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The Importance of Light for Laying Hens Light stimulation affects more than just the number of eggs that a hen lays. It also affects the reproductive function, the physical activity and will alter the laying’s hen behaviour. The affect of light is not primarily through the eyes of a chicken, but through part of the brain. In very much the same way that a photovoltaic cell works, the sun’s energy hits the chicken as photons. These photons penetrate the feathers, skin and skull to hit a part of the brain called the extraretinal receptor. The ability of light to affect this part of the brain is to do with the light intensity and wavelength. Light Intensity This doesn’t mean that the lighting for chickens has to be bright. Light intensity is often measured in lux or foot candles (not fork handles!). A typical bright summer’s day would measure around 70,000 to 90,00 lux. A typical office desk with a lamp would be 450 – 600 lux. In a poultry shed a desirable lighting would be around 10-20 lux. Too bright could have a detrimental affect,increasing the possibility of feather pecking and aggression. Conditioning the Pullet To optimise the egg production of a hen it needs to be conditioned as a pullet.That is, she needs to be taught to interpret day length. The receptors in the brain are ‘photosensitive’ between 11-16 hours after dawn, (or after the lightshave been turned on), assuming a 24 hour day. A pullet will perceive a long dayif, after 11-16 hours of light, during the photo sensitive period, there is still light. If during this period there is no light, the pullet will perceive this as a short day, such as we find in winter. To allow proper growth and weight gain, but at the same time avoid early sexualmaturity, a pullet should be allowed 8-10 hours of day length for the 8 weeks before being moved into the laying house. Once in the laying house if she is then given long days, (that is light during the photo sensitive period 11-16hours after dawn), she should be physically ready with regards to age and body condition and will start egg production quickly. Decreasing Light Levels Thehen’s egg production will climb to a peak and then slowly reduce over time.This is due to something called photo refractive. While still being stimulatedby light during the photo sensitive period, the response becomes weaker overtime. This can still, however, be manipulated by the duration of light given.If the day length is kept over 16 hours the photo refractory process speeds up,reducing egg production more quickly. If, however, the day length is reduced,but is still within the photo sensitive period, this will slow down the reduction in eggs. Lighting regimes can be very complex, perhaps too complex. While it is undoubtedly beneficial to control the lights for your pullets, if they are a spring flocknatural daylight is probably as good for the layers.
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