The duration of melatonin release from Regulin implants and the diurnal variation in plasma melatonin concentration was investigated in 18 cashmere wethers, divided into 3 treatments: C-control; T-treated with melatonin 18mg Regulin implant on 10.11.88; PT - previously treated with melatonin every 6 weeks for 10 months before receiving an implant on 10.11.88. Mean concentration of plasma melatonin in T remained high 52 pg/ml for up to 42 days after implant, then declined to 8.5 pg/ml at 50 days remaining relatively low for the rest of the sampling period. Goats from PT maintained much high concentration of plasma melatonin 226 pg/ml for 42 days after implant. Control goats showed very low mean concentration at 5 pg/ml. Between animal variation in plasma melatonin concentration was high coefficients of variation were between 100% and 200% within all treatments. At 8 days post-implant plasma melatonin concentration of goats in C showed a nocturnal increase averaging 12.5 pg/ml, between sunset and sunrise. The same diurnal fluctations were evident at 29 days post- implant. Goats in treatment T also showed a nocturnal rise in plasma melatonin concentrations with average increases of 15 and 24 pg/ml at 8 and 29 days post implant between sunset and sunrise. It can be concluded that the melatonin implants used in this trial lasted for 42 days after administration and a nocturnal rise in melatonin concentration was evident in control and treated goats.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 261-264, 1990
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