Romney breeding for parasite resistance and footrot tolerance.
Gordon Levet has been breeding Romney sheep for the past 50 years, in a challenging Northland environment in the Kaipara district near Wellsford. He has seen sheep numbers in Northland fall away sharply, because farmers were losing too many sheep with facial eczema and beef cattle were more profitable. Gordon therefore began selecting for FE resistance in his sheep, along with other productive traits. He has also been breeding for footrot resistance since the early days. Nearly 20 years ago Gordon moved on to breeding for internal parasite resistance. He has been passionate in his approach, culling anything that doesnt measure up and only breeding from or selling sheep which have verified resistance. Some of the best sheep now have confirmed resistance to FE, footrot and worms. Sheep are making a welcome return to Northland and demand and prices at Gordons annual ram sale (first Wednesday in December) has risen strongly. Last year the average ram price was $892, up from $595 in 2003. The top group of 35 rams made over $1000, with an average in that group of $1500.
In breeding for worm resistance, Gordon challenges his lambs by not drenching them and running them at high stocking rates to see the effects on individual sheep. When they have been selected, he collects and analyses the parasite content of the sheep faeces -- called faecal egg counting and then only breeds from those which have naturally occurring low parasite numbers. These are called low count rams.
Gordon began breeding for worm resistance in 1987, and in 1989 talked to Ruakura head of research Dr Tom Watson on the possibility of breeding for resistance to barbers pole worm, a major killer of sheep in warm regions. He received encouragement to carry on, and since then he has worked closely with geneticists like Chris Morriss (Ruakura) and Jon Hickford (Lincoln).
He says his original aim was to breed worm-free sheep, but he realises this was naive and undesirable. "I now believe worms have always been present in animals and, indeed, are essential for the development and maintenance of the immune system.
"No worm challenge means no immune response and, therefore, a passive immune system.
It is interesting that in the human environment British scientists have found that immune system disorders have increased since the Western world has been free of internal parasites. He says that though he has been successful in breeding for disease resistance, there are no magic formulas. "In genetics, there are no absolutes. There are sometimes surprises and often disappointments. What is supposed to happen often doesn't. "Every breed of sheep has its strengths and weaknesses. It is the stud breeder's role to strengthen the weaknesses without losing the strengths of the breed."
Breeding for worm resistance takes years because the trait must be identified and multiplied and verified each step of the way. One year of success needs to be repeated over several years because the severity of the parasite challenge varies from year to year.
Gordon warns that the task is far from completed. Although some lambs have achieved a desirable level of resistance, to bring the whole flock up to the same level will take 10 years. He says he is actually breeding for an active and responsive immune system in the sheep, which will enable them to resist the severe challenge of internal parasites in Northland. Then they will shift well and thrive in all other parts of New Zealand.
A possible link between breeding for worm resistance and footrot tolerance now has Gordon Levet excited. The first year of testing some rams for gene markers for footrot tolerance has indicated the same families and individuals with most worm resistance. Gordon believes this may be a result of healthy immune response systems.
The best worm-resistant sheep have also been tested for footrot tolerance, and scored very highly. Footrot can cost the sheep industry up to $100 million in a bad year, which might result from good falls of rain in warm conditions.
High stocking densities contribute to the spread of the disease. Improved or lush pasture, poorly drained soil with a high pH (alkali) and irrigation aggravate this. Frequent stock movement also promotes outbreaks and animals may be carrying the footrot bacterium (Dichelobacter nodosus) and show no disease symptoms. Feral goats, cattle and deer may act as disease vectors, but little is known about the role of these and other animals such as rabbits, opossums and birds in disease outbreaks and spread. Senior lecturer Jon Hickford, at Lincoln, says Mr Levets experience with sheep which are both footrot tolerant and worm resistant is a happy co-incidence and credit for 40 years of breeding high-health Romneys in a challenging climate. Both men emphasise that any sheep can still get footrot in times of high stress, perhaps only in one or two hooves. Mr Levet always selects for good foot structure, including a good gap between the digits.
One of New Zealands largest sheep breeding operations, called Kelso Composites, is run by Roger Marshall, who has high praise for Gordon Levet. "Gordon runs a worm-resistant research flock. He grades everything, and I have total confidence in him and his records. I am constantly watching Gordon to see what he's up to, because if it works up there in Northland then it will work anywhere.
Lambs pick up worms and this worm attack stimulates the immune system into action. Sheep in their natural state are able to handle this challenge as they graze over a wide area and the challenge is gradual and not too great. So the animal host and the parasite live happily ever after, with the parasite keeping the immune system in good order to ward off other problems. With modern farming methods, man has swung this happy balance into total disarray. High stocking rates plus farming sheep in a warm, moist environment has meant an explosion of parasites which will completely overwhelm the immune system. The traditional answer, keep the worm population down by the use of chemical drenches. The untraditional response is to breed sheep with greater immunal responses to counter the challenge. Gordon Levet at his field day, November 2003.
In breeding for worm resistance, Gordon challenges his lambs by not drenching them and running them at high stocking rates to see the effects on individual sheep. When they have been selected, he collects and analyses the parasite content of the sheep faeces -- called faecal egg counting and then only breeds from those which have naturally occurring low parasite numbers. These are called low count rams.
Gordon began breeding for worm resistance in 1987, and in 1989 talked to Ruakura head of research Dr Tom Watson on the possibility of breeding for resistance to barbers pole worm, a major killer of sheep in warm regions. He received encouragement to carry on, and since then he has worked closely with geneticists like Chris Morriss (Ruakura) and Jon Hickford (Lincoln).
He says his original aim was to breed worm-free sheep, but he realises this was naive and undesirable. "I now believe worms have always been present in animals and, indeed, are essential for the development and maintenance of the immune system.
"No worm challenge means no immune response and, therefore, a passive immune system.
It is interesting that in the human environment British scientists have found that immune system disorders have increased since the Western world has been free of internal parasites. He says that though he has been successful in breeding for disease resistance, there are no magic formulas. "In genetics, there are no absolutes. There are sometimes surprises and often disappointments. What is supposed to happen often doesn't. "Every breed of sheep has its strengths and weaknesses. It is the stud breeder's role to strengthen the weaknesses without losing the strengths of the breed."
Breeding for worm resistance takes years because the trait must be identified and multiplied and verified each step of the way. One year of success needs to be repeated over several years because the severity of the parasite challenge varies from year to year.
Gordon warns that the task is far from completed. Although some lambs have achieved a desirable level of resistance, to bring the whole flock up to the same level will take 10 years. He says he is actually breeding for an active and responsive immune system in the sheep, which will enable them to resist the severe challenge of internal parasites in Northland. Then they will shift well and thrive in all other parts of New Zealand.
A possible link between breeding for worm resistance and footrot tolerance now has Gordon Levet excited. The first year of testing some rams for gene markers for footrot tolerance has indicated the same families and individuals with most worm resistance. Gordon believes this may be a result of healthy immune response systems.
The best worm-resistant sheep have also been tested for footrot tolerance, and scored very highly. Footrot can cost the sheep industry up to $100 million in a bad year, which might result from good falls of rain in warm conditions.
High stocking densities contribute to the spread of the disease. Improved or lush pasture, poorly drained soil with a high pH (alkali) and irrigation aggravate this. Frequent stock movement also promotes outbreaks and animals may be carrying the footrot bacterium (Dichelobacter nodosus) and show no disease symptoms. Feral goats, cattle and deer may act as disease vectors, but little is known about the role of these and other animals such as rabbits, opossums and birds in disease outbreaks and spread. Senior lecturer Jon Hickford, at Lincoln, says Mr Levets experience with sheep which are both footrot tolerant and worm resistant is a happy co-incidence and credit for 40 years of breeding high-health Romneys in a challenging climate. Both men emphasise that any sheep can still get footrot in times of high stress, perhaps only in one or two hooves. Mr Levet always selects for good foot structure, including a good gap between the digits.
One of New Zealands largest sheep breeding operations, called Kelso Composites, is run by Roger Marshall, who has high praise for Gordon Levet. "Gordon runs a worm-resistant research flock. He grades everything, and I have total confidence in him and his records. I am constantly watching Gordon to see what he's up to, because if it works up there in Northland then it will work anywhere.
Lambs pick up worms and this worm attack stimulates the immune system into action. Sheep in their natural state are able to handle this challenge as they graze over a wide area and the challenge is gradual and not too great. So the animal host and the parasite live happily ever after, with the parasite keeping the immune system in good order to ward off other problems. With modern farming methods, man has swung this happy balance into total disarray. High stocking rates plus farming sheep in a warm, moist environment has meant an explosion of parasites which will completely overwhelm the immune system. The traditional answer, keep the worm population down by the use of chemical drenches. The untraditional response is to breed sheep with greater immunal responses to counter the challenge. Gordon Levet at his field day, November 2003.