Synchronization of estrus in goats under range conditions treated with different doses of new or recycled norgestomet implants in two seasons

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Three experiments were carried out to test the efficacy of different doses of new or recycled norgestomet implants to synchronize estrus of goats under extensive conditions, during the transitional season (early June) and breeding period (January). In Experiment 1 ( n = 126 goats), 1 3 , 1 4 and 1 5 of the Synchro-Mate B (SMB) implant was applied for 9 days. An intramuscular injection of 1.25 mg estradiol valerate and 0.75 mg norgestomet was administered concurrent with insertion of the implant. Estrus response was not affected by norgestomet dosage (61.9, 61.9 and 54.8%; 96 h post treatment for 1 3 , 1 4 and 1 5 SMB, respectively) or by month of treatment (55.2% vs. 63.2% for goats treated in early June or January). In Experiment 2 ( n = 131), goats treated with implants previously used in cattle had lower ( P < 0.05) estrus response (38.1% and 46.8% for a complete and 1 2 implant, respectively) than those treated with 1 3 of new implant (61.9%). Also, a higher ( P = 0.06) proportion of goats exhibited estrus when they were treated in January (56.3%) than when they were treated in early June (40.0%). In Experiments 1 and 2, the time of onset of estrus after norgestomet treatment was 20 h longer ( P < 0.01) in goats treated in June than in those treated in January. In Experiment 3 ( n = 106), estrus response, time to onset of estrus and reproductive performance was not affected by 1 3 , 1 4 and 1 5 fractions of new or recycled (previously used in goats) implants plus buck teasing before and after implant removal. These data indicate that, either in the transitional or breeding period, 1 5 of the SMB implant is sufficient to control estrus in goats, and that in does stimulated with androgenized castrated males, this implant can be recycled for a second time for synchronization of estrus, with similar results as the new implants.