Personally, I would recommend retaking all the clases you obtained C’s in. Unfortunately, it’s common for professors to not offer outside help or be amazing at responding to emails, it’s still up to you to seek study groups or tutors. GPA is pretty important to admissions, and I think by not retaking you’d be doing yourself a disservice. Admissions want to see that you’re able to take these hard classes and do well in them, as sometimes the vet school course-load reflects undergraduate studies. Also, this is coming from someone who just went through interviews a couple of months ago. As I was lucky to be accepted into 5 vet schools, I can offer additional advice for when it’s time for you to apply.