Environmental factors and genetic parameters for reproductive characteristics of Nelore in the through northern region from Brazil
The study was carried out to evaluate the age-at-first-calving and calving interval (IPP and IDP) in Nelore cows, using IPP and IDP data from 23,066 females reared in a grazing regime in the States of Maranhão and Piauí from 1976 to 2012. Data were analyzed statistically using the SAS (Statistical Analysis System) program. The mean and coefficient of variation for the age-at-first-calving was 1252.77 ± 125 days (10.41 months; 10.56%) and, for the calving interval, values were 591.73 ± 149.91 days (12.49 months; 38.74%). Uncharacteristic analyses were used to estimate genetic parameters for heritability values, obtaining values of approximately 0.026 and 0.006 for IPP and IDP, respectively. The repeatability estimate for the IDP characteristic, as calculated by uncharacteristic analysis, had a generally low value of 0.025. Similarly, for trait analysis, heritability values were 0.03 and 0.06 for IPP and IDP, respectively, and the estimated repeatability coefficient was 0.14. The genetic correlations between the reproductive characteristics (IPP and IDP) observed in this study were equal to 0.06. The reproductive performance of the herd studied, in tropical climate conditions, can be considered to be satisfactory, in accordance with the parameters obtained by other authors in different regions.