18 June 1999

Target use of wormers to cut the risk of resistance

By Jessica Buss

AVOIDING over-treating cattle with wormers should reduce the risks of nematode worms developing resistance to more products.

This follows a study indicating first cases of resistance to levamisole and ivermectin wormers in the UK.

In a report in the Vet Record, June 12, Gerald Coles of Bristol University says the MDC-funded study which confirmed ivermectin resistance in the UK last year (Livestock, Mar 13, 1998), also reveals some evidence of levamisole resistance on two south-west farms.

Unfortunately, Dr Coles was unable to secure research funding for live animal tests to confirm cattle worms on these farms were resistant to levamisole. But lab tests used to identify levamisole resistant cattle worms had been proven to work for levamisole resistant worms in sheep through live sheep tests, he adds. He is, therefore, fairly confident that nematode worms resistant to levamisole wormers exist in UK cattle.

Dr Coles is concerned that in the survey of 97 dairy farms providing samples for the study, over half treat animals with wormers in their second grazing season. Worming cattle in their second year restricts development of immunity and reduces worm eggs passed onto pasture to maintain challenge to younger animals.

"When you treat all cattle you imitate what happened with sheep and resistance will develop faster, as happened in New Zealand," he says.

The study report says that allowing immunity to develop in first-year animals should reduce expenditure on anthelmintics, and reduce or eliminate the need to treat older animals. Both actions should slow development of anthelmintic resistance.

"New Zealanders believe nematodirus anthelmintic resistance in cattle is eight years behind sheep. Now NZ sheep have ivermectin resistance they will soon have no nematodirus treatments at all and could lose up to a third of the lamb production," says Dr Coles.

Using a different class of anthel-mintic for calves each year may also slow resistance development, but there has not been the research to prove this will help, he adds. &#42

Low prices make for costly shearing

BRITISH wool values have slumped to levels that will make shearing a costly operation for sheep producers this year.

Average values have dropped to 39.6p/kg compared with 62p/kg last year. This 40% drop is attributed to decline in demand for wool across the globe, due in part to the far eastern economic collapse, says British Wool Marketing Board (BWMB) press officer Liz Ambler.

"For many producers it is not worth shearing. But if you keep sheep, you have to shear them for animal health reasons. It does not cost anything to make it grow, so the better the quality the better it sells. Clean, white wool will always sell," she says.

Other factors such as New Zealand competition have had a bearing on UK wool demand from carpet manufacturers.

"New Zealand lost a lot of markets and so looked to Britain and because its currency has been devalued its white wool is attractive. The UK has become one of the largest importers of New Zealand wool."

British carpet makers, although not deserting British Wool, are using more cheap New Zealand wool in their blends, she adds.

But the BWMB has continued to trade wool which means there will be little carryover, less than 2m kg when the market improves.

"There is feeling things are on the turn. If that is the case producers will receive the benefit in the balance payment," she says. &#42

RABDF restructure

A LESS complicated structure and some cost savings are behind the Royal Association of British Dairy Farmers decision to restructure at its recent AGM.

RABDF policy adviser, John Sumner, says the previous structure included a council of up to 40 producers and affiliated society representatives, and also elected a board of directors. It will now set up a single governing body of 15 elected members which will select its own chairperson. This should be in place by the end of the year.

"Committees will still be formed for specific purposes such as running the European Dairy Farming Event," says Mr Sumner.

He adds that the new structure will be more democratic and efficient. &#42

Weigh before dosing

WEIGH sheep, dose to the heaviest weight and calibrate wormer dosing guns to avoid increasing worm concerns and resistance risk in sheep.

Sheep specialist Lesley Stubbings says under-dosing will increase risk of resistance several-fold. "Besides dosing to the weight of the heaviest sheep, check dosing guns, and renew them more frequently. You might be under pressure to cut costs, but do not be tempted to shave worming costs, it will just cause problems," she warns.

"Also, with recent wet weather, many lambs have dirty backsides, but this might not be due to worms. If your flock seems to have scour, get it investigated before reducing the gap between drenching." &#42

Advice from the experts

SHEEP and beef breeding and health advice will be available free from MLC experts through a series of seminars at major shows this year.

Topics include parasites, scrapie and scrapie genotyping, electronic ID, sheep and beef cattle recording and lamb selection. The seminars will take place at the Royal, Royal Highland and Royal Welsh shows. Tickets and full details from Kathleen Rout (01908-844271). &#42

Ryegrass catch crop stops run off from maize

PREVENT run-off from maize fields this autumn by undersowing an Italian ryegrass catch crop before maize plants are too high.

Maize Growers Association member and Devon milk producer Charles Moore says nitrate leaching and run-off from maize stubble has been a big concern. But he says his two years experience of undersowing shows it reduces these risks.

"Last autumn was wet and we significantly reduced run-off with undersown grass," he says.

This was sown at half the normal grass seed rate in late June. After harvest ruts were removed with a tine harrow, but grass under maize also helps stop machinery cutting into the ground.

The undersown crop also provides extra forage in spring for cows to graze or an early cut of silage and can yield up to 2.5t/ha of dry matter (1t/acre).

Mr Moore grazed sheep on an area of the undersown grass through autumn and winter, some was used for early grazing for cows and the remainder was made into an early cut of big bale silage before ploughing again for maize.

But he stresses that maize is the main crop and yields should not be allowed to suffer by drilling the following maize crop too late. A little damage to the growing maize plants in field corners when sowing grass, however, is inevitable.

"Grass seed must be sown at least 30 days after atrazine residual herbicide is sprayed, while its still possible to drive through the crop." This is before the crop has 8-10 leaves, usually in late June.

Using other residual herbicides or late sprays of atrazine may stop grass germinating, he adds. &#42