Download
1 / 41
450 likes | 730 Views
Parasite control. Objectives. Describe the principles of control Describe types of anthelmintic usage Be aware of organised control schemes Understand the value of models in predicting the outcome of treatments. Parasite control. Flock nutrition Grazing management Stock management
E N D
Objectives • Describe the principles of control • Describe types of anthelmintic usage • Be aware of organised control schemes • Understand the value of models in predicting the outcome of treatments
Parasite control • Flock nutrition • Grazing management • Stock management • Using anthelmintics • Suppressive • Curative • Strategic • Quarantine drench • Testing for resistance
Nutrition • Feed young stock and ewes well. Under-nourished stock have a reduced capacity to resist parasites • Immunity to parasites is related closely to bodyweights. It is essential that target weights should be established and stock monitored & fed accordingly • Supplementary feeding of weaner/hogget sheep with protein feeds will increase both bodyweight and parasite immunity • Feeding in troughs preferable
Grazing Management • Use of cattle to prepare weaner/hogget pastures with a 6 month rotation • Match young stock DSE with cattle DSE • Use of dry sheep older than 3 years of age to aid decontamination of weaner/hogget pastures • The 3 year + dry sheep have well developed parasite resistance if maintained in good condition • Cell or strip grazing in some conditions
Stock Management • Tops & tail strategy. Weaner supplementation targeted at tail of mob. Monitor weights of young stock and feed accordingly • Culling sheep that are “worm factories” where possible • Consideration given to leaving 5% mob [heaviest] untreated, in mobs where natural immunity is established • Consideration could also be given to destocking sheep from pasture for 15 months and running cattle on that portion of the property, to create a safe/clean paddock
Some sheep have more worms than others.Which ones would you sell?
Drench usage • Know your drenches • Some companies sell “solutions” for resistance • Mixtures are useful • Treating only heavily infected animals is being trialed • There are Government sponsored schemes • You can use drenches in different ways
Using drenches –Quarantine Drenching • Stock purchased onto a property should receive a quarantine drench and be isolated on a contaminated paddock before being run with the main flock • The cleanout treatment should consist of ML [preferably moxidectin], BZ & LEV • “Q drench” is marketed for this purpose
Suppressive (Systematic) Treatments • Regular treatments at intervals equal to the pre-patent period of the parasite, or the ppp plus persistence period. • Advantages: Very effective, in the short, term in minimising parasite populations and production losses. • Disadvantages: Rapidly selects for drug resistance. • This strategy should not be promoted • Temporal refugia low
Curative Treatments • Treatment based on clinical diagnosis. Only animals perceived to need treatment are treated • Trigger mechanisms include: • Signs of sub-clinical and clinical symptoms • Faecal egg count monitoring. • Using bio-assays (e.g. FAMACHA) • Weight loss Benefits: it slows selection for resistance. But: production losses occur Temporal (& spatial) Refugia high
FAMACHA • Way to select anaemic sheep with haemonchosis for treatment and culling • Curative treatment • Costly in Australia (developed in RSA) • Reduces treatment frequency so reduces R selection • Various references
Strategic Drenching • Aims to prevent contamination of pastures with eggs and larvae • Requires knowledge of local conditions for egg development and larval survival • Has a proven record in control • May select strongly for resistance • Treatment is applied when larval pasture levels are low (Spatial Refugia low)
Summary - Control of resistance • Be aware of refugia issues, do not treat all sheep onto a “clean” pasture) (ie drench and move is not best) • Administer drugs correctly, give full & effective doses, starve sheep before a ML or BZ drench, yard 24h post treatment see http://www.csiro.au/WormTreatment • Use mixture of drugs with similar half lives, if this is not feasible rotate annually between drugs with a different mode of action • Where possible use non-persistent chemicals • Provide a quarantine treatment/regimen for all imports • Reduce drench frequency by using strategic control & developing a flock structure with immune hosts • Leave some sheep untreated.
Wormkill • Integrated, strategic worm control originally based on closantel • Northern Ranges of NSW in summer rainfall zones • Flock management plus monitoring • Highest compliance worm control approach in the world • Closantel resistance emerged now rotations reduce pressure on R • NSW Ag
Drenchplan • Integrated strategic control relying on 1-2 summer drenches (Nov/Dec & Feb) also drench weaners • Drenches OK but pasture management is complex • Combinations to delay R • Treat in summer so low refugia and R selection. Drench lambs at risk • NSW Ag
- + This is a model
Computer models Host/parasite systems are complex especially when environmental and management aspects are superimposed.
Examples of models for parasite control • PARABAN (cattle) • WORM WORLD (Sheep) • TROPICAL WORM WORLD (sheep in tropical climates)
Negative Binomial Distribution • Low k means more aggregation • Typically k 0.3 - 2 • As k distribution tends to Poisson. 0.40 0.35 negative binomial 0.30 k = 0.3 mean = 10 0.25 Models need to account for stochastic distributions proportion of flock 0.20 Poisson mean = 10 0.15 0.10 0.05 0 0 2 4 6 8 10 12 14 16 18 20 22 24 number of worms
Input parameters • Flocks • Number of sheep • Age • Sex • Initial worm burden • Immunity • Lethal burden • Lambing dates and data
Input parameters • Pasture • Number and size of paddocks • Initial contamination • Management • Dates • Paddock moves • Treatments • Genetics • Genes for R • Gene frequency • Efficacy against phenotypes (ie. dominant, recessive)
Outputs • Larvae on pasture • Eggs in faeces • Worms in sheep • Deaths • Drug resistance gene frequencies
More about models • Models must be validated • They allow us to ‘test’ parasite control measures before we use them • They can tell us what is important in using drugs sustainably • They can tell us about the vulnerability of different parts of the life cycle
