Sources at Defra say that 850 badgers have been shot in the area over the six-week trial, just over 40% of an initial target of 2,081.
But those sources insist the Somerset scheme has proven to be effective.
They say new population data means there are far fewer badgers in the pilot area than originally thought.
The controversial pilot culls set out to study if badgers could be killed safely, effectively and humanely.
It is being carried out in an attempt to control TB in cattle, which can be spread by badgers, though opponents say it will have no impact.
The plan was to kill 70% of the badgers in the areas of west Somerset and Gloucestershire by free shooting.
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