Thirty-six mature goats were allocated into three groups, i.e. long-day photoperiod, short-day photoperiod, natural day photoperiod groups, in each of the groups half of the goats had melatonin implanted. The results showed that there was a significant difference in body N retention and fleece N partitioning among the different photoperiod treatments and melatonin implants. Fleece N partitioning increased as the photoperiod declined, implanted subgroups had higher values than the non-implanted ones. Body composition was dramatically changed in different treatment groups.