Central West sheep producers have been encouraged to keep liver fluke in mind after abattoirs in the Forbes area detected a significant increase of the parasitic flatworm inside sheep less than two-years-old.
The National Sheep Health Monitoring Project (NSHMP), monitors conditions found in sheep sent directly to slaughter at participating abattoirs.
In the July to September 2023 report, 4.2 per cent of 48,734 lambs from Forbes had liver fluke, a dramatic increase from 2022 which had a prevalence of less than one per cent.
Affected livers are condemned at abattoirs and in some rare cases, whole carcasses too.
While liver fluke typically infects livestock in high rainfall and irrigated areas, Central West Local Land Services district veterinarian Alicia Moses, Grenfell, said outbreaks are common during dry periods after significant rain events.
"The previous year's record rainfall in Forbes, the floods, and then a dry period afterwards, may be the cause for increased favourable environments for liver fluke," she said,
"Also once it starts to dry out, sheep especially may be forced to graze closer to marshy areas where they preferably don't like to graze or wouldn't during normal years.
"Producers may also be buying in sheep from flukey areas."
Liver fluke eggs are shed in the dung of a host animal onto pasture and once hatched, larvae swim through water to find an intermediate host, a lymnaeid snail.
Once inside the sail, the larvae multiply and grow before swimming to vegetation where they attach and form a casting, known as infective cysts.
Livestock grazing near marshy areas will eat the infective cyst. The liver fluke then hatch from the cyst inside the intestine of the host before borrowing through the intestinal wall towards the liver.
"Migration through the liver causes tissue damage, thickening of the bile ducts and a lot of haemorrhage which leads to anaemia," Dr Moses said.
"Liver fluke can also cause weight loss, infertility, ill-thrift, bottle jaw, pale or yellow membranes in the mouth and eyes, complete liver failure and in some cases death.
"It can cause a lot of damage in young animals as well as older ones."
Liver fluke can also look very similar to other intestinal parasites such as barber's pole worm.
While there has been an increased detection from the abattoirs, Dr Moses said the NSHMP data does not necessarily represent the true prevalence of liver fluke in the area.
"Unfortunately it is only sheep that go directly to slaughter included (in the data) so you are missing out on sheep that go through the saleyards," she said.
"However it is still a pretty significant increase of detection, which is why producers need to have it at the back of their mind as it may be a factor they haven't considered before."
While excluding livestock from grazing on flukey habitats is the most effective method of control, Dr Moses said treatments need to be multifactorial.
As fencing out flukey habitat takes time and money, as well as reduces feed which may be needed there are other management strategies producers can use to combat liver fluke.
Chemical drenches can reduce infection levels, but producers should not rely on this method alone as individually it cannot eliminate liver fluke.
More importantly, an overuse of chemical drenches can cause resistance.
Depending on the property and susceptibility of livestock, chemical drenches can be used one to three times per year.
If flukey areas cannot be fenced off and must be grazed, producers should give an effective fluke drench two weeks before moving stock into the area.
Stock should remain in the flukey area for less than six weeks.
Animals that have grazed flukey areas through spring and summer will host immature and adult-aged liver flukes, therefore a drench that eliminates all of these life stages should be used at the early winter drench in April/May.
For sheep, the early winter drench chemical of choice is Triclabendazole.
When purchasing livestock from flukey areas, producers should treat them with a combination drench effective against all life stages of liver fluke before holding them in a non-flukey paddock for 21 days.
If you suspect your livestock may be showing signs and symptoms of liver fluke, Dr Moses said any vet can offer advice or support.
"We're always on the look-out for disease outbreaks if producers are having a higher than normal morbidity or mortality events," she said.
"We're interested to hear about that and assist where we can."