"We got him as a family cat and wanted him to get used to his new home comfortably and safely. But then he went for a walk and came back with terrible wounds," Ms Speers said.
"It totally wrecked my son's birthday - we were all crying - and it's been another day of tears after we woke up today, hoping Santa doesn't lose the sight in his left eye."
Ms Speers realised the veterinary bills would be a struggle to pay, but she "told the vet to do whatever was needed. He's more than just a cat, he's part of our family and he means everything to us".
She was anxious about Santa coming back to the neighbourhood with the culprit remaining unknown, but was determined to give her cat every chance to recover before his return home.
"All I want is for him to come home. I am scared it will happen again, very scared actually, but I'll cross that bridge when I get to it."
Dr Heidi Ward-McGrath, of VetCare Veterinary Hospital, said Santa was the second shot animal she had treated in the past week after earlier removing two large calibre slugs from the head of an older huntaway dog, which she believes was the victim of a botched attempt to put down the animal.
She understood the 13-year-old hound was from the Castlepoint area and had been since handed to Wairarapa SPCA for adoption.
She said Santa was shot three times, probably from close range, and the pellets had remained lodged in the animal's head.
One of the slugs had smashed through the cat's eye socket and eye, putting his full sight in dire jeopardy.
"We think he's been blinded. He'll have surgery to remove the pellets and possibly his left eye as well. He's doing okay but I'm not sure I can save the eye."
A Santa Fund had been launched at the VetCare clinic to help pay for the cat's treatment, she said, and she also urged anybody with information about the shooting to get in touch.
"The whole family, all of them, were extremely distressed - a young solo mother with three young boys - it's just heartbreaking," she said.
"Animals are not target practice. This is an animal welfare offence and we will be seeking to find out who did it, while trying to repair the damage they've caused as well."
Anybody wanting to donate to the Santa Fund may call the VetCare Veterinary Hospital at 06 377 7955. To share information about the shooting call SPCA Wairarapa on 06 377 1912.