breast question

My dog recently had puppies. And one of her bottom breast near her legs started to grow and its been getting hard all around. I wanted to know if this might be something dangerous or just something regular for being her first time having puppies.

[Aleda M Cheng, D.V.M., C.V.A]

It sounds like mastitis, which is an infection of mammary gland.  This is common during and after nursing where bacteria can easily ascend up the teat into the breast tissue.  This can be a serious and painful condition for your dog and can cause your dog to have a fever,  can cause her to decrease or stop eating and can spread.  Mastitis requires antibiotics so please take her to a vet ASAP for the best outcome.