The effects of genetic and environmental factors on reproductive traits, from 475 records of calving interval (CI) and 401 of real fertility (RF) of Nellore cows reared at Santa Inês county, Maranhão State, in pasture grazing system with supplementation in the dry season, from 1980 to 1994, were studied. The data were analyzed by means of linear models, which included the sire effect (random effects), month and year of the last and the actual calving, calving number and sex of calf (fixed effects). The sire effect and calving number significantly affected both studied traits, while calf sex affected only the RF. The calving interval and R F by least square means were: 433.84 ± 88.20 days and 184.69 ± 37.09 kg, respectively. The heritability coefficients estimated by intraclass correlation of paternal half-sisters were .32 ± .15 and .49 ± .19, for CI. and RF. respectively.
bovine; real fertility; heritability; calving interval; Nellore breed; reproduction
