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Argentine Farmer Folklore of Parasite-resistant Sheep Now Backed by Science


At one point, farmers’ belief that some of their sheep were naturally resistant to gastrointestinal parasites was put under the heading of “farmer folklore”. However, as parasites began to develop resistance to drugs used to kill them, and the world’s farmers dealt with losses due to parasites estimated in billions of dollars, researchers began seeking scientific evidence that would form a basis of breeding for natural resistance. As it turned out, farmers were right. Not only are some sheep naturally resistant to parasites, there are relatively easy ways to tell which ones are, such as checking the conjunctiva colour in their eyes, but also more advanced scientific ways, which identify the genetic markers of resistance. In Argentina, where mutton and wool are enormous contributors to the agriculture sector, the Joint FAO/IAEA Division works with the National Institute for Agricultural Technology (INTA), which maintains a large flock of sheep to record results of breeding. Incorporating data on natural resistance into breeding programmes has meant millions of dollars in extra income for Argentina’s sheep farmers.

Wool and mutton production is an important contributor to Argentina’s agricultural sector, bringing an annual export income of more than USD 210 million, which is second only to the country’s beef cattle production. As with other countries worldwide, Argentina’s sheep farmers are constantly at battle with gastrointestinal parasites that attack their flocks – a scourge that has an ongoing impact on quality and quantity of their production.

Research on this topic, spearheaded by the Joint FAO/IAEA Division, has concentrated on identifying animals that have natural resistance to parasites and used that information to help farmers improve their breeding programmes. Breeding for natural resistance allows farmers to reduce or even avoid the cost of drugs used to treat parasite infections, which is especially important in the developing world, where farmers often cannot afford the drugs in the first place. In addition, although veterinary pharmaceutical companies constantly release new drugs to treat parasite infections, within a few years, the parasites develop resistance. This problem is multiplied because farmers who cannot afford to buy required amounts of drugs may reduce the dosage or use it less often than recommended, both of which would speed up the process of parasites developing drug resistance. The situation is further compounded by potential contamination of food with anti-parasite drug residues.

Breeding for parasite resistance saves farmers millions of dollars

Argentina’s National Institute for Agricultural Technology (INTA) maintains a flock of 2 000 sheep on its campus in the Patagonia area where, for many years, researchers have recorded animals’ weight and wellness: if they are resistant to parasites, they should have a normal level of red blood cells and steady weight gain; if susceptible, they should lose weight and become anaemic, which is one symptom farmers could identify easily, since healthy animals have dark pink conjunctiva but anaemic ones have pale conjunctiva. It is also possible to check for parasite infections with a blood test or by counting parasite eggs in the animals’ faeces, which reflects the number of mature parasites living in the gastrointestinal tract of the animal. The more resistant the animal is, the lower the number of mature parasites, and thus fewer eggs are released in the faeces.

But parasite level is not the only parameter for breeding. Farmers also want to improve their sheeps’ wool quality, meat and milk production, growth rate, reproductive efficiency and survival rates. As the Joint Division and its counterpart institutes have increased their knowledge base, they have added a genetic element into decisionmaking for breeding. This is where the process moves from the field into a laboratory where it is possible to study an animal’s DNA. The Joint Division has introduced a nuclear-derived molecular technique to identify specific DNA markers of resistant animals across two or three generations, which can then be incorporated into a genetic evaluation that enables breeders and farmers to make the best possible breeding decisions.

Funded by the IAEA’s technical cooperation programme, the Joint Division provided INTA with guidelines and protocols for recording quality data. It also trained a local scientist in the genomic techniques and analyses of bioinformatics data, and field staff in proper ways to collect quality data and DNA samples. The breeding programmes need the data and samples to ensure that the rams chosen for breeding are parasite resistant. Once they have identified the more resistant animals, they can either sell the rams or use artificial insemination to disseminate the resistant traits among the sheep population.

Breeding for parasite resistance means helping farmers prevent loss of animals and improve wool production.Wool loss for animals infected with parasites is estimated at between 15 and 20 percent per year – equivalent to 1 kg of fleece per animal with a value of about USD 1. So if the wool is not lost due to parasites, it adds up to Argentine farmers having an extra USD 30 million each year in income. The farmers also will save about USD 70 per ewe and USD 400 per sire ram, due to longer life expectancy and increased wool and meat production.

With its success in breeding for parasite resistance, INTA and the Joint Division are sharing what they know. They are providing expert services and training professionals in other Latin American and Caribbean countries that have similar problems and, hopefully, will find similar solutions.


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