Drivers experienced lengthy queues on the A1 in Eaton Socon.
A stretch of road between the B1048 Eaton Socon and A428 Great North Road was closed due to a horse that had collapsed in a horse box.
A Cambridgeshire police spokesman said: "We were called at 10.39am by a member of the public to reports of a horse which had collapsed in-transit in a horse box."
The fire brigade and a vet were also in attendance at the scene.
There were queues on southbound to the B1041 Great North Road, the Little Paxton turn off, and northbound to the A421 Great Barford Bypass.
The road has now been reopened.