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One of the fundamental steps during the creation of the Code of Practice for the Care and Handling of Chickens, Turkeys and Breeders was a review of all the relevant scientific literature. The literature review focused on poultry management practices and environmental conditions of poultry barns and their effects on bird welfare. The poultry report from 2013 provided an objective summary of the literature without providing recommendations.
The current manuscript will follow the same format used in the previous report and update the information of the section ‘Lighting Regimens’ (Section 7, pages 43-53).
The authors of the 2013 science report concluded that:
Lighting can be categorized into three components: intensity, duration (photoperiod), and wavelength (light source). Each of these components plays a role in determining the optimal lighting conditions for rearing broilers. While light intensity and duration (daylength) have been more extensively studied in the past, there has been an increase in interest involving the use of varying wavelengths (colour) for rearing broilers particularly with the increased use of LED lighting.
Impact of light intensity on growth and feed efficiency:
Olanrewaju et al. (2014) evaluated five different light intensities (0.2, 2.5, 5.0, 10.0, or 25.0 lux) and found no effects on body weight, body weight gain, feed intake, or feed efficiency at 56 d of age. A 2016 study found that broilers reared under Light Emitting Diode lamps (LED) with bright intensity (20 lux) were heavier at 45 d than those under dim lighting (5 lux) however, feed efficiency was unaffected by treatment (Archer, 2016). Conversely Rault et al. (2017) also compared LED lights with an intensity of 5 or 20 lux and found that broilers reared with bright light (20 lux) were lighter compared with broilers reared with dim light (5 lux). The authors also noted there was no impact on feed intake (Rault et al., 2017). Another study found no significant difference in body weight, feed intake, or feed efficiency when broilers were reared under 5 or 20 lux (Olanrewaju et al., 2016).
Impact of light intensity on mortality:
Olanrewaju et al. (2014) found no effect of light intensity (0.2, 2.5, 5.0, 10.0, or 25.0 lux) on mortality at 56 d of age. When bright (20 lux) light has been compared with dim light (5 lux), there has been no observed effect on mortality (Olanrewaju et al., 2016; Rault et al., 2017).
Impact of light intensity on leg and footpad health:
Broilers reared under 5 lux compared with 20 lux demonstrated no difference in gait score (Olanrewaju et al., 2016). Rault et al. (2017) utilized latency to lie as an indicator of leg health. The authors found no differences in the latency to lie when broilers were reared under either 5 or 20 lux.
Impact of light intensity on ocular health:
Broiler eye weight can be a reflection of diurnal rhythm development in birds. Eye weight was not affected by light intensity in broilers exposed to 0.2, 2.5, 5.0, 10.0, or 25.0 lux (Olanrewaju et al., 2014). A study published in 2016, found no impact of light intensity (5 vs. 20 lux) on broiler eye weight (Olanrewaju et al., 2016). Conversely, Fidan et al. (2017a), evaluated eye weight and diameter following exposure to bright (20 lux) and increasing dim light (starting at 5 lux and decreasing to 1.25 lux by 42 d) and found that broilers reared under dim lighting had heavier and larger (mediolateral diameter) eyes compared with those reared under bright light. Another study found similar results, with broilers reared under dim light (5 lux) having eyes that were 5% heavier than that of broilers reared under bright light (20 lux; Rault et al., 2017). Since it is believed that the difference between night-time and day-time intensity is important, it is interesting to note that only Rault et al (2017) reported the scotoperiod intensity (0 lux).
Impact of light intensity on stress or fear:
Broiler stress levels, as indicated by corticosterone, were unaffected by light intensity (0.2, 2.5, 5.0, 10.0, or 25.0 lux) at d 56 (Olanrewaju et al., 2014). Archer (2016) found that LED intensity (5 vs 20 lux) did not influence stress level in broilers as indicated by corticosterone concentration, vocalizations under isolation, or tonic immobility. This was further supported by Rault et al. (2017), as no differences were seen in plasma corticosterone concentration when broilers were reared under 5 or 20 lux.
Fidan et al. (2017b) demonstrated higher H/L ratios in birds reared with bright light (20 lux) compared with dim light (5 lux on d 1 and decreasing to 1.25 lux on d 42).
Olanrewaju et al. (2016) found no impact of light intensity on tonic immobility duration in broilers at 49 d of age.
Impact of light intensity on behaviour:
Broilers reared under bright light (20 lux) were more active when compared with broilers reared under dim light (5 lux; Rault et al., 2017).
Impact of light duration and distribution on growth and feed efficiency:
The recent papers regarding broiler performance provide mixed results. Broilers reared on continuous (23L:1D) or intermittent light (2L:2D cycle) were heavier when compared with birds given a long dark period (8L:16D) (Olanrewaju et al., 2015a; Olanrewaju et al., 2018). Another study found that broilers given 18L:6D were heavier compared with broilers reared under continuous, 17L:7D, or 16L:8D (Kalaba et al., 2016). Similarly, broilers given a shorter dark period (4 or 7 h) were heavier when compared with broilers reared under a 10 h dark period (Shynkaruk et al., 2019). Of note, birds reared with 10 h of darkness were the most feed efficient when compared to those reared with 1, 4, or 7 h of darkness (Shynkaruk et al., 2019). A more recent study found that broilers reared under near continuous light (22L:2D) were heavier than those reared on 20L or 18L with either continuous or intermittent programs (Abo Ghanima et al., 2021). The authors also noted that broilers provided with 6 hours of darkness were more feed efficient compared with broilers given only 2 h of darkness (Abo Ghanima et al., 2021). Contrary to this, Mlaba et al. (2015) observed no difference in body weight in given a dark period of 0, 4, 8, or 12 h. Zhao et al. (2019) found no significant differences in body weight gain, feed conversion, or mortality; however, broilers reared on intermittent light (17L:3D:1L:3D) consumed more feed than broilers reared on continuous light (24L:0D).
Coban et al. (2014), explored the idea of providing dark access via free choice, where birds were reared under 24L:0D, 16L:8D, or provided 24L with free choice access to a dark chamber. Few birds were used in this experiment – 180 spread between three treatments. Broilers under 24L:0D and self-photoperiod were heavier than those provided with 16L:8D (Coban et al., 2014), although body weights in general were low for 42 d broilers.
Impact of light duration and distribution on mortality:
Birds reared on continuous light (24L:0D) had higher mortality levels compared with birds reared on 20L:4D, 16L:8D, or 12L:12D (Mlaba et al., 2015). Shynkaruk et al. (2019) observed the lowest mortality in broilers provided with 10 h of darkness compared with 1, 4, or 7 h. A more recent study found that broilers given longer dark periods (6 h) had lower mortality compared with broilers given shorter dark periods of 2 or 4 h (Abo Ghanima et al., 2021).
Impact of light duration and distribution on leg and footpad health:
No difference in gait score was observed in broilers reared on continuous (23L:1D), 8L:16D, or 2L:2D intermittent lighting programs (Olanrewaju et al., 2015a; Olanrewaju et al., 2018). Contrary to this, Fidan et al. (2017a) observed an increase in gait abnormalities in broilers reared on continuous light (23L:1D) compared with broilers exposed to an increasing photoperiod starting at 16L:8D (9 d) and increasing to 23L:1D (42 d).
Nelson et al. (2020a), found that broilers raised on an intermittent lighting program had lower hock and footpad dermatitis scores compared with broilers raised with a continuous photoperiod. Footpad lesions were more severe in broilers at 56 d when reared on a long dark period (8L:16D) when compared with broilers reared on continuous (23L:1D) or intermittent (2L:2D) lighting programs (Olanrewaju et al., 2015a).
Impact of light duration and distribution on ocular health:
A study evaluating the use of continuous (23L:1D), intermittent (2L:2D) and a long dark period (8L:16D) found that birds reared with continuous and intermittent light programs had heavier eye weights compared to birds reared with a long dark period (Olanrewaju et al., 2015a). Broilers reared on continuous light (23L:1D) had heavier and larger (mediolateral, dorsoventral diameter and anterioposterior size) eyes compared with broilers that were exposed to an increasing photoperiod starting at 16L:8D (9 d) and increasing to 23L:1D (42 d) (Fidan et al., 2017a). Olanrewaju et al. (2018) evaluated the use of continuous (23L:1D), intermittent (2L:2D), and short (8L:16D) daylength on eye health and found that broilers reared on continuous and intermittent light had heavier eyes compared with those on short daylength.
Impact of light duration and distribution on melatonin and other blood metabolites:
As melatonin follows a diurnal rhythm, broiler flocks raised on 14L, 17L, and 20L demonstrated significant rhythms over a 24h period however, the flock raised on 23L did not demonstrate an established rhythm (Schwean-Lardner et al., 2014). Melatonin, released in a diurnal fashion, affects immune function, growth hormone release, reproductive hormones, and behavioural responses in many species, including poultry.
Impact of light distribution and length of darkness on stress:
Nelson et al. (2020a), found that broilers reared on continuous light had lower plasma corticosterone and lower H/L ratios compared with broilers reared on intermittent lighting programs. In the study by Coban et al. (2014) described above, broilers that were provided free choice darkness and broilers that had a dark period (16L:8D) had lower H/L ratios when compared to broilers reared with continuous lighting, suggesting the birds were less stressed.
Olanrewaju et al. (2015a; 2018) found no effect of lighting program (23L:1D, 8L:16D, or 2L:2D intermittent) on the tonic immobility of broilers at 49 d.
Impact of light duration and distribution on behaviour:
Broiler resting behaviour is impacted by daylength, the proportion of birds resting immediately after the lights come on was 2, 25, 40, and 75% for 14L, 17L, 20L, and 23L respectively (Schwean-Lardner et al., 2014). The broilers reared with 14 and 17 h of light showed consistent rhythms for walking and standing behaviour. In addition, broilers reared with 14L or 17L demonstrated higher levels of feeding behaviour just after the lights came on and just prior to the lights shutting off, which has been suggested as anticipatory feeding (Schwean-Lardner et al., 2014). Length of the dark period has been further studied for its impact on broiler feeding behaviour, with frequency of feeding bouts increasing and total time at the feeder decreasing as the dark period increased (Shynkaruk et al., 2019). Broilers also demonstrated the ability to anticipate the dark period and increased their feeding activity up to 4 hours prior to the dark period (Shynkaruk et al., 2019). In addition, they maintained feed in the gastrointestinal tract throughout the dark period regardless of their photoperiod, and holding feedstuffs for longer periods of time is likely what improves feed efficiency with increased darkness exposure.
As of 2014, Natural Resources Canada has legislated that traditional incandescent bulbs will be phased out and replaced with more energy efficient options. As a result, light emitting diodes (LEDs) have become increasingly popular, as they provide low energy cost, longevity, and offer specific wavelengths. There has also been an increase in research surrounding the use of coloured lights when rearing broilers. In addition to light colour, there has been increased research regarding wavelengths in the ultraviolet spectrum.
Impact of light wavelength and source on growth and feed efficiency:
In some research, broilers reared under LED lights were heavier than broilers reared under incandescent lights (Archer, 2016). Feed efficiency was not impacted by light source (LED vs. incandescent; Archer, 2016). Other studies found similar results with broilers reared under cool LED lights being heavier than broilers reared under incandescent lights at 56d (Olanrewaju et al., 2015b; Olanrewaju et al., 2016). Light source impacted body weight, with broilers being heavier when reared with cool poultry specific filtered LEDs compared with incandescent, compact fluorescent or neutral LEDs (Olanrewaju et al., 2018). No effects of light source were observed in relation to feed intake or efficiency (Olanrewaju et al., 2016; Olanrewaju et al., 2018).
The recent literature has typically evaluated different wavelengths using LED lights. Kim et al. (2013) compared incandescent (white) to LED white, blue, red, green, and yellow light; the authors found broilers were heavier under yellow and white LEDs compared with incandescent lights at 35 d. Feed intake was higher in the birds reared with white, blue, green, and yellow light compared with the incandescent light (Kim et al., 2013). Broilers provided with cool white (6,065K) were heavier when compared with broilers reared with neutral white LEDs (4,100K); however, there was no impact of feed efficiency (Riber, 2015). Broilers raised under short wavelengths (blue – 455-461nm and green – 516- 521nm) demonstrated higher body weight gains up until 4 weeks of age compared to those reared under long wavelengths (red- 618-620nm and yellow – 587-589nm) (Yang et al., 2016). Another study conducted in 2017, confirmed that broilers reared under blue or green lights had higher weight gains compared with those reared under white lights (Mohamed et al., 2017). Feed efficiency was best in broilers reared under blue lights, followed by green, then white (Mohamed et al., 2017). Another study evaluated the use of white only LEDs or white LEDs supplemented with blue/green lights above the feeder and drinker lines and found that the white supplemented broilers were heavier at d 45 (Nelson et al., 2020b). In addition to white LED lights, the use of ultraviolet lights (both UVA and UVB) resulted in broilers that reached finishing weight more quickly (James et al., 2020).
Care must be taken in interpretation of the light wavelength work. In most research studies, light intensity across wavelengths was monitored with a lux meter – however this meter does not adjust for wavelengths. Rather a galilux light meter or spectroradiometer (measures intensity of different wavelengths) should be used. This may explain some of the variation found in the literature.
Impact of light wavelength and source on mortality:
Broilers reared with either incandescent bulbs, cool white LEDs (5,000K), or warm LEDs (2,700K) demonstrated no differences in mortality (Olanrewaju et al., 2015b). Mortality was not impacted by light source (incandescent, compact fluorescent, neutral LED, or cool poultry specific LED) (Olanrewaju et al., 2016; Olanrewaju et al., 2018).
There was no effect of LED wavelength (cool white 6,065K vs. neutral white 4,100K) on broiler mortality (Riber, 2015). The use of ultraviolet lights has also been explored in relation to mortality, with broilers exposed to UVA light having lower mortality overall compared to birds reared under white LEDs (James et al., 2020).
Impact of light wavelength and source on leg and footpad health:
Olanrewaju et al. (2018) observed no differences in gait score in relation to light source (incandescent, compact fluorescent, neutral LED, or cool poultry specific LED).
Broilers exposed to two LED spectrums (cool white 6,065 K vs. neutral white 4,100K) demonstrated no differences for gait score, footpad dermatitis, or hock burns (Riber, 2015). Nelson et al. (2020b) exposed broilers to white LED or white LED plus blue/green LEDs above the feeder and drinker line and found that broilers supplemented with blue/green light had improved hock burn scores.
Impact of light wavelength and source on ocular health:
Olanrewaju et al. (2015b) found that eye weights were heavier in broilers reared with incandescent lights compared with warm white LEDs (2,700K). Interestingly the authors also evaluated two cool white LED bulbs (5,000K), with one bulb resulting in lighter eye weights similar to that of the warm LED and one bulb resulting in heavier eye weights similar to that of the incandescent bulb (Olanrewaju et al., 2015b). In later studies there was no impact of light source (incandescent, compact florescent, neutral- LED, or cool poultry specific LED) on ocular health (Olanrewaju et al., 2016; Olanrewaju et al., 2018).
Impact of light wavelength and source on melatonin and other blood metabolites:
Broilers demonstrated increased levels of plasma growth hormone and melatonin concentrations when reared with green lights compared with white, red, or blue lights (Zhang et al., 2016). Further, Zhang et al. (2017) determined that there was an increase in melatonin receptors (Mel1a and Mel1b) when broilers were exposed to green light compared with white, red, or blue light. No mention of the type of equipment used to measure light intensity was given.
Impact of light wavelength and source on stress:
Archer (2016) found that broilers reared under incandescent lights had elevated corticosterone levels and vocalized more in isolation compared with broilers reared under LED lights. The same study found that broilers raised with incandescent lights also had longer durations of tonic immobility compared with broilers reared under LED lights (Archer, 2016). Conversely, Olanrewaju et al. (2015b) found that there was no impact of light source (LED vs incandescent) on plasma corticosterone concentration.
Another study also found that there was no impact of light source (incandescent, compact fluorescent, neutral LED, or cool poultry specific LED) on the duration of tonic immobility (Olanrewaju et al., 2018).
Mohamed et al., 2017 observed decreased H/L ratios in broilers reared under blue and green lights compared with broilers reared under white lights. Mohamed et al., 2017 found shorter durations of tonic immobility in birds reared under blue and green lights as compared with those under white lights.
Impact of light wavelength and source on behaviour:
A 2015 study evaluated the preference of broilers for cool white LEDs compared with neutral white LEDs. The authors found that more broilers were found resting in the cool white LED chamber than the neutral white chamber on d 16 and 28 (Riber, 2015). They also noted that more broilers were performing comfort behaviours in the cool white LED chamber than the neutral white chamber on d 34 (Riber, 2015).
Preference for light wavelength and source:
Broiler chicks were provided the choice of two light proof compartments with either neutral white (4,100K) or cold white (6,065K) LEDs, the authors found there was a preference cold white light with broilers spending more time in that compartment (Riber, 2015).
Recent literature provides mixed results on the impact of light intensity on body weight; however, the literature consistently states no effects on feed efficiency and mortality.
No new literature concerning synchronization of behaviour was conducted during the period covered in this study, however the literature indicates that activity levels increase at higher light intensities.
To our knowledge there is no new literature concerning light intensity preferences of broiler chickens.
Moderate dark periods tend to have heavier birds compared to either continuous light, short dark periods, or long dark periods. Improvements in feed efficiency continue to be seen in birds given longer periods of darkness, and likely are related to the increased time feed remains in the gastro-intestinal tract during the dark period.
Increased mortality continues to be seen with increasing daylength.
Increases in feeding behaviour are seen with increasing dark periods. Recent studies have also shown that broilers partake in anticipatory feeding prior to a dark period. It has also been noted that behaviours that indicate positive welfare are expressed for a longer period of time with the addition of darkness in a photoperiod program.
Production and health improvements continue to be seen with the use of blue or green lighting, although these results may be confounded by differences in light intensity when different wavelengths are tested. Welfare improvements have also been observed with the use of blue and green light; however there is still limited research on the effects of monochromatic light and broiler behaviour.
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