Abstract: 【Objective】 The purpose of the present study was to examine the efficacy of imposing intermittent lighting schedules on reduction of the incidence of ascites(or Pulmonary Hypertension Syndrome,PHS)induced by cool ambient temperature and to investigate its effect on the pulmonary vascular remodeling of broiler chickens. 【Method】 A total of three hundred and twenty broilers were randomly allocated to four groups. In one group, the continuous lighting schedule（CL）of 24 h light(L): 0 h dark (D) was maintained, ambient temperature kept normal（normal control group, NC）while in other three groups, the chickens were subjected to cool ambient temperature to induce PHS. The continuous lighting schedule of 24L:0 D (Low temperature control group,LC) and the intermittent lighting (IL) schedule of 21L:3 D(group L1) and 19 L:5D (group L2) were imposed, respectively, from 9 to 30 days of age (From day 30 onwards all groups were kept in continuous lighting). PHS incidence, body weights and feed intake were measured weekly for each group. Heart, Lung and blood samples were taken from 10 randomly selected birds per group at 14, 23, 30, 37 and 44 days of age, for the determination of the ratio of vessel wall area to total area (WA/TA), mean medial thickness in pulmonary arterioles (mMTPA),etc.【Result】The results indicated that the cool ambient temperature could increase morbidity of PHS in broilers, the values of WA/TA and mMTPA also were increased significantly, whereas the intermittent lighting (IL) schedule could successfully decrease the morbidity of PHS induced by cool ambient temperature and the values of WA/TA and mMTPA, which served as describing pulmonary vessel remodeling (P﹤0.05). Birds in IL groups were lighter than that in LC group during light restriction period, but both the final body weights and total feed conversion ratio were not significantly affected by the lighting program in all birds subjected to low temperature. 【Conclusion】It is concluded that introduction of intermittent lighting schedule during the early growing period is of benefit to reduce PHS morbidity induced by cool ambient temperature in fast-growing broilers, and attenuated pulmonary vascular remodeling may be involved in the underlying mechanisms.

Key words: Broiler, Intermittent lighting, Pulmonary hypertension syndrome, Vascular remodeling