Can Intensified Pasture Systems Reduce Enteric Methane Emissions from Beef Cattle in the Atlantic Forest Biome?

The objective of this study was to evaluate the effect of different pasture systems on beef steers' performance, dry matter intake, enteric methane emission, carcass production, forage quality, and animal production per hectare (ha). The trial was conducted at Embrapa Southeast Livestock, Sao Carlos/SP, Brazil. Sixty Cachim beef steers (5/8 Charolais x 3/8 Zebu) with initial liveweights of 255 +/- 7 kg were evaluated for two years under five different grazing production systems (EXT = Extensive; INT = Intensive; iCL = Integrated crop livestock; iCLF = Integrated crop livestock forest; iLF = Integrated livestock forest). The final liveweight was greater (p < 0.05) for the animals under the INT and iCL systems (484 +/- 51 and 466 +/- 79 kg, respectively) compared to animals in the iCLF, iLF and EXT systems (416 +/- 57, 414 +/- 50 and 429 +/- 48 kg). The dry matter intake was significantly greater under the EXT system than it was under the iCL system (9.8 +/- 2.1 and 7.5 +/- 2.9 kg day(-1)). Regarding the emission intensity in relation to the liveweight gain per unit area (g CH4 kg LWG(-1) ha(-1) year(-1)), it differed significantly among the systems (EXT = 1.6; INT = 0.6; iCL = 0.8; ICLF = 1.1; ILF = 0.7). Similarly, the methane emission intensity differed in relation to the carcass production (kg CH4 kg(-1) carcass; EXT = 0.496; INT = 0.250; iCL = 0.297; iCLF = 0.345; iLF = 0.286). Beef cattle that are raised in intensive and/or integrated pasture systems have a greater availability of forage mass and nutrients than those that are raised extensively. Pasture systems that undergo soil pH correction and fertilization, rotational grazing and/or integrated with maize cropping produce animals with greater average daily gain and final liveweights, thereby lessening the enteric methane emissions per kg of weight gain. In these systems, the efficiency in terms of the gain per land area is also greater, however, the systems that are integrated with a forest component (iLF and iCLF) are equal to that of the EXT system. The same pattern is observed in the intensity of the methane emission as for the efficiency of the animal gain per unit of land area.