Effects of Light Intensity on Growth, Anti-Stress Ability and Immune Function in Yellow Feathered Broilers

ABSTRACT

An experiment was conducted to investigate the effects of light intensity on growth, anti-stress ability, and immune function of yellow feathered broilers. A total of 480 one-day-old male Lingnan yellow feathered broilers were randomly allocated to 4 treatments based on light intensity (1, 5, 20 and 80 lx) with 8 replicates of 15 chicks each. The experiment lasted for 63 days. Compared with those under high light intensity, broilers exposed to low light intensity had higher (p<0.05) total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px), a-Naphthylacetate esterase (ANAE⁺), antibody titer, but lower (p<0.05) malonaldehyde (MDA) levels and heterophil/lymphocyte ratio (H/L). There was a linear effect for T-AOC(p=0.002), GSH-Px(p≤0.047), MDA (p=0.003), H/L(p≤0.014), ANAE⁺ (p≤0.044), and antibody titer (p≤0.021) with T-AOC, GSH-Px, ANAE⁺, and antibody titer increased significantly as light intensity decreased, whereas MDA and H/L were decreased with the decrease in light intensity. These results suggested that broilers under low light intensity could have similar performance, better anti-stress ability, stronger immune function, and more efficient in energy usage as compared with those exposed to high light intensity environment.

Keywords:
Anti-stress ability; Growth; Immune function; Light intensity; Yellow feathered broilers.

INTRODUCTION

Light intensity plays an important role in broiler’s health (Blatchford et al., 2012). Studies showed that low light intensity has negative effects on broiler’s carcass traits, early uniformity and meat tenderness, and is in relation to incidence of leg disease, eye defects, dystrophy, skeletal disorders, as well as foot pad health (Blatchford et al., 2009; Deep et al., 2012; Senaratna et al., 2016; Fidan et al., 2017; Rault et al., 2017). High light intensity can improve activity (Blatchford et al., 2012; Rault et al., 2017) and benefit bone health (Blatchford et al., 2009), increase growth and breast muscle percentage (Deep et al., 2013), and give comfort behaviors for broilers (Alvino et al., 2009). However, too strong light may enhance attack behavior of broilers and therefore compromise the health and welfare of broilers (Kjaer & Vestergaard, 1999).

Yellow feathered broiler is a special species in Asia. There were 3.73 billion yellow feathered broilers, accounting for 45.9% of total broilers slaughtered in China in 2015 (Zhang et al., 2016). Yellow feathered broilers usually have longer raising periods and slower growth rate than white feathered broilers, implying that different optimum light regimes could exist between them. Unfortunately, most of the researches involving light intensity were about white feathered broilers and few reports on yellow feathered broilers were published. The purpose of the present study was therefore to investigate the effect of light intensity on growth, anti-stress, and immune function in yellow feathered broilers.

MATERIALS AND METHODS

Bird husbandry and experimental treatments

Four hundred and eighty one-day-old male Lingnan yellow feathered broilers were purchased from a commercial hatchery in Lanzhou, China, and randomly distributed to 4 environmentally controlled rooms (120 chicks per room). Each room had a floor area of 8 m² (2.5 m width × 3.2m length) with a volume of 20m³ (2.5 m height) and was randomly assigned to 1 of 4 light intensities. In each room, 8 cages (1.3 m×0.78 m×0.58 m) were installed in a two tier battery system. Light was provided by light emitting diode.

Chickens were subjected to 1 of the 4 levels of light intensity (1, 5, 20, 80 lx). Light intensity settings were verified at feeder trough (1.3 m×0.15 m, feeder barrels were used before 3 wk of age) level. Light intensity was measured with the photoreceptor sensor of a light meter (Model: ZDS-100W; Shanghai Jiading Xuelian Meter Factory, China). Automatic timers were used for lighting cycle. All birds were provided with 23L:1D from 1 to 3 d of age. Lighting regimes were initiated at 4 d of age and natural photoperiod simulated in Lanzhou (5:47-6:00 sunrise and 20:03-20:21 sunset manual operation). The experiment lasted for 63 d. To keep consistent with the natural day-night rhythm, the lighting period was set as 5:47-20:01 for the first day, and gradually delayed to 6:00-20.21 for the 63^rd d). Temperature was set initially at 33°C and gradually reduced by 1°C every 2d until 22°C was reached. The chicks remained in their respective rooms from 1 d of age throughout the experimental period (1 to 63 d of age). Birds were provided a 3-phase feeding program (1 to 21 d, 12.10MJ AME/kg, 19.81 crude protein for starter; 22 to 42 d, 12.40MJ AME/kg, 19.01 crude protein for grower; 43 to 63 d, 12.90MJ AME/kg, 16.09 crude protein for finisher). Feeds were formulated to meet or exceed agricultural industry standard nutrient recommendations (NY/T33-2004, China). Crumbles feed was provided to the starter, and whole pellets were provided as subsequent diets. Broilers had free access to feed and water (each cage contained two nipple drinkers, bell-type drinkers were used before 3 wk of age) during the experiment. Electric exhaust fans were used to provide housing ventilation. Identical conditions except lighting schedule were provided for the 4 rooms. All chicks were vaccinated for Marek’s disease at the hatchery, Newcastle disease at 8 and 22 d, and infectious bursal disease at 15 and 28 d of age.

Measurements

Performance

Feed consumption was recorded daily on a per-cage basis. The residual feed was collected once a day before the morning feeding. Body weight of birds was measured in replicate every week. Average daily body weight gain, average daily feed intake and feed/gain from 1 to 21 d, 22 to 42 d and 43 to 63 d were calculated. The incidence of mortality was recorded daily.

Anti-stress ability

At 21, 42 and 63 d, blood samples from 8 randomly-selected chickens in each group (one chick from each cage) were taken via a wing vein, and about 5uL of blood was collected immediately to be smeared on to each of three glass slides. The smears were stained using May-Grunwald, Giemsa stains (Evrim et al., 2017). One hundred leucocytes, including heterophils, lymphocytes, monocytes, basophilsand eosinophils, were counted on each slide and the H/L ratio was calculated by dividing the number of heterophils by that of lymphocytes. Three slides were counted and the mean H/L ratio was calculated for each bird. Other blood samples were collected into an anticoagulant-free tube, centrifuged at 3000×g for 10 min to obtain plasma and, stored at -20ºC until analysis for other anti-stress and immune parameters. Serum total superoxide dismutase (T-SOD), glutathione peroxides (GSH-PX), total antioxidant capacity (T-AOC), and malonaldehyde (MDA) were measured by using colorimetric assay kits according to manufacturer’s instruction (Nanjing Jiancheng Bioengineering Institute, Nanjing, China).

Immune function assay

Peripheral blood T-lymphocytes were separated by density-gradient centrifugation as described (2000), and T-lymphocyte proliferation was determined using the method by Lin (1999). Peripheral blood T lymphocytes counts were determined by the histochemical demonstration of ANAE on blood films. The lymphocytes with reddish-brown reaction products were considered ANAE positive (Lin,1999). Antibody titers were determined as described by Olanrewaju et al. (2016).

All animal experiments and procedures were performed in compliance with NIH guidelines (NIH Pub. No. 85-23, revised 1996) and were approved by the Animal Care and Use Committee of Gansu Agricultural University, Lanzhou, P.R. China.

Statistical analysis

The data was analyzed by one-way analysis of SPSS 22.0. The main effect is light intensity and the cage was the experimental unit. Significance was designated as p<0.05 with values between p≥0.05 and p<0.10 being described as a trend. Means were compared by Duncan’s multiple-range test when significant difference was detected.

RESULTS

No difference was observed in ADG, ADFI and Feed/Gain (p>0.05, Table 1). Light intensity significantly affected anti-stress ability of chicks (p<0.05, Table 2). Broilers exposed to low light intensity had higher T-AOC and GSH-Px, but lower H/L and MDA as compared with those in broilers under high light intensity. Compared with 20 lx and 80 lx, the treatment of 1 lx increased T-AOC at 21d (p=0.004), GSH-Px at 21d (p=0.009) and 63d (p=0.019), and decreased MDA at 63d (p=0.042). At 42d, T-AOC in 1lx group was higher than that of other groups (p<0.001), GSH-Px in 1lx and 5 lx groups was higher than that in 80lx group (p<0.001). There was a linear effect of light intensity on T-AOC (p=0.002), GSH-Px (p≤0.047) and MDA (p=0.003). T-AOC and GSH-Px increased significantly as light intensity decreased, whereas MDA decreased as light intensity decreased. The H/L in the 1 lx group was the lowest (p≤0.056) and positive linear effect (p≤0.014) of the magnitude of light intensity on the H/L existed at all the three stages.

Table1
Effects of light intensity on growth performance of broilers

Parameters	Light intensity			SEM	p value
	1 lx	5 lx	20 lx	80 lx
1d Body weight(g)	34.71	34.89	34.75	34.75	0.031	0.103
1-21d
ADG*(g)	21.19	20.41	20.56	20.79	0.199	0.560
ADFI*(g)	34.11	33.61	33.43	33.58	0.241	0.791
Feed/Gain	1.54	1.57	1.55	1.56	0.007	0.479
22-42d
ADG *(g)	44.16	43.34	43.93	44.17	0.669	0.972
ADFI*(g)	108.46	106.18	108.65	108.03	0.798	0.701
Feed/Gain	2.34	2.24	2.40	2.34	0.035	0.495
43-63d
ADG*(g)	52.1	50.19	50.27	56.86	1.506	0.369
ADFI*(g)	142.23	147.23	145.5	151.5	1.956	0.420
Feed/Gain	2.93	3.01	3.12	2.78	0.097	0.678

• *ADG: Average daily gain; ADFI: Average daily feed intake.

Table 2
Effects of light intensity on anti-stress ability of broilers

Parameters	Light intensity			SEM	P value
	1 lx	5 lx	20 lx	80 lx
21d
T-AOC*(U/ml)	13.96a	12.76ab	11.94bc	10.62c	0.355	0.004
T-SOD*(U/ml)	183.95	181.03	162.61	169.97	3.267	0.067
GSH-Px*(U/ml)	1159.18a	1119.39ab	1056.33bc	1029.08c	15.923	0.009
MDA*(nmol/ml)	2.54	2.58	2.62	2.68	0.052	0.809
H/L*	0.47c	0.51b	0.51b	0.54a	0.005	<0.001
42d
T-AOC*(U/ml)	17.92a	15.02b	14.76b	14.85b	0.291	<0.001
T-SOD*(U/ml)	178.21	170.76	178.55	169.56	1.696	0.108
GSH-Px*(U/ml)	1191.67a	1198.51a	1119.05ab	1070.83b	16.009	0.006
MDA*(nmol/ml)	1.76	1.87	1.77	1.91	0.043	0.532
H/L*	0.31	0.32	0.32	0.34	0.004	0.056
63d
T-AOC*(U/ml)	16.6	14.99	14.62	16.5	0.396	0.172
T-SOD*(U/ml)	191.09	196.08	189.16	181.39	2.973	0.382
GSH-Px*(U/ml)	1466.28a	1372.31ab	1298.28b	1330.50b	20.869	0.019
MDA*(nmol/ml)	1.77b	1.91ab	1.99a	2.04a	0.037	0.042
H/L*	0.28b	0.28b	0.30ab	0.32a	0.005	0.006

• *T-AOC:Total antioxidant capacity; T-SOD:Total superoxide dismutase; GSH-Px:Glutathioneperoxidase; MDA:Malonaldehyde; H/L:Heterophil/lymphocyte ratio.
• ^a
  ^,b,cMeans with different superscripts within the same line differ significantly (p<0.05).
• ¹
  Linear effect in light intensity (T-AOC at 21 d and 42 d, p=0.002; MDA at 63 d, p=0.003; GSH-Px at 21 d, p=0.001; 42 d, p=0.019 and 63 d, p=0.047; H/L at 21 d, p<0.001; 42 d, p=0.014; and 63 d, p=0.002).

Immune functions of broilers varied significantly with light intensity (p<0.05, Table 3). ANAE⁺ (p≤0.044) and antibody titer (p≤0.065) in 1 lx were the highest. Other than antibody titer at 21 d, there were linear effects for ANAE⁺ (p≤0.044) and antibody titer at three stages (p≤0.021), which decreased as light intensity increased.

Table 3
Effects of light intensity on immune function of broilers

Parameters	Light intensity			SEM	p value
	1 lx	5 lx	20 lx	80 lx
21d
ANAE+*(%)	35.09a	33.98a	34.05a	32.51b	0.246	0.001
Antibody titer(log2)	6.22a	5.75a	5.81a	4.88b	0.148	0.006
42d
ANAE+*(%)	43.76a	42.14c	42.97b	41.38d	0.180	<0.001
Antibody titer(log2)	5.63	4.88	4.69	4.63	0.151	0.065
63d
ANAE+*(%)	49.24a	48.17ab	48.43ab	46.90b	0.303	0.044
Antibody titer(log2)	4.59a	4.41ab	3.91b	3.91b	0.099	0.015

• *ANAE⁺: a-Naphthylacetate esterase.
• ^a
  ^,b,c,dMeans with different superscripts within the same line differ significantly (p<0.05).
• ¹
  Linear effect in light intensity (ANAE+ at 21 d, P =0.004; 42 d, p=0.001 and 63 d, P =0.021; Antibody titer at 21 d, p=0.011; 63 d, p=0.007).

DISCUSSION

In this experiment, no significant difference in ADG might be due to the similar ADFI in four groups and resulted in the similar Feed/Gain. This result indicated that there was no effect of the four light intensities on broiler’s performance, with all broilers adapting equally. This result is consistent with several studies in which the light intensity ranged from 1 to 150 lx[(Blatchford et al., 2009; Ahmad et al., 2011; Olanrewaju et al., 2014a,b, 2016; Pan et al., 2014; Evrim et al., 2017). In contrast, improved BW and Feed/Gain of birds were found when the light intensities was low (Lien et al., 2008; Blatchford et al., 2012). The causes of the higher body weight were thought to be lower activity of birds when they were kept under lower light intensities.

Light intensity had no significant effect on mortality in this experiment, which is in agreement with other reports (Deep et al., 2010, Olanrewaju et al., 2014 a, b, 2016; Evrim et al., 2017).

The H/L is a sensitive indicator of stress. Increased H/L ratios existed in chickens when exposed to environmental stressors (Evrim et al., 2017). The low, optimum and high level of stress can be characterized by a H/Lratio of 0.2, 0.5 and 0.8, respectively (Siegel & Gross, 2000). Strong light is considered a stress factor in poultry production. In this study, the highest H/L ratio (0.54) was obtained for broilers in 80lx group at 21d, whereas the lowest H/L ratio (0.28) occurred in 1 and 5lx groups. These results suggested that broilers under low light intensity had a low level of stress and younger chickens were more sensitive to light intensity. Whereas, Fidan et al. (2015) and Evrim et al. (2017) reported that light intensity did not affect H/L ratios.

SOD, GSH-Px and T-AOC are indicators for assessing oxidative stress status (Wang et al., 2008). Malondialdehyde (MDA) is an end-product of the radical-initiated oxidative decomposition of polyunsaturated fatty acids, and is therefore frequently used as a biomarker of oxidative stress (Grune & Berger, 2007). In the present study, lower MDA and higher SOD, T-AOC and GSH-Px levels under low light intensity suggested that low light intensity may help to maintain the balance of oxidant-antioxidant status and may enhance the ROS scavenging by elevating the concentration of SOD, T-AOC and GSH-Px. To protect cells from the damage caused by free radicals and related reactants, organisms have evolved several defense mechanisms to rapidly and efficiently remove ROS from the intracellular environment. When the equilibrium between free radicals (oxidants) and antioxidant defense systems is disrupted in favor of oxidants, oxidative stress then occurs (Rodriguez et al., 2004). Yadav et al. (2014), reported that low light intensity didn’t enhance SOD activity but decreased MDA. Whereas, Ali et al. (2005), reported that high light intensity increased SOD activity and MDA.

Enhanced ANAE⁺ percentage and antibody titer in this experiment showed that low light intensity improved the cellular and humoral immune responses of yellow feathered broilers. This could be due either to increased melatonin (Abbas et al., 2007), or activation of peripheral T and B lymphocyte proliferation and energized antibody production (Abbas et al., 2008). Melatonin can enhance peripheral blood and splenic lymphocyte proliferation, therefore accelerating development of cellular and humoral immune responses (Moore et al., 2000). While Blatchford et al. (2009) and Olanrewaju et al. (2014 a, b; 2016) found no difference in immune parameters in broilers reared under different light intensities.

In conclusion, low light intensity can improve anti-stress ability and immune function without significant effects on growth performance of the yellow feathered broilers, which is therefore more appropriate for keeping the chicken’s health and improving the efficiency of energy usage.

ACKNOWLEDGMENTS

This project was supported by a grant from the Ministry of Science and Technology of China (CARS-42). We also deeply thank Professor Dongmin Liu for his valuable help.

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Publication Dates

• Publication in this collection
  Jan-Mar 2018

History

• Received
  05 May 2017
• Accepted
  26 Sept 2017