Light is an important management tool in broiler production. If used successfully it can influence aspects of growth, productivity and behaviour, and is therefore the subject of intense research. 

Intensity influences behaviour

In practise, however, long periods of dim lighting are commonly used, despite a growing awareness that moderate-length photoperiods with brighter light intensities could benefit the welfare of the birds. Work at the University of California looked at the effects of long and moderate photoperiods at dim and bright light intensities on behaviour and health of broilers. The long photoperiod consisted of 20 hours light and 4 hours dark, while the moderate photoperiod was made up of 16 hours light and 8 hours dark. The dim photoperiods consisted of 1 lux during the day and 0.5 lux during the night whereas the bright photoperiod was 200 lux in the day and 0.5 lux at night.

There were no differences in feed conversion ratio, but the birds subjected to dim lighting were around 70g heavier than those in bright light. The birds in bright light were more active and fed more during the day but less active and fed less at night than those reared with dim light. Birds on low light intensity had larger and heavier eyes than those receiving bright light. These results suggest that light intensity, rather than photoperiod, has more influence on broiler behaviour and eye health and that very low intensity appears to dampen behavioural rhythms.

Photoperiod and sleep deprivation

Turning attention from light intensity to photoperiod, new research has focused on sleep fragmentation, a form of sleep deprivation. Based on measurements of melatonin and behavioural data, there is a strong suggestion that flocks raised under 23 hours of light do not develop synchronised circadian rhythms. Such unsychronised activity can lead to sleep fragmentation.

The joint study by Aviagen and the University of Saskatchewan looked at the impact of day length (14, 17, 20 and 23 hours) on melatonin and behavioural rhythms in Ross male broilers. Serum melatonin in birds raised on 14, 17 and 20 hour day length showed quadratic relationships with time of day. High values coincided with the dark phase whereas low values coincided with the light phase; this suggested flock synchrony. However, no relationship between behaviour and time was found for birds raised under 23 hours, suggesting unsynchronised free-running rhythms. Clearly, this should be avoided.

Abrupt changes should be avoided

Abrupt changes to a lighting programme cause an immediate and dramatic decline in feed intake and feed conversion efficiency, which can be avoided when the changes are made gradually. This has been tested using three lighting programmes: control - 23 hours light (at 20 lux) followed by 1 hour dark; abrupt - whereby an abrupt change to the lighting schedule was made on day 10, or gradual, whereby changes to lighting rhythm were increased gradually.

At 14 and 21 days of age, birds raised under the abrupt programme were lighter than those raised under the other programmes. Daily feed consumption measured from day 7 to 13, showed a significant drop in intake when the abrupt lighting change took place, while no decline was noted in the gradual change. Feed conversion ratios were poorest for control birds, and were better for gradual birds until 14 days after which gradual and abrupt birds showed similar ratios.

Fear of the dark

Because lighting conditions during incubation affect brain development and hormone regulation, there may be an effect on post-hatch behaviour, including fear-related behaviour. A trial looked at the effects of four incubation lighting conditions on the fear responses of broilers post-hatch.

Throughout incubation, Cobb broiler eggs were provided with either 0, 1, 6, or 12 hours of 550 lux full-spectrum fluorescent light daily. Post-hatch, the broilers were subjected to a range of fear tests. During all tests, the responses of the birds receiving 12 hours of light indicated that they were less fearful than broilers in other treatment groups, indicating that providing 12 hours of light during incubation reduced the fear response of the broilers when compared with the broilers incubated in complete darkness. Further work, as indicated by corticosterone and IgG concentrations, has shown that broilers provided with 12 hours of light during incubation were less affected by stressors post-hatch.

Lighting affects meat yield

Lighting in broiler houses can have more of an influence on bird performance even than strain, and this is particularly seen in breast meat yield. Researchers at Auburn University used different lighting programmes on two different strains of broilers, either tray pack or breast yield, to look at differences in meat yields. Lighting programmes used were (1) long-bright photoperiod of 23 hours light and 1 hour dark (2) increasing-dim; ie varying the number of dark hours throughout the growth cycle, and (3) split dark period and bright intensity treatment of 16 hours light, 4 dark, 2 light and 2 dark.

Body weights at day 47 were greater for the increasing dim and split dark bright treatments than for the light bright photoperiod. Feed conversion was improved at 15 days in increasing dim light relative to the other two lighting programmes. Increasing dim yielded higher wing and drum weights compared to the two other lighting programmes, while total breast yields, fillet yields and tender yields were greater when the long bright photoperiod was used. In contrast, no strain effects were seen on meat yields.

Assessing LED

Light emitting diode (LED) light sources may be potentially beneficial to lower energy costs. The efficacy of LEDs as a light source for growing broilers has been tested using different light intensities from 5 to 25 lux, in increments of 5 lux (W325). Dimmers were installed in each pen to allow ease of adjusting lux intensities. Birds were raised for the first three days using incandescent ceiling bulbs, and on day four the LED lights were lowered to treatment intensities and the overhead lights were turned off. The LED lights were left on a 24-hour light schedule, but during daylight hours the curtains were occasionally dropped to prevent birds from overheating.

Body weight gain under 5 to 25 lux was 1472g, 1480g, 1481g, 1536g, and 1541g, respectively, although the differences were not significant. Feed to gain ratios were not affected. It was observed that birds raised under higher intensities of light exhibited more physical activity than those raised under lower light intensity. The data concluded that it is possible to raise broilers under as low as 5 lux of light, from LED sources.

Switch lights to save costs

Finally, a study of lighting in broiler houses in Kentucky looked at floor level illuminance in 37 broiler houses on 25 farms in five different production complexes in Kentucky, using a light meter to measure light intensity under both “bright” and “dimmed” light conditions that were typically used. Bright light intensities ranged from 3.2 to 49.5 lux, with the intensity on most farms being concentrated in the mid to lower part of that range. The highest intensity occurred in a house that was using oversized compact fluorescent bulbs. Dim light intensities were all less than 6 lux with most farms operating at less than 3 lux. Depending on the farm, changing existing incandescent bulbs to cold cathode or compact fluorescent bulbs may save 8,000 - 12,000 kWh/house/year.