is it usual for a bitch to go off her food at around 28 days into pregnancy?

.... yes....and no.... it entirely depends on so many things. 28 days is only 4 weeks in - so she may not even be pregnant so yes going off her food would be odd....however, of course likely enough she IS and a touch of morning sickness can hit, at any time of the day. Try feeding her at different times, it may be normal meal times are when shes feeling a little 'green'. But generally bitches tend to only fast towards the end of their pregnancy when they start to feel uncomfortable. But her homones could be messing her around, she could be off her grub for a reason totally unconnected to her pregnancy. I'd only let a couple of days go by with her eating nothing or next to nothing, with no other symptoms of illness before calling a vet.

Try and tempt her with nice things, cooked chicken breast, that sort of thing but don't pander TOO much because she may eat and mislead you from the fact she genuinely is not well and then a few more days would pass before you took her to the vets.
Good luck!
Di

Unfortunately we are going through the same thing with one of my mum's Pomeranian's, she's hardly eating anything and is 5 weeks pregnant.  She's healthy, running around and happy but it's getting very worrying, Pom's are hard enough when they are born without the mother adding to the problem before birth!

Hope all goes well with yours.

My last pregnant girl, hardly ate a thing from 3 weeks onwards until she whelped.  I was concerned, took her to the vet 3 times and each time told by a different vet, nothing to worry about and it's more common than people realise.  She had a healthy litter of 7!

dito, my girl would only eat raw mince, liver, cat food and hotdogs, loved eggs n milk

Just phoned my mum and after 2 weeks of her hardly eating she's started eating again today.  I said that she must of read that I was worried on her.

my girl would hardly eat and when she would it was tripe sticks that was for most of her pregnancy. the last week she hardly ate at all and had a litter of 10 quite big pups :)