Effects of abrupt and gradual light/dark switching on growth performance, behavior, villus development, meat characteristics, and immunity of broilers

1 INTRODUCTION

Broilers are considered a significant animal protein source that contributes to the rapidly growing world population. Due to their impact on feed conversion and growth performance, environmental factors are continually scrutinized. Broiler rearing is predominantly carried out in semi or fully environmentally controlled poultry houses. In poultry houses, the temperature, lighting, humidity, and ventilation are necessary for the growth and development of broilers. Lighting is a crucial and critical environmental factor in poultry houses because it influences the growth, development, welfare, and behavior of broilers (Arowolo et al., 2019). In lighting, there are five important factors: the source, color or wavelength, intensity, uniformity, and lighting program (Çapar Akyüz & Onbaşılar, 2019).

In broilers, continuous, intermittent, and fixed lighting programs can be applied. According to the EU Commission Directive (2007/43/EU), there should be a total of 6 hours of darkness, of which at least 4 hours should be continuous. This must be applied within the first 7 days after broilers enter the poultry house and up to 3 days before the planned slaughter time. It is also stated that the light intensity at the eye level of broilers should be at least 20 lx. The ROSS guide recommends providing 23 h of light and 1 h of darkness during the first 7 days of broiler rearing, followed by 4–6 h of darkness after the seventh day. It is suggested that, while complying with regulations, the lighting intensity should be 30–40 lx for the first 7 days (Aviagen, 2019).

In a study by Feuerborn (2022) on quails, they found lower corticosterone levels when gradually transitioning from light to darkness. Researchers simulated the sunset by gradually turning off a light in the environment each time and vice versa for sunrise. However, this study did not examine any characteristics related to performance and behavior. Van Der Pol et al. (2015) applied a transition from full brightness to complete darkness within 3 min in broilers. They determined that the relative asymmetry indicating bone development disorders was lower in the lighting program with transitions between light and dark periods. Nelson et al. (2020) examined short-term (1 min) twilight application with intermittent lighting and long-term (30 min) twilight application with increased lighting duration between light and dark periods in broiler house. They found higher body weight and lower footpad and hock burn scores in the group with intermittent lighting and short-term twilight applied on the 45th day of fattening. Also, they reported that plasma corticosterone and heterophil/lymphocyte ratio of broilers in the group with increased lighting duration and long twilight between light and dark periods were lower.

As in all animal rearing, welfare, metabolic diseases/disorders, and productivity are important issues emphasized in intensive broiler rearing. In natural conditions, there is sunset and sunrise, allowing broilers to adapt to the light and dark periods. In intensive broiler rearing, however, these periods are suddenly initiated without a gradual transition between light and dark periods. It is thought that this situation may affect the physiological functions of broilers. When the studies conducted are examined, the number of studies in which the transition is made by reducing the light intensity between light and dark periods is very limited. In the project, the aim is to determine the effect of abrupt and gradual light/dark switching in broiler rearing on performance, behavior, meat characteristics, and immunity of broilers.

2 MATERIALS AND METHODS

2.1 Animals and experimental design

In the study, 270 daily male broiler chicks (ROSS-308) were used as animal material. The study consisted of three groups based on whether the transitions between light and dark periods during the day were abrupt or gradual (by changing light intensity). Daylight-colored LED bulbs (6400 K) were used in all groups. Abrupt transition group does not include a familiarization period between light and dark periods during the day. In the second group, light intensity between light–dark and dark–light periods during the day was gradually reduced within 30 min using a dimmer and increased within 30 min. In the third group, light intensity was gradually reduced within 1 h and increased within 1 h (Figure 1). For this purpose, the broiler house was divided into three room to prevent light transmission. In each room, 10 pens measuring 90 × 80 cm were created. Nine chicks were placed in each pen. Each group consisted of 10 repetitions. For the first 3 weeks of the study, chicks were fed with feed containing 23.23% CP and 3010 kcal/kg ME, and then they were fed with feed containing 19.63% CP and 3196 kcal/kg ME. During days 0–7 of the experiment, plastic chick feeders and chick drinkers were used, and from days 8 to 42, hanging feeders and nipple drinkers were used. After providing a temperature of 32 ± 1°C at the chick level for the first 3 days, the temperature was gradually reduced until the age of 21 days and then maintained at a constant 22 ± 1°C. The experiment lasted for 6 weeks.

3 RESULTS

The study determined that the abrupt or gradual transitions between light and dark periods in the poultry house did not result in a significant difference in body weight and weight gain of broilers up to 6 weeks of age (Table 2). The only significant difference among groups in terms of feed consumption and feed utilization was found in the second week of the fattening period (P < 0.01). During the 6 weeks, in groups where abrupt, 30-min, and 1-h transitions between light and dark periods were implemented, the mortality rates were 3.3%, 2.2%, and 3.3%, respectively. However, the difference among groups was not statistically significant (P > 0.05). At the end of the fattening period, breast burns were not observed in any of the three groups. Burns on the footpad and hock are presented in Table 3. It was observed that the broilers raised in the group where abrupt transitions were applied exhibited more drinking and walking behaviors and less sitting and sleeping behaviors compared to broilers in other lighting groups (P < 0.05, Tables 4, 5, and 6, Figures 2 and 3).

When examining the changes over time, it was observed that the feeding behavior of broilers was highest in the second and third weeks of fattening (P < 0.05). Broilers exhibited more pecking at equipment behavior (P < 0.001) up to the fifth week, more pecking at each other behavior (P < 0.001) in the first 3 weeks, and more feather preening behavior (P < 0.001) at the fourth week of fattening. The frequency of sitting behavior increased with the progression of feeding in all behaviors (P < 0.001).

At the end of the fattening period, the IgG levels of broilers are presented in Table 7. No significant difference was found among groups in terms of carcass and carcass parts. The highest water-holding capacity was calculated in the thigh meat obtained from broilers raised in the group where a 1-h transition was applied between light and dark periods (P < 0.05, Table 8). In the group where transition was applied between light and dark periods, the protein and fat ratios were higher, and the water ratio was lower in thigh meat obtained from broilers (P < 0.05). In broilers reared in the group where a 1-h transition was applied between light and dark periods, villus height and crypt depth were found to be higher compared to those reared in the abrupt transition group (P < 0.05, Table 9).

4 DISCUSSION

Lighting is an important environmental factor that ensures the maintenance and synchronization of physiological and behavioral homeostasis in animals. It regulates activities such as feed consumption, nutrient metabolism, body temperature, physiological functions, immune system regulation, and the cycle of sleep–wakefulness (Jiang et al., 2023). Throughout the 6-week fattening period, a gradual transition between light and dark periods, similar to the natural environment, did not result in any differences in body weight, body weight gain, and mortality rates in broilers compared to an abrupt transition. Only during the first 2 weeks, especially in the second week, broilers raised in the group with a gradual transition between light and dark periods consumed more feed. This is attributed to the longer duration of each feeding session by broilers in this group. The absence of a significant difference in the first week may be due to the longer and more intense light applied to the chicks during this week. This may have diminished the impact of the gradual transition between light and dark periods. However, reducing both the duration and intensity of light in the second week of the fattening might have brought out the positive effect of the gradual transition. Yet, the absence of any difference in feed consumption after the second week could be explained by the broilers adapting to the environment and being less affected by sudden changes in the environment. Despite consuming more feed in the second week, the broilers in the group with a gradual transition achieved similar body weight gain to the other group, resulting in lower feed utilization. This might be due to less frequent drinking behavior observed in the group with gradual transition. When observing the behaviors of the broilers in this group, they drank less water and walked less during the day. They exhibited more sitting and sleeping behaviors. In fact, broilers moving less should increase feed utilization by reducing energy expenditure. However, the opposite occurring in the study suggests that broilers drinking less water throughout the day might be the contributing factor. Similarly, Marks (1981) demonstrated in his study that a high water-feed ratio is associated with feed utilization.

The increased occurrence of footpad and hock burns in the group where a 30-min gradual transition was applied to the broilers is attributed to the higher resting and sitting behavior. Their fewer active behaviors created longer contact time with the litter, and this situation increased the formation of burns (Hester, 1994). The most important factor affecting burns is litter quality. The amount of moisture in the litter at the end of the experiment was not determined in this study, but no difference was visually detected among the groups in terms of litter quality. In future studies, it will be important to determine the litter characteristics and the amount of drinking water.

Behavior is a part of the interaction of the broiler with its environment (Onbaşılar, 2022). The frequency of comfort behaviors such as wing flapping and wing–leg stretching is associated with the welfare status (Pichova et al., 2016). Duncan and Mench (1993) suggested that these behaviors can only be expressed when basic needs are met and negative emotional states are eliminated. When the frequencies of various behaviors of the broilers throughout the day were examined, it was determined that broilers in the group where an abrupt transition between light and dark periods was applied drank more water and walked more throughout the day but exhibited more sitting and sleeping behavior. This indicates that the broilers raised in the group with a gradual transition are calmer. No difference was observed between groups in terms of aggressive behaviors. Additionally, behaviors such as relaxation and feather preening, which broilers exhibit when they are happy, did not differ among groups. Alvino (2008) found that even at a light intensity of 1 lx, broilers engaged in active behaviors such as feeding, drinking, and food searching. In a study by Deep et al. (2012), it was reported that light intensity did not affect feeding and drinking behavior. Sherlock et al. (2010) observed a higher tendency for movement in broilers subjected to abrupt light–dark transitions compared to gradual light transitions. Alvino et al. (2009) reported no difference in feeding behavior based on light intensity, but broilers exposed to 200 lx light intensity for a 24-h photoperiod spent more time drinking than those exposed to 5 lx light intensity. During the 6-week fattening period, the highest feeding behavior in broilers was observed in the second and third weeks of the feeding, with no interaction between lighting and fattening period. Equipment pecking behavior decreased from the fifth week, and pecking each other behavior decreased from the fourth week in broilers. Broilers exhibit more pecking behavior in the early weeks to explore and familiarize themselves with the environment (Onbaşılar, 2022). The feather preening behavior in broilers was found to be highest in the fourth and fifth weeks and the lowest level observed in the first week of the fattening. The sitting behavior in broilers increased over time, and an interaction was observed between the lighting group and time. This is due to the feeding and sitting behavior increased more in the group subjected to a 30-minute transition between light and dark periods in the fifth week.

In the study, the higher IgG levels in broilers reared in the group where a gradual transition between light and dark periods was applied indicate better immunity in this group. There is a close relationship between immune and stress responses in broilers, which could be influenced by photo stimulation (Abo Ghanima et al., 2021; Xie et al., 2008; Zamanizad et al., 2019). Abruptly transition decreases the opportunity for sitting and sleeping behavior, thereby increasing fear reaction and physiological stress. So, broilers exposed to abruptly transition have a decrease in IgG level, indicating the high level of physiological stress. The primary role of IgG in the immune system is to neutralize microorganisms and toxins (Çapar Akyüz et al., 2022).

Carcass and carcass parts were not affected by the transition between light and dark periods. The pH level of meat directly affects the color, water holding capacity, tenderness, and shelf life of the meat (Çapar Akyüz & Onbaşılar, 2023). The water-holding capacity of meat also affects the weight of poultry products and, consequently, their economic value. Moreover, the content and distribution of water within muscles can influence the visual appearance, tenderness, and juiciness of meat. The highest water-holding capacity was calculated in the thigh meat obtained from broilers reared in the group with a 1-h transition between light and dark periods. In the study, since protein denaturation and cell membrane breakdown did not occur before the cooking process, only the water between muscle fibers is released. The muscle fiber type can regulate the internal metabolic structure of a muscle and affect metabolism and water-binding properties (Petracci et al., 2017). The thigh meat obtained from broilers reared in the group with a 30-min transition between light and dark periods had a higher fat content compared to the group with an abrupt transition. This could be attributed to the reduced activity of broilers throughout the day, leading to the storage of energy as fat in the thigh region. Novello et al. (2008) reported that the composition of meat could be influenced by rearing conditions.

Crypts, where epithelial cell proliferation occurs, are directly related to villus height, jejunum absorption surface, and crypt depth (Geyra et al., 2001). In the group where a 1-h transition between light and dark periods was applied, it was determined that the broilers had a greater villus width and crypt depth. However, it was found that this difference did not reflect on body weight. Several factors can influence intestinal maturation, among them include stress (Marchini et al., 2011). As a result, the decrease in villus height and crypt depth in broilers exposed to an abrupt transition may be attributed to physiological stress.

As a conclusion, the gradual transition made the broilers calmer, induced more resting behavior, and increased immunity and villus development. In particular, it has been observed that a 1-h gradual transition between light and dark periods is more appropriate than a 30-min transition.

CONFLICT OF INTEREST STATEMENT

Authors declare that they have no conflict of interest.