Effect of intermittent lighting schedules during the

3 downloads 0 Views 121KB Size Report
Farm Animals, European Association of Animal Production, Pub- ... den Tieren mit dem T3-Futterzusatz signifikant erhöht, war aber bei den. Tieren im Raum mit ...
Avian Pathology ( 2000) 29, 433–439

Effect of intermittent lighting schedules during the natural scotoperiod on T3-induced ascites in broiler chickens M. Hassanzadeh1*, M. H. Bozorgmerifard1, A. R. Akbari1, J. Buyse2 & E. Decuypere2 1

Department of Poultry Diseases, Faculty of Veterinary Medicine, University of Tehran, PO Box 14155–6453, Tehran, Iran, and 2Laboratory for Physiology and Immunology of Domestic Animals, KU Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Belgium

The influence of an intermittent lighting programme during the 12 h of the dark period on the incidence of ascites and on metabolic parameters of broiler chickens was examined. A group of 336 1-day-old male broiler chickens were randomly allocated to two open rooms At 5 days of age, an intermittent lighting schedule of 3 h of dark alternating with 1 h of light was introduced during the night in one room, while in the second room the schedule consisted of 23 h of light alternating with 1 h of dark. One-half of the birds in each room were fed a diet supplemented with 1.5 ppm 3, 39, 5-triiodothyronine ( T3 ), while the other half received a control diet. Mortality associated with ascites was significantly higher in birds fed the T3 -supplemented diet, but was significantly lower in birds in the room receiving the intermittent lighting schedule. The intermittent lighting programme was also associated with a temporary reduction in growth rate, packed cell volume and plasma T3 concentrations, suggesting reduced oxygen utilization. However, final body weights were not significantly affected by the lighting programme. It was concluded that imposing 12 h of intermittent lighting during scotoperiod reduces the incidence of ascite mortality.

Introduction Ascites in young, rapidly-growing broiler chickens is associated with pulmonary hypertension and right ventricular hypertrophy, which eventually results in heart failure and/or the accumulation of fluid in the abdominal cavity ( Julian, 1993). Ascites syndrome is a severe cause of loss to the broiler industry in many countries, not only due to high mortality, but also due to reduced weight gain and increased condemnations at slaughter ( Julian, 1993). More recently, there has been a marked increase in the incidence of ascites at low altitudes ( Maxwell & Robertson, 1997). The reasons for the increased prevalence of this condition in flocks at sea level are not clear, but it has been postulated that the high oxygen demand of fast growth raises pulmonary

arterial pressure, thus putting extra work load on the heart, and consequently increases the incidence of ascites ( Julian, 1993; Decuypere et al., 1994; Hassanzadeh Ladmakhi et al., 1997). Successful broiler production depends on fast growth rates and efficient feed conversion. In order to achieve these objectives, it is believed that food should be available ad libitum and that stock should be held under continuous or nearly continuous illumination. On the other hand, a continuous lighting programme may cause excessive locomotor activity that could use extra energy and thus impair feed conversion efficiency ( Perry, 1981). Compensatory growth after a period of feed restriction can improve performance ( K¨uhn et al., 1996). It has been shown that feed restriction, when applied from days 6 to 11, reduced the incidence of

* To whom correspondence should be addressed. E-mail: [email protected] Received 11 May 1999. Accepted 18 April 2000. ISSN 0307-9457 (print)/ISSN 1465-3338 (online)/00/050433-07 © 2000 Houghton Trust Ltd

434 M. Hassanzadeh et al.

ascites ( Shlosberg et al., 1991). In addition, manipulations of the lighting programme by either the reducing total hours of light ( 16 h light:8 h dark) ( Robbins et al., 1984) or imposing intermittent lighting schedules ( 1 h light:3 h dark) ( Buys et al., 1998) have been reported to reduce the incidence or severity of circulatory disorders. The purpose of the present study was to examine the efficacy of imposing intermittent lighting programmes at night in open poultry houses in reducing the incidence of ascites and to test its effect on the performance of broiler chickens. In Iran, intermittent lighting schedules cannot be applied over 24 h because the majority of poultry farms are open or have windows. Therefore, in this study, the effect of intermittent lighting ( 1 h light :3 h darkness) during 12 h of night ( from 8 p.m. until 8 a.m) on broiler performance and the incidence of ascites was examined. It has been found previously ( Decuypere et al., 1994) that dietary 3,39,5-triiodothyronine ( T3) supplementation ( 1 to 2 ppm) increases the incidence of ascites in broilers. Thus, this functional hyperthyroidism was used to enhance the incidence of ascites in this study.

Measurements From day 5 onwards, body weights and feed intake were measured weekly for each pen. From 10 randomly selected birds per group, venous blood samples were taken weekly from day 14 onward. Each week, blood samples were obtained during the final part of the light period, between 7 and 7:30 a.m. Blood was collected in heparinized capillary tubes for determination of packed cell volume (PCV) (at weeks 3, 4 and 7) and in heparinized tubes on ice for the separation of plasma. PCV was measured immediately, while plasma was stored at – 20°C until analysed for both thyroid hormones, T3 and T4 (thyroxine), as described previously (Decuypere et al., 1994). Total plasma protein concentrations were measured using the biuret method (Kingsley, 1942). Throughout the study, mortality was recorded daily. At the end of the experiment, 15 chickens from each group were randomly selected and slaughtered. These birds and those that died during the experimental period were examined for lesions of heart failure and ascites. The heart was removed and the atria, major vessels and fat were trimmed off. The right ventricle (RV) was dissected away from the left ventricle and septum. The right and left ventricular weights were determined separately, and the right and left ventricles and septum were added and the total ventricular weight (TV) determined. Birds having a RV/TV of over 0.299 were classified as suffering from right ventricular failure (Julian, 1987). Statistical analysis was performed using the “General Linear Model Procedure” (SAS Institute, Cary, NC, USA) with lighting programme and dietary T3 supplementation as main factors. If a significant overall effect (P < 0.05) was found, treatment means were compared using the Scheffe test.

Results Materials and methods

Ascites mortality and RV/TV ratio

Experimental design

Weekly mortality from right ventricular failure ( RVF) and ascites and corresponding RV/TV in the different groups are presented in Table 1. Over the 7-week growing period, 85 ( 25%) of the 336 birds died. Of these birds, 68 ( 20%) had right ventricular hypertrophy ( RVH) and ascites, with a mean RV/ TV of 0.32. The other 17 dead birds had no lesions of ascites and died due to other causes including neonatal infection ( twelve birds), arthritis ( two birds) and sudden death syndrome ( three birds). T3 supplementation clearly increased mortality due to ascites. The first cases of ascites occurred from week 1 in T3-treated chickens reared under the CL schedule. The mortality rate increased considerably

A total of 336 1-day-old male broiler chickens of a commercial strain (Ross) were fed a basal diet (3000 kcal mercaptoethanol/kg and 20% crude protein) and kept in nearly continuous lighting (CL) (23 h light:1 h dark). At 5 days of age, the chickens were randomly allocated to two rooms (4.5 m ´ 4 m), each containing six floor pens (28 chicks per pen). In one room, the continuous lighting schedule of 23 h light:1 h dark was maintained, while in the other room an intermittent lighting (IL) schedule of 1 h light:3 h dark was imposed during the 12 h of night from 8 p.m. to 8 a.m. In this room, lights were on from 11 to 12 p.m., 3 to 4 a.m. and 7 to 8 a.m. In each room, one-half of the chicks received the basal diet, while the other half received a diet supplemented with 1.5 ppm T3 (Sigma, St. Louis, MO, USA) from day 5 onwards. This design resulted in a 2 ´ 2 factorial experiment with lighting programme and dietary T3 supplementation as main factors, each with three replicates per treatment.

Table 1. Ascites mortality and right ventricular weight total ventricular weight ratio in commercial broiler chickens reared under different lighting regimens and on different diets. Ascites mortality Dietary and lighting groupsa CLCo CLT3 ILCo ILT3 Total a b

week 1

week 2

week 3

week 4

week 5

week 6

week 7

Total

RV/TVb

0 1 0 0 1

0 1 0 0 1

0 6 0 2 8

0 12 0 4 16

0 10 0 3 13

0 6 0 3 9

0 11 0 9 20

0 47 0 21 68

0 0.34±0.02 0 0.29±0.01 0.32±0.02

CL, continuous lighting; IL, intermittent lighting; Co, control diet; T3 , T3-supplemented diet. RV/TV, right ventricular/total ventricular weight ratio.

Effect of intermittent lighting on ascites 435 Table 2. Cardiac measurements and ascites in chickens slaughtered at 7 weeks Dietary supplement and lighting schedulea

RVH and ascitesb Right ventricle ( g) Left ventricle ( g) Total ventricle ( g) RV/TV ratios (g)

CLCo

CLT3

ILCo

ILT3

P value

0/15 1.05 ± 0.12B 5.93 ± 0.37 7.0 ± 0.46B 0.15 ± 0.01B

7/15 2.68 ± 0.30A 5.97 ± 0.34 8.7 ± 0.22A 0.31 ± 0.03A

0/15 1.28 ± 0.09B 5.78 ± 0.46 7.1 ± 0.54B 0.18 ± 0.01B

3/15 1.45 ± 0.07B 5.95 ± 0.15 7.4 ± 0.15B 0.19 ± 0.01B