12 November 1999

Breed to battle worms

Breeding stock for their

resistance to parasites could

help tackle growing industry

concerns, believes one

Wiltshire producer.

Emma Penny reports

FOR many producers, worming cattle and sheep is becoming increasingly complicated as resistance to anthelmintics spreads across farms and wormer groups.

But Wilts beef and arable producer Anne Filkins believes the way ahead is to breed stock that are resistant to worm challenge.

Travelling to research centres and farms in the US, New Zealand, Australia and Kenya as part of a Nuffield award from the Dartington Cattle Breeding Centre Trust convinced Miss Filkins that breeding for resistance to parasites is a viable option.

"We have bred stock almost solely for increased output since World War One with no regard to hardiness," she says, "for example, whether animals can withstand worm challenge.

"In addition, we have just embraced the technology of the day, which has led to increasing concern about resistance to anthelmintics and antibiotics, as well as residue worries."

While producers in the UK still rely heavily on anthelmintics to control worms and maintain stock performance, farmers in Australia and New Zealand can choose to breed animals resistant to worms, she says.

Australian producers can buy Belmont Red bulls – a composite breed that is resistant to worms – to use on their cows. Based on a Hereford cross Shorthorn, the cross is now established as a breed in its own right, and was produced by researchers in Queensland.

"Most cattle of that breeding wont survive in Australian conditions, but researchers found that some did. They used this stock – which was most adapted to withstand the hot weather and parasite challenge – as a foundation for the Belmont Red. It is a successful breed, as it is resistant to worm challenge and has good meat quality."

But sheep producers in Australia and New Zealand can also choose to breed from the most worm resistant of their own stock, says Miss Filkins.

"WormFEC and Nemesis programmes were established by researchers to help producers select from within a particular breed for resistance to parasites and other traits."

Nemesis – used in Australia – involves measuring a sheeps faecal egg count (FEC) to assess its worm burden, at a cost of about A$2 a sheep (87p a sheep). This result is then compared with its contemporaries to assess the relative performance of that sheep. If it has a lower worm burden than its contemporaries, it is likely to be more resistant.

FEC values are then used to produce estimated breeding values (EBVs) for worm resistance, which can also take the performance of that particular animal into account.

Now Australian producers can buy rams with an EBV for FEC. A ram with a value close to zero will result in little change in parasite resistance in the flock, but one with a negative breeding value will decrease FEC – and so result in better parasite resistance – in the next generation.

"Buyers can look at the individual FEC EBV for a ram and choose an animal which will have the desired genetic effect on his flock," says Miss Filkins.

New Zealands WormFEC programme is fairly similar to Nemesis, but besides doing faecal egg counts, producers can also have flocks blood tested to measure the strength of an animals immune response to parasites.

This is based on assessing the proportion of anti-roundworm antibodies in blood cells. A single antibody test gives a reliable measure of the sheeps responsiveness to roundworm infection, and has an advantage over FEC testing in that it is not affected by management practices such as drenching.

"Producers in Australia and New Zealand are using FEC as a tool and are selecting for parasite resistance – along with other important traits – so they are achieving genetic gains."

Rather than selecting within breeds, researchers in Kenya are considering changing breeds to improve parasite resistance and stock survival, says Miss Filkins.

"Haemonchus is a problem in Kenyas hot climate. Producers have access to wormers, but there are concerns about under-dosing, use of communal grazing and a high population of goats which transfer wormer resistance to sheep. Resistance to all three wormer classes – ivermectins, benzimidazoles and levamisoles – is a problem in Kenya."

Many of the native Kenyan breeds, such as Maasai Reds, are resistant to worm challenge, but the increasing proportion of breeds such as Romneys and Dorpers – a Dorset and Persian Blackface cross – cannot cope, says Miss Filkins.

"In trials where the Red Maasai replaced Romneys, FEC results were cut by 90%, which improved production and cut pasture contamination. Researchers are hoping to substitute these native breeds for other breeds which perform less well."

Kenyan researchers are also selecting sheep that are resistant to worms and are gene-mapping them, work that is also being carried out in the US. "US studies, based on work originally carried out at Glasgow University, hope to find the genes responsible for conferring parasite resistance. Researchers have identified six or seven genes involved so far."

Miss Filkins says FEC testing, identifying resistant breeds and gene-mapping all strive after the same goal – breeding stock for genetic resistance to parasites.

"A big benefit of host genetic resistance is that it reduces the number of eggs shed onto pasture, and thus sward contamination. But it also reduces the need for anthelmintics, prolongs wormer life, is better for welfare and means that stock perform better because they are not challenged by worms.

"It makes sense to breed for parasite resistance, but it is a chicken and egg situation: We want to use less wormer but we need to breed for resistance first, otherwise it becomes a welfare issue. But the science is there, it just needs to be applied in the UK."

BREEDING FOR RESISTANCE

&#8226 Worldwide research.

&#8226 Reduced wormer use.

&#8226 Needs applying in UK.