Prevention and control of parasitism in livestock

Kalyan Sarma
Contd from previous issue
4. Treat only those animals that are perceived to need treatment use of a narrow-spectrum drug, closantel, in combination with a minimum number of treatments with broad-spectrum anthelmintic. Closantel is particularly effective against Haemonchus and has a persistent effect for 2 to 3 months.
5. Proper drenching of the drug.
6. Reduce feed before drenching: Restricting access to fee for 24 hours before drenching slows the flow of gut contents containing the drench from the rumen. Reduced feed intake prolongs drench uptake, extending the effective duration of the killing effect
7. Use the only recommended dose
Anthelmintic resistance in gastrointestinal (GI) nematode populations is now widely recognised as a major problem in small ruminants and threatens the sustainability of many production systems throughout the world. Although there are several parasitological and management factors which may influence the rate of development of resistance, such as treatment frequency and under dosing, and suggested that the proportion of the parasite population in refugia could be the most important factor determining the rate of development of resistance and should be considered, above all else, throughout the development and implementation of any control strategies. Several methods have been used to reduce drug resistance:
1. Dilution of resistant with susceptible parasites: Once anthelmintic resistance has been identified to a particular drug on a farm it may be possible to substitute the resistant parasite community for a susceptible one.
2. Targeted treatments: Targeted treatments can be defined as whole flock treatments given at the most appropriate times. The targeted treatment approach serves to reduce the numbers of anthelmintic treatments given to a flock and thus minimize pasture contamination with resistant genotypes. Recent examples of the use of targeted treatments include studies conducted in Wester Australia and Italy where treatments were stopped during summer months when few parasites were present on pasture and given instead at other times when more parasites were present in refugia.
3. Targeted selective treatments (TST): Targeted treatments can be further enhanced by selective treatment of only those animals that will most benefit from treatment, leaving the rest of the flock untreated. Selective treatments should be directed towards those animals that are disease susceptible (non-resistant and/or non-resilient) or those that most contaminate pasture, however, this requires the ability to identify these individuals within a flock. Targeted selective treatments (TST) exploit both epidemiologically appropriate treatment times and treat only those animals that would benefit from treatment.
(To be contd)