Influence of Lighting Schedule and Nutrient Density in Broiler Chickens: Effect on Growth Performance, Carcass Traits and Meat Quality (Report‪)‬

INTRODUCTION Broiler chickens have usually been kept on a continuous or nearly continuous lighting (23 L:1 D, CL) schedule so as to maximize feed intake and growth rate (Campo and Davila, 2002). Several undesirable traits, however, including increased fat deposition, higher incidence of metabolic diseases, skeletal deformities, and circulatory problems can become quite prevalent for birds reared under a continuous lighting schedule (Buys et al., 1998; Kristensen et al., 2006; Olanrewaju et al., 2006). Different types of lighting programs such as intermittent (John et al., 1993; Rahimi et al., 2005; Onbasilar et al., 2007), increasing photoperiods (Blair et al., 1993; Renema and Robinson, 2001) and a wide range of light intensities (Yahav et al., 2000; Lien et al., 2007; Blatchford et al., 2009) have been tested during the last 5 decades. Some researchers observed that an intermittent lighting (IL) schedule significantly increased growth rate (Classen and Riddell, 1989; John et al., 1993; Buyse et al., 1996) and feed conversion ratio (FCR) of broilers (Apeldoorn et al., 1999; Ohtani and Leeson, 2000; Rahimi et al., 2005), whereas others indicated that photoperiod treatments had no effect on performance (Renden et al., 1996; Lien et al., 2007; Archer et al., 2009) or that IL reduced the FCR (Onbasilar et al., 2007) of chickens. Most research on effects of lighting schedule on carcass traits showed that there was no difference between IL and CL in the percentages of abdominal fat, wings, thighs and breast muscle (Renden et al., 1996; Chen et al., 2007; Onbasilar et al., 2007), whereas Malone et al. (1980) and Rahimi et al. (2005) reported that an intermittent lighting schedule significantly reduced abdominal fat ratio. Few reports have appeared, however, of the effect of IL on meat quality of broilers. Most of the above studies used short light-dark cycles (such as 1 L:3 D), which did not make full use of natural light. There was also a need to avoid natural light when the dark period was required, especially in houses with side wall curtains where natural light can leak into the shed.