A genetic anomaly traced back to prolific North American sire Maughlin Storm is resulting in calf death when it is inherited from both parents.
The abnormality, found by German research scientists, was first reported at an Interbull meeting in July.
A new discovery in the Holstein breed, it causes loss of appetite and body condition, combined with chronic/prolonged diarrhoea that is unresponsive to medical treatment and months later becomes fatal.
Known as haplotype cholesterol deficiency (HCD), blood samples from affected animals show a cholesterol deficiency that stops normal fat metabolism.
Darren Todd of Holstein-UK said it is working closely with the World Holstein-Friesian Federation (WHFF), other Holstein associations worldwide and related industry organisations, including the Animal and Plant Health Agency (APHA) in the UK, to identify carriers.
“There will only be a risk of calf mortality due to HCD if two carriers are mated,” said Mr Todd, who believes the early detection of the defect will benefit future Holstein breeding.
Prominent North American sire Maughlin Storm born in 1991 is the likely originator of the Holstein mutation.
And experts believe heavy use of this bull and his offspring will have spread the mutation worldwide.
AHDB Dairy’s Marco Winters said the other major carrier identified so far is Goldwyn, whose dam is a daughter of Storm.
“There will only be a risk of calf mortality due to HCD if two carriers are mated.”
Darren Todd of Holstein-UK
“There is no worldwide list available but we are working on a complete picture of the UK,” said Mr Winters.
However, the fact that all AI companies are now aware of the issue means it can be managed, he added.
“Farmers must first decide which bulls they want to use based on genetic qualities, then use mating programmes run on behalf of the AI companies to avoid inbreeding.
“The good programmes will also check for genetic defects and avoid carrier matings.”
And while genotyping all animals is costly and not recommended for the sole purpose of identifying genetic mutations, Mr Winters said those who have carried out genomic testing of the females will be able to look back and see if any are carriers.
He also believes AI companies will now screen young bulls for this mutation, preventing new carriers from entering the population.
“My expectation is we will have bred it out of the male side in a few years’ time, so future impacts should be bred out of the population.”
In the meantime, however, farmers should be mindful of genetics used in the past, said Mr Winters. If previously used bulls are carriers, he advised farmers to avoid using another carrier bull on any progeny.
According to a German data collection centre, an estimated 8% of the country’s cow population are carriers and early research by Holstein-UK suggests a similar level will be found here.
An APHA spokesman said: “APHA is providing support to Holstein-UK to investigate the extent of HCD carriers in the UK.
“Farmers who see clinical signs in their calves that could be associated with HCD should seek advice from their private veterinarian.”