A perspective on Worm Control  in Goats in New Zealand
Bill Pomroy,
Institute of Veterinary, Animal and Biomedical Sciences,
Massey University

Immunity
Goats develop a poor immune response to worms
they do develop some immunity but is less than sheep and cattle
experimental work at Massey showed good immunity to T.colubriformis but poor to Haemonchus contortus
® goats need additional help to control their worms throughout life
Immunity will take about 6 months to start to  develop and about 18 months before it is maximal
Immunity will decline around kidding (as with the PPR in sheep)

"Need to take every opportunity..."
Need to take every opportunity to work with the limited immunity they have
need excellent nutrition to allow immunity to be expressed
lots of green grass is a “good drench”
don’t need any intercurrent disease eg. Footrot ® increase worm burden

Goat Worms
Goats have exactly the same worms as sheep but cattle have different worm species
Worms that are drench-resistant in goats will also be resistant in sheep
If mixed sheep/goat grazing they  will cross contaminate each other
If mixed grazing with cattle they will consume and kill each other’s worm larvae ® important way to control goat worms
remember that eggs take a few weeks to develop into infective larvae on pasture so interchange should be at least this far apart

Control Programmes
Aim is to avoid infective larvae not control worms after animals infected
Stop getting infected in the first place
Generally too heavily dependent on anthelmintics
Unlike with cattle or sheep it is necessary to regularly deworm adult goats as well as young goats
1980’s in New Zealand there was a total dependence on dewormers
8-10 per year not unusual
Now is realisation that integration with other stock is way forward

Anthelmintic Resistance
-history
1980 - First case (BZ) in sheep reported
1980/81 survey of sheep farms found resistance to BZs on 5 of 86 farms and resistance to LEV on 6 of 86 farms
1983 - survey of milking goats found BZ resistance on 76%, levamisole/morantel on 49%.  Resistance to both on 38% farms
1987 - first case (BZ) in cattle reported
1990-92 first cases of ivermectin resistance in goats

"1992-94 first cases of..."
1992-94 first cases of ivermectin resistance to Cooperia in cattle reported
1996 - 16 identified cases of BZ resistance in cattle, mostly Cooperia
1996-97 - sheep -BZ resistance 68%, LEV 42% and combination BZ+LEV 39% of farms
1999 - first 2 cases of ivermectin resistance in sheep confirmed (Ostertagia)
1999 - first case of ivermectin (+BZ and ?+ LEV) resistance in Trichostrongylus colubriformis confirmed in goats and sheep

Anthelmintic Resistance
- present
Selection for drench resistance is generally in proportion to the amount of worm control achieved using drenches
not a simple matter of the  number of drenches
more effective drenches probably select more readily eg drenching lactating ewes
Goats acknowledged to have more anthelmintic resistance than sheep even though no recent surveys
Cattle tracking about 10 years behind sheep

Preventing Resistance
Avoid bringing it onto your property with imported goats
Quarantine drench with a combination
Reduce reliance on anthelmintics
If drenching adult goat > 2-3/year then heading for trouble
Not a simple matter of how many drenches given
Not all drenches are equally potent at selecting for resistance
Don’t underdose
Problem as to what is an effective dose for goats
Annual rotation of anthelmintics
Good idea but now no evidence that it works so ignore
Use of combination anthelmintics
Theory is that the chance of surviving one anthelmintic is small so the chance of surviving two is very small.  Similar concept with insecticides

Future prospects
New Drenches
at least 10 years away so plan for making do with the existing ones
not likely new drenches will be licenced for use in goats?
Vaccines
at least 5-10 years away
first one likely to be only for Haemonchus
won’t be 100% effective like drenches
Fungi
currently being researched
feed spores to stock ® fungi grow in faeces ® fungi kill worm larvae in faeces
no slow delivery system at present

"Use of specialised crops"
Use of specialised crops
mainly those with tannins
not sure how they work
looking for other crops with anthelmintic activity
would be worth investigating with goats
Breeding for enhanced immunity
possible but slow - similar heritability of about 0.3 as in sheep
some research in Scotland has shown progress over some years at a similar rate to improvements in sheep
are differences in mature immunity between breeds ?
Angoras <  New Zealand ferals (=Spanish)
Boers ???

Studies with an ivermectin-resistant T. colubriformis
Found in goats but confirmed in sheep
IVM resistance in T. colubriformis confirmation - efficacy results
Goats 13%
Sheep 39%
also resistant to BZs (white drenches) and probably levamisole
appears to be inherited as an incompletely dominant character
i.e. it will quickly emerge when introduced onto a farm as a large percentage of  worms containing the gene(s) can survive the drench (this is not the case for BZs or levamisole)

"when compared in the field..."
when compared in the field it develops at least as well as other 2 recent field isolates
similar infectivity
similar life span
produces a similar number of eggs
eggs develop into larvae at a similar rate
larvae survive for a similar time

"Comparative study of moxidectin against..."
Comparative study of moxidectin against this isolate of T. colubriformis
ivermectin oral killed 62%
moxidectin oral killed 98%
moxidectin injectable killed 4%
similar results overseas with ivermectin and moxidectin oral against ivermectin-resistant Haemonchus contortus
®  use moxidectin oral as your “quarantine drench” as it is less likely to allow survivors to establish on your property
® moxidectin oral will probably buy you some time where you have ivermectin resistance but as they kill worms the same way it is only buying time

Other ways to enhance the efficacy of existing drenches
Goats metabolise drenches faster than sheep and cattle
probably means the same dose rates are not equally effective in all ruminants
BZs (white drenches)
reduce feed by at least 50% 24 hours before drenching and for 24 hours after drenching ® BZs bind to rumen particulate matter and this will slow rumen emptying and hence slow the uptake into the blood stream so it will last longer and be more effective
repeat dosing at 12-24 hour period ® concentration of BZ in blood  similar to that of sheep

Crossover of Ivermectin-resistant Ostertagia from goats to sheep - Experiment 1
Ivermectin resistance diagnosed on Massey  research farm in 1989
Used other drenches until 1995
reused ivermectin in goats and sheep to:
see how long it would take to re-emerge?
see if it emerges in goats and sheep at the same speed?
IVM resistance in Ostertagia circumcincta rapidly re-emerged in the goats but was never convincingly diagnosed in the sheep

Experiment 2
Are sheep at risk from grazing pasture contaminated with goat-derived IVM-resistant O. circumcincta ?
Split the paddocks from Exp 1 into two and crossed half goats onto sheep pasture and vice versa
IVM resistance rapidly re-emerged in all goat groups whether they were previously goat or sheep paddocks
IVM resistance emerged in sheep on goat-paddocks
level of resistance never as high in sheep as in goats
IVM efficacy almost never < 90% in sheep on sheep-paddocks

Exp 1 and 2 Conclusions
Probably looking at several factors
the dynamics of Ostertagia in goats and sheep probably different
the metabolism of ivermectin in goats is faster than sheep so in a marginal situation the efficacy of ivermectin against developing resistance is greater in sheep than goats

Faecal Egg Count reduction tests
Need 10 animals per group
Need an average egg count of at least 200 eggs per gram
All animals should have a positive egg count
Take post treatment samples at least 7 days up to 14 days
Compare post treatment with pretreatment

Langston FECRT - albendazole

Lanston -ivermectin