As the livestock industry takes hits for its purported role in global warming, researchers are working on science-based concepts for potential methane reduction from dairy cattle.
Dr. Guillermo Boggio, University of Wisconsin post-doctoral research associate, explained that methane emissions represent 11% of the total U.S. greenhouse gas emissions. In comparison, 80% of emissions are from carbon dioxide (CO2), 7% are from nitrous oxide and 3% are from fluorine gases.
Methane has 28 times more warming power than CO2; however, the atmospheric lifetime of methane is only 10 to 12 years. CO2 lasts a lot longer.
“At the rate methane is being produced, at the same rate it is naturally removed from the atmosphere,” said Boggio. “If we can reduce the production of methane, we can reduce greenhouse gas emissions from methane.”
Methane from livestock is the result of enteric fermentation in the rumen. Methane represents an energy loss of 5% to 10%. Reducing methane production in ruminants would result in animals with greater feed efficiency.
Boggio outlined several strategies for methane reduction in livestock, including selective breeding, management and through microbial action. However, none of these strategies are valid without a reliable method of measuring methane, which is critical in determining whether a practice is successful.
“The gold standard method [for measuring methane] is respiration chambers,” said Boggio. “These are very precise because we can measure all the emissions coming from the animal but are expensive and labor intensive. Another method for … grazing animals measures methane emissions via the inert tracer gas sulfur hexafluoride (SF6).”
While the SF6 method is effective, it involves handling animals daily.
For his methane research, Boggio used the GreenFeed system, which offers a small amount of pelleted feed attractant to entice animals to visit the feeder throughout the day. Gas emissions data are logged and processed, allowing the user to access a summarized report of calculated fluxes.
“We provided access for the cows 24/7 for seven to eight weeks,” said Boggio. “The key point of the GreenFeed system is to obtain numerous short-term records across the day for multiple days.”
The feed is alfalfa pellets, and cows can visit five times a day with two-hour intervals between visits. When cows visit the GreenFeed to eat, methane production information is collected and graphed.
With the allowed visits per cow, the system generates a large amount of data. In addition to collecting daily methane emissions, the GreenFeed system tracks daily intakes, body weights, daily milk yield and weekly milk composition.
Cattle visit a GreenFeed system that measures carbon dioxide and methane emissions. Photo courtesy of Stacey Gunter/ARS
Methane information and body weight are also being collected from bulls at a bull stud facility. The plan is to compute the correlation between the methane emissions in young bulls and cows.
Boggio has data from more than 1,000 Holstein cows from 26 different on-farm studies. He reported average methane emissions of 410 grams/day/cow. In one study, peak methane production occurred about 1.5 hours after feeding.
To develop a genetic database, Boggio said it’s essential to identify phenotypes.
“We define different kinds of methane emission traits,” he said. “The first one is methane production. From the GreenFeed study we have the grams per day the cow is producing. But nobody wants to select a cow that is producing less methane and also producing less milk.”
For more accurate data, Boggio measures residual methane intensity and residual methane yield. “We correct methane emissions by the output of a cow and get the methane emissions corrected by those two factors,” he said. “Dry matter intake is one of the main factors that determines methane production. A cow that is eating more will produce more methane. If we select a cow for those two traits, we account for outputs and inputs.”
There’s significant variability in methane production among cows. In one study, the highest methane-emitting cows produced 600 to 650 grams/day, while the lowest producing cows produced 300 to 350 grams/day. Boggio said the low methane cows may be eating less or are smaller cows.
He provided an example of what he observed in the study. “We have a cow that is producing 580 grams per day of methane,” he said. “However, based on her metabolic body weight and milk energy or on her dry matter intake, she should produce 480 grams. The cow is producing 27% more of what is expected.”
A second cow is producing roughly 360 grams of methane per day. However, based on the second cow’s metabolic body weight, milk energy or dry matter intake, she should produce 480 grams of methane, or 24% less methane. Preliminary results show the more feed efficient cows are lower methane enteric cows.
Genetics and selection will play an important role in methane reduction. “We are phenotyping and building the reference population for a future genomic evaluation for methane emission traits,” said Boggio. “We are planning to phenotype 4,000 to 5,000 dairy cows.”
Boggio reviewed a management strategy for methane detection and potential reduction that involves milk media infrared spectra. Milk samples are analyzed for butterfat percentage, true protein percentage, lactose, urea and fatty acid profile.
“At the lab they pass light through the milk sample,” said Boggio, explaining the mid infrared spectra used by MilkoScan®. “Our idea is to use this information to predict methane emissions. In the future, when the producers send a milk sample to the lab, they will have not only the milk composition, but also how much methane this cow produced on that day.”
Results from the MilkoScan would allow farmers to feed additives only to animals with higher methane output.
The last component of the project involves microbial solutions. The goal is to understand the influence of the host on the composition and activity of the methanogens in the rumen that produce methane.
“We are targeting different kinds of microbial communities,” said Boggio. “We’re collecting rumen samples and buccal [oral] samples. We’re also collecting fecal samples to target methane emissions in the gut.”
Boggio said feed efficiency information can be used to select cows for feed efficiency traits.
“The rumen microbiome mediates part of the genomic effect on the trait,” he said. “We can target specific groups of bacteria to get better genomic predictions. One of the most important things is that phenotyping is in progress, and right now we have over 1,000 cows with phenotypes and genomic data. We are getting good heritability for the methane traits.”
by Sally Colby
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