Lighting Matters, Reduce Aggression & Promote Growth in the Swine Industry

Lighting, often considered a secondary environmental factor in modern industrial pig production systems, exerts a profound and frequently underestimated influence on animal behaviour and physiological state, reducing aggression and promoting growth in the Swine Industry. Its impact extends directly to overall health, welfare, and production efficiency. Historically, decisions regarding lighting in animal housing have often been made based on human convenience or the visual requirements of stockpersons, rather than the intrinsic biological needs of the pigs themselves.

This approach, where the environment’s design is centred on human perception rather than the animal’s biology, can lead to suboptimal conditions that compromise animal well-being and productivity. When lighting is configured primarily for human vision, such as bright, consistent illumination for workers, it may inherently be inappropriate for an animal whose visual system and circadian rhythms are adapted to different light patterns, including periods of dimness for rest or specific light spectrums. This suggests a fundamental misalignment in the design philosophy of many conventional indoor pig facilities, where merely meeting minimum regulatory lux levels (e.g., 40 lux) may not be sufficient. Instead, a deeper understanding and replication of the nuanced photic environment that best supports pig physiology and natural behaviour is required. This implies that what is considered “adequate” lighting from a human perspective might inadvertently be a source of chronic, subtle stress for pigs, potentially leading to unobserved welfare compromises and reduced performance. Therefore, the transition to animal-centric lighting solutions necessitates a significant shift in mindset, moving from simple illumination to biologically informed environmental control.

Optimized lighting presents a unique opportunity to address two significant challenges in swine production: managing aggression and enhancing growth. While some existing literature on the influence of light, particularly in nursery pigs, presents controversial or inconclusive results regarding its direct benefits on feed intake and performance, the potential for strategically optimizing lighting as an accessible and cost-effective method to improve health and performance parameters is considerable. Such advancements could potentially reduce the reliance on antibiotics in swine operations. Moreover, anecdotal evidence suggests that exposure to natural lighting can calm pigs and reduce fighting incidents. Furthermore, correctly configured artificial lighting has improved reproduction, increased sow productivity, and boosted growth rates in young animals.

The Science of Light: How Pigs Perceive and Respond

All living beings, including swine, are profoundly influenced by diurnal cycles and natural sunlight. These inherent light-dark cycles regulate their physiological state and dynamic behavioural patterns. Light serves as a primary “zeitgeber,” or time-giver, effectively synchronizing the endogenous molecular clocks that govern numerous circadian rhythms within the animal’s body. Disruptions to this natural light/dark cycle, particularly the exposure of animals to light at night (LAN), can severely disturb these biological rhythms, leading to widespread physiological consequences due to mechanisms such as melatonin suppression, sympathetic stimulation, and altered circadian clock gene expression. Consequently, maintaining a consistent and appropriate light/dark cycle is imperative for research reproducibility and the overall welfare of the animals.

Hormonal Regulation and Physiological Impact

The impact of light on swine extends deeply into their endocrine system, influencing the secretion and regulation of several key hormones:

• Melatonin: Light information is intricately processed and transduced into a nocturnal melatonin rhythm, frequently called the “darkness hormone.” Melatonin synthesis is naturally elevated during periods of sleep and increased dark hours. Conversely, prolonged light stimulation actively reduces its production. Elevated melatonin levels are associated with a slowdown of metabolism and an increase in body fat content, which can collectively reduce animal productivity.
• Cortisol: Blood glucocorticoid concentrations, such as cortisol, a primary stress hormone, significantly influence light-induced physiological changes. Research indicates that pigs housed under natural light exhibit lower “basal” salivary cortisol levels than those maintained under artificial lighting. This observation suggests that natural light is more effective at synchronizing the circadian rhythm of cortisol to an earlier clock time, thereby potentially reducing chronic stress in these animals.
• Prolactin and IGF-1: Increased photoperiods, such as 16 hours of light followed by 8 hours of dark, have been demonstrated to elevate prolactin levels in dairy cows. In swine, light stimulates prolactin secretion, boosting the production of Insulin-like Growth Factor 1 (IGF-1), a crucial growth hormone. This hormonal cascade supports cell growth and milk synthesis, establishing a direct physiological link between appropriate lighting and enhanced growth performance. The interplay of these hormones reveals a complex physiological mechanism: if optimal light conditions suppress melatonin and cortisol while simultaneously stimulating prolactin and IGF-1, this creates a synergistic hormonal environment. This means that by carefully managing light, producers are not merely providing illumination; they are actively modulating the pigs’ endocrine system to promote leaner growth (due to less fat accumulation from melatonin suppression and more lean yield from natural light exposure), reduce stress-related issues (through lower cortisol levels), and potentially enhance overall metabolic efficiency. This highlights that lighting is a sophisticated physiological tool, rather than just a basic environmental amenity.

Pigs’ Unique Visual World

Understanding how pigs perceive their environment is crucial for optimizing lighting strategies:

• Pigs require sufficient light to perceive their surroundings, identify pen-mates, facilitate communication, and locate essential resources such as feeders and waterers.
• Unlike humans, pigs’ eyes are not adapted for bright light; they may prefer dimmer, more natural light levels. High-intensity lighting, such as spotlights, should be avoided as it can cause eye damage and lead to weight loss in pigs.
• Pigs clearly prefer dim lighting or outright darkness (around 2.4 lux) for resting and sleeping. This strong preference indicates that designated lying areas within their enclosures should not be brightly illuminated to promote optimal resting behaviour. The consistent emphasis on the importance of dark periods for melatonin production, resting, and overall circadian rhythm regulation across multiple studies underscores its necessity. The development of innovative solutions like Dim-to-Red® lighting, which provides a “darkness equivalent” for human access, further supports the crucial role of darkness. This perspective redefines darkness from merely the absence of light to an active, essential component of the pigs’ environment, akin to a vital physiological requirement. Just as animals need specific nutrients for growth and health, they require particular periods of darkness for proper hormonal regulation, stress reduction, and adequate rest. Failing to provide sufficient darkness is not a minor oversight; it represents a deprivation that can lead to chronic stress, disrupted metabolism, and compromised welfare. This encourages producers to prioritize and strategically manage dark periods, recognizing them as integral to a holistic lighting strategy for optimal animal performance and well-being.
• Pigs possess poorer colour perception than humans, particularly a reduced sensitivity to the red end of the spectrum. Consequently, red light is perceived mainly by pigs as darkness. This unique characteristic is increasingly leveraged in modern lighting systems.
• While pigs can detect light wavelengths between 380 and 760 nm, research suggests that illumination intensity and photoperiodicity are generally more critical for securing their welfare than colour perception alone. Nevertheless, specific light spectrums offer distinct benefits: green light, for example, has been linked to improved muscle development and overall health in pigs.

Dimming the Rage: Lighting Strategies to Reduce Aggression

Aggression among swine remains a persistent and significant problem in commercial production systems. This behaviour is often exacerbated by stressful events inherent to husbandry practices, such as weaning and regrouping. These practices typically lead to substantial increases in stress hormones like plasma and salivary cortisol. Aggressive and damaging behaviours, including ear biting, tail biting, and flank biting, are major welfare concerns that result in skin lesions and alter the animals’ stress physiology. Group stress stemming from unwanted social interactions is a highly relevant welfare consequence observed across nearly all categories of pigs in commercial production systems.

Lighting’s Influence on Aggression

The strategic management of lighting can play a critical role in mitigating aggressive behaviours:

• Photoperiod and Stress: Continuous, 24-hour light exposure can significantly increase stress levels in pigs and lead to disruptive behaviours, potentially reducing productivity, particularly in young animals. Conversely, anecdotal evidence suggests that exposure to natural light has a calming effect on pigs and can reduce the incidence of fighting.
• The Complex Role of Red Light: The impact of specific light spectrums on aggression is nuanced and sometimes contradictory. One study observed that male piglets exhibited more fighting under a Triphosphor (TP) lighting system (designed to simulate daylight during the day) combined with Pascal red (PR) lighting at night, compared to those under conventional cool-white fluorescent light during the day only. This PR lighting also resulted in poorer body integument conditions in piglets, and it was hypothesized that red lighting might encourage more aggressive interactions, possibly by stimulating increased eating. Furthermore, pigs provided PR lighting on the first night of weaning engaged in higher incidences of nosing, tail sucking, head thrusting, fighting, and ear chewing. In stark contrast, the innovative Dim-to-Red® lighting concept is specifically highlighted for its positive effect on reducing tail biting and minimizing stress markers. This system effectively leverages the pig’s perception of red light as darkness, allowing for a gradual “sunrise” and “sunset” simulation and providing red service light for workers to access facilities without disturbing the pigs’ essential dark period. This apparent contradiction underscores that the colour of light alone is not the sole determinant of its effect; rather, the

context of its application—including intensity, duration, timing, and whether it disrupts or supports the natural circadian rhythm—is paramount. Installing “red lights” without a comprehensive understanding of the underlying physiological principles can be ineffective or detrimental. Producers must recognize that red light is beneficial when used to facilitate a natural light-dark cycle (e.g., as a gradual dimming transition or for non-disruptive night work), but potentially harmful if employed as a continuous or disruptive light source, particularly during periods when pigs require and expect darkness. This emphasizes the need for sophisticated, biologically informed lighting systems rather than simplistic colour choices.

• Light Intensity: A study investigating the effects of dim light (5 or 100 lux) found no reduction in fighting or wounding among newly mixed weaned pigs, suggesting that merely reducing intensity might not be sufficient to mitigate aggression in all contexts.
• The Role of Dawn/Dusk Simulation: Modern LED lighting systems can dim lights, creating simulated dawn and dusk periods. This gradual transition in light levels can significantly reduce competition for food when lights are switched on in the morning and prevent startling effects when lights are turned on or off abruptly. This smoother transition contributes to a calmer environment and improved animal welfare.

Brightening Prospects: Lighting for Optimal Growth and Performance

Optimized lighting contributes significantly to improved growth rates, feed efficiency, and overall body composition in swine, although some research areas present conflicting findings that require careful consideration.

Lighting’s Role in Feed Intake and Conversion

• Increasing day length has been observed to increase food intake in grower/finisher pigs. Theoretically, a more extended photoperiod could provide piglets with more or better access to feed, potentially stimulating performance.
• However, the scientific literature presents controversial findings regarding the benefits of extended lighting schedules for feed intake and overall performance in newly weaned pigs. One study, for instance, found no improvement in body weight or feed conversion in weaners exposed to a specific “treatment lighting” (Triphosphor/Pascal Red) compared to controls, except for a temporary improvement in feed intake during the first week post-weaning. Crucially, a study on nursery pigs revealed that an extended photoperiod (16 hours of light per day) did not significantly improve performance parameters such as Average Daily Feed Intake (ADFI) or Feed Conversion Ratio (FCR). This extended photoperiod led to worse fecal consistency scores, indicating a higher incidence of diarrhea than a shorter photoperiod (8 hours of light per day). This study also noted that piglets in the shorter photoperiod group tended to achieve higher weights and average daily gain (ADG) at the end of the nursery period. This direct contradiction to the common assumption that “more light is better” for growth, particularly for young, vulnerable animals, introduces the concept of an optimal range for photoperiod. Excessive light for nursery pigs might induce chronic stress, disrupt gut health (as evidenced by compromised fecal consistency), or interfere with crucial resting periods necessary for recovery and efficient nutrient utilization. This means producers must exercise caution regarding extending light hours and instead focus on providing a balanced light-dark cycle that supports both active feeding and essential rest, explicitly tailored to the developmental stage of the pigs. This challenges a common husbandry practice and emphasizes the need for precision lighting.

Photoperiod and Body Composition

• The regulation of melatonin by light is central to metabolic processes. Elevated melatonin levels, which occur during periods of darkness, slow metabolism and increase body fat content, thereby reducing overall productivity. This implies that appropriate light exposure, by suppressing melatonin, can support higher metabolic rates and promote leaner growth.
• Supporting this, male pigs raised under natural light conditions had significantly lower fat depth and higher lean yield than those raised under artificial lighting. This suggests that natural light promotes a more desirable body composition with its full spectrum and proper photoperiod.

The Power of Specific Light Spectra

• Beyond considerations of intensity and duration, light’s colour (spectrum) plays a significant role. Scientific research indicates that green light has been linked explicitly to improved muscle development and overall health in pigs. This finding aligns with the observation that green light is naturally more prevalent under a forest canopy, a natural habitat for pigs, as plants preferentially absorb red and blue light. This suggests that simply providing “enough” light might not equate to “optimal” light. By incorporating specific light spectrums, such as green light, producers could potentially unlock further gains in muscle development and overall health that are not achievable with conventional white light. This opens the door for more advanced, bio-optimized lighting solutions that mimic natural environments, offering a competitive edge in producing healthier, leaner pigs and transforming lighting from a basic utility into a performance-enhancing technology.
• While weanling piglets between two and five days of age demonstrated a preference for green lighting in creep areas, a study noted that the light colour did not significantly influence their overall behaviour in that specific context.

Addressing Conflicting Research

The conflicting results, particularly concerning extended photoperiods for nursery pigs, highlight the inherent complexity of lighting research in animal agriculture. Differences in study design, such as varying photoperiods, the absence of control groups, the use of specific light types and intensities, and variations in pig age or gender, can significantly complicate the interpretation of findings. This underscores the need for careful consideration and potentially more tailored approaches rather than a blanket “more light is better” philosophy across all production stages.

Implementing Optimal Lighting: Practical Recommendations for Swine Facilities

Translating scientific understanding into actionable recommendations is crucial for swine producers seeking to optimize their operations.

General Lighting Principles

• Pigs are generally adaptable to artificial light, but exposure to very bright lights can cause eye damage and lead to weight loss.
• European legislation, including the EU directive and Defra guidelines, mandates a minimum illuminance of 40 lux for at least 8 hours per day in buildings without natural light.
• Equally critical for welfare is providing a continuous dark period of at least six consecutive hours daily, with reduced light levels below 5 lux.
• Pigs prefer the dimmest illuminance (around 2.4 lux) for resting and sleeping, while simultaneously preferring brighter areas for defecation. This behavioural pattern can be strategically leveraged in pen design. Producers can encourage natural behaviours, improve animal comfort, and enhance pen hygiene by spatially differentiating lighting within a pen—providing dimmer lights over designated lying areas and brighter lights over dunging areas. This can lead to cleaner animals, reduced labour for cleaning, and potentially lower disease transmission, all contributing to improved welfare and economic outcomes. This demonstrates that lighting is about overall brightness or duration and spatial differentiation within the animal’s environment.
• It is important to ensure light level uniformity throughout the space and minimize shadows and glare. To improve visibility and accurately perceive the environment, it is recommended that both animals and stockpersons select a Colour Rendering Index (CRI) greater than 85.

Recommended Lighting Parameters by Production Stage

Lighting needs are not uniform across a pig’s life cycle; therefore, tailored strategies are essential for maximum impact on welfare and productivity at each critical phase. The following table provides a consolidated reference for optimal lighting parameters:

It is essential to note the divergence between established guidelines and emerging research concerning nursery lighting. While some recommendations suggest 50-100 lux for 8-12 hours of light, more recent studies indicate that extended photoperiods (e.g., 16 hours) for nursery pigs may not be beneficial and can even negatively impact fecal consistency and growth. This highlights a crucial research-to-practice gap: producers relying on older or generalized recommendations might inadvertently compromise the health and performance of their most vulnerable pigs. The traditional assumption that “more light stimulates feed intake” for weanlings needs re-evaluation in light of evidence suggesting that excessive light can induce stress and negatively impact gut health. Therefore, for nursery pigs, caution is advocated for shorter, more appropriate photoperiods (e.g., 8 hours of light with a clear dark period) until more definitive, large-scale studies confirm otherwise. This emphasizes the need for precision lighting based on the latest scientific understanding.

Advantages of Modern LED Lighting

Modern LED lighting systems offer significant advantages for swine facilities:

• Energy Efficiency: LED linear fixtures provide substantial energy cost savings, potentially reducing electricity bills by up to 85% compared to older incandescent lights.
• Longevity and Durability: LEDs boast an impressive average rated life of 25,000 to 100,000 hours. They are robust and can be designed to be vapour-tight and wet-rated (NEMA 4X or IP 66), enabling them to withstand the corrosive and high-pressure washing environments typical of swine facilities.
• Directional Light: Unlike omnidirectional fluorescent bulbs, LEDs are directional, focusing light within a 180° arc. This ensures efficient light delivery directly to the animals and working surfaces.
• Minimal Flicker and Heat: LEDs provide minimal flicker, which is beneficial as pigs are unlikely to perceive flicker from correctly functioning fluorescent tubes, but could be affected by failing ones. They also emit reduced heat, preventing dust build-up on bulb surfaces.
• Dimming and Spectrum Control: A key benefit of LEDs is their full dimmability (0-100%), which allows for gradual dawn and dusk periods that reduce stress and competition among pigs. Advanced LED systems can also provide specific light spectrums, such as green light, for enhanced muscle development.
• Dim-to-Red® Technology: This innovative system allows fixtures to dim to a whole red light, which pigs perceive as darkness. This enables stress-reducing sunrise/sunset functionality and provides a red service light, allowing workers to access facilities for tasks without disturbing the pigs’ essential sleep cycle.
• IHT Group LED Lighting Systems: Specifically designed for agricultural settings, IHT LED lighting solutions offer several advantages for swine barns, particularly during winter when natural daylight is reduced. These systems are engineered to improve lighting quality, enhance environmental sustainability, and lower maintenance. They enhance piglet growth and activity by providing a well-lit space for exploration, nursing, and natural behaviours. IHT Group Lights also encourages improved feeding patterns, supporting healthy weight gain and development. Their durability allows them to withstand harsh barn conditions, including moisture, dust, and temperature fluctuations, making them suitable for year-round use. Furthermore, IHT LED systems are customizable in brightness, catering to the specific needs of piglets and barn workers, and their long lifespan minimizes maintenance and replacement costs. These systems also incorporate safety features, such as being less prone to overheating, which reduces fire risks in barns.