When Oban was recovering from IBD and a human friend was recovering from heart surgery and had received high doses of good bacteria killing antibiotic both were told the probiotic in yogurt and similar things was not enough and they got acidophilus capsules.
Oban is quite recovered now and I give him a dollop (LOL, which is probably about a couple of TBSP) of yogurt or Kefir a couple of times a week, or more, as maintenance. He didn't like the yogurt when he was sick but now he will gobble it up.
Last time I bought this one:
Liberté Organic non effervescent Plain Kefir | Liberté
It's quite high in calcium but I do tend to feed it the days he gets meaty bones and I need something to hold the Chinese medicine pills he's still getting.