Why do the blind chickens lay egg more?

According to a researcher report of Guelph University, some strain of layer chicken that are naturally blind lays egg earlier than normal chicken and in production cycle they lay egg more.
The reason of more laying egg in blind chicken is currently being investigated. This issue is related to the light effect mechanism on reproduction patterns of this strains of White Leghorn which they are naturally blind and called Smokey. Discovery of this issue that how light effects on the performance of laying egg could lead to better ways to manage the light for better result in poultry farms
Reproduction in chickens usually is stimulated by increasing photoperiod. As the matter of fact the light is absorbed by the part of the brain that it`s called the hypothalamus which secretes hormones and controls part of the nervous system that is responsible for regulating automatic body functions such as temperature, blood pressure, thirst, hunger and sleep-wake cycle. But blinded light chickens are acting in the other way. Despite this fact that light directly stimulates the hypothalamus, when it`s sensed and received by retina it would cause the inhibition of reproduction and it leads to and earlier laying egg.
With comparison of light rays, two different mechanisms which are effecting on optical effect is suggested.
The first mechanism includes the wavelength of blue-green light that is mainly perceived by the retina and second mechanism involves the red spectrum, which penetrate the skull and stimulate the hypothalamus. It`s suggested that perhaps blue-green light has inhibitory properties and red rays may stimulate the laying egg.
Both of these mechanisms occur in normal birds and photoperiod causes laying egg stimulation and physiological responses. So in short days, inhibitory pathway is dominant and in long days the red light is dominant and accelerates the reproductive maturation.
Since the blind chickens don`t have retina, the inhibitory effects of blue-green light doesn’t have any effect on them, so even without increasing the day time they start laying eggs earlier. However, more research needs to be done when and how the retina should be damaged. Some blind strain chicks are born normally but they lose their sight during the first three weeks and get completely blind.
Blind chickens are less aggressive and are less stressed in dealing with people. Of course there is some problems to work with genetic blind chickens, for example it is necessary to replace the nipple mug by great cup for birds to find them easily. But it`s said that the blind birds could better get used to their environment map compared to normal birds.
However, more research is needed to determine how to use blind birds in the poultry industry.

By Dr. Maziar Mohiti Asli, Poultry Nutritionist
DGM-Technomix Scientific Group
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