Impact of Forage Diversity on Forage Productivity, Nutritive Value, Beef Cattle Performance and Enteric Methane Emissions

Greenhouse gas emissions (GHG) from the beef industry is largely attributed to the grazing sector, specifically from beef cattle enteric methane emissions. Therefore, the study objective was to examine how forage diversity impacts forage productivity, nutritive value, animal performance and enteric methane emissions. This study occurred over three consecutive grazing seasons (2018 to 2020) and compared two common Midwest grazing mixtures: 1) a simple, 50:50 alfalfa:orchardgrass mixture (SIMP) and 2) a botanically diverse, cool-season species mixture (COMP). Fifty-six steers and heifers were adapted to an Automated Head Chamber System each year (AHCS; C-Lock Inc., Rapid City, SD) and stratified into treatment groups based on acclimation visitation. Each treatment consisted of four pastures, three 3.2-ha and one 1.6-ha, with 8 and 4 animals each, respectively. Forage production was measured bi-weekly in pre-and post-grazed paddocks, and forage nutritive value was analyzed using near-infrared reflectance spectroscopy (NIRS). Shrunk body weights were taken monthly to determine animal performance. Forage availability did not differ between treatments (P = 0.69) but tended lower in 2018 (P = 0.06; 2.40 t dry matter ha -1) than 2019 (2.92 t dry matter ha -1) and 2020 (P = 0.10; 2.81 t dry matter ha -1). Crude protein was significantly lower for COMP in 2018 compared to SIMP. Forage acid detergent fiber content was significantly lower for the COMP mixture (P = 0.02). The COMP treatment resulted higher dry matter digestibility (IVDMD48) in 2018 and 2019 compared to the SIMP treatment (P < 0.01). Animal performance did not differ between treatments (P > 0.50). There was a tendency for the COMP treatment to have lower enteric CH4 production on a g d -1 basis (P = 0.06), but no difference was observed on an emission intensity basis (g CH4 kg -1 gain; P = 0.56). These results would indicate that adoption of the complex forage mixture would not result in improved forage productivity, animal performance, or reduced emission intensity compared to the simple forage mixture.

Enteric Methane Emission Estimates for the Zimbabwean Sanga Cattle Breeds of Tuli and Mashona

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.

245 Greenhouse Gas Emissions Mitigation Strategies

Livestock production contributed 3.9% to the total greenhouse gas (GHG) emission from the US in 2018. Most studies to mitigate GHG from livestock are focused on enteric methane because it contributes about 70% of all livestock GHG emissions. Mitigation options can be broadly categorized into dietary and rumen manipulation. Enteric methane emissions are strongly correlated to dry matter intake and somewhat sensitive to diet composition. Dietary manipulation methods include increasing feed digestibility, such as concentrate to forage ratio, or increasing fats and oils, which are associated with lower methane emissions. These reduce digestible fiber that are positively related to methane production and more energy passing the rumen without being degraded, respectively. Rumen manipulation through feed additives can be further classified based on the mode of action: 1. rumen environment modifiers indirectly affecting emissions and 2. direct methanogenesis inhibitors. The rumen environment modifiers act on the conditions that promote methanogenesis. These include ionophores, plant bioactive compounds such as essential oils and tannins, and nitrate rich feeds that serve as alternative hydrogen sinks and directly compete with methanogens thereby reducing methane emissions. The inhibitor category include 3-nitroxypropanol and seaweeds containing halogenated compounds. The former was reported to reduce enteric methane emissions (g/d) by 39% in dairy and 22% in beef cattle. Seaweed, in particular Asparagopsis spp., reduced emissions intensity (g/kg milk) by up to 67% in dairy and emissions yield (g/kg dry matter intake) by up to 98% in beef cattle. Because inhibitors are structural analogs of methane, their mode of action is through competitive inhibition of the methyl transfer reaction catalyzed by methyl coenzyme-M reductase, the last enzyme in methanogenesis. The combination of dietary and rumen manipulation options, including feed additives, is expected to reduce enteric methane emissions by over 30% in the next decade without compromising animal productivity and health.

Comparison of enteric methane yield and diversity of ruminal methanogens in cattle and buffaloes fed on the same diet

An in vivo study was conducted to compare the enteric methane emissions and diversity of ruminal methanogens in cattle and buffaloes kept in the same environment and fed on the same diet. Six cattle and six buffaloes were fed on a similar diet comprising Napier (Pennisetum purpureum) green grass and concentrate in 70:30. After 90 days of feeding, the daily enteric methane emissions were quantified by using the SF6 technique and ruminal fluid samples from animals were collected for the diversity analysis. The daily enteric methane emissions were significantly greater in cattle as compared to buffaloes; however, methane yields were not different between the two species. Methanogens were ranked at different taxonomic levels against the Rumen and Intestinal Methanogen-Database. The archaeal communities in both host species were dominated by the phylum Euryarchaeota; however, Crenarchaeota represented <1% of the total archaea. Methanogens affiliated with Methanobacteriales were most prominent and their proportion did not differ between the two hosts. Methanomicrobiales and Methanomassillicoccales constituted the second largest group of methanogens in cattle and buffaloes, respectively. Methanocellales (Methanocella arvoryza) were exclusively detected in the buffaloes. At the species level, Methanobrevibacter gottschalkii had the highest abundance (55–57%) in both the host species. The relative abundance of Methanobrevibacter wolinii between the two hosts differed significantly. Methanosarcinales, the acetoclastic methanogens were significantly greater in cattle than the buffaloes. It is concluded that the ruminal methane yield in cattle and buffaloes fed on the same diet did not differ. With the diet used in this study, there was a limited influence (<3.5%) of the host on the structure of the ruminal archaea community at the species level. Therefore, the methane mitigation strategies developed in either of the hosts should be effective in the other. Further studies are warranted to reveal the conjunctive effect of diet and geographical locations with the host on ruminal archaea community composition.