What Effect Do Tannin-Containing Feeds Have on Methane Emissions from Dairy Cows?

Tannin-containing feedstuffs like Acacia mearnsii and sainfoin (Onobrychis viciifolia) have a measurable impact in reducing methane emissions from dairy cows. However, since these feedstuffs in some cases lead to productivity losses, careful consideration must be given to their use.

One of the most outstanding qualities of ruminants is their ability to transform non-edible plant biomass into food for humans. Grass-based feeds generally contain high amounts of digestible fibre, which leads to increased production of methane (CH₄), a major greenhouse gas.

One possible approach to reducing CH₄ emissions is to feed tannin-containing fodder to ruminants. Condensed tannins can decrease ruminal CH₄ production by reducing the breakdown of carbohydrates (particularly fibre), or by acting directly against methanogens or hydrogen-producing microbes in the rumen. However, both of these modes of action can also reduce the energy uptake of the animals and lead to a possible increase in CH₄ release from manure owing to lower feed digestibility.

Ruminal and manure-derived methane emissions investigated

We studied the effect of feeding ryegrass, red clover and sainfoin silages with and without the addition of acacia extract on ruminal CH₄ production in dairy cows, as well as CH₄ release from manure. Feed intake and milk yield were recorded daily. Milk composition, ruminal fluid characteristics and microbiota were analysed. Individual ruminal CH₄ production was determined via the GreenFeed System. CH₄ release from liquid manure was measured in a dynamic chamber by taking the faeces and urine from a balance study running in parallel and mixing them, whilst taking the excretion ratio into account.

Tannin-containing feedstuffs do lower methane production…

The addition of acacia extract decreased daily ruminal CH₄ production by 10%, but did not lower CH₄ emission intensity (i.e. CH₄ production per litre of milk produced) or CH₄ yield (methane production per kg of dry-matter intake). The reducing effect of sainfoin silage on CH₄ production was dependent on the silage to which it was compared. Acacia extract reduced CH₄ release from liquid manure by 17% when ryegrass silage was fed, but not when sainfoin and red clover silages were fed. The feeding of sainfoin silage led to the lowest CH₄ release from manure compared to the other two silages.

… but also reduce milk yield

Acacia extract reduced milk production and feed intake when added to ryegrass silage, the silage with the lowest protein content. The feeding of sainfoin and acacia extract led to a reduction in milk protein content and yield. 

In summary, the reduction in ruminal CH₄ production and CH₄ release from manure was in some instances associated with productivity losses in the animals, and therefore careful evaluation is required before the implementation of tanniferous feeds in dairy farm practice.