Sometimes it is necessary to change the times of lights on and lights off in a breeder flock in production. That is obviously the case when we start up the production of a flock and increase the day length, but also changes between summer and winter time can make it necessary to manipulate the light schedule of a flock.
When we change the lights, it is important to realise that the moment of lights off can have an influence on the flock. The moment of lights off gives a signal to the hormonal system of the bird that ultimately results in the release in the follicle from the ovary, but that is not the only reason why the moment of light off is important.
Birds have a very strict agenda, and they know more or less exact what time it is and what to expect at a certain time. If we change the moment of lights off, and then especially if we bring the moment of lights off forward, we have to realise that we are disrupting some behaviour patterns. The birds are getting ready for sleep, take their time to find a nice place and settle themselve, and all off a sudden, unexpected, they lights goes off where they were expecting that they still would have time. It is as if a woman is getting ready for bed time, is working on taking her make up off, brushing her teeth and hair etc, and all of a sudden somebody turns off the lights.
Changing the time of lights on has less impact. The birds get ready for the day, but if the lights go on earlier, they only realise that they can start their activities earlier. Also when the lights goes on later, they are awake but have to wait until the lights goes on before they can express activities.
Also delaying the moment of lights off has less impact, as it means that the birds are totally ready but the lights stay on a bit longer. Although this has more impact than changing the moment of lights on, it is relatively less invasive than turning the lights off earlier.
When we have to change the lights, we should try as much as possible to keep the moment of lights off at the same time for the birds. Of course this is much more relevant when the birds are getting to peak than when the birds are already in the second half of production and are more stable, but it is something to keep in mind also later in production.