I'm just curious about what foods people use and whether they've had any problems with fertility (bitches missing) or low numbers of pups in a litter?

I want to choose a better food for next time....

What food?   The same good quality food as mine always have.   Towards the end of the pregnancy when if there's a good sized litter in there, I split the daily intake into several small meals, omitting a lot of the bulk and upping the protein.   I don't believe in increasing the food until after whelping, when I know how many puppies she has to cater for.   Just like with humans, there's no need to be putting on extra weight - the puppies will take all they need from mum after all.   We had one miss but later discovered others who had gone to that dog missed too!    We have had the occasional small litter however.

I DO NOT subscribe to all the puppy food for mum people seem to think is right these days.   I tried to make sure my bitches were in tip-top condition before being mated - and that included making sure boosters were utd, and they were wormed.    And further, as newborn puppies don't need lashings of milk, again watch intake - too much too soon could go to mastitis if the puppies can't draw it off fast enough 

Thanks MamaBas, I meant - what brand of foods are people using for pregnant bitches/during whelping and conception?  Are there any foods to avoid or to especially favour?  (Obviously you'd need to get her used to it before.)

Many people are feeding natural raw foods, so no brands there... The best quality is usually the right answer though.

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My dogs are all fed good quality food and have a balance of raw and kibble. If you intend to breed then you should do all you can from the start of her life to keep her in tip top condition.

If she missed last time, I would ensure you do blood tests so you're sure of ovulation and use a proven dog.

If my bitch is in whelp, I do change to the puppy variety of kibble at 6+ weeks

The best food is the one that suits your dog.

What suits one won’t be suitable for another.

Like mamabas, I don’t subscribe to the puppy food fad.

I feed what they’ve always had and break it down into more feeds a day, increasing it if they’re starving and tummies don’t get upset.

> what brand of foods are people using for pregnant bitches/during whelping and conception?

Again, I recommend you use the same tried and tested diet you have always had her on, as an adult.   And that should be a good quality food depending on what works best, for her.   You need to keep her in tip top condition for what lies ahead.