Broilers benefit from having a defined pattern of light and dark (day and night) creating distinct periods for rest and activity. A number of important physiological and behavioral processes follow normal diurnal rhythms. Therefore, defined cycles of light and dark allow broilers to experience natural patterns of growth, development, and behavior.
Lighting programs should be simple in design and easy to implement.
There are four important components to a lighting program. These are:
• Photoperiod length – the number of hours of light and dark given in a 24 hour period.
• Photoperiod distribution – how the hours of light and dark are distributed throughout a 24 hour period.
• Wavelength - color of the light.
• Light Intensity – how bright the light provided is.
The interactive effects of these factors need to be taken into account when lighting broilers. For example, some production or welfare parameters (growth, FCR, mortality) may change as the distribution of light and dark changes. Also, as light intensity changes, so does wavelength.
Light Duration and Pattern
The lighting program used by many broiler growers in the past has been to provide what is essentially continuous lighting (a long continuous light period, followed by a short dark period of up to an hour). The belief was that if lights were on continually, birds would eat and drink more, and grow faster. This assumption has now been shown to be false. Not only does continuous or near continuous light actually result in depressed market weights, it has negative impacts on broiler health and welfare as well.
Aviagen does not, therefore, recommend continuous or near continuous lighting for the life of the broiler flock.
Recent information from trials has suggested that:
• After 7 days of age around 5 hours of darkness may be optimum (4-6 hours).
• There is no reduction in growth rate to 39 days and possibly an increase to 49 days of age. Feed conversion efficiency improves particularly in the later stages of growth.
• Mortality due to sudden death syndrome (SDS or flips) and mortality and morbidity from ascites and skeletal disorders are reduced.
• Bird mobility is improved and the severity of footpad lesions may be reduced.
• The proportion of meat as leg meat may be increased.
• The welfare of the birds is improved as a more normal biological rhythm including rest is facilitated.
The degree to which a lighting program will effect broiler production is influenced by a number of factors:
• The time of program implementation: early implementation being most effective in benefiting bird health.
• Age at processing: older birds being likely to benefit more from darkness exposure.
• Environment: the effects of increased stocking density (above recommended levels) will be made worse by longer darkness exposure, but adjustments such as the use of dawn to dusk systems will help alleviate these issues.
• Feeder management: the effects of limited feeder space will be made worse by longer darkness exposure, but again, proper management of lighting programs (i.e. dawn and dusk systems) can help alleviate the problem.
• Rate of bird growth: the impact of lighting will be greater in rapidly growing birds.
All lighting programs should provide for a long daylength such as 23 hours light and 1 hour dark in the early stages of growth - up to 7 days of age. This will ensure chicks have a good early feed intake. Reducing light too early will reduce feeding and drinking activity and depress early body-weight gains.
It is recommended that a minimum 4 hours of darkness should be provided from 7 days of age. Failure to do this will result in:
• Abnormal feeding and drinking behaviors due to sleep deprivation.
• Suboptimal biological performance.
• Reduced bird welfare.