Períodos de suplementação proteico-energética para recria de novilhas mestiças Nelore em pastagem diferida de Urochloa decumbens

Abstract

Pasture stockpiling and protein-energy supplementation (PES) are appropriate strategies for beef cattle, especially during the dry season. However, the mistaken adoption of these techniques may compromise its benefit-cost (B/C). In this sense, the aim of study was to evaluate Nelore crossbred heifers performance under two PES periods, as the conditions of stockpiled pastures of Urochloa decumbens for 121 days. This, under the hypothesis that heifers submitted to lower PES would present similar body weight to others supplemented to longer period at the end of evaluation, due to "compensatory growth". Therefore, an experiment was conducted at Fazenda Santana, in Valença – RJ, under completely randomized design, with two production systems: 151 and 59 days of PES (151 and 59 SPE, respectively). In this context, 10 forage samples were collected in two pastures (8 ha each) by evaluation (total of 7), 20 Nellore crossbred heifers were used for 59 SPE, and 20 for 151 SPE. At 59 SPE, white salt was offered in first 92, of 151 days of experiment, and for 151 SPE, only multiple mixture. Data were analyzed by PROC MIXED of SAS®, with means of treatments compared by PDIFF (p<0.05). Forage allowance (OF) increased from 6.8 to 12.5 kg ha-1 of MS 100 kg-1, possibly due to the reduction in occupation periods. There was effect (p<0.0001) of time (evaluation) for forage mass (MF) and dry mass of dead material (MSMM). The MF was reduced (5984 to 3810 kg ha-1) due to grazing and climatic conditions, and MSMM increased (2881 to 3814 kg ha-1) due to the advancement of physiological age of the plant. There was interaction effect (p<0.0001) for leaf blade dry mass (MSLF) and steam dry mass (MSC). There was alternation of MSLF results for both systems, probably due to the higher OF and higher leaf consumption in some evaluations than in others. There was a reduction in MSC in the period evaluated and lower values (629 kg ha-1) were observed in 151 SPE, possibly due to the increase in grazing efficiency. There was interaction effect (p<0.0001) for total weight gain (GPT), mean daily gain (GMD) and mean weight (PM). Major GPT and GMD were obtained in the evaluation periods 1 and 7. GPT and GMD were higher for 151 SPE from period 2 to 4 and larger for 59 SPE from 5 to 7. In general, the PM increased and were equal between systems at weighing 0, 1, 2 and 7. At weighing 7 (last), heifers presented similar PM (p>0.05) of 334 and 329 kg for 151 and 59 SPE, respectively. The net present values (VPL) were negative for 151 SPE under the assessed interest rates (4, 6, 8 and 10%), while for 59 SPE, VPL was positive (R$360.14) at least at the rate of 4% for year. The internal return rate (TIR) was attractive for 151 (3.97%) and 59 SPE (4.68%) compared to opportunity cost (2.06%). A positive economic balance was obtained of R$ 17.49 per animal, to replace 151 SPE for 59 SPE. These results allow affirming that the reduction of 92 days in SPE should provide similar performance (PM) of Nellore crossbred heifers, in addition to greater economic efficiency of the production system, mainly due to the "compensatory growth" effect of 59 SPE animals