary factors are known to be associated with an increased incidence of SDS. A reduced incidence of SDS was reported when wheat was replaced with corn (Blair et al., 1990; Guenter, 1991), when meat meal partially replaced soybean meal (Blair et al, 1990), and when sunflower oil replaced animal tallow (Guenter, 1991). These dietary factors should be taken into account in formulating diets to be used in studies designed to provide more information on the etiology of SDS. ACKNOWLEDGMENTS

The technical assistance of the poultry staff of the Agriculture Canada Research Station, Agassiz, is gratefully acknowledged. We are also grateful to Heartland Lysine Inc., Chicago, IL 60632, for the Trp analyses. This study was

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Lighting Constant Increasing Significance Diet* OTrp +Trp Significance SEM

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