WHEN digesting, ruminants exhale methane. So far, the assumption has been that camels — also ruminants — produce the same amount of methane as cattle. However, researchers at the University of Zurich and ETH Zurich in Switzerland have now shown that camels release less methane than other ruminants.
Cows and sheep account for a major proportion of the methane produced around the world. Currently, around 20% of global methane emissions stem from ruminants.
Comparatively little is known about the methane production of other animal species, but one thing seems to be clear: Ruminants produce more of the gas per amount of converted feed than other herbivores.
The only other animal group that regularly "ruminates" like ruminants are camelids, which includes alpacas, llamas, dromedaries and Bactrian camels. They, too, have multi-chambered forestomachs and also regurgitate food from the forestomach in order to reduce it in size through renewed chewing. That's why people had assumed, before now, that camels produce a similar amount of methane as ruminants.
The Zurich researchers examined this assumption in a project sponsored by the Swiss National Science Foundation and have concluded that, in absolute terms, camels release less methane than cows and sheep of comparable body size. However, if comparing methane production with the amount of converted feed, then it is the same in both groups.
"To calculate the proportion of methane produced, different estimated values should be used for camels than those used for ruminants," explained Marcus Clauss from the Vetsuisse Faculty at the University of Zurich.
In cooperation with Zurich Zoo and private camel keepers, the scientists from the University of Zurich and ETH Zurich measured methane production in three types of camelids.
"The results show us that camels have a lower metabolism. Hence, they need less feed and release less methane than (other domesticated) ruminants," Clauss said.
The lower metabolism of camels could explain why they thrive in areas with a shortage of food such as deserts and barren mountain regions.
The modified calculation of the "methane budget" may be important for those countries with lots of camels — like dromedaries in the Middle East and Australia or alpacas and llamas in various South American countries.
More methane research
As noted, cattle emit methane as part of digestion, and that methane is a waste product. By reducing methane production, digestive efficiency should improve.
A few research abstracts on methane emissions of beef cattle were presented at the recent midwestern section meetings of the American Society for Animal Science and American Dairy Science Assn. in Des Moines, Iowa.
High-forage versus high-grain diets. B.E. Lehman, A.R. Green, T.L. Felix, B.C. Ramirez, L.F. Rodriguez and D.W. Shike of the University of Illinois at Urbana-Champaign presented abstract 384, which examined the effects of diet type on the feed intake and methane emissions of beef steers.
Lehman et al. used 12 fistulated steers that were approximately 725 kg of bodyweight in a crossover design with two dietary treatments:
1. High forage (HF) — 85% chopped grass hay, 10% alfalfa haylage and 5% supplement, or
2. High grain (HG) — 60% dry cracked corn, 20% corn silage, 10% dried distillers grains with solubles and 10% supplement.
Intake was evaluated for 18 days using the GrowSafe feeder system. Steers were then fed for 24 hours in environmentally controlled, hoodtype chambers during which methane concentrations were measured.
While steers were in the methane collection chambers, rumen gas was also collected via cannula puncture at zero, three and nine hours post-feeding and analyzed for methane concentration.
According to Lehman et al., HG steers had greater (P ? 0.01) dry matter intake than HF steers. When steers were fed in gas collection chambers, dry matter intake decreased (P ? 0.01) compared to when fed in GrowSafe feeders, regardless of diet; however, dry matter intake during the methane collection was correlated to dry matter intake during the GrowSafe period (r = 0.73; P ? 0.01).
Daily methane production and grams of methane per kilogram of bodyweight did not differ (P > 0.11), Lehman et al. said, but grams of methane per kilogram of dry matter intake were greater (trend; P = 0.09) for HF steers than HG steers.
Furthermore, they found that diet did not affect ruminal methane concentrations (P = 0.81). Daily methane production was correlated to ruminal methane concentration at the zero hour (r = 0.54; P ? 0.01), tended to be correlated at three hours (r = 0.38; P = 0.07) but was not correlated at nine hours (r = 0.33; P = 0.12), Lehman et al. reported.
Methane production per kilogram of bodyweight was correlated to rumen methane concentration at the zero hour (r = 0.52; P = 0.01), tended to be correlated at three hours (r = 0.41; P = 0.06) but, again, was not correlated at nine hours (r = 0.33; P = 0.12).
HG steers had greater dry matter intake compared to HF steers, which Lehman et al. said supports previous research.
Although diet did not affect daily methane production, grams of methane per kilogram of bodyweight or ruminal methane concentrations, Lehman et al. concluded that grams of methane per kilogram of dry matter intake were greater for steers fed forage-based diets than for steers fed grain-based diets.
Microbial community composition. In abstract 386, A.L. Knoell, C.L. Anderson, A.C. Pesta, G.E. Erickson, T.J. Klopfenstein and S.C. Fernando at the University of Nebraska-Lincoln pointed out that at the heart of anaerobic methane production in ruminants is a microbial food chain, which is greatly influenced by diet.
However, they said, the interactions among diet, microbial community composition and methane emission are poorly understood.
Thus, to better understand these interactions, Knoell et al. evaluated methane emissions and microbial community composition on a common diet and under different dietary conditions: high- and low-quality forage, with and without monensin supplementation and using different supplementation levels of modified distillers grain plus solubles (MDGS) in growing cattle.
Methane and carbon dioxide measurements were made during feeding using an individual feeding facility, 120 individual bunks equipped with the Calan gate system and an automated gas collection system, the researchers said. Gases were analyzed using a mobile GC unit.
Carbon dioxide was used as an internal standard, and the methane:carbon dioxide ratio was used to determine dietary effects on methane emissions, Knoell et al. said.
Samples were collected for microbial community analysis via stomach tubing, and the microbial community structure was analyzed using the Ion Torrent personal genome machine by sequencing the 16S rRNA gene.
According to the researchers, the microbial community structure and methane levels were similar in animals on the common diet and changed when different diets were fed. Diet quality (high-quality versus low-quality forage) and level of MDGS supplementation (20% versus 40%) significantly influenced (P < 0.05) the methane:carbon dioxide and microbial community composition, where high-quality forage produced higher levels of methane.
However, the level of methane emitted did not change with the level of supplementation, Knoell et al. said, suggesting that dietary intervention can be used to change the microbial community structure, which, in turn, can affect methane emission levels.
Identifying the members of the rumen microbial community from high and low methane-emitting cattle and diets would help identify microbial community members that influence methane production in cattle, which may lead to dietary and other intervention strategies to change these microbial populations in the rumen, Knoell et al. concluded.