Livestock-Based Farming Systems, Renewable Resources and the Environment
The objective of the study was to determine methane emission and to mitigate methane emission by oil and nitrate supplement in the diets of growing cattle. An experiment was carried out during 3 months (June - August) in the experimental station of Hanoi University of Agriculture (Vietnam). Twenty-four growing cattle (170 kg on average) were equally divided into 8 blocks corresponding to 8 diets based on 2% NaOH treated rice straw and cassava leaf meal (1% BW, DM basic), supplemented with 1.5%, 3.0%, 4.5%, 6.0% sunflower oil plus 4%CaNitrate or 1.5% urea as NPN source. Methane emission was determined by using CH4/CO2 ratio method. Results showed that methane emission rate (liters/kg DMI) was reduced by 24% by nitrate supplement compared with urea supplement. The increase in oil level reduced non-linearly methane emission. The best level of oil supplement was 3.0%. However, the best treatment was found with 4% CaNitrate and 1.5% oil supplement in the diet. It was also shown that estimated energy loss from the experiment diet ranged from 5-8% of diet gross energy, compared with around 12% potential energy loss from diet without supplement. As a result, it should be added nitrate and oil supplement (at a limit of 1.5%) to mitigate methane emission from growing cattle.