Abstract: This study investigated the effects of photoperiod and melatonin on nitrogen partitioning in Inner Mongolia White Cashmere goats in telogen in Inner Mongolia, north China. 18 castrated mature goats, 23~25 kg, were divided into three groups at random, each group including 6 goats were fed in pens in different rooms, which were treated with long daily photoperiod (LDPP：16L，8D), short daily photoperiod (SDPP：8L，16D) and natural daily photoperiod (NDPP), respectively. The 3 goats in each group were implanted melatonin (1.68 mg/kg) monthly from February 20 to June 20. Total deposited nitrogen (TN) was tested by general digestive and metabolism method. Body nitrogen deposited (BN) was measured by dilution technic of tritiated water at the beginning and the end of the experiment, cashmere and hair nitrogen deposited(C&HN) were calculated with C&HN= TN-BN. Results showed there was a significant difference between LDPP and SDPP in BN and C&HN. C&HN in SDPP was higher than that of LDPP evidently, the corresponding was 33.7%±0.64% vs 23.6%±0.46% (P<0.01), on the other hand, BN in SDPP was much lower than that of LDPP, the corresponding was 66.3%±0.64% vs 76.4%±0.46% (P<0.01). Intensive interaction between SDPP and implanted melatonin was also observed, the corresponding was 36.1%±0.79% for C&HN and 63.9%±0.79% for BN (P<0.01). Study showed that the hormones relative to nitrogen partitioning varied with different treatments. The level of blood melatonin was decreased with the increasing of photoperiod, implanted groups were higher than unimplanted groups. Hormones relative to protein increasing, such as PRL, IGF-I were increased with the length of photoperiod, implanted groups were lower than unimplanted groups. INS, which was related to the fat synthesization, was decreased with increasing of photoperiod, implanted groups were higher than unimplanted groups. LEP, which was related to the fat degeneration was increased with increasing of photoperiod, implanted groups were lower than unimplanted groups. As a result, average additive cashmere production was （338.83±72） g in SDPP and implanted groups, increased by 73.86%. Textile value of new cashmere was up to the standard.This study provided evidences that melatonin and photoperiod play an important role in nutrients partitioning in cashmere goats.

Key words: photoperiod, melatonin, cashmere goats, nitrogen partitioning, hormones