Effective drench combinations for optimal growth rates

A key driver of farm productivity is the weight of lambs at weaning. If lamb growth rates are good and more lambs are at higher weights at weaning this reduces the number of lambs that a farmer has to keep on into the summer. Gastrointestinal parasites can have a negative effect on these growth rates.
The key points of an effective parasite management program are to manage pastures to reduce challenge, use effective drenches and utilise refugia and combination drenches to reduce the selection for drench resistance for the future.
Around lambing parasite eggs are produced onto often low pasture covers by ewes when their immune system is under stress. In spring the parasite larvae from these eggs are taken up and can depress growth rates up until weaning. If the spring pasture growth is slow or pasture covers are low this negative effect can be increased. In situations such as this, a drench pre-weaning should be considered to maximise growth rates.
Where drenching is required all farmers should be using an effective, combination drench. Farmers can find out what drenches are working on their farm by completing a Faecal Egg Count Reduction Test or FECRT. If a farmer is unsure of their drench resistance status they should use a triple combination option such as Alliance®.
Combination drenches also have the benefit of reducing the selection pressure for drench resistance. The chance of a worm being resistant to all active ingredients in a combination is low and the proportion of resistant parasites surviving on-farm compared to sensitive parasites on pasture is less. Cattle and sheep do not share the same parasites and pasture grazed with cattle will have reduced numbers of infective larvae for sheep on it and vice versa. By rotating the grazing of sheep with cattle in the spring, the growth rates of both classes of stock can be improved.
Refugia is another tool that farmers can use to reduce the selection for drench resistance. Refugia allows parasites from un-drenched animals to populate pasture, diluting any resistant parasites that may have survived drenching. This could be leaving a proportion of the mob un-drenched, putting drenched animals onto pasture that has had un-drenched grazing on it previously or following drenched animals with a mob of un-drenched animals.
As it takes most parasites 21 days to start producing eggs once ingested, using a short acting drench at 28 day intervals ensures that some sensitive parasites, not exposed to drench, reproduce before another drench is used. These larvae are also a form of refugia and dilute any resistant parasites that have survived the previous drench.
Reducing the numbers of young stock on farm is one way that farmers can reduce the impact of parasites on production, their reliance on drenching and the potential for developing drench resistance in the future. Ensuring optimal growth rates in spring and getting more lambs to the works early is one way that farmers can achieve this. 
For further information, contact your Farmlands Technical Field Officer or the friendly team at your local Farmlands store.
ACVM No: A10249 ®Registered trademark. Schering- Plough Animal Health Ltd. Phone: 0800 800 543. www.coopersonline.co.nz NZ/ALCE/0918/0010
Article supplied by MSD Animal Health