The Regulation Of Melatonin,LH And FSH On The Seasonal Oestrus Of Sheep

Three sheep breeds (Tan Sheep, Tong Sheep and Small-Tail Han Sheep) were used in the present study. Blood samples were continuously collected for 24h in spring equinox, summer equinox and autumn equinox. Plasma melatonin was measured by ELISA to study the diurnal and seasonal changes in seasonal breeding sheep and non-seasonal breeding sheep. At the sama time , Blood samples were continuously collected for 7h from 3h before sunset ,at interview of 0.5h. Plasma LH and FSH were measured by RIA to study the diurnal and seasonal changes in seasonal breeding sheep and non-seasonal breeding sheep. Effects of melatonin on LH and FSH secretion, the seasonal changes of these effects and difference in breeds were studied by comparing the diurnal change of LH and FSH. In autumn, when sheep begun to have oestrus , blood samples were collected for continuous 24h, then plasma LH, FSH and melatonin were measured to study the effect of oestrus on LH, FSH and melatonin secretion and difference between breeds. The results were as follows:1. Plasma melatonin in sheep had significant diurnal changes, lower in period of light and higher at darkness. Plasma melatonin increased or decreased very quickly and completed the changes about 1h after sunset or sunraise, then last until sunrise or sunset. Plasma melatonin in sheep had also significant seasonal changes with higher in long-time photoperiod and lower in short-time photoperiod at night.2. There was difference in plasma melatonin between breeds. In summer equinox and autumn equinox, plasma melatonin in Small-Tail Han Sheep and Tong Sheep was lower than Tan Sheep at night. Plasma melatonin in Tan Sheep had obvious seasonal changes than Small-Tail Han Sheep and Tong Sheep.3. There were significant seasonal changes in plasma LH, FSH and the frequency of LH in Tan Sheep, Tong Sheep and Small-Tail Han Sheep, which were lower in spring equinox and higher in summer equinox and autumn equinox. There was no difference in plasma LH between breeds but plasma FSH in Small-Tail Han Sheep was always higher than Tong Sheep and Tan sheep, which indicated high plasma FSH in Small-Tail Han Sheep maybe one of the reasons to cause high fecundity and plasma LH maybe had no connection with seasonal oestrus and high fecundity. Small-Tail Han Sheep4. In autumn equinox, plasma LH in these three breeds had increasing trends after sunset. Plasma LH in Small-Tail Han Sheep was always increased after sunset in spring equinox, summer equinox and autumn equinox. In spring equinox, plasma FSH in these three breeds had increasing trends after sunset. Plasma FSH in Tong Sheep was always increased after sunset in spring equinox, summer equinox and autumn equinox.5. Plasma melatonin increased in Tan Sheep and Tong Sheep and significant increased in Small-Tail Han Sheep at the time of oestrus. There were different increases in plasma LH among three breeds and significant increases in plasma FSH in all breeds. Plasma FSH in Tong Sheep and Small-Tail Han Sheep, which are non-seasonal oestrus were significant higher than Tan Sheep, which was seasonal oestrus.