POULTRY FACT SHEET NO. 14
UNIVERSITY OF CALIFORNIA
Lighting Programs For Table Egg Layers
Ralph A. Ernst
Laying pullets are usually exposed to a stimulatory lighting program at 16 to 23 weeks of age. A stimulatory lighting program is defined as one which provides light of adequate intensity in the photo-sensitive period (see Figure 1). Chickens perceive dawn as the first light following the longest dark period in the 24 hour cycle. Therefore, photo-schedules often contain one longer dark period to establish the photo-sensitive phase and time of oviposition. Continuous light or short repeated cycles such as 1 hour light followed by 2 hour darkness (1L:2D) are photo-stimulatory because there is always adequate light within the photo-sensitive period regardless of the light period perceived as dawn. There are an infinite number of photo-schedules which would be stimulatory for chickens of an appropriate age. The challenge is to find a schedule which will optimize the profitability of the flock.
Age to Light Pullets
Research has shown that there is an optimum age for pullets to reach sexual maturity (50% lay) for each genetic stock and each set of economic conditions. In general, very early sexual maturity for the strain (produced by photo-stimulation at an early age) results in more total eggs but large numbers of small and peewee eggs. In contrast, if sexual maturity is delayed too long very few small eggs will be produced but the total mass of eggs produced will be reduced.
Decreasing or Increasing Day Lengths
Decreasing day lengths inhibit secretion of reproductive hormones from the pituitary gland and should never be allowed to occur when egg production is desired. Increasing day lengths stimulate a reproductive response even when the light does not extend into the photo-sensitive period as described in Figure 1 (e.g. increasing from an 8 hour day). Decreases in daylight are often used as part of a molting program to inhibit egg production.
The minimum recommended light intensity to photo stimulate hens is .5 ft. candles (5 lux) measured at the feed trough in the darkest part of the house. The lighting system should be designed with a slightly higher light intensity because lamps decrease in light output as they age or if they are not clean.
In photo-stimulatory photo-periods the light phase of a 24 hour cycle can be interrupted by any number of dark periods so long as none of the dark periods exceeds the length of the major dark period which determines dawn. If the later occurs the chicken will perceive this dark period as night and first light following it will become dawn, resulting in a new photosensitive period (often called phase shifting). The short repeating cycle of 1L:2D is a skeleton photo period for a 24 hr. light cycle (it affects the neuro-endocrine system of the chicken like continuous light).
This program starts from a constant short (usually 8 hour) or decreasing day length. At the age when stimulation will begin the day length is usually increased by increments of 15 or 30 minutes per week. Often a larger increase in day length is given during the first week to stimulate earlier sexual maturity. The combination of growing period day length, age step-up is started, and presence or absence of an initial abrupt increase, are all important in determining how pullets will respond. A step-up program from a constant 8 hour day length will result in later sexual maturity than either a program where a large increase is given before the step increases are started, or a program which increases day length abruptly to a photo-stimulatory photo-period. In general pullets respond more slowly to step-up programs and show a less pronounced peak but lay more eggs later in the cycle so that production to 65 weeks of age is the same. Step-up programs which start from a 12 hour day length result in earlier sexual maturity than those which start from an 8 hour day length. Step increases are usually discontinued when day length reaches 14 to 17 hours.
Researchers at Cornell University have described an intermittent lighting program which reduces energy costs. It is started by abruptly changing pullets from a constant non-stimulatory day length (e.g. 8L:16D) to a 14 hour day length with a photoschedule of 2L:4D:8L:10D. The hens respond to this program as if the 2L:4D:8L were all light. The longer dark period is essential if the bird is to respond to the first light period (2L) as dawn. A widely used modification of this program (.5L:5.5D:8L:10D) is very similar but uses slightly less energy.
Bio-MittentTM is a trademark of Purina Mills. The program was developed and tested in the company's research unit. This program uses short periods of darkness within each hour of light to reduce electrical cost and improve feed conversion. At 36 weeks of age the changes are made using the following schedule.
*the last hour of the light period must end with 15 minutes light.
Changes are made gradually to allow the birds to adjust their eating patterns to the light periods. Attempts to use the program during early lay have depressed egg production, probably due to the reduced eating time. This program assumes moderate temperatures in the house. If temperatures become extremely cold it may be necessary to temporarily substitute 30 minute light periods in all or part of the cycles.
Intermittent Programs For Open Housing
Researchers at the University of Florida have developed a skeleton lighting program for use in open houses. It utilizes one hour of light from 3:30 to 4:30 a.m. and one hour from 7:30 to 8:30 p.m. plus natural daylight as available. This program has resulted in performance comparable to traditional programs (e.g. morning and evening lights to maintain a constant stimulatory day length).
Research on ahemeral lighting (other than 24 hour day length) has demonstrated that longer light cycles increase egg size and egg specific gravity but may reduce egg numbers. Twenty-eight hour cycles have been successfully used, on commercial farms to increase early egg size. The schedule used was as follows.
Under this schedule pullets produced larger eggs with higher specific gravity without loss of egg numbers. The improved egg size continued after the birds were returned to a 24 hour cycle. If this lighting schedule is used commercially we recommend it be followed exactly.