The woman was thrown from the horse she was riding at a Huntly property on Sunday evening when a bird startled the animal.

Her thumb became tangled in the horse’s reins and was torn off.  

While the woman was taken to hospital, SES volunteers searched the property for the digit. 

But fading light, long grass and leaf litter hampered the volunteers' hunt. 

They called off the search when doctors told them the thumb could no longer be reattached.  

Bendigo SES duty officer Mike Fisher said volunteers were previously called to look for body parts lost in the course of car crashes. But this was his first time hunting for a thumb, Mr Fisher said. 

Volunteers used what is called a "forensic search" - walking within an arm's reach of one another - to scour the property. They also followed the path of the horse, which earlier bolted, in the hope of recovering the finger. 

Property owner Ian Padgham thanked the SES for their work, saying they did their best to locate the body part. 

"It was a great effort for them on a Saturday afternoon to send nine members," Mr Padgham, himself a former SES volunteer, said.  

Although the horse returned home and a neighbour found its bridle on Sunday, there was still no sign of the severed thumb. 

The woman remains in hospital in a stable condition, a Bendigo Health spokeswoman said.