The A1M was closed in both directions between junction 43 HookMoor and Junction 44 for Bramham because of three horses on the loose.
The animals were caught and moved down the road to a safe location, but the incident caused some tailbacks as of about 8am.
The road has since reopened southbound but traffic is still being held northbound as of 8.40am.
A spokesman for Highways England said: "#A1M both directions J43 #HookMoor to J44 #Bramham traffic currently stopped due to 3 horses that have been on the loose. They have now all been caught and are being walked to a safe location.
"Southbound traffic J44 to J43 has been released. Northbound traffic still held at this time."
UPDATE: A kind member of the public stopped and helped move the horses off the road.
Highways England tweeted: "UPDATE - Just to let everyone know the horses are safe and well thanks to @WYP_RPU and a kind member of public who stopped and assisted."