Lights, Colour, Action!
It is well known that hens respond to increased periods of light by coming into lay. We call hens long-day breeders meaning they become reproductively active when the day length increases, signifying spring has arrived and causing an increased release of the hormone melatonin. The opposite example to a long-day breeder would be the sheep, a short-day breeder. The ewe comes into heat in the autumn when the day length decreases so that her conception, gestation and parturition align in time for spring. The ewe’s level of melatonin increases as it would in the hen but in response to the shorter day rather than the longer. Scientists and producers have successfully manipulated the role of photostimulation to their advantage in a number of species, but perhaps none as successfully as the laying hen.
We know that for welfare requirements to be met a certain level of light must be achieved, but further to that we can use lighting intensity, again to our advantage, to safeguard welfare. Schedule 3D, paragraph 3 of the Welfare of Farmed Animals (England) (Amendment) Regulations 2002 states that; “In normal conditions, in cage and multi-level systems, light intensity should be at least 5 lux, and preferably not less than 10 lux, measured at any feed trough level; in other systems, light intensity in the perching, walking and feeding areas should be at least 10 lux measured at bird eye height. However, a temporary reduction in lighting level may assist in addressing behavioural problems such as feather pecking or cannibalism.” The measurement of light is not as straight forward as it may seem. A ‘lux’ is the unit of illuminance equal to one lumen per square metre. However, the lux scale is a perceptive scale i.e., what we (humans) perceive as brightness or illuminance. The visible capability of birds and especially the chicken are far greater than human eyesight, and we do not fully understand the way in which they perceive brightness.
The Welfare of Farmed Animals (England) (Amendment) Regulation goes on to detail; “all buildings shall have light levels sufficient to allow all hens to see one another and be seen clearly, to investigate their surroundings visually and to show normal levels of activity. Where there is natural light, light apertures must be arranged in such a way that light is distributed evenly within the accommodation.” The Regulation gives the flexibility to adjust lighting regimes after a period of conditioning, in order to prevent or control health and behavioural issues. The recommendation for a dark period within the regulation is for ‘about one third of the day’ and that the lighting regime follows a 24-hour rhythm.
Sunrise to Sunset
Dimming of the lights, or phased darkness to encourage roosting behaviour, and sufficient periods of darkness to allow for proper sleep help prevent immunosuppression, aggressive behaviours and anomalies to the eye. The natural daylight spectrum during sunsets and sunrises is different from natural light at midday. There are also significant seasonal variances in the spectral composition of sunrise and sunset light. It is proposed that birds react not only to seasonal changes in day length, but also seasonal changes in the light spectrum. These facts add to the importance of considering light spectrum in the addition of sunrise/sunset controls in artificial lighting choices.
Step-down lighting programs are used through the earlier phases of the rearing process to promote growth and skeletal development before the onset of reproductive maturity. In a typical step-down lighting program, the hours of light are gradually decreased over the first 7-8 weeks. This provides the young growing flock additional hours of feeding time for growth and development. The age of reproductive maturity and egg size is not affected if the step-down period is 12 weeks or less. When the step-down period is extended beyond 12 weeks the age, sexual maturity is delayed and egg size can increase. Step-down periods longer than 12 weeks are appropriate in commercial egg markets requiring large eggs or in breeder flocks requiring larger egg weights for hatching. After the initial step-down in lights over the first 7-8 weeks, the artificial lights are set to the longest natural day length the flock will experience during the growing period. This will negate the influence that changes in natural day length would have on pullet development and the age of first egg.
The so-called “step down” procedure in the early phases of the chick’s life can be used to make the pullets more sensitive to light. After reaching 8-10 hours of light per day, the birds are kept on constant day length for several weeks. The more time the birds have during this constant phase, the more they will eat and grow. In situations where pullet rearers have difficulties to achieve the target body-weights, a longer constant day can help to improve pullet quality.
Any step-up procedure or increase in day length when birds get to an age of 14 to 15 weeks will stimulate sexual maturation. A quick step-up will induce an earlier onset of egg production, while a slow step-up will delay the onset of lay. The combination of quick step-down and quick step-up lighting is most effective for achieving early onset of lay; slow step-down and slow step-up will delay it.
Day length must never be allowed to decrease during the laying period. In free range systems, account must be taken of the natural day length at the time of housing. A commercial layer pullet of correct bodyweight will start to become reproductively mature from approximately 18 weeks, regardless of whether any light increase is given or not. However, in this event, failure to increase day length will restrict the bird’s ability to consume adequate nutrition during a period of rapid development. This will result in poor development and possible long-term damage to the bird’s productive potential as she will use her body resources to substitute the lack of nutrition. No attempt should be made to delay maturity by delaying light increases after 18 weeks. Delayed maturity should be achieved by the use of slow step down light programmes in rear.
The trending move into the use of energy efficient LED bulbs has resulted in a cooler, whiter light which is referred to as chromaticity. This is the measure of a light source’s warmth or coolness and is expressed in degrees Kelvin. The Kelvin scale runs from 2000K to 7000K, with values of 4000K or higher being considered cool or blue light. Light sources around 3500-3600K are ‘balanced’ or ‘neutral’ and lights of 3000K or less or considered warm or red light. Incandescent lights produce a continuous spectrum compared to LEDs, therefore the colour-temperature designations of LEDs can vary.
The colour rendering index (CRI) is a measure of how true the colour of an object appears under a particular light source relative to its colour under sunlight (daylight). Since the maximum rating is 100 a light source with an index of 85 or 90 is considered very good, however, from what we know of poultry production, the chromaticity (Kelvins) is more important. Cool LEDs (around 5000 Kelvins) may be a better potential replacement light source in comparison to incandescent bulbs on performance (N.B. in relation to broiler chickens).
Colour can affect perceived light intensity in poultry and different light sources have different ranges of spectral distribution. Poultry are more sensitive to some of these ranges, with a much greater ability to visualise the red-purple end of the colour spectrum including ultra-violets. With this in mind, if the light source can be dimmed to the sensitive wavelengths, then not only can energy be saved but, adequate light can be provided to stimulate birds and maintain their productivity.
Chickens, similar to other avian species and reptiles, have a light sensitive gland (pineal gland) that sits just under the frontal aspect of the skull. Light, especially long wavelength light, can penetrate the skull of these species and stimulate the gland. The hormones (melatonin) released by the gland are involved in the daily rhythm of homeostasis and the hormonal reproductive cycle, meaning that long wavelength (typically red light) gives greater stimulation of the reproductive system than short wavelength light (typically blue-green) which is better utilised by the chicken for vision. The conclusion we draw from this is that blue-green light may be better at stimulating appetite through enhanced vision, and red-warm light may be better at stimulating the reproductive system through direct stimulation of the pineal gland.
Role of light in the poultry industry:
· Replicate sunlight on a customised spectrum to enhance growth and production
· Musculoskeletal development and weight gain and improve feed conversion
· Induce earlier and longer reproductive stage for egg production – increase egg number
Use of the Light Colour Spectrum in poultry house lighting:
· Green light significantly increases growth rate at an early age by enhancing proliferation of skeletal muscle satellite cells
· Blue light increases growth at a later age by elevating plasma androgens
· Narrow-band blue light reduces locomotion. It also reduces cannibalism rate at late age
· Red light stimulates and promotes sexual activity and increases growth rates for chickens at the beginning of the rearing period.
· Red light increases locomotion, thereby minimizing leg disorders at the end of the rearing period.
· Red light reduces the amount of feed consumption per egg laid with no differences in egg size, shell weight, shell thickness, or yolk and albumin weights
· Red light has been shown to lengthen the peak production period and increase egg production by up to 10-15% per hen, while potentially decreasing food consumption by up to 20%.
Measuring lux is very straight forward. Lux meters can be readily purchased and used to monitor light levels according to assurance scheme requirements, ensuring sufficient levels for what we perceived to be adequate to welfare. However, if that light is very bright it may have insufficient quantities of red colour. Bright light will seem more intense but may lack sufficient lux and be poor for production. A satisfactory combination of red and blue light is yet to be found. Either of these being too intense can result in over stimulation and problems such as nervousness, flightiness, stress and feather pecking. Excess levels of red light tend to increase the instance of floor eggs and therefore enough white light is required to avoid this occurring in the first place.
What the future may hold?
· Colour-mixing LED bulbs that combines monochromatic colours to enhance reds and greens and produce a more uniform, tuneable, dimmable light across the entire spectrum
· Wide dimming range to replicate sunrise and sunset
· Brood lighting of full colour range to stimulate chick growth, skeletal and muscular growth promotion (blues and greens)