Light is a vital external parameter and is now considered an important management tool in broiler production. Getting light distribution, intermittent lighting and lighting colour right can positively affect growth and produce more uniform birds.
What you can’t see, you can’t eat. One of the most important aspects of lighting in broiler houses is that adequate light helps chicks find feeders and therefore receive the right amount of nutrition to support growth. Light can also decrease bird stress while stimulating feed and water intake, thereby improving the feed conversion ratio (FCR) and increasing growth rates. In addition, light can significantly decrease the huddling of birds, which is a common problem that can lead to higher mortality and wet litter causing footpad lesions and breast blisters.
The light should be evenly distributed in the chicken houses (Table 1). The use of light reflectors helps save power and electricity. It has been estimated that a 25 Watt bulb (or LED equivalent) with a reflector could provide the same amount of light as a 40 Watt bulb without a reflector. An alternative approach is to clean the bulbs regularly. Light intensity increases by up to 100% or more when bulbs are clean.
Appropriate intermittent lighting schedules such as repeated short 1L-3D cycles improve broiler performance and hence increase profitability since only small investments are required. Such lighting schedules also have benefits for poultry health and alleviate environmental pollution: 2 issues that are currently a burden in intensive poultry husbandry.
In several experiments changing from continuous lighting to intermittent lighting at an early age initially reduces the body weight gain of broiler chickens. However, this was then followed by a period of compensatory growth with an improvement of 1.6% in final body weight at slaughter age. There was also a 3.6% improvement in feed efficiency with intermittent lighting compared with continuous lighting. This is an important advantage as feed costs represent at least 70% of the total production costs. Improving feed conversion by 3.6% under the intermittent lighting system would mean a reduction in cumulative feed intake of about 125 g per broiler.
It was also reported that broiler chickens raised in 1L-3D conditions were much more efficient in retaining dietary nitrogen than their counterparts with continuous lighting. Total excreta output on a dry matter basis was also considerably reduced using this intermittent lighting schedule. This means that if intermittent lighting schedules were to be applied on a large scale, a considerable reduction in nitrogen pollution and excreta excesses could be achieved.
Applying intermittent lighting also reduced the proportional weight of fat, suggesting a reduction in total carcass fat content at slaughter weight. The reduced carcass fat content of these broilers likely contributes to their improved feed efficiency, as well as to the image of poultry meat as a lean meat which is generally preferred by consumers.
In terms of health, it was reported that the application of the intermittent lighting schedule significantly reduced the incidence of bone disorders due to the increased physical activity of intermittent lighting broilers during the photoperiods, thereby favouring bone strength development. Intermittent lighting also reduces the occurrence of ascites (water belly). In one study, supplementing the broiler feed with minute quantities of active thyroid hormone (T3) raised metabolism dramatically and hence increased the number of birds dying from ascites when reared under continuous lighting. With intermittent lighting, however, the number of affected birds reduced by 50-60%.
Different colours have different effects on the performance of chickens, whether a given colour of light is used continuously throughout the production cycle or alternated with other colours. The choice of a lighting colour system, therefore, should be made based on the production target sought or the production problem to be solved.
Generally, birds prefer to consume feed under white light because it helps them identify texture differences they cannot see under other colours. Better results, however, could be obtained when light colours interacted with other factors, such as light intensity and feed colour. In some studies, feed intake and growth performance improved under blue or green lights provided at high rather than low intensity. In other studies, an improvement was also seen with red-dyed feed given under blue light. No other combinations of light and feed colours have yet been examined, however.
Blue or green lights may be used to keep birds calm by reducing hypothalamic gonadotropin production and thus reducing hyperactivity, pecking damage and energy costs, without compromising the welfare of the birds. In other cases, poultry producers may be prompted to use red light to control cannibalism because birds cannot see the blood stimulant under red light. Red light, however, should not be used as the sole basis for alleviating cannibalism problems. Rather, other management and feeding strategies should also be adopted in this case for better control, including beak trimming, lowering the brooding temperature, removal of severely injured birds, providing access to feed and water at all times and balancing the diet appropriately for age and type of the chickens reared, etc.
Under any given light colour, performance may decrease when chickens are reared at high stocking densities (Table 2). The reduced performance in this case may be attributed to the fact that there is a general tendency towards a reduced growth rate with increasing stocking density, not only because of the reduced feed intake under such conditions but also because of the loss of feed energy to immunological responses and other body adjustments.
The reduced growth rate may be further attributed to the disruption in gut microflora that aid digestion, the absorption of nutrients and improve intestinal micro-architecture. A high stocking density also affects the microbial profile of the litter, with a greater volume of toxins produced. The toxins affect the utilisation of feed nutrients for growth and other biological functions. Along with stocking density, other factors that negatively affect performance – such as poor nutrition, adverse microclimate, disease outbreaks, or inadequate biosecurity programmes – should all be considered.
References available on request.