Animal health challenges following autumn rain

// Worms

While recent rain may not have been enough to break the drought affecting many regions, it can be a catalyst for animal health issues.

image of Ginny Dodunski on farm with sheep


Beef + Lamb New Zealand’s Wormwise programme manager and vet, Ginny Dodunski, says cooler, wetter conditions can bring about a change in the sheep worm population on farms from a mixed species to being Trichostrongulus (also known as Black Scour wormdominant.

 When the challenge is high, this worm can cause severe scouring and even death towards the end of a drench interval.

Where there are high post-drought worm populations, lambs may have low faecal egg counts yet still look sick and scoury. This is due to large immature populations of Trichs.

 Ginny recommends farmers don’t try and extend the drench interval for lambs unless they have clean pasture or specialist forages available for them.

With increasingly widespread combination drench resistance, she says it is important farmers check the efficacy of their lamb drench by carrying out a faecal egg count on fresh faecal samples about 10 days after they have been drenched.  

“If the counts are zero or close to it, that’s good news, if not, it’s time to seek advice.”

 A knock-out drench using Zolvix Plus or Startect can help reduce the buildup of resistant worms in the lambs by removing any adult egg laying worms that have been surviving a routine combination drench. 

Ginny says it’s also important to think about where those animals have been and plan to clean up behind them. This will stop the proliferation of resistant larvae on the pasture they’ve been grazing.

Mating hoggets

If drought-affected farmers are still going to mate their hoggets this autumn, Ginny urges them to be ruthless with cut-off weights and have a solid plan to ensure the mated hoggets will continue to grow at 130-150g/day between mating and lambing.

“For every 1kg gained between scanning and set-stocking they are 10% less likely to be wet-dry.”

Well-grown hoggets also mean better two-tooths are going into the flock next year.


Ewes are likely to be the stock class most affected by current feed deficits, but they should be prioritised in the lead up to winter.

“Get some help with a feed budget if you need it and prioristise keeping condition of these ewes. It is important to have feed available for late pregnancy and lambing,” says Ginny. 

She says ewes that start winter at a Body Condition Score (BCS) of 2 or less are almost twice as likely to be dead or missing by weaning.

After the second mating cycle is over, these low BCS ewes should be identified and given priority feed to lift them a minimum of half a condition score before the end of June. Alternatively, they could be sold so limited feed resources can be partitioned into the ewes that will generate a better return at lambing time

Retained lambs will create a higher worm challenge to ewes in spring. 

“Good feeding planning is a big part of the solution here as well-fed ewes can tolerate a parasite challenge. Thin ewes under feed pressure may require extra help.”

Live fluke

Liver fluke can be an issue after dry autumns. April and May are a good time to check the livers of cull or dog tucker ewes to see any evidence of a fluke challenge.

Nitrate Poisoning

Ginny says nitrate poisoning is a real risk following drought, particularly in autumn-sown new pastures and forage crops.

Drought conditions allow the build-up of nitrate in and around roots of a plant. Following a significant rain event there is a sudden uptake of nutrients and rapid plant growth.

Overcast weather that can accompany good growing conditions limits photosynthesis, and plants are unable to convert nitrates into protein. 

Ingested plant nitrates get changed to nitrite in the rumen. This is rapidly absorbed into the bloodstream where nitrite binds with haemoglobin on the red blood cells and prevents them from doing their job of carrying oxygen to the tissues.

Animals become oxygen starved and without prompt treatment can die.

Cattle are the most susceptible, especially pregnant cattle. Pregnant ewes are more susceptible than lambs but in bad years lambs can also be affected.

The first signs of nitrate poisoning include rapid breathing, weakness, tremours and imbalance. Animals often look ‘drunk’ in the early stages. As the condition progresses, animals salivate and froth at the mouth, and then start to gasp for breath and go down. Progression of these signs can be so fast often the first signs are dead animals. Animals can ingest enough toxic feed in one hour to start showing signs.

Ginny says it is important to test any feed that could potentially be at risk. 

For more information, see the  B+LNZ Wormwise programme section on our website.