Methane Emission of Cattle Fed Urochloa brizantha Hay Harvested at Different Stages

The objective of this trial was to assess the methane emission rate, as well as the digestibility and ruminal fermentation parameters in animals fed Urochloa brizantha hay harvested at different stages of growth. Six Nellore rumen-cannulated steers (402.0 ± 51.62 kg) were assigned to a replicated 3×3 Latin square (18 experimental units). Treatments differed according to three growth stages of the forage- 15 - hay with 15 days of growth, 45 - hay with 45 days of growth and 90 - hay with 90 days of growth. Each experimental period lasted 21 days. From the 8th day, feces were sampled during 5 days to determine apparent total digestibility of dry matter and its fractions. Beginning on the 13th day and running for 7 days, methane production was evaluated using the sulfur hexafluoride (SF6) tracer technique. On the 20th day, ruminal fluid was sampled prior to and after 2, 4, 6, 8 and 10 hours post-morning feeding for evaluating pH, ammonia-N and short-chain fatty acids (SCFA). As the stage of forage growth for harvesting advanced in days, the digestibility coefficient of crude protein decreased and non-fibrous carbohydrate values increased. Methane production was affected not only by the stage of forage growth, but also by quality of its conservation after harvesting. There were significant differences among treatments when methane was expressed in g kg-1 DMI, g kg-1 OMI, % GE and % DE, with non-linear effect. The stage of forage growth did not influence ruminal pH, total concentration or molar proportion of SCFA, but decreased NH3-N concentration.