Research project estimates methane emissions from cattle

Goal is to contribute to reduction of livestock greenhouse gas emissions.

By Fabio Reynol

Agência FAPESP – Methane (CH4) is considered the second-largest contributor to global warming, closely following carbon dioxide (CO2), and human activities, including cattle husbandry, are estimated to produce 70% of the emissions of this gas.

Researchers at the São Paulo Animal Science Institute (Instituto de Zootecnia de São Paulo, IZ) in Brazil recently completed a project to produce indicators that can be used in the genetic improvement of Nelore cattle (Bos indicus), taking into consideration the need to reduce greenhouse gas (GHG) emissions from livestock.

According to the findings of the project “Selection for beef production with reduced greenhouse gas emissions”, coordinated by Maria Eugenia Zerlotti Mercadante, cattle that eat less release almost as much methane into the atmosphere as cattle that consume more to reach the same weight.

The project, which lasted from 2011 to 2014, was selected in a competitive bidding process for studies of the effects of climate change on agriculture, with financial support from FAPESP and the National Council for Scientific and Technological Development (CNPq), to consolidate the National Agrobiodiversity and Agricultural Sustainability Research Networks (Repensa).

The main GHG produced by livestock is enteric methane, which arises from fermentation in the digestive system of ruminants and is released by eructation (belching). Estimates of methane emissions by beef cattle and a detailed understanding of the factors that influence them are important to the sustainability of beef production and to efforts to reduce GHG emissions, according to Mercadante. “We don’t know much about the opportunities to mitigate this problem by genetic improvement of beef cattle,” she said.

The research project found a similarity in methane emission levels between cattle classified as more efficient or less efficient based on the ratio of feed conversion to weight gain. Both animals that consume more and those that consume less feed release, on average, slightly more than 140 grams of methane per day into the atmosphere.

“In this case, breeders should choose the more efficient animals to save feed and generate smaller amounts of manure, among other financial and environmental advantages,” Mercadante said. In other words, more efficient cattle have a less harmful impact on the environment even though their methane emissions are similar to those of less efficient animals.

The most significant results were obtained from experiments with cattle housed in feedlots: the more efficient animals consumed 10% less, on average, and displayed a 4% higher digestion rate (capacity to absorb nutrients).

The comparison was based on residual feed intake (RFI, the difference between actual and predicted feed intakes) in correlation with average daily weight gain and metabolic body weight (live weight raised to the 0.75 power) in a given period. More efficient animals were correlated with a lower RFI and less efficient animals with a higher RFI.

This finding, in turn, led to even more important results relating to the efficiency of RFI. The researchers discovered that more efficient animals had higher blood plasma concentrations of insulin and IGF-I hormones and lower concentrations of urea.

“These components can be indicators of feed efficiency for Nelore cattle,” Mercadante said, stressing that the study evaluated animals in specific conditions and that these findings may not apply to other situations.

“We analyzed growing cattle,” she said. “The results might be different for finishing cattle.”

The researchers analyzed four samples for a total of 464 growing animals. In two samples, they monitored 48 animals – 24 males and 24 females – in feedlots and pasture.

Automated feed trough and collection halter

To measure the methane emitted by each animal the research group used the SF6 tracer method for measuring eructated CH4. This method was developed at Washington State University in the United States.

A capsule of sulfur hexafluoride (SF6), an inert gas, is inserted into the animal’s rumen. The capsule’s rate of SF6 release is controlled so that this rate supplies a benchmark. In an analysis to quantify an animal’s methane emissions, the first step is to check whether the amount of SF6 released equals the benchmark rate. If so, the analyst can safely assume that methane release is also being accurately measured.

Eructated methane is constantly sampled through a collection canister fitted to a halter worn by the animal. Connected to a tube placed on top of the muzzle between the animal’s nostrils, the canister is designed to collect exhaled breath at a constant rate.

The gas collected in the tubular ‘yoke’ canister is analyzed every 24 hours. The SF6 and methane concentrations found in the canister are measured using gas chromatography. In these experiments, measurements were performed in partnership with a team led by Alexandre Berndt, a researcher with EMBRAPA, the Brazilian Agricultural Research Corporation, in São Carlos, São Paulo State.

Dry matter intake while grazing was estimated using external markers added to the diet or inserted into the digestive tract (chromic oxide for fecal output and titanium dioxide for supplement intake) and indigestible neutral detergent fiber as an internal marker.

When conducting the same study with feedlot cattle, the researchers were helped by technology in the form of an automated trough supplied by Canada’s GrowSafe Systems Ltd. The trough recognizes the animal that is feeding by reading its radio frequency identification (RFID) tag and automatically measures its consumption. “GrowSafe eliminates the need for individual stalls to perform this measurement, giving the animals more freedom and more closely resembles the situation in which cattle are raised,” Mercadante explained.

The equipment was acquired as part of the Thematic Project “Genomic tools to genetic improvement of direct economic important traits in Nelore cattle”, led by Lúcia Galvão de Albuquerque, a professor at São Paulo State University (UNESP) in Jaboticabal.

The research also included an economic analysis to estimate the costs and revenue arising from methane emissions, growth and feed efficiency.

“It’s important to know how each of these factors influences production, economically speaking, and, therefore, the weight that should be given to each factor in a genetic improvement program,” Mercadante said.

More studies of feed efficiency and GHG emissions should be conducted, the researcher argued, to reach the scale required. “Only 4,000 animals have been evaluated to date in Brazil. That’s too few in light of the large size of our herd and the widely varying conditions under which cattle are raised in this country,” she said.