Pre-lamb parasite management – horses for courses

// Breeding and Genetics

In a year where there are big differences in winter feed supplies across New Zealand, sheep farmers will need to consider their pre-lambing parasite management in the context of their own farm situation.

image of farmer drenching sheep in yards

Vet and Wormwise Programme Manager, Dr Ginny Dodunski, says it has been a long time since there’s been such extremes in the winter feed situation between districts across New Zealand.

In the Central North Island, two ‘record’ summers have given farmers the ability to lift and stabilise ewe condition and pasture covers at a high level.

"This has meant management of the various ewe groups on the farm to get both body condition and feed levels into the ‘sweet spot’ for lambing is a ‘precision management’ job. Whether or not mature ewes require worm treatment pre-lamb is not part of the conversation at all."

Conversely, in areas like North Canterbury and the Wairarapa, Dodunski says the situation on some farms is dire.

"There are also areas in both Islands that sit between these two extremes; where a niggly dry autumn has left farms with low feed covers and ewe condition that is either suboptimal or well below par."

She says on these properties, the combination of poor ewe condition and low feed levels does leave sheep exposed to production and even welfare challenges from internal parasites.

"Discussions around pre-lamb worm monitoring and treatment should focus on striking a balance between the risk of accelerating drench resistance and looking after ewes which are under pressure. "

While parasites are not the primary cause of low condition and low performance, Dodunski says underfed light ewes will certainly suffer more under a parasite challenge.

"For their welfare and for economic reasons, a long-acting pre-lamb product may be part of the package to get ewes through a tight spring."

Dodunski stresses that capsules and long-acting injections will not grow grass.

"Do your feed budget (or get help to do one), look at the gap and assess the options to fill the hole in pasture supply over lambing."

She says off-farm grazing and further stock sales to drop demand (and stress with fewer hungry faces looking through the fence every day) are often a better solution than buying poor quality baleage that won’t meet the energy demands of breeding stock as pregnancy advances.

Nitrogen may also be an option to lift feed for lactation.

If farmers elect to treat ewes with a long-acting pre-lamb product, Dodunski recommends they use faecal egg counts after treatment to monitor and understand how many worms are surviving and contaminating lambing areas with resistant worms.

"The loss of immunity in light, underfed ewes will see more of the eggs they shed hatch and develop to infective larvae, than would happen in a well-fed ewe in good order."

She says docking/tailing is a convenient time to sample sheep and depending on the results, farmers could then have a discussion with their animal health advisor about whether or not to use an exit drench.

"It’s vital that the product chosen for this job is highly effective. On most farms this is no longer a triple combination."

Dodunski also urgers farmers to consider trace elements.

She says selenium and iodine, in particular, can affect lamb survival if they are in short supply. If farmers have cut trace elements in their fertiliser budget, have been using novel drenches (which are un-mineralised), or cut a lot of ewe drenching from their system in recent years, their ewes may be running low on selenium.

"There are plenty of cost-effective options for supplementation pre-lamb. They’re unlikely to give a performance lift, but they will insure against preventable losses where these minerals are deficient."