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The effectiveness of methane mitigation in ruminant livestock production systems depends on the accuracy of estimating methane emission factors and providing accurate emission inventories. Following the Paris Climate agreement, it is recommended that countries adopt the Tier-2 approach for estimating enteric methane emissions from ruminants instead of the Tier-1 approach currently used by most countries. This study sought to provide base line enteric methane emission estimates for the Tuli and Mashona Sanga cattle breeds in Zimbabwe using the IPCC Tier-2 model. Using animal characterization data collected from 412 cattle from Grasslands Research Institute and 406 cattle from Makoholi Research Institute, net energy requirements were estimated. From this and the estimate for digestibility, gross energy intake and dry matter intake were estimated. Gross energy intakes and the estimated methane conversion factor were used to estimate enteric methane emissions. Mean emission factors for Tuli were 45.1, 56, 28.5, 28.4, 20.6kg CH4/head/year for cows, bulls, heifers, steers and calves respectively. For Mashona, they were 47.8, 51.9, 29, 29.1 and 20.7kgCH4/head/year for cows, bulls, heifers, steers and calves respectively. Generally, estimated Tier-2 emission factors were significantly different from the IPCC Tier-1 default emission factors. This study concluded that enteric methane emission factors estimated using the IPCC Tier-2 model offer insights into the controversial use of the default IPCC Tier-1 emission factors.

The work assessed the productive response and estimated enteric methane (CH4) emissions of dairy cows grazing in small-scale dairy systems. Treatments were grazing annual pasture (AP) mainly of annual ryegrass and perennial pasture (PP) mainly of perennial ryegrass, complemented daily with 3.72 kg DM/cow of commercial concentrate. Eight Holstein cows were used in a double cross-over design with three 14-day-each experimental periods for animal variables and CH4 emissions. Pasture variables were analysed with a split-plot design. AP showed higher sward height (P 0.05) in net herbage accumulation or in herbage chemical composition. Cows on AP yielded 24.6% more milk (P

Low nutrient intake of short-horn zebu (SHZ) cattle raised under extensive grazing systems results in delayed attainment of mature market weights and consequently increased methane production over time. The purpose of this study was to evaluate and compare the effect of providing grazing SHZ weaner bulls with a supplement varying in crude protein on methane emission using the Intergovernmental Panel on Climate Change (IPCC) Tier 2 and a modified Tier 3 approaches. Weaner bulls were allocated to four treatments: grazing only (GZ), grazing plus a supplement containing either 90 (GZS_90), 110 (GZS_110), or 130 g CP/kg DM (GZS_130). Across treatments, monthly CH4 emissions increased with time. Based on the IPCC Tier 2 method, the highest CH4 production from cattle was estimated from weaner bulls on GZ, while the Tier 3 estimated the highest CH4 production to be from cattle on GZS_130. Although the Tier 2 approach showed no significant difference between treatments, the Tier 3 showed that weaner bulls raised under GZS_130 had the highest production of methane as percentage of gross energy intake. Irrespective of method, weaner bulls on GZ produced more (P < 0.001) CH4 per kilogram live weight gain than supplemented cattle. Compared with Tier 3, the Tier 2 estimated 22.9% higher CH4 per kilogram live weight gain for weaner bulls on GZ. These data suggest that supplementing SHZ weaner bulls with a supplement containing110 g CP/kg DM reduces methane emission per kilogram of live weight gain by 30.7%.