Drench resistance worms in sheep –farm management options

Sheep, farming, husbandry, animal health, worms, internal parasites, management options


By Dr Clive Dalton

Happy sheep & happy worms
Sheep have been farmed intensively for centuries in Britain before some of them were brought to New Zealand. Every ancient shepherd knew that ‘a sheep’s worst enemy was another sheep’, and the only way around this was to appreciate the concept of having ‘happy sheep and happy worms’.

The so-called advancement of agricultural science with its chemicals and the drive for more production changed all this – and now we are finding it was not all progress after all.
If we go back to the old principles of ‘sheep husbandry’, things are certainly a lot more involved than just pouring drench down a sheep’s throat.

In the ‘old days’ before modern anthelmintics, farmers had to spread their risks through management. Here are some of the things that used to be called ‘integrated management’ but now you read about a ‘management tool box’. It sounds good anyway.

Option 1. Feed stock well

• This seems so obvious! A sheep in good body condition is healthy and it will have a good digestive system and an effective immune system, which will then look after most things. The sheep takes care of its own health.
• Always maintain a good pasture cover, and don’t make sheep graze down hard leaving low residuals so they will end up eating a lot of worm larvae.
  

Option 2. Use FEC to find areas of low larval contamination

• Here you use FEC on a regular basis to monitor worm output from your different groups and classes of stock – remembering that the FEC tells you what was going on in the sheep three weeks ago.
• To use this technique it would be best to have your own gear to keep costs down, and you’d need a good grazing diary to record what was where on the farm and for how long.
• You will then know which areas have had the highest contamination of eggs and then larvae.
  

You then have these options:

• Keep all sheep off that area until the larvae have been reduced naturally by time and desiccation.
• Graze the area with another species – e.g. cattle (you’ll need plenty of them).
• Graze the area with ewes that have high immunity.
• Avoid grazing with young lambs that you want to grow well.
• If you have to graze the contaminated area –use an appropriate drench at the correct time. This approach will reduce the total amount of drench used.
  

Option 3. Keep stress levels down

• This was always part of old-fashioned ‘good shepherding’, especially in lambs after weaning in the heat of summer and up through the early hogget stage.
  
• This makes a lot of sense knowing that this is when the lamb/hogget is developing its natural immunity.

Things to avoid
So here are some common sense things to avoid if possible. You see them all the time on farms where shepherds and dogs are overworked and tired.

• Bringing large mobs of lambs/hoggets into yards and holding them for long periods to do other jobs with them.
• Not providing water or shade in holding paddocks.
• Packing lambs too tightly in pens at sale yards for all day in the sun with no water.
• Doing many jobs at the one time to minimise work –e.g. weaning, drenching, shearing and dipping.
• Causing long truck journeys without rest, feed or water.
• Having crazy dogs that most times are out of control.
• Not droving any sheep (especially newly-weaned lambs) to near exhaustion on bikes!
  

Option 4. Graze pastures with mixed species of animals

• An example would be a 60-day cycle starting with lambs for 7-10 days, ewes for 28 days and cattle for the balance.
• The problem of using cattle as vacuum cleaners for sheep larvae is that you will need a lot of them – something well over 50% cattle to sheep ratio, and you may not want to farm cattle to this extent, especially if they are not making a good return on their investment and they cause more work.
• This is regularly glossed over in discussions and nobody seems to produce figures on how many cattle you need, or the costs and returns of this advice.
  

Option 5. Grow crops

• There’s a very wide array of crops to choose from and plenty of good advice from agronomists. The promotional literature would convince you that every crop and its many cultivars is a guaranteed winner.
• Before growing a crop work out the economics. Weeds and low yields are regular causes of financial disaster.
• Remember also to cost the time the paddock is out of grazing waiting for the crop to grow. This all seems common sense but the pictures in the glossy catalogues seem to swamp a lot of this.
• Many sheep farmers are not great cropping farmers – at least not in the North Island where the worm problems are generally worse than in the South Island.
• Crops such as Lotus or chicory are known to reduce the worm burden and achieve high growth rates in young stock. But again, they are not easy to grow and keep weed free, and may not last as long as the brochures say under your management.
• Do the sums first!
  

Option 6. Pasture renewal

• If you believe some agronomists this should be a regular part of all farm management programmes. Some recommend renewing 10-20% a year!
• Go back and ask why the pasture has to be renewed and what ruined it in the first place? It might be cheaper to fix that.
• If it’s being renewed just to get worm-free grazing for lambs, then make sure you do the sums first about how much profit you’ll end up with.
• In any case it’s not an option on many hill country farms.
  

Option 7. Hay and silage regrowth

• The regrowth on silage and hay paddocks should be larvae-free so is ideal for growing/finishing lambs.
• But on most sheep farms, not much conservation can be done and certainly not on hill country farms. So again this may be a limited option.
• Feeding stock well and keeping stress down look like the best options. Whatever you decide, make sure your do a full budget before choosing an option from the magic management ‘tool box’.

Conclusion:
If you are realistic, the above points are all limited options on most hill country farms, so do the best you can.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.