Broilers are currently reared under nearly continuous lighting (CL) schedules. However, the suitability of such lighting regimens may be questioned in terms of performance and welfare. This paper reviews the literature concerning the effects of intermittent lighting (IL) schedules on these issues. Final body weights at market age of broilers reared under IL schedules are equal to, or even higher than, those of broilers reared under CL schedules. However, endogenous (genotype and sex) and exogenous (dietary composition, feeder space, etc.) factors may interact with the lighting schedule. In contrast, feed conversion is consistently improved with IL, partly as a consequence of a more concave growth curve (initial growth depression followed by compensatory growth). Inconsistencies in the literature concerning the effect of IL on (abdominal) fat content and dressing yield are caused by interactions with other factors. However, it is clearly demonstrated that IL reduces leg abnormalities, in particular the incidence of twisted legs. Additional welfare benefits of IL are found in reduced physiological stress and improved eye condition. An increase in the amount of catching damage has been observed with IL, but this may be avoided by modifying light management before commencement of the catching operation. The importance of light is not restricted to the lighting schedule; aspects of the light quality are also important. Although the data related to light intensity are conflicting, it is generally recommended that an intensity of 51ux should be provided. Whilst fluorescent light does not affect broiler performance adversely, its lower use of electricity compared with incandescent lighting does reduce input costs. More research is needed to evaluate the impact of these qualitative aspects of lighting on poultry welfare.

An automatic calorimeter, based on gravimetric principles, for studies on the energy metabolism of the fowl, with simultaneous recording of the physical activity, is described. In order to reduce errors in the determination of heat production to below 3% a three hour experimental period is necessary. The length of this period in comparison to that of the Pettenkofer system is discussed. The relation between heat production and physical activity shows a good fit in a linear regression equation, from which resting heat production is derived. Up to 25% of the total heat production is related to physical activity, mainly during the day-time.

1. The influence of the flicker frequency on physical activity and energy expenditure of broilers was studied using commercially available high-frequency (HF) and low-frequency (LF) fluorescent lamps in a 23L:1D lighting schedule. 2. Broilers were reared under and adapted to HF. They were alternately subjected to HF and LF during measurement of activity and energy expenditure. 3. In comparison with HF, LF inhibited activity (number and intensity of movements), but did not influence energy expenditure. 4. It was concluded that the 100 Hz flickering of low-frequency light is detected by broilers and has measurable behavioural effects upon them. 5. The results were discussed in relation to current knowledge of human and birds' critical flicker frequency and perception.