Can methane emissions be reduced in dairy cows fed oregano and green tea extracts?

Plant-based feed additives may help curb dairy cow methane emissions, but additional work is needed, say researchers.

A team of researchers from multiple academic institutions in Brazil examined the use of oregano and green tea extracts in feed for dairy cattle.

“This study aimed to evaluate the use of oregano extract, green tea extract, and their association as feed additives on performance and methane emissions of dairy cows between 28 and 87 d of lactation,”​ the researchers said.

The researchers found that the feed additives did not alter many milk components, but they did reduce the production of methane gas (CH4). “Animal performance variables were not affected by the use of these additives,” ​they added.

“Green tea and oregano did not influence variables such as DMI [dry matter intake] and milk production by dairy cows between 28 and 87 d of lactation,” ​they said. “Oregano and green tea were able to reduce CH4 emissions per kilogram of digestible DM [dry matter] ingested, which suggests that further studies on these feed additives may be warranted.”​

There also was some speculation that larger dosages supplied in capsules could provide positive influence on animal production, they said. “We observe some additive effect of the association of green tea and oregano on total-tract apparent digestibility, molar proportions of ruminal acetate and butyrate, and fatty acid profile in milk, but the same was not noticed on milk production or methane emissions.”​

1/ Why oregano and green tea?​

As some feed additives like ionophores are banned for use, there has been an interest in using plant extracts to modify rumen fermentation or for antimicrobial and antioxidant properties, the researchers said. Plant-based compounds may provide therapeutic elements and when used in conjunction could offer additive benefits.

Green tea provides polyphenols and has been linked to antioxidant, anti-coccidial antimicrobial and antiprotozoal activities, they said. Oregano generates essential oils including carvacrol and thymol.

“Polyphenols and essential oils may modify rumen fermentation and affect methanogenesis, inhibiting growth, development, activity, and metabolism of the methanogenic Archaea, directly or indirectly and may mitigate CH4 emissions,” ​they said.

Limiting methane emissions while maintaining animal production is of interest, as the greenhouse gas is considered “potent,”​ they said. Cutting methane production could reduce around 2 to 12% of animal energy losses, although there is limited evidence regarding positive influence for animal growth, reproduction or milk and meat generation.

Supplementing diets with oregano and green tea extracts could limit methane emissions from dairy cows, said the researchers. “However, the great variety of compounds and dosages used has made it difficult to produce a meaningful compilation of the research result,”​ they added.

Previous examinations have been either in vitro or short-term trials, rendering results “uncertain”​ when considered for use at a production facility, they said. More in vivo work is needed, especially with dairy cows, to reproduce those results.

“Our hypotheses are that (1) oregano extract will reduce methane metrics and will not have a negative effect on animal production; (2) green tea extracts will reduce methane metrics and will not have a negative effect on animal production; (3) oregano and green tea extract when fed in association will present an additive effect in reducing methane metrics,”​ they said.

2/ Methods and materials​

In the feeding trial, 32 lactating dairy cows were given one of four diets for a 44-day period, after a 14-day acclimation, the researchers said. The diets had a forage-to-concentrate ratio of 60:40.

The diets included a control, the diet mixed with 0.056% oregano extract (OR), the diet with 0.028% green tea extract (GT), and a diet with both 0.056% oregano extract and 0.028% green tea extract (MIX), they said. Forage used in the diets included corn silages and Tifton hay, while the concentrate included ground corn and soybean meal.

Milk production was recorded daily and analyzed weekly, while bodyweight and body condition scores were noted daily, they said. Ruminal samples were taken to check for fatty acids.

Dry matter intake was recorded and the crude protein, (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), total digestible nutrients (TDN) and gross energy intake were determined, said the researchers. Fecal samples were collected at the end of the feeding trial and analyzed.

A respiration chamber was used to detail oxygen consumption, along with production of methane, CO2 and heat, they said.

3/ Results​

There was no link found between day and diet, the researchers said. Extracts also did not alter rumen pH, total volatile fatty acid concentration, milk yield or the majority of milk traits.

However, when used separately as feed supplements, both extracts had a positive influence on cows’ methane production, they said. “Green tea and oregano fed separately reduced gas emission in cows during the first third of lactation and have potential to be used as feed additives for dairy cows,” ​they added.

Adding GT or OR improved the digestible fraction of the dry matter and reduced methane production compared to the control diet, they said.

Supplementing diets with OR tended to reduce fat amounts in the milk, the researchers said. Both plant extracts changed some of the fatty acids, but did not alter how they were grouped according to chain length, saturation, n-3 or n-6 levels or conjugated linoleic acids.

In Holstein cows, the MIX feed lowered gross energy and tended to limit total-tract apparent digestibility coefficient for crude protein and total digestible nutrients when results were compared to cows getting the OR diet, they said.

Source: Journal of Dairy Science​

Authors: G. Kolling, S. Stivanin, A. Gabbi, F. Machado, A. Ferreira, M. Campos, T. Tomich, C. Cunha, S. Dill L. Pereira, V. Fischer