Calving interval of Nellore, Guzerath x Nellore, Red Angus x Nellore, Marchigiana x Nellore and Simental x Nellore

Two hundred and eighty-six observations on interval between first and second parturition (IEP1) and 1,106 observations on interval between parturitions considering all parturitions (IEP2) of 89 Nellore (NN), 47 F-1 Guzerat x Nellore (GN), 76 F-1 Red Angus x Nellore (RN), 35 F-1 Marchigiana x Nellore (MN) and 39 F-1 Simental x Nellore (SN) cows were analyzed in this study. Least squares means for IEP1 were: 492 +/- 22 d, 505 +/- 25 d, 433 +/- 22 d, 453 +/- 27 d e 450 +/- 24 d, respectively for NN, GN, RN, MN and SN. The contrasts RN - NN and RN - GN were highly significant whereas the contrasts SN - GN, MN - GN and SN - NN were significant. In the same order, LS means for the five groups for IEP2 were: 466 +/- 20 d. 485 +/- 22 d, 385 +/- 29 d, 432 +/- 30 d e 446 +/- 29d, with highly significant differences for RN - NN and RN - GN while the differences RN - SN e MN - GN approached the significance level of 5%. The study also revealed important environmental effects of order of parturition, year of first parturition and month of first and second parturition of interval under study upon IEP2. It can be concluded that F-1 Red Angus x Nellore cows are the best choice as genetic resources for improving reproductive performance of beef herds in the region and that judicious combination of crossbreeding with breeding season can also contribute for enhancing that performance.