The effects of exogenous melatonin implanted before lambing on the quality of colostrum and milk yield were quantified in 715 ewes. Forty days before lambing, 246 ewes (1M) received a melatonin implant; another 137 ewes (2M) received two implants, and the remaining 332 ewes (C) did not receive an implant (control). Milk analysis was based on individual monthly milk samplings (June, July, and August) after lambing. A colostrum sample was collected from 303 ewes (118 1M; 73 2M; and 112 C), and IgG concentrations were measured. Ewes implanted with melatonin had higher (p < 0.01) daily milk yield (DMY) in the three samplings than the C ewes. On average, 1M ewes produced more milk (p < 0.05) than ewes in the other two groups, and 2M ewes produced significantly (p < 0.05) more milk than C ewes. In the first and third controls, ewes that received two melatonin implants had a lower (p < 0.05) SCC than C and 1M ewes, and in the second sampling, 1M and 2M ewes had a lower (p < 0.01) SCC than C ewes. Ewes that received melatonin implants had a higher (p < 0.01) IgG concentration (21.61 1.03 mg/mL) than non-implanted ewes (16.99 1.13 mg/mL); 2M ewes had the highest IgG levels. In conclusion, ewes that received a melatonin implant 40 d before lambing produced colostrum that had a higher IgG concentration than the colostrum from nonimplanted ewes, and produced more milk, which had a lower SCC. The effect on SCC was prolonged if the sheep received a second melatonin implant.