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Journal of Animal Science logoLink to Journal of Animal Science
. 2022 Nov 26;101:skac389. doi: 10.1093/jas/skac389

Effects of light color and intensity on discrimination of red objects in broilers

Chenghao Pan 1,2, Shouyi Wang 3,4, Pengguang He 5,6, Khawar Hayat 7,8, Hao Jin 9,10, Leshang Bai 11,12, Yuchen Hu 13,14, Jinming Pan 15,16,✉
PMCID: PMC9847463  PMID: 36434786

Abstract

Poultry are sensitive to red objects, such as comb and blood on the body surface, likely inducing injurious pecking in flocks. Light is an important factor that affects the pecking behavior of poultry. A wooden box was built to investigate the effects of Light Emitting Diode (LED) light color (warm white and cold white) and intensity (5 and 50 lux) of background light on the discrimination of red objects in broilers. A piece of red photographic paper (Paper 1) was used to simulate a red object and paired with another piece of paper (Paper 2 to 8) with a different color. Bigger number of the paired paper indicated greater color difference. The experiment consisted of three phases: adaptation, training, and test. In the adaptation phase, birds were selected for the adaptation to reduce the stress from the box. In the training phase, birds were trained to discriminate and peck at Paper 1 when paired with Paper 8 under one type of background light. Twenty-three birds were tested when the paired paper was changed from Paper 7 to 2. Each pair of paper included 12 trials for every bird, and response time to peck and proportion of choices of Paper 1 in the last 10 trials were collected. The results showed that broilers tested under 5 lux light had longer response times than broilers tested under 50 lux light (P < 0.05). When Paper 1 was paired with paper 7, broilers tested under warm white light had lower proportion of choices of Paper 1 than those tested under cold white light (P < 0.05). Color difference had a significant effect on response time of broilers (P < 0.05). Moreover, the proportion of choices of Paper 1 decreased to 50% (chance-level performance) when color of the paired paper was gradually similar to Paper 1. Conclusively, rearing broilers in warm white rather than cold white light with appropriate light intensity should be recommended to reduce damaging pecking behavior in broiler production.

Keywords: broiler, light color, light intensity, pecking behavior, red object

Light color and intensity will affect the discrimination of red objects in broiler.

Introduction

Severe feather pecking is a welfare problem in the modern poultry industry. For rearing laying hens and broiler chickens, there are many factors, such as management and housing (Jung and Knierim, 2018; Cronin and Glatz, 2020), light sources (Kristensen et al., 2007; Spindler et al., 2020), genetic strain (van der Eijk et al., 2018; Falker-Gieske et al., 2022), litter and perch type (Tahamtani et al., 2016; Skanberg et al., 2021), age and gender (Iqbal et al., 2020; Rieke et al., 2021), affecting feather pecking. Light color manipulation affects the behavior and welfare of poultry (Soliman and El-Sabrout, 2020; Oke et al., 2021). Broilers showed less feather pecking behavior in warm white (reddish) light than in cold white (bluish) light (Kristensen et al., 2007). Hens treated with red light showed a lower frequency of severe feather pecking than those treated with white, yellow-orange, or blue-green light (Shi et al., 2019). In addition, a few studies have shown that higher light intensity produces more feather damage in laying hens (Kjaer and Vestergaard, 1999; Dixon, 2008). Therefore, lower light intensity should be considered to control damaging feather pecking (Kjaer and Vestergaard, 1999; Jung and Knierim, 2018).

Although there are a number of researches focused on behavioral needs and welfare of poultry, the researches regarding the effects of environment parameters on visual cognition of poultry are limited. When the environment parameters change, sensory systems adapt plastically to the new surroundings, leading to sensory-driven behaviors (Cole et al., 2019). For example, the visual environment will affect responses to color in domestic chicks (Miklosi et al., 2002). Besides green band, poultry are sensitive to red parts (630 nm) of the spectrum due to their well-developed visual system which contains four types of cone photoreceptors adapted for color discrimination (Prescott and Wathes, 1999; Barber et al., 2006; Kram et al., 2010; Makarova et al., 2019). Thus, light color plays an important role in the visual perception behavior of poultry. Furthermore, Light Emitting Diode (LED) lighting, whose color and intensity can be precisely controlled, enables light to be used for specific physiological and behavioral functions in animals (Pattison et al., 2018). In cases of inappropriate rearing lighting, cannibalistic behaviors followed by consumption of blood and tissues of conspecifics, may quickly spread to the whole block (Michel et al., 2022). Researchers investigated the effects of red contact lenses, which were designed to restrict birds’ vision, on production performance in laying hens (Adams, 1992; Gvaryahu et al., 1997). These devices exposed chickens to red light to decrease their aggressive pecking. However, whether the light environment affects the pecking behavior in poultry by conspicuousness of blood on the body surface or discrimination ability of red objects remains unclear.

This study was designed to investigate the effects of light color and intensity of background light on the discrimination of red objects in broilers and find a suitable LED light environment that could reduce damaging pecking behavior in broiler production.

Materials and Methods

The research protocol has been approved by the Laboratory Animal Welfare and Ethics Committee of Zhejiang University (ZJU20210314).

Bird management

On day 1, a total of 35 female yellow-feathered broilers (“Sanhuang”; age 49 d) were purchased from Jiaxing Lihua Livestock Co., Ltd. Feather pecking is a common behavior of this medium-growing broiler strain. All birds were randomly distributed into 5 galvanized wire pens (1 m long × 1 m wide) whose bottoms were covered with mesh. They had ad libitum access to water in the pens. The relative humidity in the pens was maintained at 60% ± 5%. These birds were reared under LED pure white light with a 12:12 light/dark cycle (light on from 08:00 to 20:00) in the experiment.

Apparatus

A wooden box (Figure 1), whose internal space was a 125,000 cm3 cube, was built to conduct this behavioral research. It had an opening at the top, from which broilers were put into the box. Five surfaces of the internal space, including the ground, were covered with black polyvinyl chloride backdrops. A feeder (16 × 10 × 6 cm, length × width × height) was pushed into and out the box through the hole in wall which was located under the acrylic frames. Two transparent acrylic frames, whose bottoms were both 7 cm above the hole, were fixed symmetrically on the inner wall of the box. Each frame had a slot at the top to place a piece of pure-color photographic paper (10 × 10 cm) at a time. As shown in Figure 2, there were eight sets of RGB (red, green, and blue) values for photographic paper, which were called from Paper 1 to 8 and printed by EPSON SureLab D700. Moreover, the colors from Paper 1 to 8 changed from red to yellow.

Figure 1.

Figure 1.

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Schematic diagram of the wooden box. 1) The wooden box; 2) light source; 3) a piece of black cardboard added from day 25; 4) a pair of photographic paper; 5) two transparent acrylic frames; 6) feeder used for feed delivery.

Figure 2.

Figure 2.

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Eight pieces of photographic paper used in the experiment. Paper 1 to Paper 8 are shown from the first row of the left to the second row of the right, and their RGB values are (255, 0, 0), (255, 36, 0), (255, 73, 0), (255, 109, 0), (255, 146, 0), (255, 182, 0), (255, 219, 0) and (255, 255, 0), respectively.

Lighting treatments

A 2 × 2 factorial design was used to evaluate the impact of two LED light colors (cold white and warm white) and two levels of light intensity (5 lux and 50 lux) on the discrimination of red objects in broilers. Although lux represents illuminance not intensity in optical researches, we still use lux to indicate light intensity in this study as many researches in broiler production do (Deep et al., 2012; Yang et al., 2018). A spectrally tunable light source (LEDCube, Thousand Lights Lighting Ltd., Changzhou, China), designed to create lighting environments with different color and luminance requirements, was disposed directly above the opening of the box to provide background light. During the experiment, the room’s lights were turned off to eliminate interference from other light sources. A creamy-white acrylic board (30 × 30 cm) was stuck to the luminous surface of LEDCube to soften the light. Spectral outputs of four types of background light (Figure 3) were measured at the center of the horizontal plane at a height of 18 cm above the box ground and measured with a spectrometer (FS, Thousand Lights Lighting Ltd., Changzhou, China). The height of the measurement point, which simulated the broilers’ eyes height at foraging, was equal to that of the center of each acrylic frame.

Figure 3.

Figure 3.

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Spectral power distribution of background light. CCT of W-L, W-H, C-L, and C-H are 2665 K, 2731 K, 6490 K, and 6520 K, respectively.

Adaptation phase

The behavioral experiment consisted of three phases: adaptation, training, and test. On trial days after day 5, all birds were fed in the pens about 90% of their daily dose according to the nutrient requirement of yellow chickens. In addition, feed was removed from the pens at 19:30 and supplied after all birds finished all trials in one day. Remove of feed for nearly a night before birds were put into the box ensured that birds would be motivated to perform the experiment. Water was supplied only in the pens.

On day 6, birds were selected for the adaptation to reduce the stress from the wooden box. A piece of Paper 1 was placed in the left acrylic frame and a piece of Paper 8 was placed in the right. The box was illuminated from above by LED white light (CCT, correlated color temperature = 4,771 K), used for adaptation with a light intensity of 58 lux. All 35 female birds were put into the box in turn. Every bird was firstly given 3 to 6 min to acclimatize to the new environment alone. Then the feeder with enough feed was pushed into the box. When a bird did not learn to search for feed in 4 sessions of 6 min, it was excluded from the adaptation phase. What is more, birds which could not learn to search for feed in a session would be put back to the pen between sessions. Finally, there were 28 birds selected after excluding seven birds in a day. They were randomly divided into four groups and reared in four pens with seven birds in each.

Training phase

In the training phase from day 7, birds were trained to associate feed reward with the choice of Paper 1. The box was illuminated by one kind of background light (Figure 3) when birds in one pen were put into the box and trained alone. According to the background light, four groups were called Group W-L, W-H, C-L, and C-H, respectively (W-L = warm white light with 5 lux; W-H = warm white light with 50 lux; C-L = cold white light with 5 lux; C-H = cold white light with 50 lux). On day 7 to 10, a pair of Paper 1 and 8 were placed in the acrylic frames, and some feed was pasted to the surface of the acrylic frame placed with Paper 1, so the bird could see the feed and Paper 1 at the same time. To stimulate birds to choose Paper 1, pecking at the frame placed with Paper 1 or the pasted feed resulted in about 3 s feed reward delivered by the feeder. Pecking at the frame placed with Paper 8, or other positions in the box, or other positions first and then Paper 1, produced no reward. Every bird was trained for up to 6 sessions of 15 minutes. A bird was thought to have learned the discrimination of Paper 1 in a trial if it successfully chose to peck the frame placed with Paper 1 and got feed from the feeder. Then it was selected for the next training phase. If a bird chose to peck the frame placed with Paper 1 but refused to eat feed or pecked other positions in the box, it was excluded from the training phase. Five birds were excluded from the first training phase. There were 5, 6, 6, and 6 birds remained in Group W-L, W-H, C-L, and C-H, respectively.

From day 11 to 15, a piece of Paper 1 was placed in the left or right frame manually to which feed was pasted, and a piece of Paper 8 was placed in the opposite frame. All birds were trained to choose the Paper 1 in at least 10 consecutive trials per day. During consecutive trials in the training and test phase, every bird stayed in the box until they completed trials in one day. From day 16 to 21, the feed pasted to the surface of left or right frame was removed and then all birds were trained to choose Paper 1 in at least 5 consecutive trials per day. From day 22 to 27, a pair of Paper 1 and Paper 8 was randomly placed in two frames according to the software generated random position. Furthermore, the positions of Paper 1 were changed 4 to 6 times in 10 consecutive trials. All birds had learned to choose Paper 1 in 10 consecutive trials per day. From day 25, a piece of black cardboard (40 cm × 40 cm), which could block the birds’ view, was added and placed in the vertical plane about 15 cm away from the plane fixed with two acrylic frames before every trial. When the cardboard was raised away from the box quickly, the bird could see the pair of paper and chose to peck at Paper 1. The cardboard was reset when the bird got its feed reward and the feeder was pushed out the box. All birds successfully learned the discrimination in 10 consecutive trials from day 25 to 27. It took 21 days for 23 birds to finish the training phase.

Test phase

In the three-day test phase, birds were numbered and required to discriminate Paper 1 from another piece of paper, which was changed from Paper 7 to 2. Each pair of paper included 12 trials, with two pairs of paper tested per bird per day. Every bird received totally 24 consecutive trials per day. A trial from the raise of the cardboard to reset lasted about 3 to 10 s. All trials were recorded on video (TL-IPC55A, TP-LINK). The procedures of every trial on test days and day 27 were identical. The first 2 of 12 trials were used for broilers to adapt to a new environment with a different pair of paper. In the last 10 of 12 trials, whether a bird choose to peck at the frame placed with Paper 1 and the response times from removal of cardboard to pecking were recorded.

Statistical analysis

For every bird in 10 trials of the test phase, the response times were averaged and the proportion of choices of Paper 1 was calculated before analysis by using SPSS software (Version 19, SPSS Inc., Chicago, IL). As for response times, every bird was treated as a statistical unit. A linear mixed model was performed to analyze the effects of light color, light intensity, and color difference on discrimination of Paper 1 in broilers. Fixed effects included three factors and their interactions, while the bird was considered as a random effect. In addition, when broilers in a group were tested with a pair of paper, response times of choices of Paper 1 (right) and the paired paper (wrong) in 10 trials were respectively averaged for every bird and then performed with the paired t test to analyze the effect of accuracy (whether peck at Paper 1) on response time. If a bird chose all Paper 1 in 10 trials, its data were excluded from accuracy analysis. As for the proportion of choices, the Friedman test was performed to analyze the effect of color difference on discrimination. Results from six pairs of paper were respectively performed with the Scheirer-Ray-Hare test (two-way nonparametric ANOVA) in R software (Version 4.1.3) through package ‘rcompanion’ to analyze the effects of light color and intensity. P < 0.05 were considered statistically significant.

Results

Response time

As shown in Table 1, means of the response times were about 2 s. Broilers tested under 5 lux light had longer response times as compared to those tested under 50 lux light (P < 0.05). The color difference significantly affected the response times (P < 0.05). However, the color difference was not negatively or positively correlated with the response times. There was no difference in the light colors (P = 0.38) and all interactions (P > 0.05). As shown in Table 2, although broilers tested with Paper 2 under warm white light with 5 lux and Paper 4 under cold white light with 50 lux had different averaged response times (P < 0.05) when they choose Paper 1 or the paired paper, no relationship was found between the accuracy and the response times in other treatments (P > 0.05).

Table 1.

Effects of light color, light intensity, and color difference on response times of broilers in the test phase

Source of variation Treatment Mean, s Lower bound, 95% Upper bound, 95% P-value
Light color Warm white 2.02 1.89 2.14 0.38
Cold white 2.09 1.97 2.21
Light intensity 5 lux 2.23a 2.10 2.35 <0.05
50 lux 1.88b 1.76 2.00
Color difference1 Paper 7 2.21a 2.08 2.34 <0.05
Paper 6 2.00abc 1.87 2.13
Paper 5 2.16a 2.03 2.30
Paper 4 2.15ab 2.02 2.28
Paper 3 1.90c 1.77 2.03
Paper 2 1.91bc 1.78 2.05
Color × intensity 0.41
Color × difference 0.24
Intensity × difference 0.38
Three-way interaction 0.44
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1Broilers (n = 23) were tested in 12 trials for every pair of paper, and results of the last 10 trials were analyzed. There were 5, 6, 6, and 6 birds in Group W-L, W-H, C-L, and C-H, respectively. Bigger number of the paper paired with Paper 1 indicates greater color difference.

a–cMeans within a column and effects that lack common superscripts differ significantly (linear mixed model with Sidak correction for multiple comparisons, P < 0.05).

Table 2.

Response times of choices of Paper 1 and the paired paper in tested broilers

Source of variation Response time, s1
Light color Light intensity Color difference Right Wrong
Warm 5 lux Paper 7 2.42 2.24
Paper 6 2.03 1.99
Paper 5 2.27 1.92
Paper 4 2.36 2.18
Paper 3 2.10 1.90
Paper 2 1.85b 2.15a
50 lux Paper 72 2.14 2.02
Paper 63 1.98 1.91
Paper 5 1.90 2.06
Paper 4 1.95 1.82
Paper 3 1.70 1.62
Paper 2 1.65 1.69
Cold 5 lux Paper 7 1.94 1.92
Paper 6 2.27 2.01
Paper 5 2.42 2.53
Paper 4 2.69 2.45
Paper 3 2.21 2.13
Paper 2 2.33 1.90
50 lux Paper 7 2.15 1.88
Paper 6 1.85 1.55
Paper 5 1.98 2.14
Paper 4 1.94a 1.66b
Paper 34 1.78 1.72
Paper 2 1.84 1.87
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1Response times were recorded in the last 10 of 12 trials for tested broilers (n = 23).

2–4Means do not meet the assumption of normality but are still analyzed by the paired t test.

a, bMeans within a row with different superscripts differ significantly (P < 0.05).

Proportion of choices

Table 3 shows that broilers tested with a lower color difference had a lower proportion of choices of Paper 1 (P < 0.05). When broilers were tested with Paper 3 or Paper 2, the proportion of choices of Paper 1 was close to 50%. In addition, differences in light color, light intensity, and interactions were not observed (P > 0.05), except broilers tested under warm white light had a lower proportion of choices than those tested under cold white light (P < 0.05) when tested with paper 7.

Table 3.

Effects of light color, light intensity, and color difference on proportion of choices of Paper 1 in tested broilers

Color difference Median, s1 Lower quartiles Upper quartiles Scheirer–Ray–Hare test Light color Light intensity Color × intensity
Paper 7 0.90a 0.90 1.00 H 3.921 1.154 0.243
P <0.05 0.283 0.622
Paper 6 0.80ab 0.70 0.80 H 0.839 0.066 0.438
P 0.360 0.798 0.508
Paper 5 0.70bc 0.50 0.70 H 2.014 0.983 0.388
P 0.156 0.322 0.533
Paper 4 0.60c 0.50 0.60 H 2.405 0.169 0.584
P 0.121 0.681 0.445
Paper 3 0.50c 0.40 0.60 H 0.528 0.002 0.003
P 0.818 0.966 0.958
Paper 2 0.50c 0.50 0.60 H 0.030 0.445 0.033
P 0.863 0.505 0.857
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1Proportion of choices of Paper 1 in the last 10 of 12 trials were analyzed (n = 23).

a–cMedians within a column with different superscripts differ significantly (Friedman test with Bonferroni correction for multiple comparisons, P < 0.05).

Discussion

Antipecking devices are applied to chicken eyes to restrict their vision to reduce damaging pecking. Li et al. (2020) suggested that an antipecking device, like a red eye mask, should be fastened to the beak of bird to block the view ahead to reduce plumage damage. This study was investigated to find whether the pecking behavior in broilers would be affected by conspicuousness of blood on the body surface or discrimination ability of red objects through light. Factors included in the light management of poultry are source, intensity, duration, uniformity, and color (Çapar Akyüz and Onbaşilar, 2018). The previous study showed that higher light intensity could increase the pecking behavior of broilers in an open field test (Mohamed et al., 2020). In this study, no significant differences were found in the proportion of choices of red paper by using different light intensities. This may occur because higher light intensity could not effectively improve the discrimination ability of red objects when birds were using photopic vision. However, broilers tested under 5 lux light had longer response times than those tested under 50 lux light. Previous studies confirmed that avian activity increased with light intensity (Deep et al., 2012; de Jong et al., 2016; Fidan et al., 2017). We could speculate that increased activity reflected impulsivity which induced shorter response times. Similar results were obtained by Chew et al. (2021) who reported that pullets reared under 5 lux had lower jumping frequency than under 30 lux while the accuracy was not affected. There is a debate regarding the optimum light intensity to be used in broiler production (Deep et al., 2012). Deep et al. (2013) recommended 5 lux as minimum light intensity. Compared with 10, 20, and 40 lux, the 1 lux light environment negatively affected broiler welfare by increased ulcerative footpad lesions (Deep et al., 2010). Because of damaging pecking under high light intensity and reduced welfare under low intensity, broilers should be reared in the environment with suitable light intensity. What is more, the European Union has recommended an intensity of at least 20 lux for broiler production (European Union, 2007).

Optimal light color is required for poultry to display their normal behavior (Oke et al., 2021). Generally, behavioral parameters of broilers were significantly affected by light color, whereas welfare parameters were slightly affected (Soliman and El-Sabrout, 2020). In this study, there was no difference in light color on proportion of choices of Paper 1, except that broilers tested under warm white light had a lower proportion of choices of Paper 1 than those tested under cold white light when Paper 1 was paired with paper 7. Moreover, although no significant difference was found for light color when Paper 1 was paired with Paper 6 to 4, the means of four groups showed that Group C-L and C-H entirely had a greater proportion of choices of Paper 1 than Group W-L and W-H for three pairs of paper respectively (Group C-L and W-L: 0.80 > 0.74, 0.67 > 0.56, and 0.58 > 0.56; Group C-H and W-H: 0.77 > 0.75, 0.68 > 0.63, and 0.62 > 0.55). It seemed that warm white light contained more red light than cold white light, which affected the discrimination of red paper. This finding was similar to Kristensen et al. (2007), who observed less feather pecking behavior in broilers when reared under warm white light than under cold white light. Shi et al. (2019) founded that hens in red light had a lower frequency of severe feather pecking than in white, yellow-orange, and blue-green light. On contrary, Hesham et al. (2018) found that broilers reared under red light showed more feather pecking than under yellow, green, and blue light. Although more feather pecking was observed, light colors had no effect on plumage condition. In addition, a few studies have shown that light color had no effect on welfare parameters (Sultana et al., 2020; Oke et al., 2021). In a word, the light color can adjust the ability of broilers to discriminate red objects. However, the effect of light color on damaging pecking depends on broilers’ management conditions. Furthermore, considering nonvisual functions of light, whether unsuitable light environment increases the damaging pecking behavior of broiler chickens by improving visual discrimination ability of red objects needs further researches to remove the physiological effects from light.

The color difference had a significant effect on proportion of choices and response time. Although the test phase could be considered another training phase that might improve discrimination ability of Paper 1 in broilers, it was expected that the proportion of choices decreased to chance-level performance when color of the paired paper was gradually similar to Paper 1. Broilers had the longest response time when Paper 1 was paired with Paper 7; broilers had the shortest response time when Paper 1 was paired with Paper 3. The response times of different color differences could be divided into two categories, Paper 7 to 4 and Paper 3 to 2. When the paired paper was Paper 7 to Paper 4, broilers mainly had longer response times than those tested with Paper 3 to 2. We proposed that broilers no longer spent enough time thinking about the choices of Paper 1 and just randomly chose a piece of paper when they could not discriminate Paper 1. Additionally, although the accuracy would affect the response times when broilers of Group W-L were tested with Paper 2 or broilers of Group C-H were tested with Paper 4, there was no difference between the accuracy and the response times in other conditions. We speculated that effects of the accuracy on the response times were accidental and the accuracy would not be improved if broilers spent more time thinking about the choices of Paper 1. Therefore, no clear relationship between the accuracy of choices and the response times was found.

In conclusion, light color had an effect on the proportion of choices of red objects and light intensity showed effects on response time. Considering response time and proportion of choices of red objects, warm white rather than cold white light and lower light intensity at an appropriate level should be recommended to reduce damaging pecking behavior in broiler production.

Acknowledgments

This research was supported by the National Natural Science Foundation of China (31972609) and the China Agriculture Research System (CARS-40).

Glossary

Abbreviations

LED

Light Emitting Diode

RGB

red, green, and blue values for color space

CCT

correlated color temperature

C-L

cold white light with low intensity of 5 lux

C-H

cold white light with high intensity of 50 lux

W-L

warm white light with low intensity of 5 lux

W-H

warm white light with high intensity of 50 lux

Contributor Information

Chenghao Pan, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Shouyi Wang, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Pengguang He, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Khawar Hayat, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Hao Jin, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Leshang Bai, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Yuchen Hu, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Jinming Pan, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Intelligent Equipment and Robotics for Agriculture of Zhejiang Province, Hangzhou 310058, China.

Conflict of Interest Statement

The authors declare no conflicts of interest.

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