I haven't used electrolytes, Or medicated feed. I have 12, 3 week olds and 5, 7 week olds. I've had these guys for almost 2 weeks (Tuesday will be 2 weeks).
I don't have an abundance of experience obviously, as new as they get, but I am confident in the benefits of probiotics and apple cider vinegar. (Unpasteurized, organic and unrefined).
I do Apple cider vinegar in their water each day. After the 2 week period I will do it once a week (day) in their water.
As far as probiotics that will be a regular thing for us. I just buy the 'human version' refrigerated and make sure it has a good dose of Acidophilus & Bifidus. (10 Billion active cells or higher). I did every day for the first week home and now I've been adding to feed every 3rd day. Mine is in pill form, I just open pill and sprinkle powder on top layer of feed.
I take a probiotic daily. I give my dogs probiotics twice a week. I can't see any reason to stop giving them an immune booster and an all around essential good nutrient.
Tip* a good live probiotics needs to be refrigerated, not shelved.