Improving the diet of dairy cattle often focuses on efficiency: how to get more milk for less input. In recent years, the focus has begun to include reducing the herd’s output of methane. As part of AMTS’s “The Nutritionist” webinar series, Joseph W. McFadden, Ph.D., recently presented “Dietary Solutions to Inhibit Ruminal Methanogenesis.”

McFadden is associate professor of dairy cattle biology in the Department of Animal Science at Cornell, a Northeast Agribusiness and Feed Alliance Faculty Fellow, Cornell Atkinson Center for Sustainability Faculty Fellow and Cornell Dairy Center of Excellence Faculty Fellow.

He quoted the Intergovernmental Panel on Climate Change 2021: “‘It is virtually certain that irreversible, committed change is already underway.’ These changes are likely to cause global warming and modified precipitation patterns. Enhancing the adaptability and resiliency of animal agriculture has and will continue to be the smart approach to maintain food security. The more approaches we can provide farmers, the more adaptable and resilient animal ag can become.”

The global emission intensities by commodity vary. He said that beef and buffalo meat are on the high end of the spectrum. Small ruminants for meat or milk and buffalo milk animals are mid-range. Dairy cattle, pork, layers and broilers are on the lowest part of the spectrum, based on the nutrients animals provide per the carbon released.

“The release of fossil carbons has to be addressed,” McFadden said.

The farmer’s location also relates to the level of ag-related carbon emissions produced. Farming resources, commodities and by extension management practices vary by region. “Latin America has the highest emissions,” McFadden said. The next lowest region is Eastern and Southeast Asia, South Asia, North America, the Near East and North Africa (tied with Western Europe), Sub-Saharan Africa, Oceania, Eastern Europe and the Russian Federation. Except for North America, the regions with the highest emissions raise more beeves and buffalo than other types of livestock. McFadden said that North America’s exception to the rule may indicate the presence of more environmentally friendly farming methods compared with other regions.

“The U.S. and other developed countries have improved milk production efficiency by dilution of maintenance,” McFadden said as an example.

By scientifically calculating an animal’s ration to avoid excess nutrition while still meeting the lactating cow’s needs, farmers can help their herds produce more milk while producing the least emissions possible. McFadden wants more cooperation with other countries to share discoveries that can help them improve their ag efficiency and reduce greenhouse gas emissions.

Dietary improvement reduces greenhouse gas output

Joseph McFadden, Ph.D. (L) and another Cornell staff member tour a farm. Photo courtesy of Cornell CALS

The variety of livestock also matters. U.S. Holsteins were found to produce 0.25 kg of methane per kg of milk, compared with 1.21 kg for Indian indigenous cattle and 2.96 for Indian crossbred cattle.

McFadden supports mitigating enteric methane emissions through improving efficiency of energy use.

“Decreasing forage to concentrate ratio reduces methane yields, but we cannot ignore lower rumen pH,” McFadden said.

Livestock in different countries eat different foods based upon their local resources and their management traditions. “Changes in crop production can increase efficiency and decrease methane in developing countries,” McFadden said.

He added that by increasing dietary lignin content, operators can reduce neutral detergent fiber digestibility and gross energy to digestible energy and increase methane per unit of milk protein.

“Feeding nitrate lowers methane production by 16%, enhancing the conversion of gross energy to metabolizable energy but does not modify milk energy,” McFadden said.

Some researchers are looking at seaweed as a methane inhibitor and finding that it reduces emissions. But farmers must also consider the overall effects of supplementing their herd’s ration with seaweed.

“What about environmental impact, whether harvesting it from the ocean or cultivating it on land?” McFadden said. “It can look great at the cow level, but if you look upstream, what does it look like? How will you process it and transport it?”

While seaweed works for reducing emissions, “rumen wall damage has been observed by European researchers,” McFadden said. Traces of bromoform, an ozone depleting substance, were also found in the milk of cows fed seaweed.

Feeding fatty acids also reduces methane emissions, but “we also need to consider how these fatty acids influence energy partitioning matter,” McFadden said.

Recent research shows that 3-nitrooxypropanol (3NOP) consistently inhibits methane production by 30%, increases hydrogen emissions, has little apparent impact on performance and has no apparent 3NOP metabolites in milk.

“Co-supplementing 3NOP and canola oil maximizes methane reduction and canola reduces 3NOP-induced H2 emissions,” McFadden said.

He further stated that using ionophores to mitigate methane does improve digestive efficiency to favor propionate production over acetate, which reduces hydrogen for methanogens. Research showed that methanogenesis inhibition is more pronounced in diets with higher fat content – possibly a 4% to 10% reduction. However, “ionophore resistance is a concern.”

Essential oil research including a blend of coriander seed oil, eugenol, geranyl acetate and geranioil at 0.8 g daily shows some promise with an increase in milk production among cows with moderate milk yields. The response depends upon feeding, but a five- to eight-week minimum shows 2% to 3% increase of milk yield and energy-corrected milk without a change in dry matter intake or milk composition.

“There are so many studies on this, and the results are fairly consistent,” McFadden said. “You have to have long-term feeding to see the methane inhibition effect.”

Plant extracts such as garlic with citrus extract, oregano with green tea extract and cinnamon oil offer mixed responses. The garlic blend offered greater efficacy in vitro than in vivo. The oregano and green tea mix did not affect nutrient digestibility or milk production and composition but showed possible reduction in ruminal protein degradation and ammonia production. It reduced methane but its efficacy in vivo is uncertain. Cinnamon oil had no effect on methane production in vivo.

“You really need to take studies out there using a holistic approach,” McFadden said. “We have to start thinking about how each of these additives reacts with other aspects of their diet and with each other and with the environment.”

by Deborah Jeanne Sergeant