The first 30 days of a piglet is very important and any diseases that it will incur will greatly affect it's growth rate.
Diarrhea is cause by many factors.
If the pen is too cold this could lead to decrease immunity then bacterial problem and will manifest as diarrhea.
If your piglet sleeps on top of one another chances are your pen is to cold for them. To correct this you could put a bulb or heater, heating pad for them to increased the environmental temperature.
Do check also if the sow have mastitis. Sometimes the milk produced by sow is undesirable for consumption. Thus, when sucked by piglets causes diarrhea. If the mother doesn't let her piglets suckle or if the milk from the udder is a bit creamy and with a foul smell chances are it has mastitis. You need to treat this condition and give supplemental milk to your piglets.
there are times also that piglet sucks water from the nipple drinker. If the piglet is too young this is not advisable. There are times that it can do harm for them especially if the water is to salty or hard. for the first 7 days it is better to close this nipple drinker.
How to treat:
You can give antibiotics intramuscular or oral. Correct the cause whether environmental , nutrional etc.
Never give iron to a piglet with diarrhea. There are some bacteria that loves iron and thus by giving it to the animal will cause the bacteria to proliferate more.
