Research by West Country scientists could soon be helping to add millions of pounds a year to the value of bull beef production.

Investigations by experts at Bristol University have shown that as many as 10 per cent of carcases are being devalued by high stress levels before slaughter.

Stress leads to so-called dark cutting beef: muscle tissue that fails to turn the typical cherry red when exposed to air, and which is generally tough and of poor eating quality. Now industry advisers at the English Beef and Lamb Executive (Eblex) have issued a new set of guidelines to farmers. They say if the advice is followed, returns from English bull beef production could be increased by £2.3 million or more a year.

Dark cutting beef is estimated to reduce carcase values by about 35 pence a kilo – or £115 an animal for an average weight young bull. On that basis the problem could be costing the industry about £2.3 million a year – and that's without counting downgrading which might stem from high levels of bruising which often accompany dark cutting.

Experts have pinpointed the cause as stress at about the time of slaughter, when livestock may be fatigued from transport and are often mixed with unfamiliar animals, leading to fighting.

But Eblex meat scientist Kim Matthews says with rising prices likely to mean more bulls being reared this year, producers should minimise needless losses in value.

"It's nothing more or less than the careful management of bulls in stable social groups which is the key to avoiding dark cutting problems," he said.

New Eblex guidelines now caution farmers against mixing bulls with unfamiliar animals at any time in the two weeks before slaughter or allowing them to mix with others in rearing pens or raceways, loading pens, transport compartments, or lairage pens, even for a short time.

Producers are also being encouraged to rear bulls in groups of 40 or more, despite more variable growth rates, so that whole consignments can be sent for slaughter without the need to make up the numbers from elsewhere.

Animals should always have water freely available and should be handled quietly. Journeys should start as soon as they are loaded; distances should be kept to a minimum and, where possible, the bulls should be slaughtered as soon as they arrive at the abattoir.