“Parasite control can best be achieved through an integrated management system and feeding programme,” says Dr Dave Midgley, technical manager at Pfizer Animal Health. ”Efficient management is important when dealing with worms, and a lack of it is often the reason why treatments fail and resistance builds up.”
Internal parasites in smallstock are becoming increasingly resistant to anthelmintic remedies, he warns. “If this isn’t checked it could have a catastrophic impact on the welfare and economic production of sheep and goats.” Anthelmintics are a necessary tool, but must be used wisely as every application increases the risk and degree of resistance in the parasite population.
“Many farmers don’t think they have a resistance problem, as after dosing they find that faecal egg counts have been reduced by 80%, which they believe is a good sign,” he explains.
“It actually means that 20% of the worms are resistant and have survived, and that only the more susceptible portion of the population has been killed, leaving the resistant portion behind and eventually leading to a more resistant total population.”
Meticulous record keeping
Farmers can combat parasites’ resistance to remedies by keeping detailed records on which future decisions can be based. “Know which parasite species are present in your flock, know their life cycles and when they appear. Know the symptoms of infection, and know which remedies work when and how well,” he says.
“The latter is especially important. It helps you avoid using the same remedy repeatedly without effect, which will eventually let the parasite population build up a resistance against it.
“Avoid the ‘blanket’ approach when dosing animals. Don’t treat them for every possible problem with every possible medicine when they get sick, in the hope that it’ll kill everything in one go. Don’t underdose either, as this doesn’t kill parasites – instead, it promotes their resistance.
“Consult your records before you dose your animals. This way you can reduce use, modify regimens and switch to narrower-spectrum anthelmintics. The more remedies you use, the greater the resistance build-up. Also, limit the parasites’ exposure to the remedies by rotating the routine.”
“Understand your animals, the parasites and the treatments,” says Dr Midgley. “If you understand how the disease-causing organism works, you can reduce the number of sick animals. Read up about disease symptoms and how to treat with the most appropriate single medication.
“Preventative treatment keeps animals healthy and less susceptible to parasites. But every farm is unique, so work out your own strategy based on your own records. Every farm needs its own management plan, so don’t necessarily do what your neighbour does. Challenge your ideas and ask yourself why you do the things you do,” he advises.
Dr Midgley advocates the practice of rotational grazing in a multi-camp system to give beneficial plants a chance to recover and set seed before being used again. If this doesn’t happen, less desirable plant species that are only grazed as a last resort will eventually replace the more desirable species.
“Implement a farm feeding programme to assist pregnant ewes that are unable to forage,” he continues. “Six weeks before lambing, ewes build up antibodies in their milk to strengthen lambs once they’re born.
Unfortunately this weakens the ewe’s resistance, making her more susceptible to diseases. If the ewe has to exert herself to forage, her chance of getting sick increases tremendously.
“Stress plays a big part in an animal’s resistance to disease. Avoid stressful situations such as overcrowding and delaying breeding. A young ewe can start breeding at 60% of her adult body weight. A delay can cause frustration in the animal.”
The refugia principle
The refugia principle is most effective in countering parasites’ anthelmintic resistance. The principle is the focus of a programme that prevents worms from developing resistance.
“First move the animals and then dose them, instead of the other way round. This reduces the parasite’s exposure to the chemical and counteracts resistance developing,” says Dr Midgley.
“Don’t treat the whole flock and then put it into a clean camp. First move the animals to sow susceptible worms. These can then breed with resistant worms to produce susceptibility in the new generation. Then, depending on the worm load, risk and other management factors, dose the animals at a later stage.
This is the move and dose technique, as opposed to the dose and move technique.“Run two different flocks in different production or physiological stages together, and dose them at different times for the above-mentioned reasons,” he ends.
Contact Dr Dave Midgley on 011 320 6000.