A good light-management program is important for maximization of laying hen productivity, since it is a means of controlling the hen's behavior, metabolism, physical activity, productivity, and egg size by advancing or retarding the onset of egg production.1-1-1 Lighting program recommendations vary slightly depending on house type, season, latitude of the farm, and layer breed, but there are components that are common to all. These components will determine the lighting program components of the rearing and laying periods, including the pattern of light and dark periods, intensity, and bird age at stimulation. Regardless of the house type, the light duration should not increase during the first 14 weeks of the pullet flock's life. In fact, pullets should be grown on decreasing day lengths (Fig. 1).
Three components of a lighting program can influence the light threshold, which is the intensity or duration of light perceived by the pullet. The first component is the light intensity. Pullets should be reared in light intensities ranging from 0.5 ft candle (fc) (5 lux) to 1 fc (10 lux). The second component, the wavelength of the light source (photons), is important for the ability of the pullet to perceive the light intensity. Different light sources used in today's poultry houses emit light of differing photon outputs, which impacts the intensity perceived by the hen. Therefore, to understand and equalize these components of light ensure that the birds are receiving the proper light intensity. The third component, duration of the light period, is designed to optimize the physiological development of the pullet during the rearing period prior to the onset of egg production. The sexual maturity of the pullets is delayed by restricting the duration of the light period to below a threshold of 11 12 hours of light. Pullets must then be exposed to increased day lengths during the latter stage of the rearing period to stimulate ovary and oviduct development. When the pullet's body weight meets the target for the strain, the maximum day length must be increased past the threshold of 14 hours to stimulate the onset of reproduction and ovulation by 18 weeks (Fig. 2). The hen is usually limited to a maximum day length of 16 to 17 hours, depending on the laying house type and the latitude, which determines the longest, day length. The maximum day length used must be as long as the longest natural day length for the area, including one-half hour before sunrise and one-half hour after sunset on June 21, for northern latitudes. Day length must not decrease during the laying phases, or the hens will react by reducing or stopping production.
The use of molting as a management tool also includes the use of a specific lighting program to take the birds out of and then return them to production. Generally, the day length is reduced to 8 hours at the initiation of the molt, resulting in the cessation of production. Regardless of the molting program, the utilization of increased day length followed by an immediate reduction in day length facilitates the cessation of egg production and initiation of the resting period.
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