I've seen posts suggesting that chickens will live longer and lay longer if they're allowed to take time off in the winter. It also seems that production strains are given added light far more often than your average backyard flock, and that production birds are more prone to reproductive tract problems, internal laying etc, tending to "burn out" more quickly than a heritage type chicken, so would this have something to do with the impression that added light shortens their lives? Just curious, trying to find out if anyone knows the science behind it ...
I've posted the link to this report before (so forgive the repeat) on research focusing primarily on how to decrease length of photorefractoriness in turkey hens (another gallinaceous bird) so as to trigger laying on `schedule', i.e., responding more rapidly and predictably to change in lighting schedule.
Siopes has found that photoperiod plays a pivotal role in regulating quail and turkey immune systems. Exposing birds to 24-hour periods when the dark period is considerably longer than the light period boosts the birds' immune systems.
"We've developed a way to regulate the immune system of an animal in a simple, inexpensive way without pharmacology," says Siopes.
The immune response to the light-dark cycle occurs quickly. "We can see effects in one to two weeks," Siopes says. The immune systems of birds kept in short-day conditions are much more robust than birds living under longer light regimes.
Siopes explains that exposing turkeys to the light equivalent of short days stimulates the pineal gland, which produces melatonin, a hormone that is a powerful immune system enhancer. The more daily darkness, the more melatonin.
It seems that 3 to 5 percent of turkey hens develop spontaneous ovarian tumors. Siopes first noticed the cancers a number of years ago when doing necropsies on turkeys. When he confirmed the masses he found in some of his birds were cancerous tumors, Siopes decided to see whether photoperiod had any effect on the cancers.
What he found was startling. By adjusting photoperiod for a shorter day length, Siopes was able to eradicate tumors. When he put the turkeys whose tumors had completely disappeared back on longer days, the tumors returned.
"We can literally make these cancers disappear and reappear by manipulating photoperiod," Siopes says. He's also found that melatonin injections will slow tumor development.
http://www.cals.ncsu.edu/agcomm/magazine/spring05/night.htm
Some lines of production chooks are more prone to reproductive problems that are genetically mediated, along with problems triggered by manipulating photoperiod one might experience increased losses. However, if maximizing egg production is the primary goal, then the hens should be `taken out' of production and processed for meat after 1.5-2yr.s.
Our production RSLs & BSLs will be 5yr. old in 3/10. They were excellent producers (with no added light) from 8/05-10/06, then the numbers dropped and the laying shifted to a more seasonal schedule (from late May- early Aug. this yr.).
We lost one Gold Sex Link to internal laying and a BSL to a large ovarian tumor that impinged on her respiratory tract (causing build up of fluid and secondary infection - pretty much drowned).
