For many farmers, it’s easy to get trapped into thinking that the easiest plan for vaccinating and drenching ewes at pre-lamb is to treat your ewes as one group; with the same treatment plan for all.

While this may be easy, this is not best-practice and may not be what is best for your sheep in terms of productivity and return on investment. The reason for this, is that you may be wasting money and time on animal health treatments for ewes within the flock who don’t require treatment. Additionally, there may be subgroups within the flock that warrant an alternative treatment which will have a more positive effect on production. So, it’s all about investing your money and time where it will have the most benefit for your ewes (and hence, your new season lamb crop) and your farming business.

An example of this is ewes in good condition that are scanned as having singles will likely not require a drench treatment pre-lamb (blanket drenching of ewes at pre-lamb is NOT recommended as it may increase the chances of developing drench resistance) and may simply require a 5-in-1 clostridial vaccine to protect the ewe and her lamb against clostridial diseases at lambing.

Conversely, at the other end of the spectrum, a poorer condition ewe scanned as having multiple lambs may require a different treatment plan and may benefit from upgrading their pre-lamb vaccine from a standard 5-in-1 like Multine® to a specialist pre-lamb vaccine like Nilvax®*. That way, the ewes can be vaccinated further out from lambing to reduce the likelihood of metabolic diseases like sleepy sickness.

A simple way to visualise how you might divide your flock post-scanning for different animal health treatments may be as follows:

So, why is Nilvax considered a specialist pre-lamb vaccine and why does it include levamisole?

Nilvax is considered a specialist pre-lamb vaccine because the inclusion of levamisole stimulates the immune response to the vaccine and ultimately results in the production of a greater number of antibodies. This allows heavily pregnant multiple-bearing ewes, which are considered higher risk for metabolic diseases, to be vaccinated earlier (up to 6 weeks prior to lambing) and thereby reducing the stress associated with yarding and being off feed too close to lambing. Additionally, Nilvax supercharges the ewe’s colostrum so there are more protective antibodies available to share between her multiple lambs. While focused on Multine® 5-in-1, to understand why ‘more is always better’ when it comes to antibodies to protect against clostridial disease, watch the following pre-lamb video

While most farmers historically associate levamisole as a drench for treating worms, in the case of Nilvax, its main purpose is an immune stimulant.

Because of it’s levamisole component (which is not recommended as a sole-treatment for internal parasites due to being a single active) when using Nilvax, if a drench is deemed necessary at the same time, it is important to discuss with your animal health advisor what is an appropriate product to use in conjunction with Nilvax (e.g. Bionic® or a long-acting moxidectin injection) so as to avoid levamisole toxicity.

For farmers questioning whether the levamisole in Nilvax will cause drench resistance, it is important to remember that drench resistance takes a long time to develop and it doesn’t happen from a single dose of a single-active. Instead it occurs as a result of repeated exposure of the parasite population to a sub-lethal dose*.

To help farmers determine the best treatment plan for subgroups within their flock check out our pre-lamb decision guide which helps by asking questions to determine which product may be suitable for different groups within your flock.

In addition our Selenium Calculator digital tool may also be helpful when considering whether you require a selenised or non-selenised vaccine this pre-lamb when considering other forms of selenium supplementation that you have on-farm.

* It is generally not considered best-practice to whole-flock treat your ewes with Nilvax. As mentioned in this article, it is advisable to selectively treat your flock. 

ACVM No’s: A3977, A934, A935, A11311 & A11788. Schering-Plough Animal Health Ltd. Ph: 0800 800 543. www.msd-animal-health.co.nz © 2025 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved. NZ-NLV-250700001