Chickens adjust to the dark: study

Research shows birds that were subject to more darkness fed more frequently and sharply increased anticipatory feeding when they knew the lights were soon going to dim. | File photo

Broiler chickens learn when their barns will go dark and adjust their feeding patterns to have feed in their systems throughout that time, research at the University of Saskatchewan has found.

This leads to better feed efficiency, reduced mortality and heavier market weights.

Dr. Karen Schwean-Lardner told the Animal Nutrition Conference of Canada that work done by master’s student Tory Shynkaruk found the birds will do this when they get four, 10 or 17 hours of darkness.

Traditional barns had only one hour of darkness within a 24-hour period, on the assumption that the birds would have more visual access to feed and water and gain more weight.

Some also thought that birds subjected to longer periods of darkness would have empty gastro-intestinal tracts and then not gain as well.

Anticipatory feeding before the lights go out means the birds actually increase their feed and use their crops as a storage system.

“I can’t stress enough that they have to know when the dark period is coming,” said Schwean-Lardner, adding that the onset and length of darkness should be held steady.

Shynkaruk’s work looked at behavioural adaptation and the weights of the GI tracts and contents. She found increases in both crop and gizzard weights with longer dark periods. This indicates the birds are slowing feed passage and adapting to the length of darkness.

Birds that were subject to more darkness fed more frequently and sharply increased anticipatory feeding when they knew the lights were soon going to dim.

Schwean-Lardner said feed efficiency is improved when the feed is retained in the GI tract.

This increased final body weight, improved animal welfare and decreased mortality.

In terms of behaviour, by watching individual birds Shynkaruk found that birds that received just one hour of darkness went to the feeder 3.1 times per hour and to drink 2.8 times per hour. That compares to those that got 10 hours of darkness that fed 4.3 times per hour and drank 5.6 times per hour.

The time intervals between those feeding and drinking times were also shorter the more darkness they experienced.

Canada’s code of practice for broilers requires a minimum of four hours of darkness but the subject is controversial, according to the conference proceedings, and the practice isn’t followed worldwide.

Earlier research goes against the traditional 23 hours of light practice.

Schwean-Lardner’s own work from 2012 showed that four hours of consecutive darkness resulted in heavier market weights and that the heaviest weights at 49 days of age were at 17 hours of light and seven hours of darkness.

She said that’s because the birds initially grow at a slower rate.

“That delaying of the rapid growth at the beginning of the production cycle is really important because it allows the broilers to develop a stronger skeletal system and a stronger metabolic system before that additional weight is put on,” she said.

Birds are more mobile and spend more time playing and preening. Culls and mortality dropped.

But what darkness provides to create these better scenarios was unknown. That’s where Shynkaruk’s research — and anticipatory feeding — come into play.

Her study “has provided evidence that birds anticipate darkness (when a set dark onset is used) and eat accordingly to maintain feedstuffs throughout the gastrointestinal tract until just prior to lights on,” said the proceedings. “The gut is not completely empty at any time.”

Schwean-Lardner said producers who use longer dark periods could be sending heavier birds to market.

She said while performance isn’t a direct indicator of welfare, “when we have an environment that we think is a very excellent environment and yet we see a reduction in performance it’s a good hint that something is wrong with those birds.”

Research into bird mobility found that the poorest mobility is at 23 hours of light and the best is at 14 hours of light.

Other benefits of darkness include better ocular health. Birds can quickly develop glaucoma in too much light.

Melatonin, which regulates many other hormones, is not as well produced in light, and birds can experience sleep deprivation.

Schwean-Lardner said if changes in barn lighting have to be made that should occur in the morning.

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