INBUILT WORM RESISTANCE

11 April 1997




INBUILT WORM RESISTANCE

By Jeremy Hunt

WORM egg counts taken from six-month-old lambs by sires identified as showing genetic resistance to infestation are 40 times less than those occurring in the progeny of susceptible sires.

This encouraging result has emerged from the long-term work on genetic resistance to nematodes being carried out by Dr Mike Stear and his team at Glasgow University. The research has been running for five years within a commercial flock of 1000 ewes and has involved the use of 40 rams.

"There is a strong genetic relationship between egg count and growth rate which makes selective breeding a feasible option for the control of nematodes," says Dr Stear.

And he believes that commercial sheep farmers may be barely a year away from being able to purchase rams with figures that will denote their heritable resistance to worms.

"We can foresee a rams heritable status for worm resistance fitting into other disease resistance data that will be available for an individual animal alongside more conventional information on growth rates and performance," says Dr Stear.

He feels confident that the results of the five years of research within the Scottish Blackface flock have provided the theory that could be applied in any flock to identify heritable status relating to worm resistance.

The Texel Sheep Society has already been in discussion with Dr Stear. This could be the first terminal sire breed subjected to evaluation.

The Glasgow University research has shown that there is an 80% correlation between growth rate and egg count in growing lambs even when treated with anthelmintics. A common gene for heritability to parasite resistance has been identified in lambs and its effective mechanisms investigated.

Dr Stears work, which is now in need of new government funding, has discovered that the gene works by controlling the size of the worms and their development.

"The gene does not work by reducing the worm burden but by controlling the ability of worms in the gut to lay eggs. Instead of the worm affecting the sheeps development, we have a situation where the sheep is interfering with the development of the worms."

Dr Stear says the situation is mutually beneficial to all animals in the flock because lambs with parasitic resistance are producing fewer worm eggs and thus benefiting those not carrying the gene and more open to infestation.

Sheep with the genetic resistance achieve greater control of worm infestation through antibody production. Dr Stear now believes his work has reached a stage where it is possible to breed for worm resistance and that rapid progress can be made within individual flocks.

He says the next stage is to apply the research findings to selective breeding schemes within individual flocks, particularly in lowland breeds where sires of superior genetic resistance can be identified.

By using body weight data at six months old and identifying the gene through a blood sampling technique, a rating for the genetic parasitic resistance of rams could be achieved.

Dr Stear says he does not believe his findings will ultimately see flocks being managed without the use of anthelmintics. "We are not in competition with anthel-mintics; they will still be used but sheep producers will be able to administer these treatments less frequently and that should reduce the risk of drug resistance."n

By Jeremy Hunt

WORM egg counts taken from six-month-old lambs by sires identified as showing genetic resistance to infestation are 40 times less than those occurring in the progeny of susceptible sires.

This encouraging result has emerged from the long-term work on genetic resistance to nematodes being carried out by Dr Mike Stear and his team at Glasgow University. The research has been running for five years within a commercial flock of 1000 ewes and has involved the use of 40 rams.

"There is a strong genetic relationship between egg count and growth rate which makes selective breeding a feasible option for the control of nematodes," says Dr Stear.

And he believes that commercial sheep farmers may be barely a year away from being able to purchase rams with figures that will denote their heritable resistance to worms.

"We can foresee a rams heritable status for worm resistance fitting into other disease resistance data that will be available for an individual animal alongside more conventional information on growth rates and performance," says Dr Stear.

He feels confident that the results of the five years of research within the Scottish Blackface flock have provided the theory that could be applied in any flock to identify heritable status relating to worm resistance.

The Texel Sheep Society has already been in discussion with Dr Stear. This could be the first terminal sire breed subjected to evaluation.

The Glasgow University research has shown that there is an 80% correlation between growth rate and egg count in growing lambs even when treated with anthelmintics. A common gene for heritability to parasite resistance has been identified in lambs and its effective mechanisms investigated.

Dr Stears work, which is now in need of new government funding, has discovered that the gene works by controlling the size of the worms and their development.

"The gene does not work by reducing the worm burden but by controlling the ability of worms in the gut to lay eggs. Instead of the worm affecting the sheeps development, we have a situation where the sheep is interfering with the development of the worms."

Dr Stear says the situation is mutually beneficial to all animals in the flock because lambs with parasitic resistance are producing fewer worm eggs and thus benefiting those not carrying the gene and more open to infestation.

Sheep with the genetic resistance achieve greater control of worm infestation through antibody production. Dr Stear now believes his work has reached a stage where it is possible to breed for worm resistance and that rapid progress can be made within individual flocks.

He says the next stage is to apply the research findings to selective breeding schemes within individual flocks, particularly in lowland breeds where sires of superior genetic resistance can be identified.

By using body weight data at six months old and identifying the gene through a blood sampling technique, a rating for the genetic parasitic resistance of rams could be achieved.

Dr Stear says he does not believe his findings will ultimately see flocks being managed without the use of anthelmintics. "We are not in competition with anthel-mintics; they will still be used but sheep producers will be able to administer these treatments less frequently and that should reduce the risk of drug resistance."n

Genetic resistance to worms benifits the whole flock – lambs with parasitic resistance produce fewer worm eggs so benefiting those not carrying the gene.


WORM RESISTANCE


&#8226 Gene which confers resistance identified.

&#8226 Interfere with development of worms.

&#8226 Now possible to breed for resistance.

&#8226 Should reduce reliance on wormers.


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