The effects of melatonin implants in advancing the breeding season and enhancing both ovulation rate (OR) and litter size in the ewe are well documented (Haresign et al., 1990; López and Inskeep, 1991). Likewise, oestrous activity and OR in the early breeding season can be stimulated by a moderately and constant body condition (BC) in Mediterranean sheep breeds (Forcada et al., 1992). However, little information is available in relation to the effect of nutritional status in ewes receiving exogenous melatonin on reproductive parameters. The present study was carried out to determine the effects of a constant BC throughout the year, and implant or reimplant of exogenous melatonin on onset of oestrous activity and OR in a reduced seasonality sheep breed.

The experiment was designed as a 2x2 factorial. Factors were two constant BC levels (≤2.50; L, and ≥2.75; H) and two forms of melatonin treatment (one implant -Melovine™- placed the 8th April; M, and a second implant 49 days later; 2M).