With ewes and lambs coming to the yards at tail docking, it’s tempting to drench the ewes ‘while they’re here’. Wormwise vet Mary Bowron urges farmers to consider the variables before getting out the drench gun. Do ewes actually need a drench at tail docking? Well, it depends!
Why the answer is usually no.
If your ewes lambed in good condition, have milked well, and there's been plenty of quality pasture on offer — particularly legume-dominant feed, a drench at tail docking is likely to be of little benefit. Ewes in this situation are unlikely to have lost much parasite immunity, and if they did, it will be building back up again. How quickly ewes regain their immunity, and how strongly, depends on the feeding and health of the ewes. Well-conditioned ewes on good pasture covers over 1200-1400 kg DM/ha will be rebuilding worm immunity pretty quickly.
What situations may warrant a tail docking drench?
There may be times where drenching individual ewes or part mobs on the basis of light body condition, scouring or poor feed availability is warranted. This approach may help younger ewes in particular (lactating hoggets and two tooths) who have a less robust immunity to worms than mixed-age ewes.
Light body condition at lambing makes it more difficult for a ewe to maintain her worm immunity. Low feed levels at lambing force ewes to consume more worm larvae, and when feed supply doesn’t meet energy demand, ewes can’t partition protein and energy towards worm immunity. That said, ewes with genetics for worm resistance maintain lower FECs over lambing.
As part of a wider study in the Wairarapa in 2014 and 2015, Chris Miller and colleagues at AgResearch found that a tail docking drench to ewes gave a variable response. On average, drenched ewes were 1.5kg heavier at weaning, but on only 1/5 farms was there a lamb weaning weight benefit, or a positive cost/benefit.
Are faecal egg counts useful?
Monitoring with faecal egg counts will give you an idea of the level of worm burden those light ewes could be carrying. Collect some faecal samples prior to tail docking so you already have a plan before the ewes are in the yards. Hold some ewes and lambs in a corner of a paddock and collect some poo samples – ideally at least 10 individual samples. Target the bigger poos - small ones are lambs.
Talk to your vet about your faecal egg count results. Deciding on a plan doesn’t just rely on the faecal egg count number.
If a drench is given, mark the ewes you treat to monitor their progress.
Sometimes a high faecal egg count in ewes at tail docking may be due to high larval contamination that has carried through from the previous autumn. This is not a quick fix, but an indication that the farm system needs to change to decrease the worm challenge. The major contaminators of pasture are young animals, so focusing on altering grazing management of this class of stock will have the biggest impact on decreasing autumn larval contamination.
If I’m going to drench ewes – all or some?
Strategic use of drench rather than treating everyone will ensure there is refugia in the system. Refugia is having a population of worms cycling through animals and on pasture which have not been exposed to drench. We want to avoid blanket drenching of mobs as this will increase the risk of resistance to drench chemicals. Refugia helps to slow down the development of drench resistance.
What other parasite management tools are available to support ewes and lambs through until weaning?
Feed – good quality and enough of it is the number one tool when it comes to managing parasites.
If feed is short, strategic use of nitrogen (N) after lambing could help lift pasture covers and support ewe recovery and lamb growth leading up to weaning. Recent work by AgResearch at Woodlands Research Station in Southland showed that by weaning time, pasture covers in paddocks that received 40 units of N after lambing, were 33 percent higher than control paddocks (1868kgDM/ha versus 1407 kg DM/ha respectively) and ewe and lamb liveweights were 5 percent (76.7kg versus 72.9 kg) and 6 percent (35.4kg versus 33.1 kg) higher, respectively. This translated into 65 and 46 kg of additional ewe and lamb liveweight/ha, respectively. It could be worth the investment.
The bottom line
Use tail docking as a chance to check how things are going. Assess things such as feed availability, ewe body condition, their milk production and the weight of their lambs. If some ewes are light and faecal egg counts indicate some high counts then only treat affected animals, rather than the whole mob.
Tail docking is already a busy job so save some time and leave the ewes undrenched where you can.