The primary concern with heavy bleeding is to locally stop or decrease continued loss. Loss of large amounts of blood will result in "hypovolemic shock", in which the body does not have enough blood volume to properly maintain circulation.
Many times, your animal will get cut without you knowing how. Some things to watch out for are metal lawn edging, barbed wire fences, and broken glass.
First Aid Tips For Bleeding
Keep the wound as clean as possible
Direct Pressure – use a clean cloth and place heavy pressure at the location of bleeding.
To protect larger wounds from further trauma and drying out, use a water-soluble lubricant gel (i.e., KY Jelly)
Transfer to a veterinary facility immediately
First Aid: Toenail Bleeding
Use hemostatic powder (Kwik Stop) to stop the bleeding.
Dampen a cotton tipped applicator and dip into the hemostatic powder.
Apply it to the bleeding toenail with slight pressure.
First Aid: Bandaging
Lightly dress the wound with a non-stick bandage.
Wrap the dressing with gauze and/or vet-rap from the foot up, tight enough to keep pressure on the wound but not to cut off the circulation of blood.