Effects of photostimulatory light intensity on ovarian morphology and carcass traits at sexual maturity in modern and antique egg-type pullets

The effects of light intensity during sexual maturation on ovarian and carc ass morphology at first oviposition [sexual maturity (SM)] were examined in two Single Comb White Leghorn (SCWL) strains. A modern commercial layer st rain (COMM; Shaver Starcross 288) and an antique randombred control strain (ANT) were used to compare the effects of changes in laying stock on their response to varying light intensities from photostimulation (PS) until SM. Two hundred pullets from each strain were reared following COMM breeder gui delines. At 18 wk of age, 32 COMM and 32 ANT pullets were individually cage d in individually lit cages and photostimulated with light intensities of 1 , 5, 50, and 509 lx. Each bird was processed when it reached SM, and carcas s and ovarian morphology were assessed. The ANT birds came into production 9.1 d later than the COMM birds, on aver age. The ANT pullets consumed 7.0% more feed per day than COMM pullets but gained at a slower rate (ANT = 12.9 g/d; COMM = 15.0 g/d). The ANT birds re ached SM at a greater weight and with a smaller ovary than did COMM birds. Although the number of large yellow follicles (LYF) was similar between str ains (mean = 6.72), both LYF weight and first egg weight were lower in ANT birds than in COMM birds. The COMM layer strain was more growth efficient a nd had a greater emphasis on ovary maintenance. Light intensity had no effect on the timing of SM or on BW at SM, indicatin g that all intensities used were effectively able to stimulate the sexual m aturation process. However, ovary weight and number of LYF exhibited an inc reasing dose response to light intensity, particularly in the COMM birds. O verall, the birds photostimulated with 1 lx of light had reduced ovary deve lopment and were heavier than their counterparts exposed to 50 and 500 lx. Within the ANT strain, LYF numbers were not significantly affected by light intensities, whereas, within the COMM strain, LYF numbers were 4.88, 6.63, 7.88, and 8.13 for the 1-, 5-, 50-, and 500-lx intensity groups, respectiv ely. Although light intensity did not affect the rate of sexual maturation, it altered ovarian morphology and carcass lipid stores. A light intensity of 1 lx was limiting to ovarian follicle formation and caused increased car cass weight compared with birds on higher light intensity treatments. The C OMM birds were more negatively affected by low light intensity than were th e ANT birds, indicating that light intensity may be a more critical environ mental factor with modern, highly efficient SCWL strains than has previousl y been thought. Light intensity can affect the reproductive development and likely the associated egg production potential of modem layer stocks.