Selective worming of lambs - Is anyone partially dosing their lamb flock?

[Cow1]

For the first season on our farm we are fully EID with lambs tagged against their mothers. This is giving us an opportunity to find out who is performing in our flock and look at growth rates.

The majority of our flock run on a free range hen unit split into individual paddocks which gives great flexibility in grouping to age and helps with grazing management by being able to rotate and rest paddocks. We don't over worm our lambs these days as we are not over stocking. In a dry season we have been known to only worm at weaning. The ewes are treated once per year post lambing and I rotate the 3 old groups of wormers annually. The only concession is if I have to treat for nermatodirus early season or fluke late season on hoggets.

I have not used FEC's before and am interested about it but I read somewhere about selective worming being even better. This interests me as for the first time I have the ability to weigh and identify individual lambs and plot their growth rate. I could then not worm the best 10% of the group or maybe even more.

I just wonder if anyone is doing this or any advice would be appreciated.

 

[beardface]

This year I opted to leave around 10% untreated after there first dose for nemo. Found it quite easy and just left 1 or 2 of the biggest cleanest lambs undone in each race full. Also been using fec for the first time this year to decide when to worm based on mob samples has reduced amount of times we used to worm and allowed us to worm later and so Hoover up more of the little buggers.

 

[Poorbuthappy]

Sometimes work it the other way and if fec is borderline just drench the poorer / any dirty ones.
Would like to drench to weight gain across the board in later season but have only dabbled with this so far.

 

[Global ovine]

The practice of REFUGIA is now the common recommendation in NZ, and should be globally. This allows the worms in the untreated sheep (the better doers) to remain in the system to breed with the worms remaining in the treated sheep and on the ground thereby slowing down the selection to chemical resistance by the worm population that occurs every time one treats with a repeat of that anthelmintic chemical.
Worm burdens in a flock of lambs can range from a few hundred eggs per gram to several thousand. Some sheep are also more resilient to the affects of a worm burden. By measuring sequentially on animals per EID, you can easily find those less affected by worms. These are precisely the candidates to carry out controlled refugia.

 

[Tim W]

Used selective worming here for a number of years in conjunction with FEC. Once a high count is found & I decide to treat I will dose from 20% to 75% of a mob, selection based on growth rate, ill thrift & gut feeling. Dosing 20% of a mob can reduce flock FEC by 80% or more

 

[Cow1]

The practice of REFUGIA is now the common recommendation in NZ, and should be globally. This allows the worms in the untreated sheep (the better doers) to remain in the system to breed with the worms remaining in the treated sheep and on the ground thereby slowing down the selection to chemical resistance by the worm population that occurs every time one treats with a repeat of that anthelmintic chemical.
Worm burdens in a flock of lambs can range from a few hundred eggs per gram to several thousand. Some sheep are also more resilient to the affects of a worm burden. By measuring sequentially on animals per EID, you can easily find those less affected by worms. These are precisely the candidates to carry out controlled refugia.

How hard would you select then? 10% undosed seems to be the figure banded about. Or would you base the decision on growth rates? And would you still FEC?

 

[Global ovine]

How hard would you select then? 10% undosed seems to be the figure banded about. Or would you base the decision on growth rates? And would you still FEC?

FEC the mob for management of parasites. If you are buying tups from a breeder making gains in the trait Resistance to worms, you will find that over time the undrenched group will increase in number as the more susceptible individuals decrease. As @Tim W posted above, it is the worst animals that contribute the most contamination.
My own experience showed that drenching interval increased more than 3 fold by breeding for resistance to worms over 15 years, even then many did not need it, but I treated all prior to going onto winter forage crops as it was the 2nd and last time they got anthelmintic drench in their lifetime with me. In cases like this where only occasional drenches are administered the development of worm resistance to chemicals is slowed greatly, so refugia is not a priority as it should be in a flock unselected for host resistance.

 

[exmoor dave]

Sometimes work it the other way and if fec is borderline just drench the poorer / any dirty ones.
Would like to drench to weight gain across the board in later season but have only dabbled with this so far.

Now I've got my magic psion I'm hoping to do the same.