Why did my 21M cat die during mating

This is my first breeding so hope to learn a lot from here. <br><br>My breeding cat is from Poland and came to ome on the 8th of January. We thought she was pregnant after mating once, then on the 2nd of march she came into season again and we covered her with a stud and over a week later we had 2 sets of kittens. <br><br>The stud was an 8M boy who had had a couple of litters as he used to be a stud with our breeder as well. <br><br>We have about 17 years experience in moggie behaviour. <br><br>For breeding we took the choice to split the stud and queens house. We did this so we could monitor the breeding cats better. <br><br>Our breeding cat was used to being on her own as she did in Poland and she adjusted well. The stud was used to being around cats so we gave him a kitten when he was neutered, so he wasn't alone. <br><br>We didn't mingle the breeding cat with the stud until she was due to come into season. <br><br>I know this will get me some backlash but we decided to breed early. The stud has always been aggressive during mating. He's got good quality semen, and we felt it was better to get her pregnant before he got <br>too old for mating. We've been advised to only have one litter of his then retire him. <br><br>He started to get slightly more aggressive on the 25th of March but our breeding cat was very tired and pregnant at this point. The stud would just try to mount but I felt it was getting dangerous. He wasn't trying to harm her exactly but when she got tired of being watched and tried to get away he would chase her. So we tried to keep them separated to reduce stress. <br><br>On the 19th the breeding cat gave birth to one set of kittens but a few days later we saw another sac and thought she had another set. <br><br>The stud was more aggressive but we felt it was best to retire him. <br><br>He was attacking the breeding cat and we tried to separate them by giving her a room with the kittens and letting him use his usual space. He broke through the barrier and got into the room. Luckily the breeding cat can get away but she was very stressed. <br><br>We accepted he was too aggressive but wanted to give him the life he deserved. We took him to the vet and got him castrated on the 31st of March. <br><br>He adjusted well and was very relaxed. <br><br>On the 2nd of April we felt it was okay to reintroduce him to the breeding cat. We did this with little steps. First they would see each other. Then on the 7th we thought she was too stressed so we gave them a tote box each. She eventually relaxed and went back to her old self. <br><br>I never left them alone. The breeding cat was still pregnant at this point. <br><br>She gave birth on the 11th. <br><br>As the stud is part Maine coon he was still getting used to the little tiny kittens. He was confused and wanted to play with them but eventually learned to be gentle. <br><br>Fast forward to a week ago, the stud was very relaxed, the breeder cat was <br>Enjoying the freedom of the whole house. Then the breeder cat got pregnant. <br><br>We let them mate, I was watching. I had to stop him twice but this time he listened. He jumped off. But the breeding cat took over and started to attack him. She never had a problem with him before. <br><br>We did a post natal check up and all the kittens were healthy. The breeding cat was also healthy so we thought everything was fine. <br><br>For 4 days she let him do anything but on the 5th day she attacked him again and he lost all his teeth. <br><br>I had to separate them instantly. <br><br>He got a little better and was able to eat. Yesterday he ate a little and got up once with difficulty. But today he can't move nor eat or drink. He hasn't had a poo for 2 days either. <br><br>We took him to the vet today and they done an x-ray. He has a puncture in the colon and the vet feels he will not survive the surgery. He's been given a 2 day expectancy. <br><br>I've never had a cat die before and don't know what to do. The breeder cat is relaxed and happy. I'm posting this because I want to know a few things. <br><br>1. What do you think happened? <br><br>2. What would you do? <br><br>3. Should I separate the breeder cat and stud altogether? <br><br>4. Is there any cats that are suitable for stud that are not aggressive during mating?