Abstract
Light flicker is a commonly overlooked factor of artificial light sources. This study aimed to determine the impacts of light-flicker frequency on performance, general health, and mortality of 11-wk Nicholas Select turkey hens. The experiment consisted of 2 trials (block) in a randomized complete block design, with 3 light-flicker frequency treatments (30, 90, or 195 Hz). Turkeys (n = 364 per replicate) were randomly placed into environmentally controlled rooms (3 room replicates per treatment per trial). Group body weight (BW) and feed consumption were measured at 0, 4, 8, and 11 wk, and feed efficiency (mortality corrected feed-to-gain; F:Gm) was calculated for each period. Mortality and culls were collected twice daily. Flock uniformity, feather condition and cleanliness, footpad score, and mobility were evaluated at 10 wk (30 birds per room). Litter quality and ocular weight and dimensions were evaluated (11 wk; 4 birds per room). Data were analyzed using Proc Mixed (SAS 9.4) and significance was declared when P < 0.05. At 8 wk, BW was lower under 30 Hz compared to 195 Hz (P = 0.03). Feed consumption was lowest under 30 Hz (0–4 wk and 4–8 wk; P < 0.01). Mortality-corrected F:G was improved under 30 Hz for 8 to 11 wk and 0 to 11 wk (P = 0.05 and P = 0.04, respectively). Total mortality was lower under 195 Hz compared to 30 Hz (P = 0.02). Uniformity, gait score, feather condition, and litter quality were unaffected by flicker. Footpad scores were improved under 90 Hz (P = 0.01), leading to an improved average footpad score (P = 0.02). Feather cleanliness was improved under 90 Hz compared to both 30 Hz and 195 Hz (P<0.01). Right eyeball dimensions differed across lighting treatments, with the dorso-ventral diameter being larger in birds under 30 Hz compared to 195 Hz (P = 0.05). The anterior-posterior size also increased in birds under 30 Hz compared to 90 Hz (P = 0.03). Light flicker impacted turkey hens, with the results demonstrating negative impacts on early growth and changes to ocular characteristics.
Key words: body weight, feed efficiency, mortality, footpad lesions, flicker frequency
INTRODUCTION
Light flicker is a common characteristic of artificial light sources that is often found in poultry barns, but its effects have not been investigated extensively in poultry species. Light flicker is only visible to a viewer when it is below their flicker fusion frequency (FFF), which is the point at which a light flickering at a higher frequency is perceived as a continuous stream of light. Light flicker can be unconsciously perceived when the frequency of the flicker is between the FFF and critical flicker fusion frequency (CFF). The CFF is the point at which the viewer can no longer unconsciously perceive light flicker. Few studies have attempted to determine the effects of light flicker on poultry species (Boshouwers and Nicaise, 1992; Widowski and Duncan, 1996; Raabe et al., 2024).
Very few studies have been conducted on light flicker and its influence on laying hen preference, behavior, and performance. Widowski and Duncan (1996) examined the impact of fluorescent light flicker at high (20,000–60,000 Hz) or low frequencies (120 Hz) on Shaver 288 laying hens and determined that hens displayed no frequency preference. Light flicker in broiler chickens has also been evaluated, with no effect of light-flicker frequency (high- 26,000 Hz or low- 100 Hz) on the energy expenditure of Pilch broiler chickens (Boshouwers and Nicaise, 1992).
It is difficult to make comparisons between turkeys and other poultry species, and there is limited turkey-specific research. A recent research note evaluated the effects of light-flicker frequency on turkey toms and found no effect of light flicker (165 Hz, 500 Hz, or 16 kHz) on turkey tom body weight, feed consumption, or mortality (Raabe et al., 2024). The flicker frequencies that have been tested in literature are greater than the visible flicker frequencies recorded for other poultry species, therefore there is a knowledge gap regarding the impact of visible light-flicker on turkeys. With limited research available and a lack of research focusing on turkey hens, the objectives of this study were to determine the impacts of white-LED light-flicker frequency on the performance and health of turkey hens.
MATERIALS AND METHODS
The following procedures of this experiment were approved by the University of Saskatchewan Animal Care Committee under the animal use protocol number 20210090. The birds were cared for following the Guide to the Care and Use of Experimental Animals by the Canadian Council of Animal Care (2009). The experiment consisted of 2 trials, with 3 light-flicker frequency treatments: 30 Hz (flicker visible to humans and birds), 90 (flicker visible to some birds but not humans), or 195 Hz (flicker not visible to humans or birds).
Housing and Management
A total of 3,276 Nicholas Select turkey hens were used for each trial. Birds (n = 364) were housed in 1 of 9 light-tight environmentally controlled rooms (6.7 m x 10.0 m), resulting in 6 room replicates for each treatment. Birds had ad libitum access to a 5-phase commercial diet via aluminum tube feeders (pan diameter 36 cm until d 27, then 44 cm) and water via 4 pendulum nipple drinker lines equalling 12 drinker cups (Lubing EasyLine; Lubing, Cleveland, TN). Wood shavings were used at an initial depth of 7 to 10 cm for bedding. For the first 9 d, 3 brooder rings (approximately 5.0 m x 7.0 m) were used in each room with supplemental feeders and drinkers. For the first 7 d, portable humidifiers were used to ensure humidity was above 50%. Temperature started at 34°C with a gradual reduction to 16°C by 11 wk (Turkeys, 2015).
The initial photoperiod was 23L:1D and was gradually reduced to 18L:6D by 9 d (Turkeys, 2015). In each room, light was supplied by ten 11-Watt white LED lamps (AgriLamp 11W ES26/27; Greengage Lighting Ltd., Edinburgh, UK). The 30 and 90 Hz treatment flicker frequencies were created using a purpose-built electronic system (Greengage Lighting Ltd., Edinburgh, UK). The flicker in the 195 Hz rooms was created using a Symmetry Dimmer (Greengage Lighting Ltd., Edinburgh, UK) and natural fluctuations in the existing power source. This was to mimic conditions where the light flicker is beyond the CFF of birds. Flicker frequencies were monitored weekly using a spectrometer (Lighting Passport Spectrometer, ASENSETEK) for the 30 and 90 Hz treatments and an oscilloscope (TDS 210 Digital Real-Time Oscilloscope, Tektronix, Beaverton, OR) and Lichtflimmer (LiFli) (Messgerat LiFli, Fauser Elektrotechnik, München, Germany) for the 195 Hz treatment to ensure experimental conditions were maintained. Light intensity was initially set at 40 lux and was gradually reduced to 10 lux by 8 d. Light intensity was measured weekly (Lighting Passport Spectrometer, ASENSETEK) to ensure the correct light intensity was maintained throughout the trial.
Data Collection
Body Weight and Uniformity. Group BW were measured on a room basis at 0, 4, 8, and 11 wk, and average BW was calculated. At 10 wk, a subsample of birds from each room (n = 30) were randomly selected and individually weighed to assess flock uniformity. The handler selecting the bird entered the room and counted 5 birds closest to them, selecting the fifth bird. The handler alternated selecting birds from the front, middle, and back of the room.
Feed Consumption and Feed Efficiency. Feed was weighed on a room basis at 4, 8, and 11-wk. Feed efficiency (mortality corrected feed-to-gain ratio (F:Gm)) was calculated for the following periods: 0 to 4 wk, 4 to 8 wk, 8 to 11 wk, and 0 to 11 wk.
Mortality. All rooms were checked twice daily for mortality and culls, which were sent to an independent laboratory (Prairie Diagnostic Services Inc., Saskatoon, Canada) for necropsy to diagnose cause. Causes were categorized into 1 of 6 categories; metabolic (round heart, sudden death with peri-renal hemorrhage), infectious (yolk sac infection, osteomyelitis, peritonitis, polyserositis, arthritis/synovitis, pericarditis, general infection), mechanical (trauma, broken bone), aggressive damage, unknown (no visible lesions), and other (emaciation/starveout, pendulous crop, decomposed, general).
Mobility, Footpad Scores, and Litter Quality. At 10 wk, the same subsample of 30 birds per room used for uniformity were tested for gait scoring and footpad lesion scoring. Gait scoring was conducted by 2 observers using a scale of 0 to 5 (Table 1), and the score for each bird was averaged (Beaulac and Schwean-Lardner, 2018, as adapted from Garner et al., 2002, Vermette et al., 2016). Footpad lesions were scored by a single trained observer on a scale of 0-4 (Table 2; Hocking et al., 2008). Litter quality was assessed at wk 11, using a visual scale adapted from Welfare Quality Consortium (2009) and Adler et al. (2021). Four measurements were collected per room (middle rear, right rear wall, under left front drinker, and middle front) to get an average litter score for the room. A score of 0 indicated dry and flaky, score 1 indicated dry but clumps form when compacted, score 2 indicated ball forms but falls apart, score 3 indicated readily sticks into a ball and score 4 indicated cap/crust must be broken and sticks into a wet ball.
Table 1.
Gait scoring technique modified from broilers (Garner et al., 2002) for turkeys by Vermette et al. (2016).
| Score | Degree of impairment | Description |
|---|---|---|
| 0 | None | Smooth, fluid locomotion. The foot is furled while raised. |
| Straight legs. | ||
| 1 | Detectable, but unidentifiable abnormality | The bird is unsteady or wobbles when it walks. However, the problem leg is unclear, or cannot be identified in the first 20s of observation. The bird readily runs from the observer in the pen. The foot may remain flat when raised, but the rest of the stride is fluid and appears unimpaired. |
| Gait appears unstable (shaky or stomping) | ||
| 2 | Identifiable abnormality, that has little impact on overall function | The leg producing the gait defect can be identified within 20s of observation. If a problem leg is identified after 20s of observed locomotion, then the bird is classed as gait score 1. However, the defect has only a minor impact on biological function. Thus, the bird will run from the observer spontaneously or if touched or nudged with the padded stick. If the bird does not run at full speed, it runs, walks or remains standing for at least 15s after the observer in the pen has ceased to move towards or nudge it. Birds in this and previous scores are often observed to scratch their face with their feet-again indicating little impact on function. (The most common abnormality in this score is for the bird to make short, quick, unsteady steps with one leg, where the foot remains flat during the step.) |
| 3 | Identifiable abnormality which impairs function | Although the bird will move away from the observer when approached or touched, or nudged, it will not run, and squats within 15s or less of the observer in the pen ceasing to approach or nudge it. If the bird squats after 15s have elapsed, it is classified as gait score 2. |
| 4 | Severe impairment of function, but still capable of walking | The bird remains squatting when approached or nudged. This criterion is assessed by approaching the bird, and if it remains squatting, gently nudging or touching the animal for 5s. Animals may appear to rise but still rest upon their hocks. Only rising to stand on both feet within 5s of handling is counted—a bird which takes longer than 5s to rise, or which does not rise at all is scored as 4, while a bird that rises in 5s or less is counted as a 3 (or lower if its gait is good). Nevertheless, the bird can walk when picked up by the observer and placed in a standing position, but squats following one or two steps. (Squatting often involves a characteristic ungainly backwards fall.) |
| Bird requires wings for balance. | ||
| 5 | Complete lameness | The bird cannot walk, and instead may shuffle along on its hocks. It may attempt to stand when approached but is unable to do so, and when placed on feet unable to complete a step with either leg. |
Table 2.
Footpad dermatitis scoring system (Hocking et al., 2008).
| Score | Description of foot pad |
|---|---|
| 0 | No external signs of footpad dermatitis. The skin of the footpad feels soft to the touch and no swelling or necrosis is evident. |
| 1 | The pad feels harder and denser than a non-affected foot. The central part of the pad is raised, reticulate scales are separated, and small black necrotic areas may be present. |
| 2 | Marked swelling of the footpad. Reticulate scales are black, forming scale shaped necrotic areas. The scales around the outside of the black areas may have turned white. The area of necrosis is less than one quarter of the total area of the footpad. |
| 3 | Swelling is evident, and the total footpad size is enlarged. Reticulate scales are pronounced, increased in number and separated from each other. The amount of necrosis extends to one half of the footpad. |
| 4 | As score 3, but with more than half the footpad covered by necrotic cells. |
Feather Condition and Cleanliness. At 10 wk, the same 30 birds per room were scored by a single trained observer for feather condition and cleanliness. Feather condition was scored on 4 areas of the body (breast, wing, tail, and back) using a scale of 1 to 4 (Table 3; Beaulac and Schwean-Lardner, 2018, as adapted from Davami et al., 1987 and Sarica et al., 2008). Feather cleanliness was scored on a scale of 1-4 (Table 3; Forkman and Keeling, 2009).
Table 3.
Feather condition scoring technique was developed by Davami et al. (1987) and Sarica et al. (2008) as adapted by Beaulac and Schwean-Lardner (2018) and feather cleanliness scoring was developed by Forkman and Keeling (2009) as adapted by Wilkins et al. (2003).
| Feather condition score | Description |
| 1 | No feather cover |
| 2 | More than half of the plumage is missing. |
| 3 | Few or less than half of the plumage is missing. |
| 4 | Full, intact plumage. |
| Feather Cleanliness Score | Description |
| 1 | Very clean – more than 75% of the body feathers free from soiling |
| 2 | Moderately clean – 50–75% of the body feather are free from soiling |
| 3 | Moderately dirty – 25–50% of the body feathers are free from soiling |
| 4 | Very dirty – less than 25% of the body feathers are free from soiling |
Ocular Weight and Dimensions. At 11 wk, 4 birds per room were randomly selected, weighed, and euthanized using an electric stunning knife, followed by exsanguination. The right eye was enucleated, and any excess tissue was removed. The eye was weighed, and mediolateral diameter, dorso-ventral diameter, and anterior-posterior size were measured using a digital caliper (Mastercraft Digital Caliper 6-in, Canadian Tire Corporation, Toronto, ON).
Statistical Analyses
The experiment was a randomized complete block design, with 2 trials (trial as block), with a one-way factorial arrangement. The experimental unit was room, resulting in 6 replicates per treatment. Treatment means and standard error of the mean was obtained using Proc Means (SAS 9.4). Proc Univariate (SAS 9.4, Cary, NC) was used to test data for normality prior to analyses, and data were log-transformed (log + 1) as required. An analysis of variance was conducted using Proc Mixed (SAS 9.4, Cary, NC). All data were tested for block significance, with block removed as a random factor if it was not significant. The categorical data (footpad score, feather condition score, and feather cleanliness score) were analyzed using Proc Glimmix (SAS 9.4). Tukey's range test was performed to achieve mean separation and differences were considered significant when P < 0.05.
RESULTS
Body Weight and Uniformity
There were no differences in BW at d 0, 4, or 11 wk of age. At 8 wk, the birds in the 30 Hz treatment weighed less (P = 0.03) than those in the 195 Hz treatment (Table 4). Flock uniformity, expressed as percentage of birds within 5, 10, or 15% of the room mean, was not impacted by light-flicker frequency (P = 0.67, 0.35, and 0.44, respectively; data not shown).
Table 4.
Effect of LED light-flicker frequency (30, 90, or 195 Hz) on turkey hen average body weight, feed consumption, and mortality-corrected feed-to-gain ratio reared to 11 wk of age.
| Age (wk) | Light-flicker frequency (Hz) |
SEM1 | P-value | ||
|---|---|---|---|---|---|
| 30 | 90 | 195 | |||
| Average body weight | |||||
| 0 | 0.06 | 0.06 | 0.06 | 0.001 | 0.59 |
| 4* | 0.75 | 0.75 | 0.78 | 0.010 | 0.20 |
| 8* | 3.77b | 3.84ab | 3.86a | 0.019 | 0.03 |
| 11* | 7.28 | 7.16 | 7.28 | 0.032 | 0.10 |
| Feed consumption | |||||
| 0–4* | 0.84b | 0.89a | 0.88a | 0.009 | <0.01 |
| 4–8* | 4.64b | 4.75a | 4.75a | 0.019 | <0.01 |
| 8–11* | 6.99 | 6.73 | 6.90 | 0.080 | 0.19 |
| 0–11* | 12.46 | 12.37 | 12.53 | 0.069 | 0.62 |
| Feed-to-gain mortality corrected | |||||
| 0–4 | 1.222 | 1.273 | 1.223 | 0.0159 | 0.32 |
| 4–8 | 1.518 | 1.529 | 1.529 | 0.0043 | 0.49 |
| 8–11* | 1.964b | 2.010a | 1.989ab | 0.0224 | 0.05 |
| 0–11* | 1.703b | 1.725a | 1.714ab | 0.0113 | 0.04 |
Block differed significantly: included as a random factor (P < 0.05).
Values with different letters within the same row differ significantly (P < 0.05).
Standard error of the mean.
Feed Consumption and Feed Efficiency
During the 0 to 4 wk and 4 to 8 wk periods, turkeys in the 30 Hz treatment consumed less feed than those in the 90 and 195 Hz treatments (P < 0.01; Table 4). No other differences were noted. When corrected for mortality birds reared under 30 Hz had improved feed conversion compared to those under 90 Hz at 8 to 11 wk and 0 to 11 wk (P = 0.05 and P = 0.04, respectively; Table 4).
Mortality
Total mortality (0–11 wk) was highest in hens reared under 30 Hz, compared to 195 Hz (P = 0.02; Table 5). Within categories, only one difference was noted, mortality due to infectious causes was higher under 90 Hz compared to 195 Hz (P = 0.05; Table 5).
Table 5.
Effect of LED light-flicker frequency (30, 90, or 195 Hz) on total and cause of mortalities and culls as a percent (%) of birds placed in turkey hens reared to 11 wk of age.
| % of birds in category | Light-flicker frequency (Hz) |
SEM1 | P-value | ||
|---|---|---|---|---|---|
| 30 | 90 | 195 | |||
| Aggressive Damage | 3.30 | 2.88 | 3.30 | 0.294 | 0.79 |
| Metabolic | 0.55 | 0.37 | 0.33 | 0.075 | 0.62 |
| Round Heart | 0.44 | 0.32 | 0.27 | 0.047 | 0.51 |
| Sudden Death/Peri-Renal Hemorrhage | 0.11 | 0.05 | 0.05 | 0.040 | 0.84 |
| Rotated tibia* | 0.11 | 0.00 | 0.05 | 0.028 | 0.10 |
| Infectious | 0.27ab | 0.41a | 0.05b | 0.064 | 0.05 |
| Yolk Sac Infection | 0.05 | 0.09 | 0.00 | 0.028 | 0.42 |
| Osteomyelitis | 0.11 | 0.09 | 0.00 | 0.031 | 0.33 |
| Peritonitis | 0.11 | 0.00 | 0.05 | 0.028 | 0.28 |
| Polyserositis | 0.00 | 0.09 | 0.00 | 0.023 | 0.17 |
| Arthritis/Synovitis | 0.00 | 0.05 | 0.00 | 0.017 | 0.47 |
| Pericarditis | 0.00 | 0.05 | 0.00 | 0.017 | 0.47 |
| General Infection | 0.00 | 0.05 | 0.00 | 0.017 | 0.47 |
| Mechanical | 0.38 | 0.46 | 0.38 | 0.094 | 0.96 |
| Trauma | 0.16 | 0.23 | 0.33 | 0.075 | 0.72 |
| Broken Bone | 0.22 | 0.23 | 0.05 | 0.061 | 0.45 |
| Unknown (no visible lesions) | 1.04 | 0.73 | 0.44 | 0.152 | 0.34 |
| Other | 0.82 | 0.50 | 0.66 | 0.123 | 0.57 |
| Emaciation/Starveout | 0.11 | 0.05 | 0.00 | 0.028 | 0.31 |
| Pendulous Crop | 0.66 | 0.27 | 0.55 | 0.102 | 0.28 |
| Decomposed | 0.00 | 0.09 | 0.00 | 0.023 | 0.17 |
| General | 0.05 | 0.09 | 0.11 | 0.033 | 0.82 |
| Total | 6.48a | 5.36ab | 5.22b | 0.307 | 0.02 |
Block differed significantly: included as a random factor (P < 0.05).
Values with different letters within the same row differ significantly (P < 0.05).
Standard error of the mean.
Mobility, Footpad Scores, and Litter Quality
Flicker treatment had no effect on mobility, assessed through gait score (Table 6). Footpad scores were affected by flicker frequency, with a higher percentage of hens with a score of 0 (no lesion) when reared under 90 Hz (P = 0.02) compared to 30 or 195 Hz. Additionally, a lower percentage of hens reared under 90 Hz scored in category of 4 (severe lesion) than in the 30 or 195 Hz (P = 0.01; Table 6). As a result, average footpad lesion scores for the 90 Hz treatment were lower (improved) compared to the other treatments (P = 0.02; Table 6). Flicker did not affect litter quality (P = 0.50; data not shown).
Table 6.
Effect of LED light-flicker frequency (30, 90, or 195 Hz) on average and individual scores for mobility (gait scores; scale 0–51) and average and individual scores for footpad lesions (scale 0–42) in 10-wk-old turkey hens.
| % in each category | Light-flicker frequency (Hz) |
SEM3 | P-value | ||
|---|---|---|---|---|---|
| 30 | 90 | 195 | |||
| Gait Scores | |||||
| 0* | 64.67 | 48.61 | 49.33 | 5.270 | 0.11 |
| 1* | 30.00 | 42.22 | 40.67 | 4.070 | 0.18 |
| 2* | 5.33 | 9.17 | 10.00 | 1.691 | 0.30 |
| 3* | 0.00 | 0.00 | 0.00 | - | - |
| 4* | 0.00 | 0.00 | 0.00 | - | - |
| Average Score* | 0.41 | 0.61 | 0.61 | 0.067 | 0.10 |
| Footpad Lesion Scores | |||||
| 0 | 10.67b | 24.44a | 10.67b | 3.855 | 0.02 |
| 1 | 16.67 | 26.11 | 15.33 | 3.256 | 0.10 |
| 2 | 24.00 | 28.89 | 28.67 | 2.674 | 0.57 |
| 3 | 27.33 | 14.44 | 25.33 | 3.347 | 0.06 |
| 4 | 21.33a | 6.11b | 20.00a | 4.093 | 0.01 |
| Average Score* | 2.32a | 1.52b | 2.29a | 0.262 | 0.02 |
Block differed significantly: included as a random factor (P < 0.05).
Values with different letters within the same row differ significantly (P < 0.05).
Score of 0 = no impairment, 5 = complete lameness (adapted from Garner et al., 2002 by Vermette et al., 2016).
Score of 0 = no external signs of a lesion, 1 = harder and denser footpad than score 0, 2 = swelling and less than ¼ area necrotic, 3 = swelling and ½ area necrotic, 4 = more than ½ area necrotic (Hocking et al., 2008).
Standard error of the mean.
Feather Condition and Cleanliness
Flicker treatment had no effect on feather condition of 10-wk-old turkey hens (Total Score P = 0.16; Table 7). Feather cleanliness scores are displayed in Table 7. A higher percentage of turkey hens scored in category 1 (very clean) under 90 Hz compared to 30 and 195 Hz (P < 0.01). A lower percentage of hens reared under 90 Hz scored in category 2 (moderately clean) than the other treatments (P = 0.01). A higher percentage of hens scored in category 3 (moderately dirty) when reared under 195 Hz (P < 0.01). The average cleanliness scores of hens reared under 90 Hz were reduced (cleaner birds) compared to 195 Hz (P = 0.02).
Table 7.
Effect of LED light-flicker frequency (30, 90, or 195 Hz) on average feather condition score (scale 1–41) for each body location and feather cleanliness score (scale 1–42; percentage of hens in each category) of turkey hens at 10 wk of age.
| Light-flicker frequency (Hz) |
SEM3 | P-value | |||
|---|---|---|---|---|---|
| 30 | 90 | 195 | |||
| Feather condition score | |||||
| Back | 4.00 | 3.99 | 3.98 | 0.005 | 1.00 |
| Wing | 3.98 | 3.99 | 3.98 | 0.006 | 1.00 |
| Tail | 3.91 | 3.85 | 3.83 | 0.022 | 0.93 |
| Breast | 3.82 | 3.83 | 3.80 | 0.021 | 0.94 |
| Total Score4 | 15.71 | 15.66 | 15.59 | 0.032 | 0.16 |
| Feather cleanliness score | |||||
| 1 | 42.00b | 62.78a | 26.67c | 7.722 | <0.01 |
| 2 | 54.00a | 35.56b | 56.67a | 5.828 | 0.01 |
| 3 | 4.00b | 1.67b | 16.00a | 2.780 | <0.01 |
| 4 | 0.00 | 0.00 | 0.01 | 0.208 | 1.00 |
| Average Score* | 1.62ab | 1.39b | 1.91a | 0.100 | 0.02 |
Block differed significantly: included as a random factor (P < 0.05).
Values with different letters within the same row differ significantly (P < 0.05).
Score of 1 = no feather cover, 2 = greater than 50% of plumage missing, 3 = less than 50% of plumage missing, 4 = full intact plumage (Davami et al., 1987 and Sarica et al., 2008)
Score of 1 = very clean, 2 = moderately clean, 3 = moderately dirty, 4 = very dirty (Forkman and Keeling (2009) as modified from Wilkins et al. (2003).
Standard error of the mean.
Sum of 4 parts: back, wings, tail, breast scored on a scale of 1 to 4.
Ocular Weight and Shape
The dorso-ventral diameter was largest in birds raised under 30 Hz and smallest in turkeys reared under 195 Hz (P = 0.05; Table 8). The anterior-posterior size was largest in the 30 Hz treatment and smallest in the 90 Hz treatment (P = 0.03). No differences were noted in weight or medio-lateral diameter (P = 0.39 and P = 0.21, respectively).
Table 8.
Effect of LED light-flicker frequency (30, 90, or 195 Hz) on eye weight (g), medio-lateral diameter (mm), dorso-ventral diameter (mm), and anterior posterior size (mm) of turkey hen eyeballs at 11 wk of age.
| Light-flicker frequency (Hz) |
SEM1 | P-value | |||
|---|---|---|---|---|---|
| 30 | 90 | 195 | |||
| Eye weight | 5.75 | 5.63 | 5.67 | 0.039 | 0.39 |
| Medio-lateral diameter* | 24.45 | 24.25 | 24.35 | 0.060 | 0.21 |
| Dorso-ventral diameter* | 24.56a | 24.42ab | 24.33b | 0.069 | 0.05 |
| Anterior posterior size | 18.89a | 18.60b | 18.62ab | 0.048 | 0.03 |
Block differed significantly: included as a random factor (P < 0.05).
Values with different letters within the same row differ significantly (P < 0.05).
Standard error of the mean.
DISCUSSION
With very little known about the effects of light-flicker frequency in poultry species, this study focused on a wide range of parameters to evaluate the effects of flicker frequency on turkey hens. A reduction in BW or growth of poultry may suggest that a management practice or environmental factor is having a negative impact on the birds and compromising their welfare. The current study observed minor differences in BW at 8 wk, but these differences were no longer present when hens reached market weight. Similarly, Raabe et al. (2024) found no differences in BW by the end of production (20 wk) in turkey toms exposed to 165 Hz, 500 Hz, or 16 kHz, however it should be noted that no additional BW measurements were taken throughout the grow-out period (Raabe et al., 2024). It should also be noted that the flicker frequencies evaluated by Raabe et al. (2024) were well above the CFF of laying hens (Lisney et al., 2012), and therefore likely the assumed CFF of turkeys. This suggests that the treatments evaluated would not be perceived by the birds as flicker either consciously or unconsciously. The minor differences noted during the production cycle in the current study were likely related to a decrease in feed consumption early in life. It is possible that the hens reared under 30 Hz became habituated to the flicker or there may have been an age effect which contributed to the lack of difference in final body weight. In addition, improvements in the F:Gm later in production suggest that birds may be exhibiting compensatory gain.
Light flicker was hypothesized to be stressful, potentially impacting the health of turkey hens during the rearing phase. To the authors’ knowledge, the influence of visible light flicker on stress and/or mortality in poultry species has not been well documented. However, effects of chronic exposure to visible light flicker in humans has been studied, with data demonstrating negative impacts including migraines, eye strain, anxiety, and epileptic episodes (Wilkins et al., 1989; Veitch and McColl, 1995; Inger et al., 2014; SCHEER, 2018; Batra et al., 2019). Chronic stress negatively impacts the immune system of poultry, reducing the number of circulating immune cells, making birds more susceptible to infection (Shini et al., 2010; Abo-Al-Ela et al., 2021). Although differences in infectious mortality in the current study may have been related to stress and immune function, it should be noted that the incidence was quite low (0.05–0.41%). The current study observed an increase in overall mortality associated with lower flicker frequencies (30 Hz), however there were no observed effects on stress parameters evaluated (Hammond et al., 2024). Raabe et al. (2024) documented no effect of flicker on turkey tom mortality when birds were exposed to frequencies of 165 Hz, 500 Hz, or 16 kHz.
Other health parameters, such as mobility, footpad lesions, and feather condition/cleanliness of poultry raised under light flicker have not previously been examined. The occurrence of footpad lesions and poorer feather cleanliness at both high (195 Hz) and low (30 Hz) frequencies are not well understood, as there is no clear cause. It is important to note that litter quality did not differ and therefore was not a likely cause of these differences.
Lighting characteristics including daylength, light intensity and flicker have been shown to impact the shape and size of bird eyeballs (Thompson and Forbes, 1999; Vermette et al., 2016; Leis et al., 2017; Lin et al., 2020). The findings of Lin et al. (2020) partially support those found in this study with reductions in the axial length (anterior-posterior size), although they did not define flicker frequency and focused on chicks. Differences in eye shape (myopia/hyperopia) through the shortening of the anterior-posterior size and increase in dorso-ventral diameter, may alter the birds’ vision, causing them to interact with their environment differently (Prescott et al., 2003; Leis et al., 2017). Changes in the eye shape without changes in weight, may lead to increased intraocular pressure resulting in cataracts or glaucoma (Whitley et al., 1984; Vermette et al., 2016).
CONCLUSION
In conclusion, visible light flicker had effects on turkey hen performance including BW, feed efficiency, and mortality, particularly in early life. The birds appear to adapt and show compensatory gain later in production. The increase in overall mortality demonstrates that visible flicker could be detrimental to production and bird well-being. Light flicker had minimal effects on parameters such as gait score, footpad lesion score, and feather score. The shape of the eye was influenced by light flicker, but effects on vision have not been evaluated and therefore should be considered in future studies. In addition, detrimental effects on human health should also be considered and therefore eliminating visible flicker from barns would be advantageous for producers. Overall, LED light-flicker frequency had minor impacts on the performance and health of turkey hens. The mortality of turkey hens could be reduced under light-flicker frequencies past the point of unconscious perception (CFF) compared to visible light flicker. Further research could extend to turkey toms to evaluate the effects of visible light-flicker.
Acknowledgments
ACKNOWLEDGMENTS
The authors would like to appreciatively acknowledge The Natural Sciences and Engineering Research Council of Canada, The Canadian Poultry Research Council, Aviagen Turkeys Inc., and Turkey Farmers of Saskatchewan for their financial contributions and Charison's Turkey Hatchery Ltd. for their in-kind contributions to this study. The authors also like to acknowledge Greengage Lighting Ltd. for their technical expertise on the setup of this project.
DISCLOSURES
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Karen Schwean-Lardner reports financial support was provided by Natural Sciences and Engineering Research Council of Canada. Karen Schwean-Lardner reports financial support was provided by Canadian Poultry Research Council. Karen Schwean-Lardner reports financial support was provided by Aviagen Turkeys Inc. Karen Schwean-Lardner reports financial support was provided by Turkey Farmers of Saskatchewan. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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