Since the onset of wet weather a number of sheep and lambs have been discovered with high worm burdens.

Since the onset of wet weather a number of sheep and lambs from the North Central Catchment have been referred to Department of Primary Industries (DPI) Animal Health staff with extremely high worm burdens.

Worms or more precisely intestinal parasites in lambs and sheep have not been seen in recent years due to the string of dry autumns and winters we have experienced.

Department of Primary Industries (DPI) District Veterinary Officer Rachael Holmes said internal parasites cause diarrhoea and death in lambs.

"Seasonal conditions have been perfect for one particular intestinal parasite named Nematodirus, commonly known as the thin-necked intestinal worm," Dr Holmes said.

"Thin-necked intestinal eggs can survive in pasture for a long time over dry periods, such as those we experienced in the past few years.

"Eggs accumulate on the pasture during the dry period and mass hatching can occur when there are extended periods of moist conditions as recently experienced.

"What has further aided the heavy burdens is the fact that pasture is still very short and any hatching worm larvae are concentrated in the few centimetres of growth that is present."

Dr Holmes said this has allowed large worm burdens to occur especially in young stock.

"Lambs are particularly susceptible to thin-necked intestinal worms and as few as 3000 worms in the intestine can cause serious damage to the lamb resulting in death.

"Once pasture growth improves there is a dilution effect from the extra pasture that reduces the uptake of larvae taken in with the eaten pasture."

Dr Holmes said producers need to actively monitor worm burden in their flocks by conducting faecal egg counts at regular intervals; this should be done before drenching is contemplated.

"Producers should also consider having a drench resistance test conducted to determine the level of drench resistance in their flock and whether the drench in current use is effective for the job."