Poultry Lighting
Proper lighting for broiler breeders

It is well know that lighting patterns strongly influence the maturity of broiler and turkey breeders. However, applying the lighting programme properly demands an understanding of the physical development and response of these birds to lighting.


Photorefractoriness is a natural physiological condition that differentiates broiler breeders and turkey breeders from egg-type breeders and commercial layers, particularly regarding their response to lighting. It is a phenomenon that needs to be understood before lighting patterns can be correctly designed for either broiler or turkey breeders. The condition has long been recognised in turkeys but has only recently been acknowledged in broiler breeders. As a result, broiler breeder lighting recommendations have frequently been incorrect. It is worth noting that egg-laying hybrids no longer exhibit

photorefractoriness and therefore have fewer constraints imposed on their lighting requirements. Photorefractoriness simply means the inability to respond to light, but more specifically the lack of a sexual response to an otherwise stimulatory day length. All seasonal breeding birds are hatched in a refractory state, termed juvenile photorefractoriness, which generally prevents them from breeding in their first year. The condition is dissipated in full-fed birds by exposure to about two months of short days, which are neutral in their ability to sexually stimulate an animal (note they are not negative) and are usually no longer than nine hours. Birds, such as broiler breeders, that have their growth controlled by the feeding programme take longer to become photoresponsive. In nature, dissipation of photorefractoriness is achieved by the short days of winter, which allows the bird to commence breeding the following spring. However, after prolonged exposure to stimulatory day lengths during the summer months, the birds again become unresponsive to light, a condition called adult photorefractoriness, and generally go out of production until they have gone through a second period. 

Rearing broiler breeders

It is essential to rear broiler breeders from an early age on short days, usually 8 or 9 hours, to ensure that all birds in the flock have had their juvenile photorefractoriness dissipated by the time they are transferred to long days (≥ 11 hours) at about 20 weeks of age. When broiler breeders are reared in open-sided or inadequately light-proofed buildings, and it is not possible for them to be given short days, it is advisable to simply let them experience the naturally changing day lengths, be the photoperiods increasing or decreasing. They should not be reared on a day length equal to the expected longest natural day length (as is frequently recommended in breeder management manuals) because this will unacceptably delay maturity and reduce egg numbers. This may be the correct recommendation for egg-type stock; precocity will not be a problem even when birds are reared on increasing day lengths during the rearing period. The data in Table 1 from a study at the University of KwaZulu-Natal shows that there were no significant differences in age at 50% egg production between broiler breeders reared on increasing or decreasing day lengths and others maintained on 14 hours from day-old through to 20 weeks. However, the constant 14-hour birds laid fewer eggs, had a smaller average egg weight, and produced a lower total egg output than the birds reared under simulated naturally changing day lengths. If broiler breeders are reared on 8-hour days and photostimulated at about 20 weeks, as routinely recommended, their sexual maturity will be 3-4 weeks earlier and their egg numbers and total egg output higher than birds reared on long days (Table 2). The indisputable answer to poor light control during the rearing period is to light-proof the buildings and not to tinker with the lighting programme.

Short days required

The significant reduction in growth achieved in broiler breeders by controlling their feed intake means that none of the birds will be responsive before 10 weeks of age and at least 18 or 19 weeks of short days will be required for all birds in the flock to become photoresponsive; a stark contrast to the two months required for full-fed photorefractory species to become photosensitive. Although the time taken for a flock of broiler breeders to complete the attainment of photosensitivity is much longer than the 5-9 weeks necessary for full-fed egg-type pullets, the commencement of photoresponsiveness in a flock and the point when all birds are able to respond occur at similar points on their growth curves (0.2 and 0.4 of mature body weight for the first and last birds to respond). If, for whatever reason, a flock of broiler breeders is underweight or uneven (CV more than 10%) when they would normally be transferred to long days, increases in day length should be delayed by a week or so, depending on the size of the problem.

Accelerating body weight gain

Photostimulation of a flock that contains underweight, unresponsive birds will result in a marked delay in those particular birds’ sexual maturation and the development of a sexually uneven flock that will be difficult to manage. Even when a flock has satisfactory uniformity (CV less than 10%), photostimulation should still not be contemplated before the average body weight has reached 2 kg. Transferring broiler breeders with normal body weights to long days before they have had sufficient short days to fully dissipate juvenile photorefractoriness will result in delayed sexual maturation and sub-optimal egg production. This is because the premature photostimulation will result in the birds maturing as if they have always been on long days. Research findings show that broiler breeders transferred from 8 to 16 hours at 10 weeks of age, when they were still photorefractory, matured at a similar age to birds maintained on 16 hours but two weeks late than non-photostimulated birds maintained on 8 hours and 7 weeks later than birds transferred to 16 hours at the more usual 20 weeks (Figure 2). Although accelerating body weight gain in broiler breeders above normal breeder-targets of 2-2.2 kg speeds up the dissipation of photorefractoriness and enables them to be transferred to long days before 20 weeks, thus advancing sexual maturation and extending the laying cycle, the extra income derived from the increased egg numbers will invariably be cancelled out by the extra feed costs incurred in producing the faster growth and the increased production of un-settable, double-yolked eggs.

Day length during lay

It has been traditional to give broiler breeders an initial transfer from 8 to 11 or 12 hours at 20-22 weeks followed by a series of increases to reach a maximum of 15-16 hours at about 27 weeks of age. However, recent research has shown that the onset of adult photo-refractoriness is advanced and rates of lay during the final three months of the laying cycle depressed when broiler breeders are provided with such long days. Studies conducted at the University of KwaZulu-Natal in South Africa have suggested that the ideal programme for broiler breeders, assuming body weights and uniformity are satisfactory, is to increase day length from 8 to 13 hours at 20 weeks, either abruptly or incrementally, and to maintain this photoperiod for the remainder of the laying cycle. No benefits will be derived from giving further increases to 14, 15 or 16 hours, and shell quality will be depressed. Although 11 and 12 hours have been shown to give superior egg production to 16-hour days (Figure 3), egg-laying time occurs much earlier in the day under these day lengths and the increased proportion of eggs laid before the lights come on is likely to lead to an unacceptable number of eggs being laid outside the nest box. The risk of floor-laying is minimised by giving a 13-hour day.

Lamp, light intensity, and colour

The effect of light intensity during the rearing period on subsequent laying performance is minimal. Following an initial 2-3 days of bright light, the provision of an illuminance of at least 10 lux will be optimal and ensure that sufficient light is available for the satisfactory inspection of birds (as commonly required by welfare regulations). Whilst there is no interaction between the light intensity used during the rearing period and that given in lay, and there is no effect of light intensity on the rate of sexual development or total egg production so long as the light intensity at bird-head height is at least 10-15 lux, the recommended light intensity in the laying period is >30 lux. This brighter-than-necessary recommendation is not made for biological reasons, but rather to help minimise the number of eggs laid outside the nest box.

There is no clear evidence that the performance of broiler breeders will be increased by using other than white light, that ultraviolet light provides any benefit, or that any one particular type of lamp is superior to any other. Whilst fluorescent lamps are currently the most economic method of lighting, LED lamps will undoubtedly be the method of the future.