Poultry prefer to be active during the day and rest when it is dark. Provision of daily light and dark periods therefore has important implications for poultry productivity and welfare. Although many lighting programs that include one or more dark periods per day are used by the industry, many questions need to be answered to optimize lighting programs that further enhance bird welfare without unduly compromising productivity. Dr. Hank Classen and his team at the University of Saskatchewan have been working to help answer some of these questions:
How should the darkness be distributed?
A given number of hours of darkness can be given to a flock all at once, or in short periods distributed throughout the day. Dr. Classen’s team looked at six or nine hours of darkness provided in one, two or three periods per day. The researchers found that splitting up the dark period had no effect on growth rate, body weight at market age, or feed conversion ratio. However, they did notice a slight increase in breast meat yield when darkness was given in two or three periods rather than just one. On the other hand, providing the dark hours all at once consistently resulted in less mortality. When the researchers observed the behaviour of the birds given the various lighting programs, they noted more preening, dust-bathing and stretching when the birds were given darkness all at once (especially for the longer, nine-hour dark period), which may suggest improved welfare.
When should darkness first be given to chicks?
In another experiment, broiler chicks were started off on 23 hours of light and one hour of dark per day (23L:1D). They were then switched to a daily program with six hours of darkness (18L:6D) at one, four, seven or 10 days of age. The lighting change resulted in an immediate decline in the rate of body weight gain, but in all cases the birds given more darkness were just as heavy by market age (39 days) as those given only one hour of darkness. Longer exposure to darkness had no effect on feed conversion ratio. Mortality was less when the switch to 18L:6D was made early. However breast meat yield (percent of live weight) was lowest when the program was started on day one. The researchers suggest starting a lighting program when the chicks are four days of age.
How bright should the lights be?
An important consideration in any lighting program is light intensity. Dr. Classen’s group started chicks at 40 lux light intensity and 23 hours of light for the first seven days. Birds were then switched to 17 hours of light at 1, 10, 20, or 40 lux. Production traits (body weight, feed conversion, mortality) were not affected by light intensity in this trial but carcass, thigh and drum yield decreased as light intensity increased. Increasing light levels also resulted in decreased incidence of foot pad lesions during these trials. Birds exposed to low light levels displayed fewer behaviours that the researchers associated with welfare. The lowest level also affected eye development. Based on these results, it is recommended that lighting programs for broilers use 10 lux as a minimum light intensity.
How do lighting programs affect leg weakness?
Throughout these studies, Dr. Classen’s group looked at the effect of various lighting programs on bird mobility and leg weakness. One method of doing so is known as gait scoring. It is performed by trained technicians watching birds walk and scoring their movements using predetermined and well-defined criteria. The most common gait scoring system uses a range from 0 (no visible leg issues) to 5 (unable to stand). Previous research has shown that birds scoring 3 or higher are experiencing some degree of pain. Dr. Classen’s work suggests that birds scoring a two may also be in pain, which may represent a welfare concern. Accurate and consistent gait scoring requires training. Even with training, scoring is somewhat subjective and the technique is time consuming. As such, it may not be a useful assessment tool on farm. Dr. Classen’s group has been evaluating the use of force plate analysis as an objective measure of leg weakness. As the name suggests, the technology can measure the amount of force, both vertically and laterally, that a bird exerts on each leg. While the technology shows some potential, it needs to be more fully developed to become a reliable, objective measure of leg weakness in birds.
Results from this work are published in the journal Poultry Science. For more details on any CPRC activities, please contact Gord Speksnijder at the Canadian Poultry Research Council, 483 Arkell Road, R.R. #2, Guelph, ON, N1H 6H8, by phone at 289-251-2990, by fax at 519-837-3584, by e-mail at info@cp-rc.ca, or visit us at www.cp-rc.ca.
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