I agree with Dlhunicorn on this one.
In the states, the 'medicated' feed you want will be a chick-starter or starter-grower for chickens (not goats) that contains Amprolium. It should not contain BMD (Bacitracin) as that's a ration for industrial chicken growing plants. BMD is an antibiotic. Amprolium is a coccidiostat.
Now, because it's a coccidiostat (designed not to sterlize the environment from cocci, but to help prevent cases of the actual illness of coccidiosis) it will not prevent coccidiosis if environmental conditions favor the illness. It's designed to be weak enough to still allow chicks to develop an immunity to low levels of cocci by being exposed to low levels. High levels of cocci overcome the medicine and then must be treated with "coccidiocides".
The same medicine, amprolium, is also used in one of the best coccidiocides - only in a much stronger dosage to treat illness, not help control the number of incidents.
Corid is the med in the states I'd buy. If you can't get it and need it now, try Sulmet. The difference is that Sulmet is a sulfur drug. It's both antibacterial (an 'antibiotic') as well as a coccidiocide. Because of that, it's more harsh on the babies. But not as harsh as coccidiosis! So in a pinch....
I find that in most cases, the potential for coccidiosis can be stopped by giving probiotics (the yogurt - given as dlhunicorn has mentioned) in combination with disinfecting the brooder, making sure all bedding is completely dry, cleaning and disinfecting the waterers and feeders, and removing droppings from feeders/waterers immediately when soiled and cleaning with hot soap and water. Then replacing.
I can't stress 'dryness' enough. While the bedding should not be dusty, it should be the most absorbant material you can use. Newspaper, while absorbant, still leaves droppings on top to be accessed by chickens. Sand, while dry, can still leave droppings up on top unless you constantly rake them out. Shredded newspaper, to me, is the same as regular newspaper - only fluffier, not any more absorbant. My choice is shavings. Others use hay (which again I feel is less absorbent and more prone to mildew because it doesn't dry as fast.)
In any case, dry dry dry and dry. Water spilling into the bedding or a warm brooder makes the perfect condition for coccidiosis to occur. So clean it up, and the underlayer if applicable, and try putting waterers at back-level to the chicks so that they don't walk through it (with the poop that inevitably is on their feet) and don't poop in it - as much. (Chicks are talented in finding ways to poop in it anyway!)
As for probiotics, if you can get them to eat it alone, that's best! Otherwise, sometimes I will mix it with water and then mix a little of that water with a tiny bit of crumbles, let sit 10 minutes to absorb, and feed that first thing in the morning when they're quite hungry. I make a very small amount - one that can be cleaned up within 10 minutes. i make sure every baby gets it. If some gets more than others, I put him aside so that others can get their share. At the end of 10 minutes, I remove that bowl, clean and dry, and replace their free-choice chick starter for the rest of the day and the rest of the week. Do NOT mix it with mash and leave for more than 10 minutes. And I'd agree to stop the sand at this point.
With my babies, I will often give them a prepared probiotic (Probios powder or an avian specific probiotic) on their second day of eating. Babies come without enough good bacteria in their gut. Mother Nature provides for that by giving chicks and amazing curiosity which often leads them to peck their mother's vent and droppings. That's how they naturally acquire both good and bad bacteria from their mom. Because their mom is healthy, the good outnumber the bad and colonize the gut faster and more thoroughly. Remember that otherwise their gut is pretty much free real estate! If the bad got to it first, they could just as easily take over. Because my babies aren't hen-raised, I give that insurance to my chicks that the good will outnumber the bad. I do probiotics up to weekly through the growth period, and then occassionally thereafter even to adults to re-innoculate their guts.
They will NOT grow dependent on probiotics for gut bacteria if you feed them. They will just benefit from them.
The bacteria help your bird actually absorb their food by finishing the digestion process on what the gizzard mechanically breaks down. They also help control pathogens by literal competition for that same 'real estate' of the gut!
So... when babies "might have' coccidiosis, I always start them on probiotics. If I see pasty-vent, I use probiotics daily until it either goes away, or until other symptoms present. If I see diarrhea in chicks (not just the occassional cecel chocolate-pudding droppings) I give probiotics first if the chicks are all active, eating, not sleeping too much. If the babies at all get lethargic, then I treat with Corid AND probiotics. I continue probiotics every other day after medication for 2 weeks. Then I go back to "occasionally", etc.
Keeping the environment very dry and clean, boosting natural gut bacteria with a probiotic (like lovely yogurt), and being very keen to watch droppings carefully daily has allowed me to have a flock without coccidiosis in nearly 10 years with many babies raised. I do have pasty vent babies come in (when I buy hatchery, shipped, or feed store stock) but this program always keeps them from going further than that.
It might work for you, too, along with dlh's wonderful advice.
As dlh mentioned, as well, be sure to carefully watch the babies (and I'll add feel their weight daily to every other day during brooding and growth). If you do that, you can usually see problems before they get too far. Just as you've noticed one of your babies tends towards pasty vent. Doing so will probably show you that the smaller babies might not be getting enough feed. I will sometimes take out the smaller babies and brood them all in a separate brooder. They often zoom up in size and readily catch up!
I hope everyone's information is helpful. Please do let us know how your babies do, won't you?
I also agree with the avi-charge.
p.s. If you do the fecal sample from the vet, ask for a "fecal egg count" and for them to check for the oocysts of coccidiosis. Remember to ask for both specifically (vets have a lot on their minds and will assume less). Looking at just the feces for worms is an undependable way to determine if your adults have worms as worms more often shed their eggs than themselves. And just note that finding cocci oocysts (their method of spread) isn't always reliable, unfortunately. But a "fecal egg count (adults) and fecal check for coccidiosis" is highly recommended if you REALLY want to know!
