Productivity to weaning of Nellore and F1 Guzerath X Nellore and Bos taurus X Nellore heifers

Production efficiency of a beef cow-calf herd is determined by the ability of the cows in converting the ingested food into calf weight. This ability is related to cow size, fertility and milk production. The present study evaluated efficiency at weaning after first calving of 100 Nellore (N), 47 F-1 Guzerath x Nellore (GN), 67 F-1 Red Angus x Nellore (RN), 37 F-1 Marchigiana x Nellore (NIN) and 38 F-1 Simental x Nellore (SN) heifers at Estacao Experimental Paranavai/IAPAR. The traits analyzed were age at first calving (IPP), the ratio of calf weaning weight to heifer weight at calving, divided by the age of the heifer at calving (PDPV) and the ratio of calf weaning weight to heifer metabolic weight at calving, divided by the age of the heifer at calving (PDPM). Least squares means for IPP in days, PDPV [((kg/kg)/day) x 1000] and PDPM [((kg/kg(0.75))/day) x 100] were: 1416, 1340, 1053, 1187 and 1117; 0.394, 0.414, 0.422, 0.379 and 0.418; and 0.169, 0.179, 0.187, 0.169 and 0.188, respectively for N, GN, RN, MN and SN. The contrasts N - RN (362 days), GN - RN (287 days) and RN - MN (-133 days) were significant for IPP. For PDPV, the contrast RN - MN [-0.04287((kg/kg)/day) x 1000] was significant while for PDPM the contrasts N - RN [-0.01803((kg/kg0.75)/day) x 100], RN - MN [0.01841((kg/kg0-75)/day) x 100] and MN - SN [-0.01915((kg/kg(0.75))/day)x 100] were significant. It can be concluded that RN and SN heifers had greater production efficiency at first weaning than MN heifers, which did not differ from N and GN heifers.