If you look for this preventative in a local feed store, be sure you're getting the type with 0.5% Decoquinate. They sell a stronger variety that contains 6.0% Decoquinate, which is much too strong for dogs/puppies. You'll be buying Medicated Livestock Feed (cattle). There are several brands, such as Kent Feeds. Try to get the ground/powder form, not pellets. Else you'll have to grind the pellets into powder with a coffee grinder.

Deccox CocciGuard
https://www.revivalanimal.com/product/cocciguard-10x
"Decoquinate is an easy way to prevent Coccidia - simply add it to your puppy's food. Decoquinate works by preventing Coccidia from reproducing so they die of attrition (old age). It is safe for pregnant dogs! The mother should also be fed puppy food with decoquinate; feed the last two weeks of pregnancy. This decreases the number of Coccidia the mother can give to the puppies. When you wean the puppies onto decoquinate, it controls the issue until you move them to their new home."  

You simply sprinkle the powder on the dog's food and shake/stir it in. It's easiest to add the appropriate amount to the top of an entire bag of food, then jiggle the bag to distribute the CocciGuard down through the food. It doesn't have to be perfect.

2C = 40lb
1C = 20lb
1/2C = 10lb
1/4C = 5lb (18C Diamond Naturals All-Stages Chicken & Rice)
2tsp = 3C (Diamond)

Begin feeding the pregnant bitch and your other adult dogs CocciGuard on their food at least 2 weeks prior to whelping. Start feeding it on the puppies' food as soon as they start eating solids. It's OK to soak the puppies' food with the CocciGuard on it. None of my adult dogs nor my puppies seem to have any problems eating their food with the CocciGuard on it.  

CocciGuard is a symptom preventative only. It will not treat symptoms. It also won't ever completely eradicate the Coccidia bugs from the premises. Nearly every kennel in the Midwest has Coccidia living in the ground from the dogs pooping on it. Therefore, the protocol for kennels is to use preventative treatments on all dogs/puppies on the premises starting at least 2 weeks before puppies are born. Once the puppies are at least 8-weeks old and settled into their new homes, their immune systems should be strong enough to handle life with Coccidia and not get symptoms. Symptoms of Coccidia occur in young puppies with developing immune systems and older dogs with compromised immune systems (i.e. from stress, illness).

If the puppies get symptoms (mucousy/bloody diarrhea) despite using CocciGuard, you'll have to treat them with Marquis or Albon. The protocol for treating symptoms is different than for prevention of symptoms, so check the directions. Hopefully the CocciGuard works well enough that your puppies don't get symptoms. Still, you might want to give your puppies a preventative treatment of Albon or Marquis within a couple of weeks of them going to their new homes. The stress of travel and going to a new home can compromise their immune systems which in turn can bring on Coccidiosis symptoms.

Your vet can test a feces sample for Coccidia, so you could take a sample in from one of your adult dogs or one of your puppies at their 6-week appointment to see if they carry the bugs. If one of the dogs has them, they all do, so there's no reason to test more than one sample. Then you'll know if it's necessary to do the Albon/Marquis preventative treatment before sending the puppies home. (Although treating the puppies if they don't have the bugs won't hurt anything.)

More detailed information about Coccidia is at http://brushdale.com/training/Health_and_Nutrition/Illnesses/Coccidia_Coccidiosis_-_A_Cause_of_Diarrhea.pdf