The effects of lighting regimes on the oviposition time and egg quality in laying hens (review)

Oviposition is a complex process where oviposition time (OT), clutch length (CL), and interval length (IL) are interrelated (B.G. Roy et al., 2014). The review presented highlights the effects of lighting regimes on the oviposition time in laying hens ( Gallus gallus domsticus L.) in the relation with egg productivity and quality. OT is directly related to the ovulation time which, in turn, depends on the time of peak circulatory concentration of the luteinizing hormone (LG) released by the anterior pituitary (S.C. Wilson et al., 1984). In standard 24-hour light-dark cycles with single dark-to-light switch oviposition occurs predominantly during the light phase (F. Noddegaard, 1998; G.A. Kirdyashkina et al., 2009) while in conditions of intermittent asymmetric lighting regimes it occurs during the «subjective day» period (P.D. Lewis et al., 1990; A.Sh. Kavtarashvili et al., 2002; A.Sh. Kavtarashvili, 2007). The most of daily laid eggs in a flock are laid during ca. 5-6 hours after the switch-on (A.H. Zakaria, 2005), corresponding to average OT 13-15 hours after the switch-off (K. Lillpers, 1991; P.H. Patterson, 1997; R.J. Etches, 1990; A.Sh. Kavtarashvili et al., 2019). Average OT is determined by complex interaction of «dawn» and «dusk» signals, the latter being the most influential in this case (S.S. Liou et al., 1987; B.M. Bhati et al., 1988). In 24-30-hour light-dark cycles every 1 hour of the cycle length with the same length of the light phase decreases average OT by 1.89-1.90 hours. The increase in the length of the light phase within given light-dark cycle by 1 hour shifts average OT by 0.26-0.27 hours toward the «dusk» point. OT is known to affect egg quality. E.g. the weight of eggs laid in the morning is higher in compare to the eggs laid later (E. Tůmová et al., 2010; M. Akif Boz et al., 2014; S. Samiullah et al., 2016; A.J. Kryeziu et al., 2011). Some researchers (R.H. Harms, 1991; E. Tůmová et al., 2009) reported that egg weight, eggshell thickness and strength were higher in the eggs laid in the morning while in other studies (E. Tůmová et al., 2005, 2007; A.J. Kryeziu et al., 2011; C. Hrnčár et al., 2013) these parameters of egg quality were better in the eggs laid in the midday. The eggs laid in the morning were reported to have more intense brown eggshell pigmentation as compared to eggs laid in the midday (S. Samiullah et al., 2016; A.J. Kryeziu et al., 2011) and higher calcium content in the eggshell (E. Tůmová et al., 2014), 22.8 % lower content of cholesterol (E. Tůmová et al., 2008; M.A. Abdalla et al., 2018), as well as lower phosphorus and magnesium levels (E. Tůmová et al., 2014). Hens that laid eggs preferably in the morning were reported to have longer CL and higher egg production in compare to hens which preferably lay eggs later. The heritability coefficient (h2) of OT varies from 0.38 to 0.78 (K. Lillpers, 1991). The positive correlation ( r = 0.54) between the CL and egg production was also reported (M. Bednarczyk et al., 2000; P. Miandmients et al., 1993). In view of the above mentioned average OT and CL can be reasonably included as the criteria into the selection programs for laying hens and broiler parental hens. In addition, the optimization of OT can improve egg quality and facilitate the rational organization of egg collection in the farms. The studies on the effects of lighting regimes on OT and egg quality were performed primarily in conditions of constant lighting schemes. The further research is necessary for the intermittent lighting regimes, on individually caged hens (with the recording of egg position within the clutches) and on hens kept in group cages.