Trials at Rural College in Scotland show that a mixture of garlic and citrus extract reduced methane emissions by up to 38 per cent.
The research indicates that 15 grams per cow per day is enough.
Milk production also increased by up to eight per cent, said the Swiss company that makes the supplement. It may be that garlic kept pesky flies away.
The supplement is produced in Abertillery in Monmouthshire by the Swiss company Mootral.
There was no effect on the taste or odour of milk from cows eating the supplement.
Trials at the University of California have shown that seaweed could reduce methane by 60 per cent, but Mootral said garlic costs less and is more readily available.
