Yesterday my femal whippet went into labour 5 days early. She found it stressful and even though we supported her though every step an accident happened. On the 5th pup it came out feet first and got stuck. We gently supported the sac to come out but she snapped at the sac to tear it open in a panic. Instead of this being the feet end the pups head and eye were pieced by a tooth. The poor little mite I took to the emergency vet to be put down. The following and last pup was still born with its insides on the outsides.

She is doing fine now but I don't understand how it went wrong. Would a deformed dead pup induce premature Labour?

The living pups are small. The largest died with the head wound. I am topping the runt up with royal canin milk as the litter are very small.

Should I get mum checked out incase the dead pup causes an infection? The pups are too weak to be left at the moment and she seems well. She is restless and keeps stepping on the pups so I have spent all day in the pen.

What is your '5 days early' based on?  Bitches whelp 63 days plus or minus 48 hours from ovulation.  Unless you did progesterone timing to identify accurately when ovulation occurred, you don't know when she is due.  You have a huge whelping window instead: It could be 55-70 days from her first breeding. So I'm afraid she most likely was not 5 days early at all and probably right on time, going by when she ovulated.

Please don't top the puppies up with Royal Canin milk unless they are losing weight. And it is normal for them to lose weight in the first 48 hours after birth, then they should adjust and put it on. The milk the bitch will make, is designed specifically for their needs.  If you fill them up with Royal Canin, they are not going to drink her milk. If you reduce the demand for milk from her, then she will produce less milk in turn... Please don't interfere with a natural process unless something is going wrong and your intervention is needed.

The dead pup is very unlikely to cause an infection and no, you don't need her to be vet checked unless she appears to be unwell or runs a temperature. 

I think she most likely panicked or perhaps something happened whilst she gave birth which caused her momentary pain and she just responded instinctively to that and accidentally killed a pup...

Thanks.
The only reason I topped up the runt is because it went limp and downhill quickly not feeding. Two of the pups are very much smaller than the other two who happily drink her milk. After the formula the runt got some life back and is suckling.
As I speak though my partners taken the second smallest to the vet because the mum isn't stimulating the pup to poo, we tried but only passed urine and it is bloated up and refused to suckle.

You say small & I am assuming she had 6 pups in total. We weigh at 24 hours, what weight are you pups, as I can tell you if their weight is right or not?

You may need to stimulate for poo if she isn't. You can try a bit of honey on the area to entice her however if no luck then stimulate yourself, try using baby wipes for that.

This pup has now been checked over with the vets and they can't find anything wrong with it but it won't suckle.
It's causing the bitch a lot of distress because it simply can't latch on yet root's and cries constantly for food. I really don't know what to do at this point

I got the pup to defacate which is a plus and have been trying to get it to the latch without success. The pup won't suckle even the tip of the finger.
They locked on 4th April so I was expecting the litter this weekend. We've had one still born in labour and two small pups.
I've tried the bottle but the pup has no suck. It is moving around the mum but won't suckle its pretty heart breaking.
I'm going to give the vets another call to see if I can try and catheter.

Mum may need Calcium and I’d give the poorly one some Puppy Stim.

Thanks what a difference a few hours makes. I am breastfeeding a baby with cleft palate. I do remember how distressing it was to struggle to feed. Instead of concentrating on the pups I worked on making the mum happy. She was refusing food so I went out and bought wet puppy food. I am giving her the formula for a bit to boost her energy reserves. I bought a herbal calming plug in and treats. I brought in her dog bed into the whelping pen. Mum is now eating and drinkkng and feels comfortable enough to leave briefly to go outside and have a wee. She's being more gentle and allowing the pups to feed. They are passing stools so getting enough now. Even the pup who wouldn't suckle is now content and stopped crying. I do think they are early and I think she was caught off guard. She had such a horrendously stressful birth that she was exhausted and anxious. My last litter were 10 and wasn't as stressful as these 4 pups

I am still able to let you know if the pups are small or not if you want, as I am experienced in Whippets. 10 is a large litter