Wormwise programme manager and vet Ginny Dodunski discusses the management of light ewes going into winter.
Scanning is a great time to start identifying and managing groups of ewes on the basis of feeding priorities.
Ewes that have become light in early winter are at particular risk of poor lambing performance and poor survival. And it’s very difficult to get weight back on ewes in the last part of pregnancy, so management decisions about these light girls are an early winter job.
Will a drench at scanning help these girls?
It might. But drenching alone is unlikely to be enough.
In a study on five North Island hill country farms, light ewes that were drenched in early winter lost less weight than their skinny counterparts who were left undrenched. Overall, both groups of light ewes continued to lose weight – highlighting the need to identify these girls and do something more for them, aside from just drenching.
Are parasites the main cause of skinny ewes?
When ewes are under pressure for feed, have another underlying disease or are not coping with being part of a large mob, they can come under pressure from parasites. The parasites might not be the primary problem.
Getting some post-mortems done on light ewes in your flock can be very helpful.
After a tough facial eczema season in parts of the country, light ewes will continue to show up through winter as the liver damage they are carrying limits their ability to compete under winter feed conditions.
Johne’s disease cases can spike when ewes have been under feed pressure earlier in the season. Ewes with Johnes disease can look just like they have worms and it’s really important not to lamb these girls – their progeny are likely to be born with Johne’s, and the ewes will be a big source of infection to other lambs.
Light ewes frequently have higher faecal egg counts than their better conditioned mates and won’t be helping your pasture contamination situation.
Source: Kahn et al WAAVP 2023 (Merino ewes)
What to do?
Once you’ve scanned, you know who’s who in your flock, and what their feed priorities are. Skinny multiples (especially triplets) are at greatest risk of poor lambing performance. Not lambing the worst of these is a very valid option.
For light ewes that you think are worth persevering with, reducing mob pressure and feeding them better to meet their increasing energy demands in the last month or pregnancy are key. Choosing safer lambing paddocks will also help. If you drench these ewes, make sure they are identified so you can observe which ones respond.
How much of a resistance risk is winter ewe drenching?
Probably fairly minimal; environmental conditions are not favourable to high development rates from worms in ewes at this time. The risk is low if only a proportion of the flock are drenched with a short acting product, and especially if drenched ewes are also fed better, allowing their immune systems to deal with any parasites left behind and limit shedding of resistant eggs.