| Melatonin is a highly efficient free radical scavenger, has multiple antioxidant activity and physiological activity, palys a key role in reproductive and immune. It’s a great significance to study on the use of MT to reduce the number of somatic cells and improve the reproductive efficiency of dairy1.Experiment I investigated the variation of plasma MT concentration within 24 hours, the changes of plasma MT concentration with different MT treatment including intravenous injection, subcutaneous injection, subcutaneous implant and orally administrated and the secretory characteristics and metabolic rate of MT in Holstein cows. Plasma MT concentration changes obviously in one day, the highest value of MT concentration (8.30±1.46ppb) appeared at 4:00 in the morning and the lowest value of MT concentration (2.09±0.07ppb) appeared at 4:00 in the afternoon. The plasma MT concentration increased rapidly after intravenous and subcutaneous injection of 4.64mg MT, reached the highest value at 0.5 hours and 1 hours respectively. The highest value of plasma MT concentration were much smaller after subcutaneous implant and orally administrated. In conclusion, Plasma MT secretion demonstrated a distinct diurnal rhythm, and the plasma MT concentration increased rapidly after intravenous and subcutaneous injection MT.There is a close relationship between the metabolic rate of MT and the plasma MT concentration.With the increase of plasma MT concentration, the metabolism rate of MT accelerated apparently.2.Experiment Ⅱ studied the effect of MT in reducing somatic cell count in milk, and analyzed the mechanism.4.64mg MT was given as subcutaneous injection everyday on the mastitis of dairy cows. 4.64mg MT was also given as subcutaneous injection everyday on healthy cows for 4 consecutive days. MT can significantly shorten the treatment time of mastitis and reduce somatic cell count. The result is more better especially for the high producing dairy cows which the SCC is between 300-1000 thousand /mL. The effects of MT on blood physiological, biochemical and immune indexes of dairy cows were also studied here. MT can reduce the concentration of COR, increase the concentration IgG, IgM, ALB, ALT, LDH and the number of WBC, LYM, GRN. There is no effect of MT on the concentration of GLU and the number of RBC. In conclusion, MT can enhance the immunity of dairy cows by enhancing humoral and cellular immunity. It also can decrease the somatic cell count of milk. Subcutaneous injection of melatonin is a safe, fast and convenient method for the treatment of mastitis, reducing somatic cell count in dairy cows.3.Experiment Ⅲ evaluated the change of plasma MT concentration from Postpartum to Insemination, and the effects of melatonin on the First-cycle conception rate, stillbirth rate, gender and birth weight of calves in dairy cows. There is a MT concentration peak in the blood around the time of ovulation and the average value (66.40±40.04ppb) is significantly higher (P<0.05)than that at diestrus (4.98±4.31ppb). The plasma MT concentrations at insemination of all the pregnant cows were more than 60ppb, and those blow 30ppb were not pregnant. Melatonin subcutaneous injection during insemination can increase the first-cycle conception rate of high-producing holstein dairy Cows in spring (44.00±2.28%vs.35.93±1.56%) and summer (26.15±2.00%vs.17.91±1.75%), it can also reduce the stillbirth rate(4.95±3.41% vs.6.94±4.74%), but it has no effect on the gender and birth weight of calves. In conclusion, there is a Close relationship between plasma MT concentration and the first-cycle conception rate. Subcutaneous injection of melatonin can significantly improve the reproductive efficiency, reduce the stillbirth rate, and improve the benefit of the farm.4.Experiment IV was performed to investigate the effect of melatonin, melatonin receptor agonist (IIK7) and antagonist (luzindole) on bovine oocytes maturation in vitro and explore the expression of melatonin receptor MT1 and MT2. RT-PCR confirmed the presence of MT1 and MT2 gene expression in oocytes, cumulus cells and granulosa cells. With the use of melatonin receptor agonist(IIK7) and antagonist(luzindole), we found that the melatonin receptor agonist improved and melatonin receptor antagonist did not inhibited oocyte maturation in vitro.In conclusion, our present study demonstrated that melatonin can effectively improve the efficiency of bovine oocyte maturation in vitro, and this beneficial effect of melatonin is mediated by melatonin receptor.In summary, Plasma MT secretion demonstrated a distinct diurnal rhythm, and the plasma MT concentration increased rapidly after intravenous and subcutaneous injection MT. It can reduce the concentration of COR, increase the concentration IgG, IgM, ALB, ALT, LDH and the number of WBC, LYM, GRN, improve the immunity and decrease the SCC of diary cows in finally. Furthermore, MT subcutaneous injection during insemination can increase the first-cycle conception rate and decrease the stillbirth rate, has no effects on the gender and birth weight of calves.MT1 and MT2 gene express in oocytes, cumulus cells and granulosa cells. Melatonin can effectively improve the efficiency of bovine oocyte maturation in vitro, and this beneficial effect of melatonin is mediated by melatonin receptor.This may be one of the reasons that the subcutaneous injection of melatonin can improve the reproductive efficiency of dairy cows. |
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