The response to melatonin expression is one way that circadian rhythms of many biological processes are regulated. To evaluate the relationship between the melatonin receptor 1A (MTNR1A) gene and reproductive performance, records were compared in Dorset and 3/4-Dorset x 1/4-East Friesian ewes expressing different genotypes at the MTNR1A gene in the Cornell University sheep flock. There were 116 ewes with first lambing records, consisting of 91 Dorset and 25 crossbred ewes. Of these, 104 ewes had second lambing records. Genotypes were determined by PCR amplification of a fragment of the ovine MTNR1A gene followed by digestion with MnlI and RsaI restriction enzymes. The effects of breed, year of birth, season of birth or season of first conception, and each polymorphism on days to first lambing and days between first and second lambings were evaluated. Our results show that ewes with at least 1 M allele are able to conceive at younger ages, better able to breed and conceive out-of-season, and have shorter intervals between first and second lambings than ewes expressing only the m allele. The results presented in this study show, for the first time, an association of the MTNR1A gene and lambing frequency and confirm the importance of the MTNR1A gene as a potential DNA marker for out-of-season breeding.