Unfortunately during breeding, especially an inexperienced male, the penis can be traumatized. The descritption you give sounds much like a prolapse. My recommendation is to try to separate him from the female...then take KY jelly and lubricate the penis and make sure the prepuce ...which is the skin..is lubricated too and you are able to move it up and down the shaft. Sometimes the skin gets pushed up and rolls on itself and dries and doesn't allow the penis to retract in. Now after you do this he obviously will be stimulated, but if the skin is moving and penis is moist, as soon as he is relaxed, it should slide back in.
My main concern is that the penis can be seriously damaged if it is out an drying and being damaged.
Let me know, if you are unable to handle the dog or get the skin loose, you may need to proceed to an emergency vet.
Dr.Vamvakias
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Dr. D.A. Vamvakias
Veterinarian
