Desempenho e emissões de gases de efeito estufa de bovinos zebuínos e cruzados em sistema intensivo e integrado de produção

Abstract

This study aimed to evaluate animal performance and enteric methane (CH4) production from two breed compositions in a Brazilian beef cattle production system– rearing in integrated crop-livestock (ICL) system and finishing in feedlot (FL), besides to determine nitrous oxide (N2O) and CH4 emissions and the associated emission factor (EF; percentage of urine and dung-N lost as N2O-N) for beef cattle excreta deposited onto a FL land. In trial I, to assess how breed composition affects performance and methane emissions, 70 animals of two breed compositions, Angus x Nellore crossbred (AN) and Nellore (Nel), were compared in an intensive production system. At trial onset, 10 mo old steers grazed Megathyrsus maximus 'Mombaça' in the rearing phase (stocking rate 5.5 AU/ha, herbage mass 4,884 kg DM/ha, forage allowance 5.9 kg DM/100kg BW) and then were finished in FL (35:65% corn silage:concentrate diet).Steers (n = 8) from each breed composition were randomly selected in each phase to measure CH4 production using a sulfur hexafluoride technique and DMI using titanium dioxide. Compared with Nel, AN had both superior total gain and ADG in the grazing period. Also, the AN presented greater ADG in FL with a shorter finishing period, and resulted in greater carcass yield and carcass ADG. Methane production (kg/period) was lower in Nel (19% less) than AN in grazing (P<0.01), and no difference in FL was observed. Nel had greater CH4 intensity (g CH4 per unit of ADG) compared to AN in FL. Breed composition did not influence the CH4 yield (g CH4 per unit of DMI) in grazing or FL, despite the difference in DMI (kg/day) in FL. In our study the introduction of Angus into Nellore has potential to reduce CH4 intensity in tropical climates, resulting in less methane emission per kg beef produced. In trial II, to investigate the effects of excreta type deposited in feedlot soils on N2O andCH4emissions, sample’ pool of each excreta were obtained from 25 steers in feedlot (Average BW = 393 kg). Urine (1.3 l) and dung (1.3 kg) were applied once and gases fluxes were monitored lasted 92 days, by using static chambers technique. The results showed that N2O fluxes had two peaks for the urine treatment, the first at 1stday after application (DAA) of excreta and the 2ndafter the rainfall events (70 DAA). Also, the N2O fluxes for the dung had a peak at 70 DAA. The CH4fluxes were unstable and presented several pulses throughout the measurement period and was altered between positive and negative flow values. Soil CH4 emissions remained near zero and the treatments showed low levels up CH4 uptake (-8.4, -3.2 and -14.8 μgC m−2 h−1 for dung, urine and control, respectively). The excreta presence increased soil moisture by 44.5 and 55.4% for dung and urine, respectively, compared to control. The high mineral N concentration in the urine caused that high values and significant difference of ammonium (NH4 +) and nitrate (NO3 -) compared to dung and control. The NH4 + and NO3 - soil concentrations in the cattle urine treated soils peaked at 13 DAA, while for dung treated soils peaked at 42 DAA. The N2O EF from urine was significantly (P<0.0001) higher than the EF from feces (2.83 vs. 0.32%, respectively), resulting in a combined excretal EF of 1.83%, which is <8.5% of the IPCC default EF for excretal returns.