Worming and weaning lambs
Beth Tamblyn, Veterinary Surgeon, BVSc MRCVS
With lambing season ending, it’s time to start thinking about weaning lambs and there are several factors to consider depending on your farming system.
Efficient growth of lambs has a huge effect on the environmental impact and economic success of a farm.
Generally weaning occurs between 12 and 14 weeks but can vary based on growth rates, forage availability and ewe body condition scores. Monitoring growth rates can give key information about ewe and lamb nutrition and the potential impact of disease and parasite burdens.
Weighing at eight weeks provides this information and can influence weaning decisions. The AHDB states the industry eight week target weight is more than 20kg, excluding pure hill breeds.
This will vary between farm systems but under eight weeks a daily liveweight gain of more than 250g per day should be the target.
At around eight weeks old the lambs and ewes will begin competing for forage. If lamb growth rates are less than 200g a day at this point, consider weaning lambs earlier to reduce competition and allow lambs to be moved to better forage.
Transition to new forage should be gradual as the rumen takes three weeks to adapt to new leys. Lack of adaptation can cause unnecessary stress and reduced growth rates at weaning.
The ewe’s body condition score should also be considered when weaning. The AHDB target body condition scores for ewes are below:
It takes around a month to gain 0.5 of a condition score so ewes need plenty of time to gain condition before tupping. Weaning lambs can give ewes more time if they are under target at lambing.
Parasite burdens are also a challenge to lamb growth rates and the timing of weaning. It is vital to prevent and treat parasite burdens in lambs and use testing to ensure treatment is necessary and effective. This will avoid furthering anthelmintic resistance and reduce the environmental impact of anthelmintics on biodiversity and soil health.
Resistance is a serious and growing problem. Studies in Ireland in 2013 found benzimidazole (white wormers) was only 30% effective on the farms tested, with levamisole (yellow) and macrocyclic lactone (clear) being 52% and 76% effective respectively.*
There have also been several reported cases of farms with multiple drug resistance leaving farmers with limited treatment options.
Sustainable Control of Parasites in Sheep (SCOPS) advise farmers to perform a faecal egg count on the lamb group at weaning. This will give you an idea of the parasite burden they are facing, if any.
If treatment is required, it is recommended to remove ewes from the field and leave lambs there for four to five days after treatment. It is advised to avoid dosing and moving immediately as this selects for resistance. Avoiding this reduces the stress on the lambs at weaning and reduces the selection pressure for resistance.
When thinking about moving lambs you should always consider the parasite risk level of the pasture which can be ranked from low to high risk based on several factors. Pastures grazed the previous spring by lambs or calves will be at high risk for nematodirus burdens and pastures grazed by ewes or stores the previous autumn are at high risk of other gut parasite burdens.
Low risk pastures include new leys or those cut for hay and silage or grazed by cattle last year. Using low risk pastures can reduce reliance on anthelmintic treatment, while also reducing the effect on lamb growth rates and treatment costs.
Always discuss worming with your vet or one of our in-store Registered Animal Medicines Advisors (RAMA) as different treatments are required depending on the species of parasite and time of year.
White wormers are useful for prevention of nematodirus in lambs, these should be used based on the SCOPS forecast for nematodirus risk in your area. However, resistance to white wormers has been found in several other species of worm. Make sure your treatment has been effective with post-drench testing or Faecal Egg Count
Resistance Testing (FECRT)
FECRT can now be performed on your farm as part of the Animal Health and Welfare Pathway, funding is received once a FECRT and a veterinary health and welfare review is performed.
*Keane, O.M., Keegan, J.D., Good, B. et al. High level of treatment failure with commonly used anthelmintics on Irish sheep farms. Ir Vet J 67, 16 (2014). https://doi.org/10.1186/2046-0481-67-16
