March 5, 2010

Breeding sheep to eliminate dags and worms. 4.

By Dr Clive Dalton


Selecting female replacements from the A team

Docking ewe lambs

  • Do NOT drench any ewe (or ram) lambs at docking - and this means both the A team and commercials. At this stage, the lambs’ immunity is starting to develop and anthelmintic drenching will damage it.
  • Vets will not agree but we don’t know enough about the complex immune system, and until we do, don’t drench. The only exception would be a major animal health crisis, confirmed by a veterinarian.
  • Mark all the ewe lambs with ear-markers to cut a bit out of the ear or punch a hole. Hopefully they will all be twins, but don’t worry about any singles in the mob.

Weaning ewe lambs

Polled Dorset weaned lambs being picked for slaughter
  • Barring obvious culls, all the A team ewe lambs should be keepers and need priority.
  • You’ll need to keep more of them as replacements than normal to apply intense selection pressure and cull heavily from weaning on.
  • Hopefully you won’t need to go too deeply into the ewe lambs from the single scanned (SS) ewes to make up numbers. But this will depend on twinning rate, the season and the size of the nucleus you want. Don’t be too ambitious at this stage.
  • As a target, plan to cull around 30% of the ewe lamb crop, but this will depend on the final numbers needed. There’s a fair way to go before they reach two-tooths and their final selection.


NO drenching at weaning, unless you have a crisis confirmed by a veterinarian.

  • Do NOT drench any A team ewe lambs at weaning.
  • If any pack up around weaning, then cull them.
  • The exception would be an outbreak of Barber’s Pole worms in the whole lot, but make sure you seek veterinary advice for a correct diagnosis (after Faecal Egg Counts) before drenching. Use a specific Barbers Pole drench and not a broad spectrum one.
  • Any ewe lambs for sale from the remainder of the flock can be drenched with a conventional combination drench if they look wormy, and this is confirmed by a FEC on a sample. Decide if this will improve their sale prospects.
  • Before sale and after conventional drenching, run these sale ewe lambs separately from the A team ewe lambs. You don’t want any cross-contamination of worms.
  • But don’t run the A team ewe lambs on clean pasture. Put them on pasture that has had sheep on it to challenge their immunity.


  • Seeing tapeworms can panic people as they look so big.
  • Don’t drench unless you have clear evidence of ill thrift, or if their scouring is attracting blowfly.
  • If a drench is justified because the lambs look poor, use a product specific to tapes and not a broad spectrum one.
  • Mark for culling any ewe lambs from the A team that have physical defects or fail to meet your standards.

Developing natural immunity

It's an easy enough job running hoggets through the yards and drafting off the dirties, even if some are keen to escape!
  • By weaning, all lambs should be well on their way to developing natural immunity, so expect great variation in the number of daggy backsides you’ll see.
  • You’ll see these ‘dag storms’ with feed changes, which are great to challenge immune development. Be ruthless, especially on dirty backsides that never clear up.
  • It’s good to see those that go through a daggy stage and then permanently dry up. It’s the ones that don’t that you need to mark for culling.
  • So make your final decision in early autumn when they are hoggets (see below).
  • Nutrition of young growing animals is critical so make sure there are well fed in this.
  • Minerals and trace elements are well known to enhance immunity so give these a boost.

Ewe hoggets
  • Now the top ewe lambs from the A team ewes have grown into hoggets, they should be looking good, and it’s time to put more Dag-Free and Worm-Free selection pressure on them.
  • Do NOT drench them.

These ewe hoggets have never had an anthelmintic drench in their lives. They have only had a nutritional supplement containing minerals to boost immunity.

  • Keep going through the hoggets every 2-3 weeks (a month is too long), for the first three months after weaning, and draft off any tail-enders for culling.
  • Mark for culling any hoggets that are regularly daggy. Any that get daggy and dry up quickly are OK as they’re still be developing their immunity under the natural worm challenge, and the ‘autumn rise’ of worm larvae is an ideal time for this.
  • The tail end culls. If you think any of these need a drench, then use a conventional combination drench and finish them for sale.
  • After drenching, don’t mix the drenched hoggets with the replacements.
  • They should be run under your normal farming conditions on paddocks that have been regularly grazed by sheep.
  • Don’t run these ewe hoggets on clean pasture. They need a worm challenge all the time.

Ewe hoggets -initial check for worms

Hoggets intensively selected for Dag-Free and Worm-Free traits.


  • This is a good time to do an initial FEC to see what kind of parasite load the hoggets are carrying.
  • It’s the ‘autumn rise’ of worm larvae which will give the hoggets’ immune system a really good challenge.
  • January/February is too early to do this in my view, but many WormFEC™ breeders do it at this time, arguing that they want to find sheep with early immune development. It’s too ambitious in my view.
  • Do a FEC from a composite sample mixed from 10 fresh droppings from the paddock. Send the sample to a recognised lab through your vet.
  • Use a trigger level of 500 epg to see how things are going.
  • If the sample is way up in the thousands, then don’t panic, as this would suggest that little immunity to worms had developed yet.
  • Don’t be tempted to drench if the hoggets are looking healthy and growing well.
  • The only reason to drench would be if their health and welfare were at risk, confirmed by FECs and your veterinarian.
  • Barber’s Pole worms would be a classical reason to drench, making sure you used a drench specific to that parasite and not a broad spectrum one.
  • If the sample is below 500 then that’s good news, but again don’t get excited, as it’s only one sample, and look at the animals to see how they are doing.
  • Veterinarians use 500 epg as a trigger to drench the whole mob. Don’t be tempted as you are involved in a ‘breeding project’ and you’ll need to point this out to your vet.
  • Again, keep a note of any hoggets that get dirty and mark for culling any that don’t dry up, as their immune systems are not coping.

Ewe hoggets - Serious check for worms

  • After the initial check in March/April during the ‘autumn rise’, early winter (May/June) is the ideal time to put more selection pressure on these replacement hoggets for dags and worms, as worm burdens are a big challenge to these young sheep in winter.
  • Get an individual FEC done on each hogget.
  • This will cost around $5/sample. This must be corrected for Faecal Consistency Score (FCS) so remember to record this at the time of sampling, and build the score number into the sample ID number.
  • See Part 8 for details of how to do this.
  • If the cost of the FEC is going to be a major issue, just do a FCS on them.
  • Ewe hoggets producing marbles need to be marked as the top group, followed by hand grenaders. Then anything below this with sloppy dung needs to be given a separate mark as potential culls.
  • Keep the drench gun locked away unless there is a worm blow-out (e.g. Barber’s pole) and animal welfare is compromised and confirmed by your vet.
  • Good feeding is vital during this winter period so don’t confuse worms with under nutrition.
  • If you haven’t put a good permanent ID tag (numbered and readable from a distance) into these hoggets, then do it now. They are your top genetics.
  • It would pay to put a duplicate tag (eg a numbered brass tag) in them to be doubly sure of ID incase the initial plastic tag comes out. This cost is well worthwhile.

Ewe hogget weight

Clean hoggets that could be further culled on weight.
  • If you have more hoggets than you need and have to find a reason for reducing numbers, you can always use weight.
  • Find the range by weighing a few of the smallest then a few of the biggest, and then decide a cut-off ‘target’ weight.

Ewe hogget fleece weight
  • In the past it would have been worthwhile recording fleece weight and culling the lowest – but don’t bother. Just cull hoggets with the ‘off-type’ fleeces.
  • Hoggets with high liveweight will also have the genes for high fleece weight (the genetic and phenotypic correlations between the two traits are highly positive).
  • If you breed fine wool, then it would certainly be worth culling on hogget fleece weight and quality.

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