Effects of photoperiod and melatonin on nitrogen partitioning and production performance of Inner Mongolia White Cashmere Goats

Abstract

This study investigated the effect of photoperiod and melatonin (MT) on nitrogen partitioning in Inner Mongolia White Cashmere goats in telogen in order to regulate nitrogen partitioning between the body and the fur, and promote cashmere production. Thirty-six castrated mature goats, with live weights ranging from 23 to 25 kg, were randomly allocated into three groups then exposed to different photoperiods (long daily photoperiod, LDPP; short daily photoperiod, SDPP; natural daily photoperiod, NDPP). In each group, half of the goats were implanted with MT. Total nitrogen sediment (ΔN) was tested with a general digestive and metabolism method. Body nitrogen sediment (N_B) was measured by isotope dilution technique of tritiated water at the beginning and at the end of the experiment (N_B = BN_end-BN_beg) and fur nitrogen deposited (N_F) was calculated using the formula N_F = ΔN-N_B. Results showed that: (1) there was a significant difference in N_B and N_F partitioning in different treatments of photo period and MT. The NF partitioning was increased with the shortening of photoperiod and it was higher in the implanted groups than in the non-implanted groups. The minimum and maximum percentages in LDPP and SDPP+MT were (23.6±0.46)% and (36.1±0.79)% respectively. There was a strong interaction between SDPP and implantation of MT; while BN partitioning showed the reverse for photoperiod and implantation of MT; (2) there is an additional cashmere production of (338.83±72) g in SDPP and implanted groups with an average increase of 73.86%. The traits of the newly grown cashmere were all in the range of the textile standard; (3) hormones related to nitrogen partitioning and body composition varied with different treatments: the levels of MT and insulin (INS) increased with the shortening of photoperiod and were higher in the implanted groups than in the non-implanted groups, and there was a strong interaction between SDPP and MT implantation; prolactin, insulin like growth factor I and leptin showed the opposite results to MT and INS. This study provides evidence that MT and photoperiod can be used to regulate nitrogen partitioning, modulate cashmere goat body composition and improve cashmere production in practice. The technique can be extended to Inner Mongolia and other cashmere goat raising areas in China.