"I didn't want to watch him bleed out in front of me. I hopped into the float and applied a pressure bandage to the wound until the vet arrived and the blood eventually stopped flowing. The vet managed to sedate him, and we were thankfully able to get the horse into a nearby paddock, until a specialist horse vet arrived and was able to stitch up the damaged veins and arteries."
Ms Willemsen said she ended up wearing a lot of the blood but the best thing was that the horse - named Hunter - got through okay and was now on the mend.
Hunter's owner Anna Cuming said Ms Willemsen dealt with the situation calmly and with care.
"I was impressed with how Rachel dealt with the whole situation and I'm really thankful that she was there. She was incredibly helpful and level-headed," Ms Cuming said.
Wanganui resident Sue Cruickshank, who was walking her dog at the time of the incident, witnessed the officer's life-saving actions.
"Rachel acted very confidently and took charge of the situation immediately," she said.