A switch to new lighting ideas

The lighting pattern in most free range sheds is as predictable as night following day.

Pullets which have come off a 10 hour day on the rearing farm are switched to 12 hours on arrival and then extended to 16 hours over the next few weeks.

But just in case you think there is a lighting law which lays down that this must be so just consider the following:

There is no need for a modern layer’s day length to be any longer than 13 or 14 hours.

Longer days mean more seconds and increased mortality.

Switching pullets from eight or ten hours to a full day length in one go has almost exactly the same effect as the traditional ’step-up’ system.

These eye-opening facts come from a new book called Poultry Lighting, the theory and practice written by two of the world’s leading authorities on the subject, Peter Lewis and Trevor Morris.

Their book, the first ever published on the subject, covers everything from how poultry see to the affects of wavelength on sexual development. It covers broilers, turkeys and waterfowl as well as laying hens and is no doubt destined to become the ’lighting bible’ for students. But it also contains practical advice for poultry farmers, even if it does overturn some long held beliefs.

Pullet arrival

On arrival it is recommended to give pullets a single long day of 20 hours to allow them to find feed and water, with access to water only for the first two or three hours. This will have no effect on the timing of sexual development because pullets require at least a week of long days to induce sexual maturation.

Stimulating the onset of lay

The ovary and the oviduct take about 14 days to mature. So assuming that pullets are transferred at 15 or 16 weeks and are expected to reach five per cent production by 18 weeks they need to be photo-stimulated immediately after arrival. If they are not stimulated by 16 weeks then the first birds to mature will do so in response to the rearing base day length and not to any step-ups by the producer. Research has shown that the most ’stimulatory transfer’ is a move from 10 hours to 14 hours.

Ignoring the traditional step-up programme and going for just one four hour increase has no adverse effects on performance it merely modifies it. The total egg output will be the same but one-step flocks tend to mature earlier and have a slightly higher peak. They will also lay more eggs but of a slightly smaller size than birds on a multi-step regime.

Photo-stimulating pullets later than 17 weeks has minimal effect on the timing of 50 per cent lay. It will, however, still encourage an increase in feed intake, influence the time of day at which eggs are laid and may well speed up the onset of lay in later maturing individuals in the flock.

Interestingly the strongest response to an increase in day length is at 9 to 10 weeks when birds can become sexually mature. But at these ages they have too low a bodyweight and too small a skeletal frame and will subsequently have poor egg production.

It is recommended that pullets are not photo-stimulated before 14 weeks of age nor when their bodyweight is below 75 per cent of mature weight.

Stimulating feed intake

The other purpose of increasing day length is to stimulate feed intake. Researchers at Bristol University moved two batches of pullets at 15 weeks. They kept one batch on 8 hours a day and switched the other to 14 hours at 17 weeks. At 20 weeks the birds on 8 hours were still eating less than on arrival. The intake of the 14 hour birds had increased by 40g/day within two weeks.

Daylength during lay in lightproof housing

The 16 hour day is now standard. But its use stems from the time when poultry houses were not adequately light-proofed and was to comply with the golden rule of never allowing daylength to decrease during lay.

There is now no need for daylength to be any longer than 13 or 14 hours for brown egg hybrids and 10 or 11 hours for white egg hybrids.

The laying hen produces more heat during light hours than during darkness and so longer daylength results in an increase in feed intake to satisfy the extra demand for energy. Daily intake goes up by a little over 1g per bird for every extra hour of daylength, which matches the 1 per cent increase in heat output. As a consequence average egg weight increases by about 0.25g for each 1 hour extension of the light period.

But in addition to extra electricity usage longer days have three other negative consequences; thinner shells, more body-checked eggs and higher mortality. The thinning of shells is actually a result of shorter nights than longer days and part of the increased mortality can be attributed to the higher intake of energy that predisposes the birds to ruptured fatty livers.

Body-checked eggs are thought to be caused by a stress induced surge of adrenalin causing a strong muscular contraction at a time when the shell is fragile. The shell cracks around the ’equator’ and is then repaired, causing the bulge. It seems that the adrenalin surge is associated with lights-out for hens on a long daylength. The end of light for hens on shorter days occurs before most eggs have reached the fragile stage.

Attempting to correct this problem by decreasing the daylength can lead to a production drop. The answer is do not put birds on a daylength longer than 14 hours in the first place.

Light intensity

Today’s hybrids are far more tolerant of low light intensities than earlier strains but there appears to be no reason to change from the long-standing recommended minimum figure of between 5 and 10 lux at the feed trough for optimum performance. Brighter light intensities do not stimulate feed intake. In fact if anything they marginally suppress it. Bright intensities are also associated with a very small, but significant, decrease in egg weight.

Natural lighting

In some free range and organic units it is unavoidable that the birds receive natural daylight inside the shed. And at certain times of the year natural daylength may exceed 16 hours.

Even when pullets have been reared in lightproof housing on a 10 hour day an immediate transfer to 16 hour days will not adversely affect performance. The important point is that there must be no decrease in daylength after the longest day. This is easily achieved by supplementing the decreasing natural daylength with artificial lighting.

Where birds are exposed to natural lighting throughout the rearing and laying period satisfactory egg production can still be achieved by providing a constant 14 hour daylength from day old to death.

’Poultry Lighting, the theory and practice’ written by Peter Lewis and Trevor Morris is published by Northcot, price £40 including postage. An order form can be obtained from www.poultrylighting.co.uk or by writing directly to Northcot, PO Box 1876, Andover SP10 9AT