Effects of melatonin implants during lactation were assessed in 72 dairy ewes of 2 breeds (Manchega, MN; n = 36, 72.4 ± 1.9 kg BW; Lacaune, LC; n = 36, 77.7 ± 2.3 kg BW) differing in milk yield and composition. Ewes were under intensive conditions, lambed in autumn and received a TMR ad libitum (forage:concentrate = 55:45). After the weaning of the lambs (d 28), they were penned in 12 balanced groups of 6 and randomly assigned to a 2 × 2 × 3 factorial design (treatment × breed × replicate) during early lactation (d 28 to 114). Treatments were: Control (CO, n = 36) and Melatonin (MEL, n = 36) that was subcutaneously implanted in the left ear-base (18 mg/ewe; Melovine, Ceva Animal Health, Barcelona, ES) at d 35 ± 1. Milk yield was recorded daily using automatic milk meters (MM25 SG, DeLaval, Tumba, SE) and ruminal bolus transponders (Datamars, Bedano, SW), whereas milk composition was measured biweekly. Data were analyzed by the PROC MIXED for repeated measurements of SAS (v.9.4, SAS Institute Inc., Cary, NC, USA) and LS means separated by PDIFF at P < 0.05. No MEL effects were detected on DM intake (P = 0.12) or milk yield (P = 0.60), although they were 51% and 87% greater (P < 0.001) in LC ewes when compared with MN, respectively. Milk composition varied by breed, the LC producing lower fat and protein contents than the MN ewes (P < 0.001), but no CO vs. MEL effects were detected on milk composition (P = 0.25 to 0.99) nor milk-fat standardized milk (P = 0.73). Nevertheless, numerical greater persistence coefficients of milk yield were estimated for the groups CO vs. MEL of both breeds (LC, –0.015 vs. –0.013 L/d; MN, –0.012 vs. –0.010 L/d, respectively), resulting in a decrease in milk yield of MEL by 7 and 3% in MN and LC ewes, respectively. On the other hand, BW and BCS did not vary by MEL treatment or by breed throughout the experiment. In conclusion, the use of exogenous MEL implants, together with the endogenous MEL secreted under decreasing photoperiod conditions, had no effects on the lactational performances of dairy sheep in early lactation, despite their milk yield and composition potential.